350
Braflt Research, 126 (1977) 350-354 (('~ Elsevier/North-Holland Biomedical Press, Amsterdam - Printed in The Netherlands
Origins of primary afferent fibers in the spinal ventral roots in the cat as demonstrated by the horseradish peroxidase method
TEIJI Y A M A M O T O , K Y O Z O TAKAHASHI, H A J I M E SATOM1 and H I R O M I ISE
The First Department of Anatomy, Sapporo Medical College, Sapporo 060 (Japan) (Accepted January 28th, 1977)
One of the principles in the organization of the vertebrate nervous system is that the spinal dorsal roots are sensory and the ventral roots are motor in nature. However, there have been sufficient data in the anatomic 1,4-6,1a,16,1v and physiologic literature z,3,7,s,14,15 indicating the presence of primary afferent fibers in mammalian ventral roots. Among them, there appear to be two major opinions regarding the origins of primary afferent fibers in the ventral roots. One opinion is that the cell bodies to the ventral root afferent fibers are aberrant nerve cells scattered in the ventral roots v,8,13 while the other is that the dorsal root ganglion cells are the ones contributing to these afferent fibers 4,11A~. To clarify this question, an attempt was made to investigate the origins of afferent fibers in the ventral roots of the lumbosacral spinal cord utilizing the horseradish peroxidase (HRP) method 9,1°. Two groups of experiments were carried out on 9 adult cats (Table 1). Animals were anesthetized with sodium pentobarbital (30 mg/kg, i.p.) and fixed in a stereotaxic apparatus. Five cats underwent a lumbosacral laminectomy and the dorsal roots (L7 or S1-$2 or $3) of one side were identified intradurally and sectioned near their entrance to the cord. Then, 3-5 mg of HRP (type VI, Sigma Chem. Co.) diluted to a 10-30 ~ concentration in normal saline was injected into multiple sites of the L7-$3 areas of the spinal cord bilaterally. In the other 4 cats, a lumbosacral laminectomy was done and the dorsal roots (L7-$2 or $3) of one side were sectioned in the same fashion. Following this procedure, a suboccipital craniectomy was performed to expose the dorsal surface of the caudal portion of the medulla oblongata. H R P (3-5 rag) (10-30 ',"i~ concentration) was injected into the nucleus gracilis bilaterally. The animals were allowed to survive for two or three days after the operation and were sacrificed by intracardiac perfusion of 2 ~ paraformaldehyde and 0.5 o.i~ glutaraldehyde in Millonig's phosphate buffer (4 °C, pH 7.3). The brain stem, spinal cord and spinal roots were removed and stored in wash buffer with 5 ~'o sucrose overnight. The following day, the entire length of the ventral roots (L7-$3) with the dorsal root ganglia and adjacent mixed nerves distal to the ganglia was sectioned longitudinally at 60 # m by a freezing microtome. The lower medulla oblongata or lumbosacrai spinal cord was also sectioned in order to identify the area of H R P injection. The
351 TABLE l
Segments o f dorsal rhizotomy, sites o['H RP bljeetion and the presence o f aberrant cell bodies in the ventral roots in each cat Cat
Site o f HRP hljection
Segments o / dorsal rhizotomy
Presenceoflabelledaberrantcellbodies . . . . Rhizotomized side Non-rhizotomized side
H R-30 HR-36 HR-43 HR-44 HR-46 HR-33 HR-38 HR-40 HR-47
L 7 - $ 2 cord segments L 7 - $ 2 cord segments L7-$3 cord segments L7 $3 cord segments L7 $3 cord segments N. gracilis bilat. N. gracilis bilat. N. gracilis bilat. N. gracilis bilat.
