Numerous factors external to the nerve cell can support and enhance nerve regeneration after injury. The definition of these factors and the elucidation of their mechanisms of action are the central goals of much contemporary neurobiologic research. This research will hopefully lead to the discovery of factors that will prove to be therapeutically beneficial for patients with either peripheral nervous system (PNS) injury or central nervous system (CNS) injury. This article reviews the biology of the regeneration response of the nerye to injury and discusses many of the factors that enhance nerve growth. Finally, the nerve guide or nerve regeneration chamber model for the evaluation of putative nerve regeneration enhancing agents in vivo is also discussed. Key words: nerve repair nerve regeneration neural regeneration nerve guide nerve regeneration chamber neurotropic factors neuronotrophic factors nerve growth factor entubulation nerve repair MUSCLE & NERVE 13:785-800 1990

BROOKE R. SECKEL. MD

Adult mammalian peripheral nerve is capable of generous regenerative growth but the return of normal function after nerve injury or repair is uncommon. Although significant advances in the understanding of anatomy and pathology,'24 the use of antibiotic^,'^^ and recent1 , in the use of microsurgical techniques' 1,L8,44,J,91,98,149 have improved results of surgical nerve repair in the 40 years, functional return is rarely complete. In the past decade, interest has shifted from the technology of surgical nerve repair to the understanding of the cellular and molecular events occurring in the microenvironment of the tip of the regenerating axon- the growth cone. Although it has long been postulated that biologic factors peripheral to the nerve cell body exert a significant influence on the development, growth, survival, and re eneration of the nerve cell and its processes,38952,184 the discovery of nerve growth

ESt

~

From the Department of Plastic and Reconstructive Surgery, Lahey Clinic Medical Center, Burlington, Massachusetts. Acknowledgment: Supported in part by a Grant from the Eleanor Naylor Dana Charitable Trust. Presented at AAEE (now AAEM) Annual Meeting, International Syrnposium on Peripheral Nerve Regeneration, Washington, DC,September 17, 1989. Address reprint requests to Dr. Seckel at the Department of Plastic and Reconstructive Surgery. Lahey Clinic Medical Center, 41 Mall Road, Burlington, MA 01805. Accepted for publication December 6, 1989. CCC 0148-639W90/090785-016 $04.00 0 1990 John Wiley & Sons, Inc.

Peripheral Nerve Regeneration

factor (NGF) by Levi-Montalcini and Hamburger in 195175truly revolutionized the-study of the biology of nerve regeneration. Furthermore, advances in cell culture methodology' have provided in vitro models with which to isolate and study specific agents that play a role in the nerve regeneration process. More recently, the demonstration that the peripheral nerve microenvironment will allow regeneration of central nervous tissue as well as peripheral axons stimulated significant interest in and brought talent to the study of peripheral nerve r e g e n e r a t i ~ n .The ~~ fund of information concerning the cellular and molecular events in the regenerative process -has reached a level of sophistication where we can realistically begin to contemplate the manipulation or enhancement of the nerve regeneration process by biologic as opposed to surgical means. This report reviews some of the current information regarding the biologic events occurring during the peripheral nerve regeneration process and the factors that promote or enhance nerve growth. In addition, I will describe in detail the nerve guide or nerve regeneration chamber model and its use in evaluating substances that promote the regenerative growth of nerve tissue. 5717,24,34,36,109

PEREPHERAL NERVE REGENERATION RESPONSE

Axotomy induces profound morphological, biochemical, and physiological changes in the nerve cell body and its processes (Fig. l).8p42,"5 If death of the nerve cell does not occur, regenerative ac-

MUSCLE & NERVE

September 1990

785

Schwann Cell Nucleus

Cell Body

Myelin

Traumatic

Na*

Wallerian

Protein

Basal Lamina Tube’

w”w

UNCY CLINIC 0 ,.b,

FIGURE 1. Peripheral nerve regeneration. (A) Diagrammatic representationof a normal nerve cell body and processes. A typical peripheral nerve will contain thousands of such axons. (B) Traumatic and wallerian degeneration. Note ion shifts and changes in the cell body. (C) Regeneration. Note axonal growth cone growing into empty basal lamina. (D)Ensheathment. Note Schwann cell alignment around axon to form bands of Bungner. Degree of myelination will be determined by the type of axon. (Printed by permission of the Lahey Clinic.)

tivity in the form of nerve sprouts emanating from the proximal stump may begin as early as 24 hours after injury. After axotomy, the central nerve cell body becomes swollen, the Nissl substance is dispersed, and the nucleus is displaced peripherally (Fig. 1B). This process, chromatolysis, reflects a change in metabolic priority from that geared for the production of neurotransmitters needed for synaptic activity to the production of materials for axonal repair and growth. The central cell must synthesize new messenger RNA, lipids, and cytoskeletal proteins.45 The components of the cytoskeleton that are most important Nerve Cell Body.

786

Peripheral Nerve Regeneration

for axonal regeneration are actin, tubulin, and neurofilament protein, which are carried by slow anterograde axonal transport at a rate of 5 to 6 mm per correlating with the maximum rate of axonal elongation during regeneration. 150 Another group of proteins whose synthesis is increased during the regeneration of nerve cells are growth-associated proteins (GAPs), which travel by fast axonal transport at a rate of up to 420 mm per day. Although GAPs do not initiate, terminate, or regulate growth, they are necessary for regeneration.“ The synthesis of GAP-43 is increased 20 to 100 times during successful reg&neration of mammalian peripheral nerve and is a major component of the growth cone membrane.”” In addition, the signal from the periphery to the cell body that injury has occurred is also believed to be conveyed by retrograde axonal t r a n s p ~ r t ” ~ as are other growth-promoting or trophic factors (Fig. 2).‘*l Other architectural changes that reflect a decrease in synaptic activity are- the retraction of the synaptic boutons from the soma of the cell body and the insertion of the processes of neuroglial cells between the boutons and the cell body (Fig. 1B). Electrophvsiologic changes occur in the cell body that represent a dedifferentiation toward a more lastic or embyronic state permitting Some investigators postulate that this response is secondary to a loss of trophic factor from the periphery.’19 After axotomy, the proximal axon undergoes a variable degree of “traumatic d e g e n e r a t i ~ n , ” ”which ~ minimally extends back to the next node of Ranvier or maximally may result in cell death. In actively regenerating axons, the structural border between parent and regenerating axon and, thus, the area emanating the regenerating nerve sprout, is the first node of Ranvier proximal to the area of traumatic degeneration (Fig. lC).”O The regenerative sprouting of the proximal axon requires elongation of the axon. This process is mediated by the growth cone, which is a specialized motile exploring apparatus at the tip of the regenerating nerve fiber (Fig. 3). Ramon Y Cajal,Io4 who first described the growth cone, compared the growth cone’s ability to advance through solid tissue to a battering ram. More recent research, however, has revealed that the growth cone releases a protease that dissolves the matrix, permittin a more subtle advance through tissues (Fig. 3A). Proximal Axon Stump.

8

MUSCLE & NERVE

September 1990

FIGURE 2. Axonal transport. Structural proteins reach the periphery by slow anterograde axonal transport while neuronotrophic factors travel to the soma from the periphery by fast retrograde transport. Growth-associated proteins (GAPS) travel in the fast anterograde component. (Printed by permission of the Lahey Clinic.)

FIGURE 3. Growth cone. (A) Protease is released by the growth cone to facilitate its advance through the matrix. (B) Growth cone responding to contact guidance clues from laminin and possibly, fibronectin, which are components of the Schwann cell basal lamina. The growth cone can also respond chemotropically to neurotropic clues from neuronotrophic factors in the periphery or target organ. (Printed by permission of the Lahey Clinic.)

