Quantitative comparison of growth-associated protein-43 and substance P in ulcerative colitis.

The aim of this study was to compare immunoreactivities for substance P with other enteric neuropeptides and GAP-43, a general marker for enteric nerves, in normal human colon and in different stages of ulcerative colitis. Tissue samples from normal colon and regions of ulcerative colitis colon were obtained at surgery and immunostained for substance P, vasoactive intestinal polypeptide (VIP), somatostatin, calcitonin gene-related peptide (CGRP), enkephalin, galanin, GAP-43, and neuron-specific enolase (NSE). Visual examination and semiquantitative analysis revealed a clear increase in the immunoreactivity for substance P in ulcerative colitis, whereas no differences were observed in the distribution of the other peptides. Therefore, quantitative analysis was performed only for substance P immunoreactivity in the lamina propria, circular muscle layer, and myenteric ganglia. In the lamina propria, the score of total intensity of substance P immunoreactivity was 0.55 +/- 0.15 (mean +/- SEM) in normal colon, 1.30 +/- 0.35 (p = 0.087) in least affected colon, and 2.22 +/- 0.28 (p < 0.001) in moderately affected colon, whereas no significant differences were observed in immunoreactivities for GAP-43. Similar results were obtained for the mean substance P- or GAP-43-immunoreactive area. In the circular muscle layer, the number, density, total intensity, and perimeter of substance P- and GAP-43-immunoreactive fibers were essentially similar in normal colon, and in mild or moderately affected colon. We conclude that ulcerative colitis does not change the density of gut innervation as a whole. However, the density of substance P-containing nerves is specifically increased, probably due to increased peptide synthesis leading to better visibility of the fibers.     

Quantitative comparison of growth-associated protein GAP-43, neuron-specific enolase, and protein gene product 9.5 as neuronal markers in mature human intestine.

This study was performed to compare GAP-43, PGP 9.5, synaptophysin, and NSE as neuronal markers in the human intestine. GAP-43-immunoreactive nerve fibers were abundant in all layers of the ileum and colon. GAP-43 partially co-localized partially with every neuropeptide (VIP, substance P, galanin, enkephalin) studied. All neuropeptide-immunoreactive fibers also showed GAP-43 reactivity. By blind visual estimation, the numbers of GAP-43-immunoreactive fibers in the lamina propria were greater than those of PGP 9.5, synaptophysin, or NSE. In the muscle layer, visual estimation indicated that the density of GAP-43-immunoreactive fiber profiles was slightly greater than that of the others. The number and intensity of GAP-43-, PGP 9.5-, and NSE-immunoreactive fibers were estimated in sections of normal human colon and ileum using computerized morphometry. In the colon, the numbers of GAP-43-immunoreactive nerve profiles per unit area and their size and intensity were significantly greater than the values for PGP and NSE. A similar trend was observed in the ileum. Neuronal somata lacked or showed only weak GAP-43 immunoreactivity, variable PGP 9.5 immunoreactivity, no synaptophysin immunoreactivity, and moderate to strong NSE immunoreactivity. We conclude that GAP-43 is the superior marker of nerve fibers in the human intestine, whereas NSE is the marker of choice for neuronal somata. (J Histochem Cytochem 47:1405-1415, 1999)     

Helodermin, but not cholecystokinin, somatostatin, or thyrotropin releasing hormone, acutely increases thyroid blood flow in the rat

In the present study, we investigated whether peptides located within the thyroid gland, but not directly found in nerve fibers associated with blood vessels, might influence thyroid blood flow. Specifically, we evaluated the effects of helodermin, cholecystokinin (CCK), somatostatin (SRIF) and thyrotropin releasing hormone (TRH) given systemically on thyroid blood flow and circulating thyroid hormone levels. Blood flows in the thyroid and six other organs were measured in male rats using 141Ce-labeled microspheres. Circulating thyrotropin (TSH) and thyroid hormone levels were monitored by RIA. Helodermin (10(-10) mol/100 g BW, i.v. over 4 min) markedly elevated thyroid blood flow (52 +/- 6 vs. 10 +/- 2 ml/min.g in vehicle-infused rats; n = 5). Blood flows to the salivary gland, pancreas, lacrimal gland and stomach (but not adrenal and kidney) were also increased during helodermin infusions. CCK, SRIF, and TRH were without effect on blood flows to the thyroid and other organs even though these peptides were tested at higher molar doses than helodermin. Helodermin, CCK, or SRIF did not affect thyroid hormone or plasma calcium levels. As expected however, plasma TSH and T3 levels were increased at 20 min and 2 h, respectively, following TRH infusions. Since helodermin shares sequence homology with VIP, we next compared the relative effects of these two peptides on thyroid and other organ blood flows. VIP (10(-11) mol/100 g BW, i.v.) was more potent in increasing blood flows to the thyroid, salivary gland, and pancreas than an equimolar dose of helodermin. This study shows that while helodermin, like VIP, has the ability to increase thyroid and other organ blood flows, it appears to be a less potent vasodilator.     