Left Left Left Left Left Left Left Left Left
yes yes yes yes yes none none none none
SI-$3 L7-$2 L7-$3 Sl-$3 S1-$3 L7-$2 L7 $3 L7 $2 L7 $3
yes yes yes yes yes none none none none
sections were incubated for 40 min in a solution containing 0.03"Ji; 3,3'-diaminobenzidine tetrabydrochloride and 0.01 ~ hydrogen peroxide in Tris buffer (20 °C, pH 7.6). The sections were then mounted on gelatin-coated slides and lightly counterstained with cresyl violet acetate. Observation was made in bright- and dark-field illuminations. The group of animals which underwent H R P injection into the lumbosacral spinal cord following a unilateral dorsal rhizotomy showed many ganglion cells which contained fine granular reaction products in their perikarya in the dorsal root ganglia of the non-rhizotomized side. These labelled cells were varied in size and the number of labelled cells seems to have depended on the appropriateness of the site of HRP injection and the quantity of HRP injected. There appeared to be no particular organization in distribution of labelled cells in the ganglia. There were many aberrant cell bodies scattered in the ventral roots of $2 and $3 which were solitary, in a row or clustered. They were generally much smaller in number in the L7 and SI ventral roots. These aberrant cell bodies were smaller than ones in the dorsal root ganglion proper. Some of these aberrant cell bodies contained various amounts of HRP reaction products in their cytoplasm and others did not. The ratio of labelled cell bodies to nonlabelled ones appeared to parallel the number of ganglion cells in the dorsal root ganglion which were labelled. Some of the labelled cell bodies were found in the segment of mixed nerve distal to the dorsal root ganglia. Dorsal root ganglia on the rhizotomized side showed complete abolition of labelled ganglion cells in almost all the sections examined (Fig. 1A). However, in several sections, there were a few small labelled ganglion cells along the marginal zone of the dorsal root ganglia where the ventral roots were merging into the sensory fibers (Figs. IB and 5). The number of labelled aberrant cell bodies in the ventral roots on the rhizotomized side were about the same in number as the ones on the nonrhizotomized side. The labelled aberrant cell bodies were distributed throughout the entire length of the ventral roots (Figs. 1A, 2, 3, 4) and some were found in the portion of mixed nerve distal to the ganglia (Fig. 1B).
352
A ~----
DR
•
:
g
G
B
T Fig. 1. Camera tucida tracings of labelled aberrant cell bodies (arrows) in relation to non-labelled ones, the ventral root (VR), dorsal root (DR), ganglion proper (G) and mixed nerve distal to the ganglion (MN). A: three labelled cell bodies among several non-labelled in the ventral root. Note the absence of labelled ganglion cells in this rhizotomized example. HR-44. Left $2. B • several labelled aberrant cell bodies in the mixed nerve portion. Note a labelled cell in the marginal zone of the ganglion proper (large arrow). HR-43. Left $3. The other group of animals, which underwent H R P injection into the nucleus gracilis of both sides following an unilateral lumbosacral dorsal rhizotomy, showed labelled ganglion cells on the non-rhizotomized side of the dorsal root ganglia. However, there was a complete absence of labelled cells on the rhizotomized side of the ganglia. Aberrant cell bodies found on either side of the ventral roots contained no labelled activity. There have been many reports which have shown the presence of aberrant cell bodies in the ventral roots of the mammalian spinal nerves including those of cats 7,13,16,17, dogs 17 and humans 17. Among them, K a t o and Hirata 7, and K a t o and Tanji 8 demonstrated electrophysiologically the presence of afferent fibers in the ventral roots of the lumbosacral spinal cord in the cat and assumed that they might originate from aberrant cell bodies in the ventral roots and mixed nerves distal to the spinal ganglia. Contrary to the above observations, Coggeshall and his colleagues 5 stated that approximately 29 ~ of the axons in the ventral roots of L7 and S 1 in the cat were unmyelinated and that these unmyelinated axons were greatly reduced in number proximal to but not distal to a ventral rhizotomy. After a dorsal root gangtionectomy, the number of these unmyelinated axons was also greatly reduced. Their subsequent studiesl, 2 indicate that the $3 and Cal ventral roots similarly contain a large number of unmyelinated fibers, half of which are afferents to the spinal cord. They, therefore,
353
Fig. 2. A low power view of the $2 ventral root of the rhizotomized side showing several aberrant cell bodies within the fascicles. Some of them contain HRP reaction products (black arrows) and the others do not (empty arrows). The following figure is a higher magnification of the area enclosed by the square. HR-43. ~ 30. Fig. 3. A higher magnification of the area indicated by the square on Fig. 1. Two aberrant cell bodies containing reaction products (arrows) are seen. HR-43. Left $2. × 300. Fig. 4. A dark-field micrograph of an aberrant cell body stippled with fine granular reaction products (arrowhead). HR-44. Left $2. × 525. Fig. 5. A dark-field micrograph showing a spindle-shaped small ganglion cell which is brightly illuminated by the reflection of reaction products (arrow). This is located in the marginal zone of the ganglion of the rhizotomized side where the ventral root is merging into the sensory fibers. HR-44. Left S3. ~ 250.