Peripheral Nerve Regeneration

MUSCLE & NERVE

September 1990

787

Growth cones have mobile filopodia extruding from a flattened sheet of lamellipodia enabling them to move actively and to explore the microenvironment of the regenerating axons. Actin influences this motility because cytochalasin, an agent that interferes with actin assembly, causes growth cone retraction and stops axonal elongation. The growth cone plays an essential role in axon guidance and is believed to be capable of responding to contact guidance clues afforded by laminin and fibronectin, two major glycoprotein components of the basal lamina of the Schwann cell and other portions of the extracellular matrix. Growth cones can also respond to chemotropic molecules, e.g., NGF, in vitro (Fig. 3B).49 In addition, after axotomy of the rat sciatic nerve, NGF receptors are induced distal to the lesion that presumably bind NGF molecules upon the Schwann cell surface to provide trophic support and chemotactic guidance for re enerating sensory and sympathetic neurons. 12‘ Recent research involving the development of the vertebrate nervous system has demonstrated that axons are capable of precise and speciJc selection of pathways and targets of innervation and that axonal growth is not a random process.32 In the developing embryonic vertebrate nervous system, however, NGF synthesis does not commence in the target field until the arrival of the sensory nerve fibers.28 In vivo research has suggested that precise target-specific axonal regeneration is also possible in the adult regenerating nervous system.”3’114 Zone of Injury. Shortly after nerve transection and before the onset of wallerian degeneration, severe and rapid traumatic degeneration of the tip of the proximal and distal stump regions occurs. This injury is secondary to an influx of sodium and calcium and a massive loss of potassium and prOtein3031.56,1 1 1 (Fig. 1B) and results in what de Medinaceli and Seaber3’ refer to as “chemical burn,” which may extend one or two full internodes p r ~ x i m a l l y This . ~ ~ “no-man’s-land” of axonal debris prevents the growth cone of the proximal regenerating axon sprout from reaching a healthy distal stump. No Schwann cell basal lamina are available to guide the axon sprout growth cones. The result is a change in direction of the axonal sprout or branching or the formation of a n e ~ r o m a .The ~ ~ ’result ~ ~ in surgical nerve repair is catastrophic (Fig. 4).

After axotomy, a sequence of events called wallerian degeneration ensues.

Distal Axon Stump.

788

Peripheral Nerve Regeneration

Forty-eight to 96 hours after axotomy, deterioration of the myelin begins and no axonal contents are r e ~ o g n i z a b l e .The ~ ~ Schwann cells proliferate and begin to phagocytose the myelin debris, a process that may require u p to three months to complete. T h e basal lamina tubes or endoneurial tubes that ensheathe the myelinated nerve fibers persist after the myelin and axonal debris have been cleared. The remaining proliferating Schwann cells align longitudinally within the confines of the basal lamina or endoneurial tube, creating a continuous column of cells called the bands of BungWhen the endoneurial tube ner (Fig. ID).95.128*130 is not entered by a regenerating axonal sprout, the tube progressive1 diminishes in size by a factor of 80 to 90%.126,1y7 In addition, collagen is laid down longitudinally along both surfaces of the basal lamina tube. In spite of these changes, the distal stumps can accept regenerative axons for several years after injury. The basal lamina surrounding the Schwann cell contains laminin, type IV colla en heparan sulfate, proteoglycan, and entactin.F6,2i The behavior of Schwann cells inside the basal lamina depends on the presence of an axon. The initial breakdown products of axons after axotomy stimulate Schwann cell multiplication in preparation for phagocytosis of debris.’ Subsequently, a regenerating axon is required for differentiation of the Schwann cell and production of myelin for the remyelination of the axon by the Schwann cell. The degree of remyelination is determined by the type

FIGURE 4. Conventional versus nerve guide repair. Conventional repair: axonal branching and directionalchange secondary to obstruction by scar tissue in the area of traumatic degeneration. Nerve guide repair: the axons can begin distal migration without obstruction by the closely opposed, imperfectly aligned degenerating fascicles of the distal stump. (Printed by permission of the Lahey Clinic.)

MUSCLE & NERVE

September 1990

of axon regenerating into the basal lamina.55~'42 T h e importance of a clear definition is apparThe Schwann cell and its basal lamina collagen ent when one considers the confusing variety of also provide a supportive and possibly growthterminology used to describe the various factors promoting microenvironment for regenerating that are believed to influence the process of peaxons. These nonneuronal supporting elements of ripheral nerve regeneration. For example, the the peripheral nervous system are thought to be a term neurite-promoting factor (NPF) can be used reservoir of growth- romotin factors for periphgenerally to describe a number of agents that have eral nerve t i ~ ~ ~ e 1'!136213~7 ~ In~ addition, * ~ ~ ~ the ~ ~ effect ~ , of ~ promoting neurite extension in David and Aguayo" have presented evidence that ~ i t r o . However, ~ ~ , ~ ~ agents that have neuronothe nonneuronal components of the distal nerve trophic factor (NTF) characteristics, e.g., NGF, also promote neurite extension in vitro and thus can also support the regeneration of central nermay also be called neurite-promoting factors vous tissue. Recent work by Waxman and Black14' (NPFs). For the purpose of this review, I will list has begun to elucidate the basic macromolecular under NPFs factors that are predominantly suborganization of the axon membrane and the axon strate-bound and that strongly promote neurite glial interface. initiation and extension, adhesion, or both. In the The study of the role of the nonneuronal supinterest of simplicity and consistency, I will use the porting structure of basal lamina and Schwann classification system of Varon and Adler, 1343135 cell as both contact guidance and growth-promotwhich parallels a general classification of growth ing structures for nerve repair is one of the most factors reported in the l i t e r a t ~ r e . ' ~In addition, exciting areas of nerve regeneration research toone general class of growth factors is listed as day and is described in more detail in the section "metabolic and others," which is not categorized as on the nerve guide model. such by Varon and Adler.'34'135 The following four classes of growth factors Distal Targets of Innervation will be discussed: (1) neuronotrophic factors Muscle. After axotomy of a motor neuron, (NTFs) or survival factors; (2) neurite-promoting the denervated muscle undergoes atrophy. Alfactors (NPFs) controlling axonal advance, which though in normal muscle only the motor endaffect the rate, incidence, and direction of neurite plate region is responsive to acetylcholine (ACh), outgrowth; these factors are usually substrate in denervated muscle the entire muscle membrane bound; (3) matrix-forming precursors (MFPs), becomes responsive to ACh. If regenerating mopossibly fibrinogen and fibronectin, which contribtor nerve axons reach muscle, they selectively ute fibrin products to the nerve gap and provide reinnervate old end-plate sites.46 Considerable evscaffolding for the ingrowth of cells; and (4)metidence exists that growth-supporting or trophic abolic and other factors, which are purported to factors from the denervated muscle chemotropiinfluence peripheral nerve regeneration but are cally guide regenerating axons and provide supnot readily classified in any of the first three port for the cells of origin of the motor a x ~ n . ~ ~ " ' ~ classes. Sensory Receptor. Research on the reinnervation of muscle spindles suggests that reinnervation Neuronotrophic Factors. Neuronotrophic factors of sensory receptors or end organs is somewhat (NTFs) are most commonly macromolecular promodality specific,g4 although not as strongly as teins derived from various sources that promote that of motor fibers.I4 the survival and growth of specific neuronal

population^.'^^

FACTORS INFLUENCING NERVE GROWTH

Successful nerve regeneration requires neuronal growth. A formal definition of the components of neuronal growth has been provided by Crutcher" and includes ". . . neuronal survival, neurite formation, and elongation, synaptogenesis, and synthesis of specific components such as transmitters and related enzymes." C r ~ t c h e ralso ~ ~ defined a neuronal growth factor as ". . . an endogenous substance of any chemical composition that affects the growth and differentiation of neurons. . . ."

Peripheral Nerve Regeneration

Neuronotrophic factors are present in the target of innervation or the distal structure to be innervated, i.e., distal stump, or muscle or sensory receptor where they are taken up by the nerve terminals and transported back to the cell body by retrograde axonal transport where they exert supportive or survival-promoting effects (Fig. 3B). The archetypal NTF is nerve growth factor (NGF), which was first identified as a substance released by a mouse sarcoma that, when transplanted into chick embryos, caused sensory and

MUSCLE & NERVE

September 1990

789

sympathetic axons to grow toward the tumor. This factor has been purified, and the acidic fragment, beta-NGF, has been shown to be a polypeptide with a molecular weight of 26,000 daltons that binds to high-affinity receptors on responsive cells, notably sympathetic and sensory neurons of the peripheral nervous system.74 Nerve growth factor controls survival, neurite extension, and transmitter production in nerves from dorsal root ganglion cells and sympathetic ganglion cells. Nerve growth factor is synthesized in tissues innervated by sympathetic and sensory nerves (e.g., mouse salivary gland) and is transported from the axon terminals to the cell body where it exerts trophic or survival-promoting effect^.^ These functions have been demonstrated in vitro and in V ~ V O .Furthermore, '~' NGF can affect neurite navigation by c h e r n o t r o p i ~ mand ~ ~ has been shown to affect growth cone morphology." Nerve growth factor is important in nerve repair as well as in devel~pment,'~'and NGF and NGF receptors are synthesized in Schwann cells distal to the site of axotomy in rat sciatic nerve and are presumed to have trophic and tro ic effects on the regenerating proximal axons. 1& Considerable research is in progress to find new neuronotrophic factor^.'^ Recently, ciliary neuronotrophic factor (CNTF), trophic for ciliary ganglion cells, has been purified from denervated chick-eye intrinsic muscle6 where it can be found in increased amounts. There is also considerable evidence for a motor nerve growth factor (MNGF) released by normal muscle, denervated muscle,' l 8 and embryonic muscle.59 Furthermore, recent research in nerve regeneration chamber models after sectioning of the sciatic nerve in the rat has demonstrated the presence of factors neuronotrophic to all the components of the sciatic nerve- sensory, spinal motor, and sympathetic axons.*O This finding supports the theory that NTFs are important for the survival and regeneration of damaged adult neurons as well as for developing neurons. Factors. Neurite-promoting factors (NPFs) are substrate-bound glycoproteins that bind to the polycationic culture substrata in nerve culture and to the basal lamina of Schwann cells in vivo and strongly promote neurite initiation and extension (Fig. 3B).* The glycoprotein, laminin, is a major component of the basal lamina and binds to several other components of the membrane including type IV collagen, proteoglycan, and e n t a ~ t i n . ~Laminin ' can be produced by

