Some Thoughts on Current Research With Somatostatin Roger Guillemin
T
HE ISOLATION, characterization, synthesis, and early biologic studies of somatostatin (SRIF) was the result of the work of several of us in the Laboratories for Neuroendocrinology at the Salk Institute, particularly Paul Brazeau, Roger Burgus, Nick Ling, Jean Rivier, and Wylie Vale. Within a few days of Jean Rivier having completed the synthesis of relatively large quantities of highly purified SRIF, it was distributed to many friends and colleagues. The program of this symposium indicates the extraordinary and unexpected developments that rapidly occurred as a result of the early availability of the synthetic replicate-particularly recognition of the effects of SRIF on multiple targets totally unrelated to a direct action of SRIF on the secretion of GH, for which it was isolated and characterized, and its possible physiologic and therapeutic roles. I think it is obvious from the papers at this meeting that the real physiology of SRIF is just beginning to take shape. Certainly, we are still in the early phenomenology of these studies, but there is no shame in phenomenology; knowledge in physiology has to start and evolve that way. From a purely hypophysiotropic substance involved in the secretion of growth hormone we have seen SRIF considered in terms of multiple paracrine functions. We now see that reconsidered with the new observations from Roger Unger and collaborators that “nonnegligible” amounts of SRIF are being secreted in the regional pancreaticoduodenal circulation and that SRIF secretion can be actively stimulated by various nutrients and by several gastrointestinal hormones such as cholecystokinin. Radioimmunoassayable somatostatin appears also to be present in significant amounts in peripheral blood. Today we also heard in the paper by Uvnas-Wallenstein, Luft, and EfendiC that SRIF may also be released directly into the gastric antrum following vagal stimulation. This is remarkable. Of all these new subjects, I have chosen to say a few words about another area in which SRIF, still somewhat unexpectedly, is very much at the forefront. This will reflect my interest in various aspects of the significance of peptides in brain functions, as shown in my work with the endorphins over the past 2 years. I would like to discuss new data concerning the possible significance of SRIF in several types of neuronal systems. We know now that SRIF is to be found throughout the brain, not in a random manner but in a very discrete distribution. Figure 1 shows the presence of SRIF in a large number of neuronal fibers and nerve cells with a specific distribution: hypothalamus, limbic system, amygdala, hippocampus, scattered areas of the cortex, and midbrain. With SRIF as an example, we can say that practically every peptide that has been isolated in the hypothalamus has later been observed in other parts of the central nervous system. With the example of SRIF, we can also expand that statement by saying
From the Laboratories Address
reprint
for Neuroendocrinology.
requests
to Dr. Roger
Salk Insiitute.
Guillemin.
Laboratories
La Jolla, Calij for Neuroendoerinology.
Salk
In-
stitute, La Jolla, Calij: 92037. (8 1978 by Grune & Stratton.
Inc. 0026-049S/78/2713HWfj2$01.00/0
Metabolism, Vol. 27. No. 9. Suppl. 1 (September). 1978
1453
1454
ROGER
Fig.
1.
Multiple
localization
of immunoreactive
somatostatin
in the
GUILLEMIN
rat brain
that almost every peptide with biologic activity found originally either in the nervous system or in the gastrointestinalLpancreatic system has now been found in both systems. This is true not only for SRIF and substance P, the latter known since the early studies of von Euler and Gaddum, but also for $-endorphin, the enkephalins, cholecystokinin, thyrotropin-releasing factor, and neurotensin. This statement is based on data from immunoreactivity in radioimmunoassays or immunocytochemistry. In the case of substance P and neurotensin the peptides have been isolated from both sources and shown to be chemically identical. Coming back to SRIF, we know that its action on the secretions of one polypeptide or another is always inhibitory. Similarly, there is evidence that its administration in the central nervous system, either by microiontophoresis or by microcannula into a lateral ventricle, the third ventricle, or directly into the cisterna, usually has inhibitory effects on the target being studied. Can this be related to any of the inhibitory neuronal systems recognized as such on the basis of classical electrophysiology? What I will show now is an extension of the work on anatomic localizations presented earlier at this symposium by Dr. Elde and Dr. Feldman. The following pictures (Figs. 2-6) were sent to me several months ago by Dr. Petrusz and his colleagues from the Department of Anatomy, School of Medicine, University of North Carolina in Chapel Hill (see Petrusz et al.‘). I personally think that these are remarkable observations that may be pertinent to possible roles of SRIF in the nervous system. The immunostaining method involved is the bridge technique with unlabeled antisera to horseradish peroxidase followed by application of the enzyme, using antibodies to SRIF of frozen specificity. In Fig 2 we can see in the area of hypothalamus (rat brain) the same sort of nerve fiber pattern presented yesterday by both Dr. Elde and Dr. Feldman. In other areas of the rat brain, such as the anterior horn of the hippocampus, we see a new picture (Fig. 3): a large number of neurons (shown by the light blue staining of their nucleus), some of which have punctual endings around their cell bodies. Figure 4, at a higher magnification, shows hippocampal pyramidal cells of the rat brain (CA1 and CA2 area of hippocampus). Here every pyramidal cell is sur-
CURRENT
RESEARCH
Fig. 2.