Effects of VIP, PHM and substance P on blood vessels and secretory elements of the human submandibular gland

The effects of the neuropeptides VIP, PHM and substance P (SP) on vascular smooth muscle tone, K+ secretion from exocrine elements and tissue content of cyclic AMP (cAMP) in the human submandibular gland were studied in vitro. All three peptides caused relaxation of noradrenaline contracted human submandibular arteries at nM concentrations. SP was slightly more active than VIP and PHM which had a similar potency as vasodilators. Only carbachol but not VIP, PHM or SP stimulated K+ secretion from exocrine elements of the human submandibular gland. Principally similar in vitro effects on K+ secretion were obtained on the cat submandibular gland, but in the rat not only carbachol but also SP stimulated K+ secretion. VIP and PHM increased cAMP production of exocrine elements in the human submandibular gland in nM concentrations. VIP was about 5-fold more potent than PHM with regards to cAMP production. In conclusion, VIP, PHM and SP relaxed human submandibular arteries in vitro. Both VIP and PHM stimulated cAMP production in glandular tissue but none of the three peptides induced K+ secretion from human submandibular gland tissue. This suggests that, in contrast to the situation in the rat, SP does not cause watery salivation in man, while VIP and PHM may modulate protein e.g. amylase content of the saliva.     

The distribution of peptide-containing nerves in the synovia of the cat knee joint.

Synovial capsule in cats is extensively innervated by a network with axonal diameter ranging from 0.6-3 microns according to its position and neuropeptide content. Nerve markers such as Neuron Specific Enolase (NSE) and Neurofilament triplet protein (NF) could be observed only when the axonal fibre attained a critical diameter of over the 3 microns limit. The relatively thick fibres (1-3 microns) show positive immunoreactivity for Substance P (SP), 5-hydroxytryptamine (5-HT), and Vasoactive Intestinal Peptide (VIP), and seldom coreact with NSE and NF, whereas, the thinnest fibres (0.6-0.8 microns) characterized to contain either Methionine or Leucine Enkephalin (M-Enk, L-Enk) did not coreact positively with axonal markers. We found that different anesthetics may effect variably the immunoreactivity of some neuropeptides (SP, L-Enk, 5-HT) while others (VIP, M-Enk) remained unaffected. Based on our data and the few reported ones in the pertinent literature, it is judged that urethane is the anesthetic of choice in experimental studies of neuropeptides. Our findings of isolated positive immunoreactive cell bodies to enkephalin in synovia might suggest the presence of intrinsic relay system, where the enkephalin acts as suppressor of SP and VIP release from the sunovium nerve terminals. Such a local inter-relationship between different neuropeptide systems might have a practical role on the understanding of the pathogenesis of different arthritic processes as well as therapeutic strategy in the future.     

Immunohistochemical studies on peptide- and amine-containing endocrine cells and nerves in the gut and the rectal gland of the ratfish Chimaera monstrosa