Schwann cells'3 and promotes neurite growth.' Recent in vivo research has shown that the addition of a laminin-collagen gel to a nerve guide speeds the progress of cell migration and axonal regeneration across a gap.86 Another component of the basal lamina, fibronectin, has been shown to promote the growth of neurites in v i t r ~ . Fibronectin ~,~~ is believed to mediate cell attachment and when bound to substrate, promotes neurite outgrowth. The neuronal response to fibronectin, however, is weaker than that to laminin, and fibronectin is unable to exert directional navigation of neurites as laminin does7 Although substrate-bound NPFs have been presumed to exert their neurite-promoting activity by increasing the adhesion of the growth cone to the surface of the basal lamina, recent studies have failed to show a correlation between attachment efficiency and neurite outgrowth promoting activity.lS5' Neurite-promoting factors appear to have an ability to promote neurite outgrowth that is independent of the ability to affect growth cone adhesion. Neural cell adhesion molecule (N-CAM) and N-cadherin are membrane glycoproteins present in develo ing neural cells that promote cell adhe~ion.~'These molecules are also present on the axons of differentiated nerve cells. Antibodies to N-CAM and N-cadherin reduce the outgrowth of' central and eripheral axons on cellular substrates in vitro. 3 r After section of the rat sciatic nerve and insertion of the proximal and distal cut stumps into the opposite ends of a nerve guide, a polymerized fibrin matrix is formed from fibrinogen and fibronectin contained in exudate from the cut nerve ends (Fig. 5 ) . This matrix is an important substrate for Schwann cell and other cell migration into the environment of the gap between the nerve ends. Nerve regeneration through the chamber can be enhanced by the early addition or modification of this fibrin matrix. 145,148 Matrix Factors.

Neurite-Promoting

790

Peripheral Nerve Regeneration

Metabolic and Other Factors Promoting Nerve Regeneration

Sex Hormones, Estrogen has been shown to affect the growth of neurites from hypothalmic explants, and testosterone has been shown to stimulate the regeneration of transected hypoglossal or crushed sciatic nerve. 159 Thyroid Hormone. Thyroid hormone has been shown to enhance the rate of nerve regeneration

MUSCLE & NERVE

September 1990

FIGURE 5. The microenvironment of the nerve regeneration Note fluid, chamber as described by Williams and c011eagues.'~~ matrix, cellular, and axonal phases (see text for details). (Printed by permission of the Lahey Clinic.)

in peripheral nervelg and central nervous tissue.35 Adrenal Hormones. Corticotropin has been shown to promote more rapid axonal regeneration in rats122and to increase the number of regenerating fibers, presumably by increasing the availability of structural proteins to the axon terminal and increasing axonal t r a n ~ p o r t . ~ Org. ' 2766, a corticotropin analog, has recently been shown to enhance motor neuron collateral sprouting after peripheral nerve injury.29 Insulin. Insulin and insulinlike growth factor I1 have also been shown to induce neurite growth in various cell lines in Gangliosides. Gangliosides are major structural components of the neuronal plasma membrane that are synthesized in the neural soma and transported distally by fast axonal transport. Research has shown that gangliosides enhance the formation of neuromuscular junctions, stimulate neuronal sprouting, and promote nerve regeneration

Peripheral Nerve Regeneration

after injury.43 Results of clinical studies using this agent are mixed.58 Glia-Derived Protease Inhibitor. Glia-derived protease inhibitor, a polypeptide purified from glial-conditioned medium, promotes neurite outgrowth in neuroblastoma cells; the mechanism of action is unknown.47 Acidic and Basic Fibroblast Growth Factors. Acidic and basic fibroblast growth factors, which are related polypeptide growth factors found in brain tissue, mimic the effects of nerve growth factor in PC12 cell cultures. Acidic fibroblast growth factor has also been shown to enhance peripheral nerve regeneration in viva.*' Forskolin. A 40% increase in the rate of sensory nerve regeneration in the sciatic nerve of Rana pipiens has been achieved by the addition of forskolin.66 Forskolin, an adenylate cyclase stimulator, is believed to stimulate regeneration by increasing cyclic adenosine monophosphate (AMP) concentration and subsequently increasing protein synthesis. Leupeptin. The protease inhibitor, leupeptin, has been shown to inhibit wallerian degeneration and possibly traumatic degeneration. This results in an increase in the number of regenerating fibers and a lessening of muscle atrophy after transection of rat sciatic nerve." Catalase. Catalase has been shown to support neuronal survival in ~ i t r o 'and ~ possibly in V ~ V O . ~ ~ It is possible that catalase protects neurons against peroxide change.g3 Pyronin. The addition of a 0.1% solution of the dye, pyronin, to the drinking water of rats has been reported to accelerate axonal sprouting at the node of Ranvier in partly denervated soleus and gastrocnemius muscle.57 A more recent study by KeynesF4 however, has suggested that pyronin accelerates the removal of' degenerating axonal debris after nerve injury in the mouse. Keynes64 concluded that pyronin accelerates axonal sprouting by speeding the process of wallerkan degeneration. Isaxonine. Isaxonine has been shown to enhance axonal sprouting in rats but does not significantly increase the rate of axonal regenerati~n."~ Any potential therapeutic value is, however, limited by its hepatotoxicity.58 Muscle-Basement Membrane. Several studies have shown that rat peripheral nerve regenerates into muscle-basement membrane of degenerated rat muscle a l l ~ g r a f t s . ~ ~ ~ ~ ~ ~ ' ~ ~ Electrical Stimulation. Direct current electrical stimulation has been reported to enhance nerve

MUSCLE & NERVE

September 1990

791

regeneration in vivo.9,63,103Pulsed electromagnetic field therapy has been shown to improve recovery from peripheral nerve injury in the cat. The mechanism of this effect is not clear.g7 Conditioning Lesions. Peripheral nerve regeneration can be accelerated by a preexisting "conditioning" lesion, such as transection or crush, distal to the second lesion. This effect occurs when the conditioning lesion is made 2 weeksBgor 4 daysI3 before injury. The conditioning lesion may enhance regeneration by accelerating protein synthesis in the cell body. A recent study, however, suggests that the conditioning lesion simply provides additional time for wallerian degeneration. l 3 de Medinaceli "Reconnection Technique". In an attempt to improve the alignment between proximal axons and distal basal lamina tubes and to minimize the effect of traumatic degeneration, de M e d i n a ~ e l i has ~ ~ ' frozen ~~ cut nerve ends while bathing them in a physiological solution (Collins' solution) and then cut the ends with a vibrating razor blade. The nerve is then reconnected without tension and without sutures at the proximal and distal stump interface. This technique has resulted in improved functional results after re~air.~'.'~~ NERVE GUIDE REPAIR AND THE NERVE REGENERATION CHAMBER MODEL

The concept of bridging a gap between nerve ends with a nonneural conduit or nerve guide is of considerable contemporary interest. Known historically as tubulation or entubulation repair,I2' this method was re orted experimentally over 100 years ago by Cluck" who used decalcified bone as a neural conduit. Renewed interest in this concept has been engendered during the last decade (initially by Lundborg and Hansson8* in 1979), partially by the belief that the nerve guide concept may ultimately prove to be superior to conventional nerve repair and nerve graft techniques (Fig. 4).""."' First, surgical trauma to the nerve is less because the nerve stumps are usually placed into the guide with only one epineurial suture. This presumably results in less traumatic degeneration. Secondly, the nerve guide may prevent the ingrowth of fibrous scar tissue, which can become interposed between the proximal and distal stumps and interfere with the distal migration of the nerve sprouts. Thirdly, once the proximal stump is suspended in the nerve guide, the axons can begin distal migration without obstruction by the closely opposed, imperfectly aligned degenerating fascicles of the