lmmunoreactive
somatostatin
Fig. 3. lmmunoraactive somatostatin, pocampus. rat brain fields CA1 and CA2
in fibers in the ventral hypothalamus
presumably
(rat brain).
in nerve fibers and synaptic terminals
in the hip-
1456
ROGER GUILLEMIN
Fig. 4. High magnification of some of the pyramidal cells of the hippocampus shown in Fig. 3 surrounded by immunoreactive somatostatin structures, presumably synaptic terminals of axonic or dendritic nature.
rounded by large numbers of small dots; these are interpreted by Petrusz and collaborators as synaptic endings. The cells of origin of these presumptive terminals could not be traced. Figure 5 shows a series of scattered neurons in the neocortex of the rat brain with SRIF-positive formations; again these do not appear to be intracellular. As shown in higher magnification in Fig. 6, there are a series of boutons containing SRIF immunoreactive material covering cell bodies and proximal dendrites. Petrusz and colleagues report that after extensive search they have not been able to trace nerve fibers leading to these terminals. As pointed out by Petrusz and collaborators, these remarkable pictures are reminiscent of the description years ago of the so-called “basket cells,” recognized in the same regions of both the neocortex and the hippocampus. These basket cells have been recognized by classical electrophysiology to be inhibitory cells. Remember the exclusively inhibitory activity of SRlF on all neuronai systems as observed in various laboratories. The observations shown in Figs. 2--6 and their interpretation are reminiscent of and consistent with several hypotheses proposed a year ago in a review by Schmitt et a1.2 They discuss the so-called focal circuit neurons as recently observed with the electron microscope and electrophysiology techniques. In this review the proposal is made that perhaps one should recognize dendritic endings as being much more than just plain feeding pseudopods or passive receptor surfaces. Recent electron microscopic evidence as well as observations using intracellular electrical recordings suggest that dendrite endings may be involved in true synaptic contacts either with other dendrites (dendrodendritic synapses), with cell bodies, or with
1457
CURRENT RESEARCH
L
, _‘.
:
-
-.
Fig. 5. Neurons in the pyramidal cortex of the rat with immunoreactive somatostatin nerve endings around the cell body.
Fig. 6.
Higher magnification of one neuron from Fig. 5.
1458
.i..._ .,/ .* : :P
ROGER
GUILLEMIN
electrotonic
-.._ ,-;”
_/ --...*
jt%Y?on
*-._
Fig.
**.*
:
‘*..
:
*.
rocal
**.
‘5
IU
that
‘serial synapse
only
illustrating
dendrites
interactions
postsynaptic
. . ..___._..’
/’
Diagram
7.
proposal
is shown
are
hypothesis
rochemicals
several
enzymes,
may
junction
be
another.
in the
connections
The
can
to one
diagram,
between is
inhibitory
from
Schmitt,
and axon
all other
several
points
neuat
the
(peptides. etc.)
activity. et
preOne
involved
catecholamines,
either
recip-
dendrites.