concluded t h a t the ventral r o o t s o f the l u m b o s a c r a l enlargement contain a large p o p u l a t i o n o f u n m y e l i n a t e d fibers originating f r o m d o r s a l r o o t ganglion cells. More recently, L o e b 11 d e m o n s t r a t e d that ventral r o o t m y e l i n a t e d afferents can arise from cell bodies in the ganglion p r o p e r a n d t r a n s m i t typical somesthetic i n f o r m a t i o n to t e r m i n a t i o n as yet u n k n o w n . The present experiment would indicate that a b e r r a n t cell bodies in the ventral r o o t s o f the l u m b o s a c r a l enlargements c o n t r i b u t e to afferent fibers in the ventral roots, since the dorsal r h i z o t o m y did n o t abolish the r e t r o g r a d e t r a n s p o r t o f H R P f r o m the spinal cord gray to the a b e r r a n t cell bodies. In addition, there a p p e a r to be a small n u m b e r o f ganglion cells in the marginal zone o f the ganglion where the ventral r o o t merges into the dorsal c o m p o n e n t i m m e d i a t e l y distal to the ganglion p r o p e r . However, these are infrequent observations and the m a j o r c o m p o n e n t o f the ventral r o o t afferent fibers a p p e a r s to come from a b e r r a n t cell bodies.
354 Similar experiments to ours by the H R P m e t h o d were performed by M a y n a r d et al. ~'2 a n d the results are seen as a n abstract. The report appears to be c o n t r a r y to the present study, since, according to them, m a n y labelled dorsal root ganglion cells were f o u n d even after the dorsal rhizotomy. It is n o t certain why there is a discrepancy between our results a n d theirs. However, it can be said that the complete t r a n s e c t i o n of the dorsal roots is crucial for this study. Our preliminary experiments prior to this study indicated that when a single dorsal rootlet was left intact, there were more t h a n several labelled cells in the dorsal root ganglion. The t e r m i n a t i o n o f these afferent fibers is still u n k n o w n . The present study indicates, however, that at least a p o r t i o n of ventral root afferent fibers terminate in the spinal cord gray which is within a few segments from the level of emergence of the ventral rootlets. The absence of labelled a b e r r a n t cell bodies in the ventral roots following injection of H R P into the nucleus gracilis, despite the presence of labelled dorsal root ganglion cells, suggests that the afferent fibers originating from a b e r r a n t cell bodies in the ventral roots do n o t terminate in the posterior c o l u m n nucleus.
1 Applebaum, M. L., Clifton, G. L., Coggeshall, R. E., Coulter, J. D., Vance, W. H. and Willis, W. D., Unmyelinated fibers in the sacral 3 and caudal 1 ventral roots of the cat, J. Physiol. (Lond.), 256 (1976) 557-572. 2 Clifton, G. L., Coggeshall, R. E., Vance, W. H. and Willis, W. D., Receptive fields of unmyelinated ventral root afferent fibers in the cat, J. Physiol. (Lond.), 256 (1976) 573-600. 3 Clifton, G. L., Vance, W. H., Applebaum, M. L., Coggeshall, R. E. and Willis, W. D., Responses of unmyelinatedafferents in the mammalian ventral root, Brain Research, 82 (1974) 163--167. 4 Coggeshall, R. E., Applebaum, M. L., Fazen, M., Stubbs III, T. B. and Sykes, M. T., Unmyelinated axons in the human ventral roots. A possible explanationfor the failure of dorsal rhizotomy to relieve pain, Brain, 98 (1975) 157--166. 5 Coggeshall, R. E., Coulter, J. D. and Willis, W. D., Unmyelinated axons in the ventral roots of the cat lumbosacral enlargement, J. comp. NeuroL, 143 (1974) 39-58. 6 Dimsdale, J. A. and Kemp, J. M., Afferent fibers in the ventral nerve roots in the r'at, J. Physiol. (Lond.), 187 (1966) 25-26P. 7 Kato, M. and Hirata, Y., Sensory neurons in the spinal ventral roots of the cat, Brain Research, 7 (1968) 479-482. 