792

Peripheral Nerve Regeneration

distal stump. Finally, the ideal nerve guide would permit the introduction of various growth-promoting factors into the lumen of the nerve guide and, thus, enable one to modulate or enhance the nerve regeneration process. Another and presently more important factor responsible for the new interest in the nerve guide technique is the realization that this surgical preparation provides an ideal window through which we may directly observe, examine, sample, and manipulate the microenvironment of the regenerating peripheral nerve, a major focus of contemporary research in both the peripheral and central nervous systems. This experimental synthetic nerve regeneration chamber model provides an in vivo model that is currently being used b man

Y

~a~orator~es,14,6~2,8~,83-86,92,102,1 10.1 12- 114.13 ,138.14

Y

Successful nerve regeneration has been achieved through nonneural conduits of many materials in various species from rat through rima ate."^ Microenvironment of the Nerve Guide. Williams and a s s ~ c i a t e s ' ~ " - ' ha ~ ~ve carefully studied the cellular and molecular events occurring in the microenvironment of the silicone nerve regeneration chamber model. These landmark studies have elucidated the early in vivo events occurring in the nerve guide microenvironment during nerve regeneration. T h e following sequence of events occurs (Fig. 5): 1. Day 1: The chamber fills with fluid, most likely an exudate from the proximal and distal stump. 2. Week 1 (2 to 6 days): Material in the fluid coalesces to form an acellular fibrin matrix. 3. Week 2 (7 to 14 days): Cells from both the proximal and distal stumps migrate into the chamber. Cells that will become perineural-like supporting cells migrate in first and are followed by Schwann cells and endothelial cells. 4. Week 3 (15 to 21 days): Axons begin to grow in from the proximal stump only at a rate of 1 to 2 mm per day and enter the distal stump at the end of the third week with myelination following after a 5-day lag. 5. Lastly, axons enter the distal stump to reinnervate the end organs. These authors146-148 theorize that NTFs are in the chamber fluid early in the regeneration process and provide support for the proximal nerve via retrograde axonal transport. Furthermore, the fluid contains precursors for the fibrinfibronectin matrix, which favors the immigration

MUSCLE &.NERVE

September 1990

of Schwann and other cells. Cellular elements then condition the matrix and with the addition of NPFs, promote the onset and guidance of axonal migration. Interestingly, neuronotrophic factor activity is greatest in the first few days of regeneration. Sensory neuronotrophic factor activity peaks at 3 hours, sympathetic at 1 day, and motor at 3 days. Neurite-promoting factors peak during the third week when axon migration begins. This enlightening research will obviously lead to significant further advances. Nerve Regeneration Through the Nerve Quide: Im. portance of the Innervation Target. The sciatic

nerve of the adult rat will regenerate across a gap through an inert tubular prosthesis and form an anatomically well-defined multifasciculated nerve that effectively establishes communication with the distal stump (Figs. 6A and 6B) as long as the distal stump is present in the nerve guide.”* A gap length greater than 10 mm o r no distal stump in the guide resulted in the failure of proximal stump nerve re eneration through nonpermeable tubes in the rat!2~83~11zT h e distal stump is an important source of NTFs, documented not only by the failure of regeneration when the distal stump

is omitted but also by the discovery that fluid removed from the chamber at 1 week contains a trophic factor for rodent dorsal root ganglia.84 In subsequent studies, trophic factors toward all components of the sciatic nerve-sensory, spinal motor, and sympathetic- have been found in the chamber fluid.80 of Nerve Regeneration. Accurate growth to and innervation of the appropriate distal target is of critical importance to the success of nerve regeneration. An appreciation of this principle underlies the attention to detail exerted in the current microsurgical techniques of nerve repair that emphasize accurate fascicular alignment.” The results of the best modern nerve repair, however, are still di~appointing.~’ Results from several new studies using Yshaped modifications of the nerve guide model suggest that biologic processes may provide targetspecific nerve regeneration across a gap. These data have forced us to question whether or not our surgical manipulations might obstruct or hinder rather than help this intricate biologic process. The idea that the target of innervation can exert a guiding or attracting “neurotropic influence” on a regenerating proximal axon is not new. Target-Specificity

FIGURE 6. Nerve regenerationthrough a nerve guide. (A) The nerve guide is used to bridge rat sciatic gaps of various lengths. (B) The sciatic nerve will regenerate across a 10-rnm gap as long as a distal nerve is present. (Reproduced with permission from Seckel BR, Chiu TH, Nyilas E,Sidrnan RL: Nerve regenerationthrough synthetic biodegradable nerve guides: regulation by the target organ. flast Reconstr Surg 74173- 181, 1984.)

Peripheral Nerve Regeneration

MUSCLE & NERVE

September 1990

793

FIGURE 7. Target specificity of nerve regeneration. Regenerating peroneal nerve fibers selectively grow to distal peroneal fibers. (Printed by permission of the Lahey Clinic.)

F o r ~ s m a nin~ ~1898 and subsequently Ramon Y Cajallo4 and Harrison52 have all provided supporting evidence that the advancing tip of the regenerating axon is chemotropically attracted to its appropriate distal nerve target. Weiss and Taylor'43 challenged this theory of target-specificity or neurotropism by reporting in 1944 that nerve fibers placed into the single proximal limb of a Y-shaped arterial tube graft failed to distinguish between nerve tissue and nonnerve tissue laced in the distal Y-limbs. Weiss and Taylorg3 theorized that contact guidance, possibly by fibrin clot, and not neurotropic chemoattraction determined the course the regenerating axon would take. Recent experimental evidence has, however,

given strong support to the original ForssmanRamdn Y Cajal theory of neurotropism. In one study,' l4 the proximal peroneal fascicle of the rat sciatic nerve was sutured into the single proximal limb of a Y-shaped nerve guide opposite to an appropriate distal peroneal stump and an inappropriate distal tibia1 stump in the opposing Y-ends 8 mm away (Fig. 7). In this study, the proximal peroneal axons grew preferentially by an average ratio of 2 : 1 to the appropriate distal peroneal fascicle.' l4 These findings concur with those of and co11eagues'02 and OChig6 and suggest that fascicle-to-fascicle target-specific nerve regeneration is possible. Other recent studies using Y chambers have shown that peripheral nerve tissue can distinguish between distal nerve and tenand that proximal motor axons can distinguish and preferentially grow to distal motor axons as opposed to sensory ax on^.'^ All of these findings support the theory of neurotropism and suggest that adult peripheral nerve tissue is capable of discriminative target-specific growth. It is to

f

a DS

PS

FIGURE 8. Enhancement of nerve regeneration in vivo. Acidic fibroblast growth factor (aFGF) plus collagen is added to the lumen of the nerve guide. (Reproduced with permission from Cordeiro PG, Seckel BR, Lipton SA, D'Amore PA, Wagner J, Madison R: Acidic fibroblast growth factor enhances peripheral nerve regeneration in vivo. Plast Reconstr Surg 88:1013-1020, 198%)

794

Peripheral Nerve Regeneration

FIGURE 9. HRP-labeling technique. Retrograde horseradish peroxidase (HRP) labeling studies are used to label regenerated neurons and to correlate axonal and neural counts. Both axonal and neural counts were increased following the addition of aFGF to the nerve guide, which proved that the increases in the axonal counts were not due to branching. (Printed by permission of the Lahey Clinic.)