that be
the
in their
al:
with
(Adapted Science
193:114-120.1976
axons (Fig. 7). Pictures like those shown in Figs. 2 6 would further imply that peptides, in this case SRIF, could be involved after being released not only at axon terminals but also at many dendritic terminals. There are other interesting aspects to these observations. The nerve endings, or dendritic endings, containing SRIF-like immunoreactive peptides, occur in the same area in which Henriksen and Bloom’s group at the Salk Institute have recently found fi-endorphin to be an activating peptide producing typical, classical, well-recognized, limbic epileptic seizures.” Figure 8 shows the electruphysiologic evidence of this activation in the hippocampus and also in the anterior nucleus of the amygdala in animals that received an intracisternal dose of synthetic $-endorphin. This type of seizure lasts for hours, depending on the dose ofpeptide injected. It precedes by IO- I5 min the initiation of the striking catatonia that follows injection of @-endorphin. It would thus be of interest to study whether SRIF would modify in an inhibitory manner any of these activating phenomena. If SRIF is indeed an inhibitory peptide in some parts of the brain. how would it work? We do not know at the moment. We have only fragmentary evidence of possible modes of action in a simple model: In a simple neuronal system such as the myenteric plexus of the guinea pig ileum, I showed a couple of years ago that SRIF is a profound inhibitor of the release of acetylcholine.’ Figure 9 shows the results of such an experiment: In the absence of the electrical stimulation, addition of exogenous acetylcholine will produce a rapid contraction of the smooth muscle. By adjusting the dose of the transmitter one can produce a contraction of the smooth muscle identical to that produced by one electrical pulse. With the stimulator off, addition of acetylcholine in the presence of the inhibitory dose of SRIF results in a normal smooth muscle contraction. The best explanation of this observation is that it represents a presynaptic inhibition by SRIF of the release of acetylcholine. Such a simple system may well be a model of what SRIF may do in other neuronal networks in the central nervous system. The myenteric plexusslongitudinal muscle preparation discussed here has also yielded a rather surprising observation that has not, to my knowledge, been made in any other system in which SRIF is active. The myenteric plexusssmooth muscle system of the guinea pig is the only system, to my knowledge, in which SRIF
CURRENT
1459
RESEARCH
90
EEG
set post inj.
CTX
23 min. post inj.
5 min. post inj.
CHEWING HIPPO
(’
I.... ..-*,
1 !!LI i 4
&
,
t -9
HIPPO
- I_
_A,
.-e-_--_
CROUCHED
*.. NOMVT
/
Fig. 8. Injection of @-endorphin (5 rg) in the lateral ventricle of the brain of a rat. Recording with permanently implanted electrodes in the frontal cortex (CTX), the hippocampus (HIPPO), and the amygdala (AMYG) up to 5 min after injection. EMG is from an electrode in the neck muscles. WDS, wet-dog shake; MVT. movement.
shows profound tachyphylaxis (Fig. 90, p, r). The first addition of SRIF produces a profound inhibition, as described above, which lasts approximately 30 min. If one keeps adding SRIF in increasing amounts in the next minutes or for as long as 2 hr, however, the inhibitory effect of SRIF disappears. It takes several hours for this tachyphylaxis to disappear. During this time, cu-endorphin in rather gmall amounts is definitely active (Fig. 9r); this means that the effect of SRIF in inhibiting the myenteric plexusssmooth muscle system is not mediated by the opiate receptors that it is known to contain. Moreover, we know from other observations that the effect of SRIF is not modifiable by the opiate antagonist naloxone. What is the role of SRIF in the central nervous system? At the-moment it is open to speculations. It is difficult for the pharmacologist and the physician not to rationalize that this peptide is in the brain for some physiologic purpose. Indeed, when one considers that the current textbooks of psychiatry and neurology simply ignore these observations because they were just not available when these texts were written, it would seem obvious that some revolutionary statement will be
1460
ROGER
3.5nM
GUILLEMIN
7nM
Fig. 9.
&h 7nM
Recordings
from
periments
with
different
(a-d;
strips
m-r)
ileum
&M 0.7pM
S%M 1.4pM
r ‘1,‘,,I
with -
O?-5% tion,
CO, 0.14
open for
events
zontal
&
-endor IOnM
5-ml
bath - 95%
0.2
stimula-
msec,
Stimulator
a,
b. d,
open
pig
plexus.
- glucose
37” C, field Hz,
circuit.
m,
arrows
SO-V is off
q.
Hori-
indicate
continuity
in the
recording,
here
space
convenience.
for
Speed
S&i?Ach 2.lpM 7nM
are
Ringer
ex-
of guinea
myenteric
Conditions Krebs
two
for original
cm/min. events-m,
Time
n 7 min;
p, r 15 min. chloride; tu-endor,
recording
elapsed Ach.