8 Kato, M. and Tanji, J., Physiological properties of sensory fibers in the spinal ventral roots in the cat, Jap. J. Physiol., 21 (1971) 71 77. 9 Kristensson, K., Olsson, Y. and SjOstrand, J., Axonal uptake and retrograde transport of exogenous proteins in the hypoglossal nerve, Brain Research, 32 (1971) 379-406. 10 LaVail, J. E. and LaVail, M. M., Retrograde axonal transport in the central nervous system, Science, 176 (1972) 1416-1417. 11 Loeb, G. E., Ventral root projections of myelinated dorsal root ganglion cells in the cat, Brain Research, 106 (1976) 159-165. 12 Maynard, C. W., Leonard, R. B., Coulter, J. D., Coggeshall, R. E. and Willis, W, D., Cells of origins of ventral root afferents, Soc. Neurosci. Abstr., (1975) 141P. 13 O'Donnell, J. E. and Windle, W. F., An experimental study of the sensory neurons in the ventral spinal nerve roots of the cat, Anat. Rec., 55 (1933) 117-127. 14 Ryall, R. W. and Piercey, M. H., Visceral afferent and efferent fibers in sacral ventral roots in cats, Brain Research, 23 (1970) 57-65. 15 Vance, W. H., Clifton, G. L., Applebaum, M. L., Willis, W. D. and CoggeshaU, R. E., Unmyelinated preganglionic fibers in frog ventral roots, J. comp. NeuroL, 164 (1975) 117-126. 16 Webber, R. H. and Wemett, A., Distribution of fibers from nerve cell bodies in ventral roots of spinal nerves, Acta anat. (Basel), 65 (1966) 579-583. 17 Windle, W. F., Neurons of sensory type in the ventral roots in man and other mammals, Arch. Neural. Psychiat. (Chic.), 26 (1931) 791-800.
Braflt Research, 126 (1977) 350-354 (('~ Elsevier/North-Holland Biomedical Press, Amsterdam - Printed in The Netherlands
Origins of primary afferent fibers in the spinal ventral roots in the cat as demonstrated by the horseradish peroxidase method
TEIJI Y A M A M O T O , K Y O Z O TAKAHASHI, H A J I M E SATOM1 and H I R O M I ISE
The First Department of Anatomy, Sapporo Medical College, Sapporo 060 (Japan) (Accepted January 28th, 1977)
One of the principles in the organization of the vertebrate nervous system is that the spinal dorsal roots are sensory and the ventral roots are motor in nature. However, there have been sufficient data in the anatomic 1,4-6,1a,16,1v and physiologic literature z,3,7,s,14,15 indicating the presence of primary afferent fibers in mammalian ventral roots. Among them, there appear to be two major opinions regarding the origins of primary afferent fibers in the ventral roots. One opinion is that the cell bodies to the ventral root afferent fibers are aberrant nerve cells scattered in the ventral roots v,8,13 while the other is that the dorsal root ganglion cells are the ones contributing to these afferent fibers 4,11A~. To clarify this question, an attempt was made to investigate the origins of afferent fibers in the ventral roots of the lumbosacral spinal cord utilizing the horseradish peroxidase (HRP) method 9,1°. Two groups of experiments were carried out on 9 adult cats (Table 1). Animals were anesthetized with sodium pentobarbital (30 mg/kg, i.p.) and fixed in a stereotaxic apparatus. Five cats underwent a lumbosacral laminectomy and the dorsal roots (L7 or S1-$2 or $3) of one side were identified intradurally and sectioned near their entrance to the cord. Then, 3-5 mg of HRP (type VI, Sigma Chem. Co.) diluted to a 10-30 ~ concentration in normal saline was injected into multiple sites of the L7-$3 areas of the spinal cord bilaterally. In the other 4 cats, a lumbosacral laminectomy was done and the dorsal roots (L7-$2 or $3) of one side were sectioned in the same fashion. Following this procedure, a suboccipital craniectomy was performed to expose the dorsal surface of the caudal portion of the medulla