MUSCLE & NERVE

September 1990

be hoped that further research to provide a better understanding of this process will lead to techniques of enhancing this biologic guidance system and improving the functional results of nerve regeneration and repair. Although the nerve guide model is a research tool, the concept that growth-promoting agents could be introduced into the regenerative microenvironment in the guide lumen in a therapeutic regimen is most appealing. This type of enhancement has recently been achieved in the rat.*l Acidic fibroblast growth factor (aFGF) was added to a collagen-filled nerve guide into which the proximal and distal stumps of the cut sciatic nerve had been inserted and separated by a 5 mm gap (Fig. 8). Axon counts revealed a significant increase in the number of axons regenerating across this guide. Furthermore, retrograde horseradish peroxidase labeling studies (Fig. 9) revealed that a greater number of primary sensory and motor neurons extended axons through the nerve guide treated

Enhancement of Nerve Regeneration in Vivo.

with aFGF. Thus, the effect of aFGF in enhancing nerve regeneration is not simply an increase in axonal branching in the guide. Acidic fibroblast growth factor is a heparin-binding protein purified from bovine brain'" and has mitogenic activity for capillary endothelial cells, astrocytes, and fibroblast^.^^*'^^^^^ Acidic fibroblast growth factor is angiogenic in vivo. It induces neuritelike extension by PC12 cells'3' and can increase neurite extension by rat retinal ganglion cells in ~ i t r o . ~ ~ , ~ Whether aFGF exerts this growth-promoting activity by a direct effect on the neural cell body via retrograde axonal transport or via surface effect on the basal lamina of the supporting nonneural cells or indirectly by increasing the vascular supply via an angiogenic effect is not known. Trophic or guidance influences have been ,demonstrated for aFGF in peripheral nerve.'" Laminin, an important basal membrane component, is associated with neurite-promoting activity in vitro and has also been tested in a nerve guide model. Although these investigators86 found that laminin enhanced regeneration in the

Table 1. Factors reported to enhance nerve regeneration. Factor Nerve growth factor (NGF) Ciliary neuronotrophic factor (CNTF) Motor nerve growth factor (MNGF) Fibronectin Laminin Neural cell adhesion molecule (N-CAM) N-cadherin Fibrin Fibronectin Hormones Estrogen Testosterone Thyroid hormone Corticotropin Org. 2766 insulin Catalase Acidic fibroblast growth factor (aFGF) Basic fibroblast growth factor (bFGF) Forskolin Glia-derived protease inhibitor (GdNPF) GM-1 Gangliosides lnsulinlike growth factor lsaxonine Leupeptin Muscle basal lamina Pyronin Conditioning lesion Electrical stimulation de Medinaceli technique

Peripheral Nerve Regeneration

Type/Mechanism of action Neuronotrophic factor (NTF) NTF NTF Neurite-promoting factor (NPF) NPF ? NPF ? NPF Matrix factor (MF) MF (Precursor) Metabolic ? increased protein synthesis Metabolic ? increased protein synthesis Metabolic ? increased protein synthesis Metabolic ? increased protein synthesis Metabolic ? increased protein synthesis Metabolic ? increased protein synthesis Protection from peroxide damage '? NTF ? NTF Increased protein synthesis ? NPF ? ? NTF Increased axonal transport, increased polymerization of tubulin Inhibits traumatic degeneration ? NPF ? NTF Speeds wallerian degeneration Earlier wallerian degeneration ? Minimize traumatic degeneration

MUSCLE & NERVE

September 1990

795

guide at 2 weeks, at 6 weeks, nerve regeneration was inhibited, an event which the authors attributed to acceleration of biodegradation of the nerve guide by laminha6 Williams and ~ o l l e a g u e s ' ~have ~ ~ 'been ~ ~ able to increase the size of the regeneration cable, the speed of the regeneration process, and the gap distance bridged from 10 mm to 15 mm by modifying or enhancing the acellular fibrin matrix bridge in the silicone nerve regeneration chamber model. These investigators have proposed that the fibrin matrix serves as a substrate for circumferential, endothelial, and Schwann cell migration into the nerve regeneration chamber (Fig. 5). Further study has shown that a mixture of laminin, testosterone, ganglioside GM- 1, and catalase enhances the progress of nerve regeneration in the 16-day nerve regeneration ~ h a m b e r . ' ~ SUMMARY

The microenvironment of the tip of the regenerating peripheral nerve is a major focus of contemporary research into methods of enhancing peripheral nerve regeneration. The discovery that the peripheral nerve microenvironment will sup-

port CNS tissue regeneration coupled with the failure of purely technical microsurgical repair techniques to improve nerve function after injury has resulted in an intensified research effort in this area. Progress toward isolating new growth-promoting agents has been accelerated by in vitro cell culture methods and more recently by the nerve guide or nerve regeneration chamber model in which agents can be tested for the ability to promote nerve regeneration in vivo. Research in the past century has resulted in isolation of many factors that are reported to enhance peripheral nerve regeneration. A partial list is summarized in Table 1. The nerve guide o r nerve regeneration chamber model is an in vivo surgical preparation in which we may observe, sample, and manipulate the microenvironment of the regenerating peripheral nerve. This technique coupled with methods for histologic and functional assessment of nerve regeneration will hopefully lead to the discovery of therapeutically useful agents for the treatment of patients with either peripheral or central nervous system injury.

REFERENCES 1. Adler R, Jerdan J, Hewitt AT: Responses of cultured

neural retinal cells to substratum-hound laminin and other extracellular matrix molecules. Deu Biol 1985;112:100-114. 2. Adler R, Manthorpe M, Skaper SD, Varon S: Polyornithine-attached neurite-promoting factors (PNPFs). Culture sources and responsive neurons. Brain Res 1981;206:129- 144. 3. Aguayo AJ, Epps J, Charron L, Bray GM: Multipotentiality of Schwann cells in cross anastomosed and grafted myelinated and unmyelinated nerves. Quantitative microscopy and radioautography. Brain Res 1976;104:1-20. 4. Akers RM, Mosher DF, Lilien JE: Promotion of retinal neurite outgrowth by substratum-hound fibronectin. Dev Biol 1981;86:179- 188. 5. Bandtlow CE, Heumann R, Schwab ME, Thoenen H: Cellular localization of nerve growth factor synthesis by in situ hybridization. E M B O J 1987;6:891-899. 6. Barbin G, Manthorpe M, Varon S: Purification of the chick eye ciliary neuronotrophic factor. J Neurochem 1984;43:1468- 1478. 7. Baron-Van Evercooren A, Kleinman HK, Seppa HE, Rentier B, Dubois-Dalcq M: Fihronectin promotes rat Schwann cell growth . and motility. Cell Biol 1982;93:21 1-2 16. 8. Barron KD: Neuronal responses to axotomy: consequences and possibilities for rescue from permanent atrophy or cell death, in Seil FJ (ed): Frontzers of Clinical Neuroscience. Neural Regeneration and Transplantation. New York, Alan R. Liss, 1989, vol 6 , p p 79-99. 9. Beveridge JA, Politis MJ: Use of exogenous electric current in the treatment of delayed lesions in peripheral nerves. Plast Reconrtr Surg. 1988;82:573-579. 10. Bisby MA, Redshaw JD, Carlsen RC, Reh TA, Zwiers H:

796

Peripheral Nerve Regeneration

Growth associated proteins (GAPS) and axonal regeneration, in Gordon T, Stein RB, Smith PA (eds): Neurology and Neurobiology. The Current Status of Peripheral Nerue Regeeneration. New York, Alan R. Liss, 1988, vol 38, p p 3552. 1 1 . Bora FW Jr, Pleasure DE, Didizian NA: A study of nerve regeneration and neuroma formation after nerve suture by various techniques. J Hand Surg 1976;1 : 138- 143. 12. Bothwell M: Insulin and somatemedin MSA promote nerve growth factor-independent neurite formation by cultured chick dorsal root ganglionic sensory neurons. J Neurosci Res 1982;8:225-231. 13. Brown MC, Hopkins WG: Role of degenerating axon pathways in regeneration of mouse soleus motor axons. J Physiol (Lond) 1981 ;318:365- 373. 14. Brushart TM: Preferential reinnervation of motor nerves by regenerating motor axons. J Neurosci 1988;8:10261031. 15. Bunge RP: Changing uses of nerve tissue culture 19501975, in Tower DB (ed): The NeruouJ System. New York, Raven Press, 1975, pp 31-42. 16. Bunge RP, Bunge MB: Interactions between Schwann cell function and extracellular matrix production. Trends Neurosci 1983;7:499-505. 17. Bunge RP, Bunge MB: Tissue culture observations relating to peripheral nerve development, regeneration, and disease, in Dyck PJ, Thomas PK, Lambert EH, Bunge KP (eds): Pe+eral Neuropathy, ed 2. Philadelphia, W.B. Saunders, 1984, vol 1 , pp 378-399. 18. Cahaud HE, Rodkey WG, McCarroll HR Jr, Mutz SB, Niehauer JJ: Epineurial and perineurial fascicular nerve repairs: a critical comparison. J Hand Surg 1976; 1:131137. 19. Cockett SA, Kiernan J A : Acceleration of peripheral ner-