SOM.
cut is 1
between
0, p 7.5 min; acetycholine
somatostatin;
n-endorphin.
made sooner or later about the role of peptides not only in normal central nervous system functions, but probably also in nervous diseases and mental illness; that is for the future. In closing, 1 would like to make a few comments that will represent my own thinking, in a pragmatic way, about the future use of SRIF or any of its analogues in clinical medicine for some of the possible indications we have heard about at this meeting. Since 1973 our group at the Salk Institute has distributed several grams of synthetic SRIF, all prepared by small-scale solid-phase synthesis. Several grams of this peptide is about all we can produce at a relatively small academic laboratory. If from now on there is to be a meaningful relatively large-scale series of clinical studies (either with SRIF or one of the more interesting analogues that several groups have been describing over the past few months), it seems to me that industry will have to become active in the picture. Industry will have to take over the production and distribution of these peptides. Small laboratories like ours simply cannot afford to make gram quantities of any one of these peptides for distribution. The relatively large quantitites of SRIF necessary for extensive clinical studies will have to come from sources that are much better equipped than we are and can make use of methodology designed to make 100-g or kilogram batches of the peptide. When we realize that what we have heard today was totally unheard of, unconceived of, less than 4 yr ago, I am not too unhappy to use a favorite litotes. In
CURRENT
RESEARCH
1461
another 4 yr should there be another symposium on SRIF, I would hope that half of its time will be devoted to discussing results of long-term clinical studies, and the other half devoted to discussing our knowledge (on that day) of the physiologic roles of somatostatin (so ill named!) in its ubiquitous domains. REFERENCES 1. Petrusz P, Sar M, Grossman GH, et al: Synaptic terminals with somatostatin-like immunoreactivity in the rat brain. Brain Res 137:181-187, 1977 2. Schmitt, Dev, Smith: Electronic processing of information by brain cells. Science 193:i 14-120.1976 3. Guillemin R, Bloom F, Rossier J. et al:
Recent physiological studies with the endomorphins, in Goodman M (cd): Peptides: Proceedings of the Fifth American Peptide Symposium. New York, Halstead Press, John Wiley & Sons, 1977, pp 579-580 4. Guillemin R: Somatostatin inhibits the release of acetycholine induced electrically in the myenteric plexus. Endocrinology 99:1653, 1976
T
HE ISOLATION, characterization, synthesis, and early biologic studies of somatostatin (SRIF) was the result of the work of several of us in the Laboratories for Neuroendocrinology at the Salk Institute, particularly Paul Brazeau, Roger Burgus, Nick Ling, Jean Rivier, and Wylie Vale. Within a few days of Jean Rivier having completed the synthesis of relatively large quantities of highly purified SRIF, it was distributed to many friends and colleagues. The program of this symposium indicates the extraordinary and unexpected developments that rapidly occurred as a result of the early availability of the synthetic replicate-particularly recognition of the effects of SRIF on multiple targets totally unrelated to a direct action of SRIF on the secretion of GH, for which it was isolated and characterized, and its possible physiologic and therapeutic roles. I think it is obvious from the papers at this meeting that the real physiology of SRIF is just beginning to take shape. Certainly, we are still in the early phenomenology of these studies, but there is no shame in phenomenology; knowledge in physiology has to start and evolve that way. From a purely hypophysiotropic substance involved in the secretion of growth hormone we have seen SRIF considered in terms of multiple paracrine functions. We now see that reconsidered with the new observations from Roger Unger and collaborators that “nonnegligible” amounts of SRIF are being secreted in the regional pancreaticoduodenal circulation and that SRIF secretion can be actively stimulated by various nutrients and by several gastrointestinal hormones such as cholecystokinin. Radioimmunoassayable somatostatin appears also to be present in significant amounts in peripheral blood. Today we also heard in the paper by Uvnas-Wallenstein, Luft, and EfendiC that SRIF may also be released directly into the gastric antrum following vagal stimulation. This is remarkable. Of all these new subjects, I have chosen to say a few words about another area in which SRIF, still somewhat unexpectedly, is very much at the forefront. This will reflect my interest in various aspects of the significance of peptides in brain functions, as shown in my work with the endorphins over the past 2 years. I would like to discuss new data concerning the possible significance of SRIF in several types of neuronal systems. We know now that SRIF is to be found throughout the brain, not in a random manner but in a very discrete distribution. Figure 1 shows the presence of SRIF in a large number of neuronal fibers and nerve cells with a specific distribution: hypothalamus, limbic system, amygdala, hippocampus, scattered areas of the cortex, and midbrain. With SRIF as an example, we can say that practically every peptide that has been isolated in the hypothalamus has later been observed in other parts of the central nervous system. With the example of SRIF, we can also expand that statement by saying
From the Laboratories Address
reprint
for Neuroendocrinology.
requests
to Dr. Roger
Salk Insiitute.