oblongata. H R P (3-5 rag) (10-30 ',"i~ concentration) was injected into the nucleus gracilis bilaterally. The animals were allowed to survive for two or three days after the operation and were sacrificed by intracardiac perfusion of 2 ~ paraformaldehyde and 0.5 o.i~ glutaraldehyde in Millonig's phosphate buffer (4 °C, pH 7.3). The brain stem, spinal cord and spinal roots were removed and stored in wash buffer with 5 ~'o sucrose overnight. The following day, the entire length of the ventral roots (L7-$3) with the dorsal root ganglia and adjacent mixed nerves distal to the ganglia was sectioned longitudinally at 60 # m by a freezing microtome. The lower medulla oblongata or lumbosacrai spinal cord was also sectioned in order to identify the area of H R P injection. The
351 TABLE l
Segments o f dorsal rhizotomy, sites o['H RP bljeetion and the presence o f aberrant cell bodies in the ventral roots in each cat Cat
Site o f HRP hljection
Segments o / dorsal rhizotomy
Presenceoflabelledaberrantcellbodies . . . . Rhizotomized side Non-rhizotomized side
H R-30 HR-36 HR-43 HR-44 HR-46 HR-33 HR-38 HR-40 HR-47
L 7 - $ 2 cord segments L 7 - $ 2 cord segments L7-$3 cord segments L7 $3 cord segments L7 $3 cord segments N. gracilis bilat. N. gracilis bilat. N. gracilis bilat. N. gracilis bilat.
Left Left Left Left Left Left Left Left Left
yes yes yes yes yes none none none none
SI-$3 L7-$2 L7-$3 Sl-$3 S1-$3 L7-$2 L7 $3 L7 $2 L7 $3
yes yes yes yes yes none none none none
sections were incubated for 40 min in a solution containing 0.03"Ji; 3,3'-diaminobenzidine tetrabydrochloride and 0.01 ~ hydrogen peroxide in Tris buffer (20 °C, pH 7.6). The sections were then mounted on gelatin-coated slides and lightly counterstained with cresyl violet acetate. Observation was made in bright- and dark-field illuminations. The group of animals which underwent H R P injection into the lumbosacral spinal cord following a unilateral dorsal rhizotomy showed many ganglion cells which contained fine granular reaction products in their perikarya in the dorsal root ganglia of the non-rhizotomized side. These labelled cells were varied in size and the number of labelled cells seems to have depended on the appropriateness of the site of HRP injection and the quantity of HRP injected. There appeared to be no particular organization in distribution of labelled cells in the ganglia. There were many aberrant cell bodies scattered in the ventral roots of $2 and $3 which were solitary, in a row or clustered. They were generally much smaller in number in the L7 and SI ventral roots. These aberrant cell bodies were smaller than ones in the dorsal root ganglion proper. Some of these aberrant cell bodies contained various amounts of HRP reaction products in their cytoplasm and others did not. The ratio of labelled cell bodies to nonlabelled ones appeared to parallel the number of ganglion cells in the dorsal root ganglion which were labelled. Some of the labelled cell bodies were found in the segment of mixed nerve distal to the dorsal root ganglia. Dorsal root ganglia on the rhizotomized side showed complete abolition of labelled ganglion cells in almost all the sections examined (Fig. 1A). However, in several sections, there were a few small labelled ganglion cells along the marginal zone of the dorsal root ganglia where the ventral roots were merging into the sensory fibers (Figs. IB and 5). The number of labelled aberrant cell bodies in the ventral roots on the rhizotomized side were about the same in number as the ones on the nonrhizotomized side. The labelled aberrant cell bodies were distributed throughout the entire length of the ventral roots (Figs. 1A, 2, 3, 4) and some were found in the portion of mixed nerve distal to the ganglia (Fig. 1B).