MUSCLE & NERVE

September 1990

vous regeneration in the rat by exogenous triiodothyronine. Exp Neural 1973;39:389-394. 20. Connolly JL, Seeley PJ, Greene LA: Regulation of growth cone morphology by nerve growth factor: a comparative study by scanning electron microscopy. J Neurosci Res 1985;13:183- 198. 21. Cordeiro PG, Seckel BR, Lipton SA, D’Amore PA, Wagner J , Madison R Acidic fibroblast growth factor enhances peripheral nerve regeneration in vivo. Plast Reconstr Surg 1989;88:1013-1020. 22. Cornbrooks CJ, Carey DJ, McDonald JA, Timple R, Bunge RP: In vivo and in vitro observations on laminin production by Schwann cells. Proc Natl Acad Sci USA 1983;80:3850-3854. 23. Cornbrooks CJ, Carey DJ, Timpl R, McDonald JA, Bunge RY: Immunohistochemical visualization of fibronectin and laminin in adult rat peripheral nerve and peripheral nerve cells in culture. Soc Neu.rosci Abstr 1982; 8(pt 1):240. 24. Crain SM: Neurophysiologic Studies in Tissue Culture. New York, Raven Press, 1976. 25. Crutcher KA: The role of growth factors in neuronal development and plasticity. CRC Crzt Rev Clin Neurobiol 1986;2:297-333. 26. D’Amore PA, Klagsbrun M: Endothelial cell mitogens derived from retina and hypothalamus: biochemical and biological similarities. J Cell Biol 1984;99(4 pt 1):15451549. 27. David S, Aguayo AJ: Axonal elongation into peripheral nervous system ‘bridges’ after central nervous system injury in adult rats. Science 1981;214:931-933. 28. Davies AM, Bandtlow C, Heumann R, Korsching S, Rohrer H, Thoenen H: Timing and site of nerve growth factor synthesis in developing skin in relation to innervation and expression of the receptor. Nature 1987; 326:353- 358. 29. cle Koning P, Verhaagen J, Sloot W, Jennckens FG, Gispen WH: Org. 2766 stimulates collateral sprouting in the soleus muscle of the rat following partial denervation. Muscle Nerve 1989 ;12 :353 - 359. 30. de Medinaceli L, Seaber AV: Experimental nerve reconnection: importance of initial repair. Microsurgery 1989;10:56- 70. 31. de Medinaceli L, Wyatt RJ, Freed WJ: Peripheral nerve reconnection: mechanical, thermal, and ionic conditions that promote the return of function. Exp Neural 1983;81:469-487. 32. Dodd J, Jessell TM: Axon guidance and the patterning of neuronal projections in vertebrates. Science 1988; 242 :692-699. 33. Dyck PJ, Karnes J, Lais A, Lofgren EP, Stevens JC: Pathologic alterations of the peripheral nervous system of humans, in Dyck PJ, Thomas PK, Lambert EH, Bunge R (eds): Peripheral Neuropathy. Philadelphia, W.B. Saunders, 1984, VOI 1, pp 760-870. 34. Federoff S, Hertz L (eds): Cell, Tissue and Organ Cultures in Neurobiology. New York, Academic Press, 1978. 35. Fertig A, Kiernan JA, Seyan SS: Enhancement of axonal regeneration in the brain of the rat by corticotrophin and triiodothyronine. Exp Neural 1971 ;33:3?2-385. 36. Fischbach GD, Nelson PG: Cell culture in neurobiology, in Brookhart JM, Montcastle VB (eds): Handbook of Physiology series, The Nervous System, sect 1 , part 2. Bethesda, MD, American Physiological Society, 1977, vol 1, pp 719774. 37. Foehring RC, Sypert GW, Munson JB: Properties of selfreinnervated motor units of medial gastrocnemius of cat. 11. Axotomized motoneurons and the time course of recovery. J Neurophysiol 1986;55:947-965. 38. Forssman J: Ueber die Ursachen, welche die Wachsthumsrichtung der peripheren Nervenfasern bei der Regeneration bestimmen. Beitr Pathol Anat 1898;24:56- 100.

Peripheral Nerve Regeneration

39. Friede RL, Bischhausen R: The fine structure of stumps of transected nerve fibers in subserial sections. J Neural Sci 1980;44:181-203. 40. Glasby MA, Gschmeissner S, Hitchcock RJ, Huang CL: The dependence of nerve regeneration through muscle grafts in the rat on the availability and orientation of basement membrane. J Neurocytol 1986;15:497-510. 41. Cluck T : Ueber Neuroplastik auf dem Wege der Transplantation. Arch Klin Chir 1880;25:606-616. 42. Gordon T: Dependence of peripheral nerves on their target organs, in Burnstock G, OBrien RA, Vrbov’a G (eds): Somatic and Autonomic Nerve-Muscle In.teractions. Amsterdam, Elsevier, 1983, pp 289-325. 43. Gorio A, Vitadello M: Ganghoside prevention of neuronal functional decay, in Seil FJ, Herbert E, Carlson BM (eds): Progress in Brain Research. Neural Regeneralion. Amsterdam, Elsevier, 1987, vol 71, pp 203-208. 44. Grabb WC, Bement SL, Koepke GH, Green RA: Comparison of methods of peripheral nerve suturing in monkeys. Plat Recomb Surg 1970;46:31 - 38. 45. Grafstein B, McQuarrie JG: Role of the nerve cell body in axonal regeneration, in Cotman CW (ed): Neuronal Plusticity. New York, Raven Press, 1978, pp 155-196. 46. Grinnell AD: Synaptic plasticity following motor nerve injury in frogs, in Gordon T, Stein RE, Smith PA (eds): Neurology and Neurobiology. The Current Status of Peripheral Nerve Regeneration. New York, Alan R. Liss, 1988, vol 38, pp 223-234. 47. Guenther J, Nick H, Monard D: A glia-derived neuritepromoting factor with protease inhibitor activity. EMBO J 1985;4:1963- 1966. 48. Gundersen RW: Response of sensory neurites and growth cones to patterned substrata of laminin and fibronectin in vitro. Deu Biol 1987;121:423-431. 49. Gundersen KW, Barrett JN: Charactcrization of the turning response of dorsal root neurites toward nerve growth factor.] Cell Biol 1980;8?(sec 3 pt 1):546-554. 50. Hafteck J, Thomas PK: Electron-microscope observations on the effects of localized crush injuries on the connective tissues of peripheral nerve. J Anat 1968;108:233-243. 51. Hall DE, Neugebauer KM, Reichardt LF: Embryonic neural retinal cell response to extracellular matrix proteins: developmental changes and effects of the cell substratum attachment antibody (CSAT). J Cell Biol 1987;104:623-634. 52. Harrison RG: The outgrowth of the nerve fiber as a mode of protoplasmic movement. J Exp Zoo1 1910;9:787846. 53. Henderson CE, Huchet M, Changeux JP: Denervation increases a neurite-promoting activity in extracts of skeletal muscle. Nature 1983;302:609-61 I. 54. Henderson CE, Huchet M, Changeux JP: Neurite-promoting activities for embryonic spinal neurons and their developmental changes in the chick. Deu Biol 1984;1 04:336- 347. 55. Hillarp NA, Olivecrona H: Role played by the axon and the Schwann cells in the degree of myelination of the peripheral nerve fibre. Acta Anut 1946;2:17-32. 56. Hodgkin AL, Katz B: Effect of calcium 011 the axoplasm of giant nerve fibres. J Exp Biol 1949;26:292-294. 57. Hoffman €1: Acceleration and retardation of‘the process of axon-sprouting in partially denervated muscles. Aust J Exp Biol Med Sci 1952;30:541-566. 58. Horowitz SH: Therapeutic strategies in promoting peripheral nerve regeneration. Mu.scle Nerve 1989;12:314322. 59. Hsu L, Natyzak D, Trupin GL: Neuronotrophic effects of skeletal muscle fractions on neurite development. Muscle Nerve 1984;7:2 11- 2 17. 60. Hurst LC, Badalamente MA, Ellstein J, Stracher A: Inhibition of neural and muscle degeneration after epineural neurorrhaphy. J Hand Surg [Am] 1984;9:564-572.

MUSCLE & NERVE

September 1990

797

61. Ishii DN: Relationship of insulin-like growth factor I1 gene expression in inuscle to synaptogenesis. Proc Natl Acud Sci U S A 1989;86:2898-2902. 6‘2. J e n q CB, Coggeshall RE: Long-term patterns of axon regeneration in the sciatic nerve and its tributaries. Brain Res 1985;345:34-44. 63. Kerns JM, Freeman JA: Enhancement of nerve regeneration and functional recovery by DC electrical stimulation, Abstract, p 197, in Jenq C-B, Coggeshall RE: Does optimal peripheral nerve regeneration require cells from the general connective tissue? in Gordon ‘I-, Stein RB, Smith PA (eds): Neurology and Neurobiology. The Current Status of Peripheral Nerve Regeneration. New York, Alan R. Liss, 1988, vol 38, pp 187- 199. 64. Keynes RJ: The effects of pyronin on sprouting and regeneration of mouse motor nerves. Bruin Res 1982;253:13- 18. 65. Keynes RJ, Hopkins WG, Huang LH: Regeneration of mouse peripheral nerves in degenerating skeletal muscle: guidance by residual muscle fibre basement membrane. Bruin Res 1984;295:275-281. 66. Kilnier SL, CarIscn RC: Forskolin activation of adenylate cyckase in vivo stimulates nerve regeneration. Nature 1984;307:455-457. 67. Kimrnel DI., Moyer EK: Dorsal roots following anastomosis of the central stumps. J Camp Neuroi’ 1947;87:289319. 68. Krystosek A, Seeds NW: Plasrninogen activator release at the neuronal growth cone. Science 1981;213:1532- 1534. 69. Kuno M: Target-dependence of the survival and electrophysiological properties of spinal motoneurons in the mammal, in Gordon T, Stein KB, Smith PA (eds): Neurology and Neurobiolo,~.The Current Status of Peripheral Nerve Regeneration. New York, Alan R. Liss, 1988, vol 38, p p 3 13.