Guillemin.
Laboratories
La Jolla, Calij for Neuroendoerinology.
Salk
In-
stitute, La Jolla, Calij: 92037. (8 1978 by Grune & Stratton.
Inc. 0026-049S/78/2713HWfj2$01.00/0
Metabolism, Vol. 27. No. 9. Suppl. 1 (September). 1978
1453
1454
ROGER
Fig.
1.
Multiple
localization
of immunoreactive
somatostatin
in the
GUILLEMIN
rat brain
that almost every peptide with biologic activity found originally either in the nervous system or in the gastrointestinalLpancreatic system has now been found in both systems. This is true not only for SRIF and substance P, the latter known since the early studies of von Euler and Gaddum, but also for $-endorphin, the enkephalins, cholecystokinin, thyrotropin-releasing factor, and neurotensin. This statement is based on data from immunoreactivity in radioimmunoassays or immunocytochemistry. In the case of substance P and neurotensin the peptides have been isolated from both sources and shown to be chemically identical. Coming back to SRIF, we know that its action on the secretions of one polypeptide or another is always inhibitory. Similarly, there is evidence that its administration in the central nervous system, either by microiontophoresis or by microcannula into a lateral ventricle, the third ventricle, or directly into the cisterna, usually has inhibitory effects on the target being studied. Can this be related to any of the inhibitory neuronal systems recognized as such on the basis of classical electrophysiology? What I will show now is an extension of the work on anatomic localizations presented earlier at this symposium by Dr. Elde and Dr. Feldman. The following pictures (Figs. 2-6) were sent to me several months ago by Dr. Petrusz and his colleagues from the Department of Anatomy, School of Medicine, University of North Carolina in Chapel Hill (see Petrusz et al.‘). I personally think that these are remarkable observations that may be pertinent to possible roles of SRIF in the nervous system. The immunostaining method involved is the bridge technique with unlabeled antisera to horseradish peroxidase followed by application of the enzyme, using antibodies to SRIF of frozen specificity. In Fig 2 we can see in the area of hypothalamus (rat brain) the same sort of nerve fiber pattern presented yesterday by both Dr. Elde and Dr. Feldman. In other areas of the rat brain, such as the anterior horn of the hippocampus, we see a new picture (Fig. 3): a large number of neurons (shown by the light blue staining of their nucleus), some of which have punctual endings around their cell bodies. Figure 4, at a higher magnification, shows hippocampal pyramidal cells of the rat brain (CA1 and CA2 area of hippocampus). Here every pyramidal cell is sur-
CURRENT
RESEARCH
Fig. 2.
lmmunoreactive
somatostatin
Fig. 3. lmmunoraactive somatostatin, pocampus. rat brain fields CA1 and CA2
in fibers in the ventral hypothalamus
presumably
(rat brain).
in nerve fibers and synaptic terminals
in the hip-
1456
ROGER GUILLEMIN
Fig. 4. High magnification of some of the pyramidal cells of the hippocampus shown in Fig. 3 surrounded by immunoreactive somatostatin structures, presumably synaptic terminals of axonic or dendritic nature.
rounded by large numbers of small dots; these are interpreted by Petrusz and collaborators as synaptic endings. The cells of origin of these presumptive terminals could not be traced. Figure 5 shows a series of scattered neurons in the neocortex of the rat brain with SRIF-positive formations; again these do not appear to be intracellular. As shown in higher magnification in Fig. 6, there are a series of boutons containing SRIF immunoreactive material covering cell bodies and proximal dendrites. Petrusz and colleagues report that after extensive search they have not been able to trace nerve fibers leading to these terminals. As pointed out by Petrusz and collaborators, these remarkable pictures are reminiscent of the description years ago of the so-called “basket cells,” recognized in the same regions of both the neocortex and the hippocampus. These basket cells have been recognized by classical electrophysiology to be inhibitory cells. Remember the exclusively inhibitory activity of SRlF on all neuronai systems as observed in various laboratories. The observations shown in Figs. 2--6 and their interpretation are reminiscent of and consistent with several hypotheses proposed a year ago in a review by Schmitt et a1.2 They discuss the so-called focal circuit neurons as recently observed with the electron microscope and electrophysiology techniques. In this review the proposal is made that perhaps one should recognize dendritic endings as being much more than just plain feeding pseudopods or passive receptor surfaces. Recent electron microscopic evidence as well as observations using intracellular electrical recordings suggest that dendrite endings may be involved in true synaptic contacts either with other dendrites (dendrodendritic synapses), with cell bodies, or with
1457
CURRENT RESEARCH
L
, _‘.