352
A ~----
DR
•
:
g
G
B
T Fig. 1. Camera tucida tracings of labelled aberrant cell bodies (arrows) in relation to non-labelled ones, the ventral root (VR), dorsal root (DR), ganglion proper (G) and mixed nerve distal to the ganglion (MN). A: three labelled cell bodies among several non-labelled in the ventral root. Note the absence of labelled ganglion cells in this rhizotomized example. HR-44. Left $2. B • several labelled aberrant cell bodies in the mixed nerve portion. Note a labelled cell in the marginal zone of the ganglion proper (large arrow). HR-43. Left $3. The other group of animals, which underwent H R P injection into the nucleus gracilis of both sides following an unilateral lumbosacral dorsal rhizotomy, showed labelled ganglion cells on the non-rhizotomized side of the dorsal root ganglia. However, there was a complete absence of labelled cells on the rhizotomized side of the ganglia. Aberrant cell bodies found on either side of the ventral roots contained no labelled activity. There have been many reports which have shown the presence of aberrant cell bodies in the ventral roots of the mammalian spinal nerves including those of cats 7,13,16,17, dogs 17 and humans 17. Among them, K a t o and Hirata 7, and K a t o and Tanji 8 demonstrated electrophysiologically the presence of afferent fibers in the ventral roots of the lumbosacral spinal cord in the cat and assumed that they might originate from aberrant cell bodies in the ventral roots and mixed nerves distal to the spinal ganglia. Contrary to the above observations, Coggeshall and his colleagues 5 stated that approximately 29 ~ of the axons in the ventral roots of L7 and S 1 in the cat were unmyelinated and that these unmyelinated axons were greatly reduced in number proximal to but not distal to a ventral rhizotomy. After a dorsal root gangtionectomy, the number of these unmyelinated axons was also greatly reduced. Their subsequent studiesl, 2 indicate that the $3 and Cal ventral roots similarly contain a large number of unmyelinated fibers, half of which are afferents to the spinal cord. They, therefore,
353
Fig. 2. A low power view of the $2 ventral root of the rhizotomized side showing several aberrant cell bodies within the fascicles. Some of them contain HRP reaction products (black arrows) and the others do not (empty arrows). The following figure is a higher magnification of the area enclosed by the square. HR-43. ~ 30. Fig. 3. A higher magnification of the area indicated by the square on Fig. 1. Two aberrant cell bodies containing reaction products (arrows) are seen. HR-43. Left $2. × 300. Fig. 4. A dark-field micrograph of an aberrant cell body stippled with fine granular reaction products (arrowhead). HR-44. Left $2. × 525. Fig. 5. A dark-field micrograph showing a spindle-shaped small ganglion cell which is brightly illuminated by the reflection of reaction products (arrow). This is located in the marginal zone of the ganglion of the rhizotomized side where the ventral root is merging into the sensory fibers. HR-44. Left S3. ~ 250.
concluded t h a t the ventral r o o t s o f the l u m b o s a c r a l enlargement contain a large p o p u l a t i o n o f u n m y e l i n a t e d fibers originating f r o m d o r s a l r o o t ganglion cells. More recently, L o e b 11 d e m o n s t r a t e d that ventral r o o t m y e l i n a t e d afferents can arise from cell bodies in the ganglion p r o p e r a n d t r a n s m i t typical somesthetic i n f o r m a t i o n to t e r m i n a t i o n as yet u n k n o w n . The present experiment would indicate that a b e r r a n t cell bodies in the ventral r o o t s o f the l u m b o s a c r a l enlargements c o n t r i b u t e to afferent fibers in the ventral roots, since the dorsal r h i z o t o m y did n o t abolish the r e t r o g r a d e t r a n s p o r t o f H R P f r o m the spinal cord gray to the a b e r r a n t cell bodies. In addition, there a p p e a r to be a small n u m b e r o f ganglion cells in the marginal zone o f the ganglion where the ventral r o o t merges into the dorsal c o m p o n e n t i m m e d i a t e l y distal to the ganglion p r o p e r . However, these are infrequent observations and the m a j o r c o m p o n e n t o f the ventral r o o t afferent fibers a p p e a r s to come from a b e r r a n t cell bodies.