70. Kuno M, Miyata Y, MuAoz-Martinez EJ: Differential reaction of fast and slow alpha-motoneurones to axotorny. J Physiol (Lond) 1974;240:725- 739. 7 1 . Kurie T: Microtechniques in neurological surgery. C h n Neurosurg 1964;11:128-137. 72. Lander AD: Molecules that make axons grow. Mol Neurobiol 1987; 1213-245. 73. 1,asek RJ, Hoffman PN: T h e neuronal cytoskeleton, axonal transport and axonal growth, in Goldman R, Pollard T, Rosenbaum J (cds): Microtubules and Related Proteins. Cell Motility, Book C. Cold Spring Harhor Co~ferenceon Cell Proliferation. New York, Cold Spring Harbor, 1976, vol 3 , p p 1021-1049. 74. I.evi-Montalcini R: ‘The nerve growth factor: thirty-five years later. B M B 0 . J 1987;6:1 145-1154. 75. Levi-Montalcini R, Hamburger V: Selective growth stimulating effects of mouse sarcoma on the sensory and sympathetic nervous system of the chick embryo. J Exp Zoo1 1951; 116321 -362. 76. Lipton SA, Wagner JA, Madison RD, D’Amore PA: Acidic fibroblast growth factor enhances regeneration o f processes by postnatal mammalian retinal ganglion cells in culture. Soc Neuroscz Abstr 1987;13(pt 3):433.11. 77. Lipton SA, Wagner JA, Madison RD, D’Amore PA: Acidic fibroblast growth factor enhances regeneration of processes by postnatal mammalian retinal ganglion cells in culture. Proc Natl Acad Scz USA 1988;85:2388-2392. 78. Lobb R, Sasse J, Sullivan K, Shing Y, D’Aniore P, Jacobs J, Klagsbrun M: Purification and characterization of‘ heparin-binding endothelial cell growth factors. J Biol Chem 1986;261:1924- 1928. 79. Longo FM, Hayman EG, Davis GE, Ruoslahti E, Engvall E, Manthorpe M, Varon S: Neurite-promoting factors and extracellular matrix components accumulating in vivo within nerve regeneration chambers. Bruin Res 1984; 309: 105- 117. 80. Longo FM, Manthorpc M, Skaper SD, Lundborg G,

798

Peripheral Nerve Regeneration

Varon S: Neuronotrophic activities accumulate in vivo within silicone nerve regeneration chambers. Brazz Res 1983;261: 109- 116. 81. Lundborg G, Dahlin LR, Danielsen N, Nachenison AK: Tissue specificity in nerve regeneration. Scand J Plast Reconsti Surg 1986;20:279-283. 82. Lundborg G, Hansson HA: Regeneration of peripheral nerve through a preformed tissue space. Preliminary observations on the reorganization of regenerating nerve fibres and perineurium. Brain Res 1979; 178:573-576. 83. Lundborg G, Hansson HA: Nerve regeneration through preformed pseudosyrrovial tubes. A preliminary report of a new experimental model for studying the regeneration and reorganization capacity of peripheral nerve tissue. J Hand Surg 1980;5:35-38. 84. Lundborg G, Longo FM, Varon S: Nerve regeneration model and trophic lactors in vivo. Brain Res 1982;252:157- 161. 85. Mackinnon SE, Dellon AI,, Lundborg G, Hudson AR, Hunter DA: A study of neurotropltism in a primate mode1.J Hand Surg (Am) 1986;11:888-894. 86. Madison K, da Silva CF, Dikkes P, Chiu T H , Sidman RL: Increased rate of peripheral nerve regeneration using bioresorbable nerve guides and a laminin-containing gcl. Exp Neural 1985;88:767-772. 87. Manthorpe M , Skaper SD, Williams LR, Varon S: Purification of adult rat sciatic nerve ciliary neuronotrophic factor. Bruin Res 1986;367:282-286. 88. McQuarrie IG: Regulatory proteins enter regenerating axons ahead of. microtubules. Soc Neurosci Abstr 1986;12(pt 1):513. 89. McQuarrie IG, Grafstein B, Gershon MD: Axonal regeneration in the rat sciatic nerve: effect of a conditioning lesion and of dbcAMP. Bruin Res 1977;132:443-453. 90. Millesi H: Reappraisal of nerve repair. Surg Clin North Am 1981 ;61 :321-340. 91. Millesi H: Nerve grafting. Clin Plast Surg 1984;11:105113. 92. Molander H , Olsson Y, Engkvist 0, Bowaki S, Eriksson I: Regeneration of peripheral nerve through a polyglactin tube. Muscle Nerve 1982;5:54-57. 93. Miiller H, Williams LR, Varon S: Nerve regeneration chamber: evaluation of exogenous agents applied by multiple injections. Brain RPS1987;413:320-326. 94. Munson JB, Collins WF 111, Mendell 1.M: Reinnervation of muscle spindles by groups Ia and Ib fibers is consistent with specificity in the reinnervation process, in Gordon T, Stein RB, Smith PA (eds): Neurolqg and Neurobiology. The Current Status of Peripheral Newe Regeneratzon. New York, Alan R. Liss, 1988, vol ?A, p p 259-268. 95. Nathaniel EJ, Pease DC: Degenerative changes in rat dorsal roots during Wallerian degeneration. ,I Ulti-usiruct Res 1963;9:511-532. 96. Ochi M: Experimental study on orientation of regenerating fibers in the severed peripheral nerve. HirosA%maJ Med Sci 1983;32:389-406. 97. Orgel MG, OBrien WJ, Murray HM: Pulsing electromagnetic field therapy in nerve regeneration: an experimental study in the cat. Plast Reconstr Surg 1984;73:173- 183. 98. Orgel MG, Terzis JK: Epineurial vs. perineurial repair. An ultrastructural and electrophysiohgical study of nerve regeneration. Plast Reconstr Surg 1977;60:80-91. 99. Pecot-Dechavassine M, Mira JC: Effects of isaxonirie on skeletal muscle reinnervation in the rat: an electrophysiologic evaluation. Muscle Nerve 1985;8:105- 114. 100. Pettman B, Weibel M, Sensenbrenner M, Labourdette G: Purification of two astroglial factors from bovine brain. FEBS Lett 1985;189:102- 108. 101. Politis MI: Retina-derived growth-promoting extract supports axonal regeneration in v h . Bra& Re.\ 1986; 364:369-371. 102. Politis MJ, Ederle K, Spencer PS: Tropism in nerve re-