:
-
-.
Fig. 5. Neurons in the pyramidal cortex of the rat with immunoreactive somatostatin nerve endings around the cell body.
Fig. 6.
Higher magnification of one neuron from Fig. 5.
1458
.i..._ .,/ .* : :P
ROGER
GUILLEMIN
electrotonic
-.._ ,-;”
_/ --...*
jt%Y?on
*-._
Fig.
**.*
:
‘*..
:
*.
rocal
**.
‘5
IU
that
‘serial synapse
only
illustrating
dendrites
interactions
postsynaptic
. . ..___._..’
/’
Diagram
7.
proposal
is shown
are
hypothesis
rochemicals
several
enzymes,
may
junction
be
another.
in the
connections
The
can
to one
diagram,
between is
inhibitory
from
Schmitt,
and axon
all other
several
points
neuat
the
(peptides. etc.)
activity. et
preOne
involved
catecholamines,
either
recip-
dendrites.
that be
the
in their
al:
with
(Adapted Science
193:114-120.1976
axons (Fig. 7). Pictures like those shown in Figs. 2 6 would further imply that peptides, in this case SRIF, could be involved after being released not only at axon terminals but also at many dendritic terminals. There are other interesting aspects to these observations. The nerve endings, or dendritic endings, containing SRIF-like immunoreactive peptides, occur in the same area in which Henriksen and Bloom’s group at the Salk Institute have recently found fi-endorphin to be an activating peptide producing typical, classical, well-recognized, limbic epileptic seizures.” Figure 8 shows the electruphysiologic evidence of this activation in the hippocampus and also in the anterior nucleus of the amygdala in animals that received an intracisternal dose of synthetic $-endorphin. This type of seizure lasts for hours, depending on the dose ofpeptide injected. It precedes by IO- I5 min the initiation of the striking catatonia that follows injection of @-endorphin. It would thus be of interest to study whether SRIF would modify in an inhibitory manner any of these activating phenomena. If SRIF is indeed an inhibitory peptide in some parts of the brain. how would it work? We do not know at the moment. We have only fragmentary evidence of possible modes of action in a simple model: In a simple neuronal system such as the myenteric plexus of the guinea pig ileum, I showed a couple of years ago that SRIF is a profound inhibitor of the release of acetylcholine.’ Figure 9 shows the results of such an experiment: In the absence of the electrical stimulation, addition of exogenous acetylcholine will produce a rapid contraction of the smooth muscle. By adjusting the dose of the transmitter one can produce a contraction of the smooth muscle identical to that produced by one electrical pulse. With the stimulator off, addition of acetylcholine in the presence of the inhibitory dose of SRIF results in a normal smooth muscle contraction. The best explanation of this observation is that it represents a presynaptic inhibition by SRIF of the release of acetylcholine. Such a simple system may well be a model of what SRIF may do in other neuronal networks in the central nervous system. The myenteric plexusslongitudinal muscle preparation discussed here has also yielded a rather surprising observation that has not, to my knowledge, been made in any other system in which SRIF is active. The myenteric plexusssmooth muscle system of the guinea pig is the only system, to my knowledge, in which SRIF
CURRENT
1459
RESEARCH
90
EEG
set post inj.
CTX
23 min. post inj.
5 min. post inj.