354 Similar experiments to ours by the H R P m e t h o d were performed by M a y n a r d et al. ~'2 a n d the results are seen as a n abstract. The report appears to be c o n t r a r y to the present study, since, according to them, m a n y labelled dorsal root ganglion cells were f o u n d even after the dorsal rhizotomy. It is n o t certain why there is a discrepancy between our results a n d theirs. However, it can be said that the complete t r a n s e c t i o n of the dorsal roots is crucial for this study. Our preliminary experiments prior to this study indicated that when a single dorsal rootlet was left intact, there were more t h a n several labelled cells in the dorsal root ganglion. The t e r m i n a t i o n o f these afferent fibers is still u n k n o w n . The present study indicates, however, that at least a p o r t i o n of ventral root afferent fibers terminate in the spinal cord gray which is within a few segments from the level of emergence of the ventral rootlets. The absence of labelled a b e r r a n t cell bodies in the ventral roots following injection of H R P into the nucleus gracilis, despite the presence of labelled dorsal root ganglion cells, suggests that the afferent fibers originating from a b e r r a n t cell bodies in the ventral roots do n o t terminate in the posterior c o l u m n nucleus.
1 Applebaum, M. L., Clifton, G. L., Coggeshall, R. E., Coulter, J. D., Vance, W. H. and Willis, W. D., Unmyelinated fibers in the sacral 3 and caudal 1 ventral roots of the cat, J. Physiol. (Lond.), 256 (1976) 557-572. 2 Clifton, G. L., Coggeshall, R. E., Vance, W. H. and Willis, W. D., Receptive fields of unmyelinated ventral root afferent fibers in the cat, J. Physiol. (Lond.), 256 (1976) 573-600. 3 Clifton, G. L., Vance, W. H., Applebaum, M. L., Coggeshall, R. E. and Willis, W. D., Responses of unmyelinatedafferents in the mammalian ventral root, Brain Research, 82 (1974) 163--167. 4 Coggeshall, R. E., Applebaum, M. L., Fazen, M., Stubbs III, T. B. and Sykes, M. T., Unmyelinated axons in the human ventral roots. A possible explanationfor the failure of dorsal rhizotomy to relieve pain, Brain, 98 (1975) 157--166. 5 Coggeshall, R. E., Coulter, J. D. and Willis, W. D., Unmyelinated axons in the ventral roots of the cat lumbosacral enlargement, J. comp. NeuroL, 143 (1974) 39-58. 6 Dimsdale, J. A. and Kemp, J. M., Afferent fibers in the ventral nerve roots in the r'at, J. Physiol. (Lond.), 187 (1966) 25-26P. 7 Kato, M. and Hirata, Y., Sensory neurons in the spinal ventral roots of the cat, Brain Research, 7 (1968) 479-482. 8 Kato, M. and Tanji, J., Physiological properties of sensory fibers in the spinal ventral roots in the cat, Jap. J. Physiol., 21 (1971) 71 77. 9 Kristensson, K., Olsson, Y. and SjOstrand, J., Axonal uptake and retrograde transport of exogenous proteins in the hypoglossal nerve, Brain Research, 32 (1971) 379-406. 10 LaVail, J. E. and LaVail, M. M., Retrograde axonal transport in the central nervous system, Science, 176 (1972) 1416-1417. 11 Loeb, G. E., Ventral root projections of myelinated dorsal root ganglion cells in the cat, Brain Research, 106 (1976) 159-165. 12 Maynard, C. W., Leonard, R. B., Coulter, J. D., Coggeshall, R. E. and Willis, W, D., Cells of origins of ventral root afferents, Soc. Neurosci. Abstr., (1975) 141P. 13 O'Donnell, J. E. and Windle, W. F., An experimental study of the sensory neurons in the ventral spinal nerve roots of the cat, Anat. Rec., 55 (1933) 117-127. 14 Ryall, R. W. and Piercey, M. H., Visceral afferent and efferent fibers in sacral ventral roots in cats, Brain Research, 23 (1970) 57-65. 15 Vance, W. H., Clifton, G. L., Applebaum, M. L., Willis, W. D. and CoggeshaU, R. E., Unmyelinated preganglionic fibers in frog ventral roots, J. comp. NeuroL, 164 (1975) 117-126. 16 Webber, R. H. and Wemett, A., Distribution of fibers from nerve cell bodies in ventral roots of spinal nerves, Acta anat. (Basel), 65 (1966) 579-583. 17 Windle, W. F., Neurons of sensory type in the ventral roots in man and other mammals, Arch. Neural. Psychiat. (Chic.), 26 (1931) 791-800.