MUSCLE & NERVE

September 1990

generation in vivo. Attraction of regenerating axons by diffusible factors derived from cells in distal nerve stumps of transected peripheral nerves. Brain Res 1982;253: 112. 103. Poh& MJ, Zanakis MF, Albala BJ: Facilitated regeiieration in the rat peripheral nervous system using applied electric fields.] Trauma 1988;28:1375- 1381. 104. Ramon Y Cajal S: Degeneration and Regeneration of the Nervoiw System. London, Oxford University Press, 1928. 105. Recio-Pinto E, Rechler MM, Ishii DN: Effects of insulin, insulin-like growth factor-11, and nerve growth factor on neurite formation and survival in cultured sympathetic and sensory neurons.] Neurosci 1986;6:1211-1219. 106. Richardson PM, Ebendal T: Nerve growth activities in rat peripheral nerve. Brain Res 1982;246:57-64. 107. Richardson PM, Verge VM: The induction of a regenerative propensity in sensory neurons following peripheral axonal injury. J Neurocytol 1986;15:585-594. 108. Sanes JR, Marshall LM, McMahan UJ: Reinnervation of muscle fiber basal lamina after removal of myofibers. Differentiation of regenerating axons at original synaptic sites.] Cell Biol 1978;78:176- 198. 109. Sato G (ed): Current topic^ in Neurobiology Series. Tissue Culture oflhe Nervous System. New York, Plenum Press, vol 1, 1973. 110. Scaravilli F: The influence of distal environment on peripheral nerve regeneration across a gap. J Neurocylol 1‘384;13: 1027- 104 1. 1 1 1 . Schlaepi‘er WW: Experimental alterations of neurofilamerits and neurotubules by calcium and other ions. Exp Cell Res 1971;67:73-80. 112. Seckel BR, Chiu I‘H, Nyilas E, Sidman KL: Nerve regeneration through synthetic biodegradable nerve guides: regulation by the target organ. Plast Reconstr Surg 1984;74:173- 181. 113. Seckel BR, Ryan SE, Gagne RG: Accuracy of reinnervation following nerve gap bridging, in Proceedings of the 30th Annual Meeting of the Plastic Surgery Research Council, Portland, Oregon, May 22-25, 1985, pp 93-95. 114. Seckel BR, Ryan SE, Gagne RG, Chiu TH, Watkins E Jr: Target-specific nerve regeneration through a nerve guide in the rat. Plast Reconstr Surg 1986;78:793-800. 115. Seil FJ: Axonal sprouting in response to injury, in Seil FJ (ed): Frontiers of Clinical Neuroscience. Neural Regmeration and Tramplantation. New York, Alan R. Liss, 1989, vol 6, 123- 135. 116. Skene JH, Jacobson RD, Snipes GJ, McGuire CB, Norden JJ, Freernan JA: A protein induced during nerve growth (GAP-43) is a major coniponent of growth-cone nienibranes. Science 1986;233:783-786. 117. Skene JH, Willard M: Axonally transported proteins associated with axon growth in rabbit cenlral and peripheral nervous sys1ems.J Cell Biol 1981;89:96- 103. 118. Slack JR, Hopkins WG, Pockett S: Evidence for a motor nerve growth factor. Muscle Nerve 1983;6:243-252. 119. Smith PA, Shapiro J, Gurtu S, Kelly MEM, Gordon T: The response of ganglionic neui-ones to axotomy, in Gordon T, Stein RB, Smith PA (eds): Neurology and Neurobiology. The Current Status of Peripheral Nerve Regeneration. New York, Alan R. Liss, 1988, vol 38, pp 15-23. 120. Snyder RE, Chan H, Smith RS: Structural and functional properties of the junction between the parent and regenerating portions of myelinated axons, Abstract, pp 8485, in Yu WHA: Testosterone prevents axotomy-induced motoneuron death in adult rat, in Gordon T , Stein RB, Smith PA (eds): Neurology and Neurnbiology. The Current Stutw .f Peripheral Nerve Regeneratzon. New York, Alan R. I&, 1988, vol 38, pp 79-88. 121. Stocckel K , Thoenen H: Retrograde axonal transport of nerve growth factor: specificity and biological importance. Brain Kus 3975;85:337-341. 122. Strand FL, Kung T I ’ : ACTH accelerates recovery of neu-

Peripheral Nerve Regeneration

romuscular function following crushing of peripheral nerve. Peptides (Fayetteville) 1980;1 :135- 138. 123. Suematsu N: Tubulation for peripheral nerve gap: its history and possibility. Microsurgery 1989;10:71-74. 124. Sunderland S: Nerves and Neriie Injuries, ed 2 . Edinburgh, Churchill Livingstone, 1978. 125. Sunderland S: The old order changeth. Periph.era1 Nerve Rep Regeia 1986;1:5-7. 126. Sunderland S, Bradley KC: Denervation atrophy of the distal stump of a severed nerve. J Comp Neurol 1950;93:401-409. 127. Sunderland S, Bradley KC: Endoneurial tube shrinkage in the distal segment of a severed nerve. J Comp Neurol 1950;93:411-420. 128. Sunderland S, Bradley KC: Perineurium of peripheral nerves. Anat Rec 1952;113:125-141. 129. Taniuchi M, Clark HB, Schweitzer JB, Johnson EM Jr: Expression of nerve growth factor receptors by Schwann cells of axotomized peripheral nerves: ultrastructural location, suppression by axonal contact, and binding properties. J Neurosci 1988;8:664- 68 1. 130. Thomas PK: The connective tissue of peripheral nerve: an electron microscope study. J Anat 1963;97:35-44. 131. Togari A, Dickens G, Kuzuya H, Guroff G : The effect of fibroblast growth factor on PC12 cells. J Neurosci 1985;5:307- 3 16. 132. Turner JE, Delaney RK, Johnson J E : Retinal ganglion cell response to axotomy and nerve growth factor antiserum treatment in the regenerating visual system of the goldfish (Carassius auratus): an in vivo and in vitro analysis. Brain Res 1980;204:283-294. 33. Uzman BG, Villegas GM: Mouse sciatic nerve regeneration through semipermeable tubes: a quantitative model. J Neurosci Res 1983;9:325-338. 34. Varon S, Adler R: Nerve growth factors and control of nerve growth. Curr Top Deu Biol 1980;16:207-252. 35. Varon S, Adler R: Trophic and specifying factors directed to neuronal cells. Adu Cell Neurobiol 1981;2:115163. 36. Varon S, Bunge RP: Trophic mechanisms in the peripheral nervous system. A n n Rev Neurosci 1978;1:327-361. 37. Varon S, Skaper SD, Manthorpe M : Trophic activities for dorsal root and sympathetic ganglionic neurons in media conditioned by Schwann and other peripheral cells. Brain Res 1981 ;1:73-87. 38. Varon S, Williams LK: Peripheral nerve regeneration in a silicone model chamber: cellular arid molecular aspects. Peripheral Neroe Rep Kegen 1986;1:9-25. 139. Vita G, Dattola K, Girlanda P, Oteri G, Lo Presti F, Mcssina C: Effects of steroid hormones on muscle reiriNeurol nervation after nerve ULUsh in. rabbit 1983;80:279-287. 140. Wagner JA, D’Amore PA: Neurite outgrowth induced by an endothelial cell mitogeri isolated from retina. J Cell Biol 1986;103: 1363- 1367. 141. Waxman SG, Black JA: Macromolecular structure of the Schwann cell membrane. Perinodal rnicrovilli.J Neurol Sci 1987;77:23-34. 142. Weinberg HJ, Spencer PS: Studies on the control of myelinogenesis. 1. Myelination of regenerating axons after entry into a foreign unmyelinated nerve. J Neurocytol 1975;4:395-418. 143. Weiss P, Taylor AC: Further experimental evidence against “neurotropism” in nerve regeneration. J ExP Zoo1 1944;95:233-257. 144. Wikholni RP, Swett JE, Torigoe Y, Blanks RH: Repair of severed peripheral nerve: a superior anatomic and functional recovery with a new “reconnection” technique. Otolaryugol Head Neck Surg 19883993353-361, 145. Williams LR, Danielsen N , Miiller 11, Varon S: Influence of the acellular fibrin matrix on nerve regeneration success within the silicone chamber model, in Gordon T,

MUSCLE & NERVE

September 1990

799

Stein RB, Smith PA (eds): Neurology and Neurobiology. The Current Sta&usof Peripheral Nerve Regeneration. New York, Alan R. Liss, 1988, vol 38, pp 1 1 1- 122. 146. Williams LR, Longo FM, Powell HC, Lundborg G, Varon S: Spatial-temporal progress of peripheral nerve regeneration within a silicone chamber: parameters for a bioassay. J Comp Neurol 1983;218:460-470. 147. Williams LR, Powell HC, Lundborg G, Varon S: Competence of nerve tissue as distal insert promoting nerve regeneration in a silicone chamber. Brain Res 1984; 2931201-2 1 1 . 148. Williams LR, Varon S: Modification of fibrin matrix formation in situ enhances nerve regeneration in silicone chambers./ Comp Neurol 1985;231:209-220.

800

Peripheral Nerve Regeneration

149. Wise AJ Jr, Topuzlu C, Davis P, Kaye IS: A comparative analysis of macro- and microsurgical neurorrhaph y technics. A m / Surg 1969;117:566-572. 150. Wujek JR, Lasek RJ: Correlation of axonal regeneration and slow component B in two branches of a single axon./ Neurosci 1983;3:243-251. 151. Yamada KM, Spooner BS, Wessells NK: Axon growth: roles of microfilaments and microtubules. Proc Natl Acad Sci USA, 1970;66:1206- 1212. 152. Yankner BA, Shooter EM: The biology and mechanism of action of nerve growth factor. Ann Rev Biochem 1982;51 :845-868.

MUSCLE & NERVE

September 1990

Enhancement of peripheral nerve regeneration.

Numerous factors external to the nerve cell can support and enhance nerve regeneration after injury. The definition of these factors and the elucidati...
2MB Sizes 0 Downloads 0 Views