CHEWING HIPPO
(’
I.... ..-*,
1 !!LI i 4
&
,
t -9
HIPPO
- I_
_A,
.-e-_--_
CROUCHED
*.. NOMVT
/
Fig. 8. Injection of @-endorphin (5 rg) in the lateral ventricle of the brain of a rat. Recording with permanently implanted electrodes in the frontal cortex (CTX), the hippocampus (HIPPO), and the amygdala (AMYG) up to 5 min after injection. EMG is from an electrode in the neck muscles. WDS, wet-dog shake; MVT. movement.
shows profound tachyphylaxis (Fig. 90, p, r). The first addition of SRIF produces a profound inhibition, as described above, which lasts approximately 30 min. If one keeps adding SRIF in increasing amounts in the next minutes or for as long as 2 hr, however, the inhibitory effect of SRIF disappears. It takes several hours for this tachyphylaxis to disappear. During this time, cu-endorphin in rather gmall amounts is definitely active (Fig. 9r); this means that the effect of SRIF in inhibiting the myenteric plexusssmooth muscle system is not mediated by the opiate receptors that it is known to contain. Moreover, we know from other observations that the effect of SRIF is not modifiable by the opiate antagonist naloxone. What is the role of SRIF in the central nervous system? At the-moment it is open to speculations. It is difficult for the pharmacologist and the physician not to rationalize that this peptide is in the brain for some physiologic purpose. Indeed, when one considers that the current textbooks of psychiatry and neurology simply ignore these observations because they were just not available when these texts were written, it would seem obvious that some revolutionary statement will be
1460
ROGER
3.5nM
GUILLEMIN
7nM
Fig. 9.
&h 7nM
Recordings
from
periments
with
different
(a-d;
strips
m-r)
ileum
&M 0.7pM
S%M 1.4pM
r ‘1,‘,,I
with -
O?-5% tion,
CO, 0.14
open for
events
zontal
&
-endor IOnM
5-ml
bath - 95%
0.2
stimula-
msec,
Stimulator
a,
b. d,
open
pig
plexus.
- glucose
37” C, field Hz,
circuit.
m,
arrows
SO-V is off
q.
Hori-
indicate
continuity
in the
recording,
here
space
convenience.
for
Speed
S&i?Ach 2.lpM 7nM
are
Ringer
ex-
of guinea
myenteric
Conditions Krebs
two
for original
cm/min. events-m,
Time
n 7 min;
p, r 15 min. chloride; tu-endor,
recording
elapsed Ach.
SOM.
cut is 1
between
0, p 7.5 min; acetycholine
somatostatin;
n-endorphin.
made sooner or later about the role of peptides not only in normal central nervous system functions, but probably also in nervous diseases and mental illness; that is for the future. In closing, 1 would like to make a few comments that will represent my own thinking, in a pragmatic way, about the future use of SRIF or any of its analogues in clinical medicine for some of the possible indications we have heard about at this meeting. Since 1973 our group at the Salk Institute has distributed several grams of synthetic SRIF, all prepared by small-scale solid-phase synthesis. Several grams of this peptide is about all we can produce at a relatively small academic laboratory. If from now on there is to be a meaningful relatively large-scale series of clinical studies (either with SRIF or one of the more interesting analogues that several groups have been describing over the past few months), it seems to me that industry will have to become active in the picture. Industry will have to take over the production and distribution of these peptides. Small laboratories like ours simply cannot afford to make gram quantities of any one of these peptides for distribution. The relatively large quantitites of SRIF necessary for extensive clinical studies will have to come from sources that are much better equipped than we are and can make use of methodology designed to make 100-g or kilogram batches of the peptide. When we realize that what we have heard today was totally unheard of, unconceived of, less than 4 yr ago, I am not too unhappy to use a favorite litotes. In
CURRENT
RESEARCH
1461
another 4 yr should there be another symposium on SRIF, I would hope that half of its time will be devoted to discussing results of long-term clinical studies, and the other half devoted to discussing our knowledge (on that day) of the physiologic roles of somatostatin (so ill named!) in its ubiquitous domains. REFERENCES 1. Petrusz P, Sar M, Grossman GH, et al: Synaptic terminals with somatostatin-like immunoreactivity in the rat brain. Brain Res 137:181-187, 1977 2. Schmitt, Dev, Smith: Electronic processing of information by brain cells. Science 193:i 14-120.1976 3. Guillemin R, Bloom F, Rossier J. et al:
Recent physiological studies with the endomorphins, in Goodman M (cd): Peptides: Proceedings of the Fifth American Peptide Symposium. New York, Halstead Press, John Wiley & Sons, 1977, pp 579-580 4. Guillemin R: Somatostatin inhibits the release of acetycholine induced electrically in the myenteric plexus. Endocrinology 99:1653, 1976