Summary The occurrence and distribution of endocrine cells and nerves were immunohistochemically demonstrated in the gut and rectal gland of the ratfish Chimaera monstrosa (Holocephala). The epithelium of the gut mucosa revealed open-type endocrine cells exhibiting immunoreactivity for serotonin (5HT), gastrin/cholecystokinin (CCK), pancreatic polypeptide (PP)/FMRFamide, somatostatin, glucagon, substance P or gastrin-releasing peptide (GRP). The rectum contained a large number of closed-type endocrine cells in the basal layer of its stratified epithelium; the majority contained 5HT- and GRP-like immunoreactivity in the same cytoplasm, whereas others were immunoreactive for substance P. The rectal gland revealed closed-type endocrine cells located in the collecting duct epithelium. Most of these contained substance P-like immunoreactivity, although some reacted either to antibody against somatostatin or against 5HT. Four types of nerves were identified in the gut and the rectal gland. The nerve cells and fibers that were immunoreactive for vasoactive intestinal peptide (VIP) and GRP formed dense plexuses in the lamina propria, submucosa and muscular layer of the gut and rectal gland. A sparse network of gastrin- and 5HT-immunoreactive nerve fibers was found in the mucosa and the muscular layer of the gut. The present study demonstrated for the first time the occurrence of the closed-type endocrine cells in the mucosa of the rectum and rectal gland of the ratfish. These abundant cells presumably secrete 5HT and/or peptides in response to mechanical stimuli in the gut and the rectal gland. The peptide-containing nerves may be involved in the regulation of secretion by the rectal gland.     

Neuropeptide expression in the airways of COPD patients and smokers with normal lung function

Neurogenic mechanisms seem to play a role in the pathogenesis of chronic obstructive pulmonary disease (COPD), as suggested by a number of in vitro data. However, few studies have investigated the presence of neuropeptides in the airways of patients with COPD, and they have yielded conflicting results. The aim of this study is to compare the expression of the neuropeptide substance P (SP), vasoactive intestinal peptide (VIP), and neuropeptide Y (NPY) in the airways of smokers with and without COPD. Surgical lung samples were obtained from 15 smokers with COPD and 16 smokers with normal lung function, who underwent lobectomy for a solitary lung carcinoma. Airway expression and distribution of SP, VIP, and NPY were identified by immunohistochemistry and analyzed by a computerized image analysis system. Compared to smokers with normal lung function, COPD patients exhibited an increased immunoreactivity for SP and VIP, paralleled by a decreased NPY expression in the epithelium and glands, and a decreased expression of all these three neuropeptides in the smooth muscle layer. Therefore, in the present study we have documented a different expression and distribution of the neuropeptides SP, VIP, and NPY in the airways of smokers with and without COPD. These findings suggest a possible involvement of such neuropeptides in the pathogenesis of some changes occurring in COPD.     

Neuropeptidergic control of cyclic AMP accumulation in human thyroid cell

Somatostatin (SRIF), cholecystokinin (CCK), gastrin and substance P, as single agents, do not influence baseline cellular cAMP levels in human thyroid cultures. SRIF inhibits TSH-induced cAMP accumulation in human thyroid cell, while CCK, gastrin and substance P do not modify cAMP response to TSH. Vasoactive intestinal peptide (VIP) increases cellular cAMP levels in human thyroid cultures and its effect is additive to increases produced by norepinephrine (NE) and isoproterenol (ISO). Neither SRIF nor the other tested peptides influence adrenergic and VIP-ergic cAMP stimulation.     

Distribution of five peptides, three general neuroendocrine markers, and two synaptic-vesicle-associated proteins in the spinal cord and dorsal root ganglia of the adult and newborn dog: an immunocytochemical study

This study describes the immunocytochemical distribution of five neuropeptides (calcitonin gene-related peptide [CGRP], enkephalin, galanin, somatostatin, and substance P), three neuronal markers (neurofilament triplet proteins, neuron-specific enolase [NSE], and protein gene product 9.5), and two synaptic-vesicle-associated proteins (synapsin I and synaptophysin) in the spinal cord and dorsal root ganglia of adult and newborn dogs. CGRP and substance P were the only peptides detectable at birth in the spinal cord; they were present within a small number of immunoreactive fibers concentrated in laminae I-II. CGRP immunoreactivity was also observed in motoneurons and in dorsal root ganglion cells. In adult animals, all peptides under study were localized to varicose fibers forming rich plexuses within laminae I-III and, to a lesser extent, lamina X and the intermediolateral cell columns. Some dorsal root ganglion neurons were CGRP- and/or substance P-immunoreactive. The other antigens were present in the spinal cord and dorsal root ganglia of both adult and newborn animals, with the exception of NSE, which, at birth, was not detectable in spinal cord neurons. Moreover, synapsin I/synaptophysin immunoreactivity, at birth, was restricted to laminae I-II, while in adult dogs, immunostaining was observed in terminal-like elements throughout the spinal neuropil. These results suggest that in the dog spinal cord and dorsal root ganglia, peptide-containing pathways complete their development during postnatal life, together with the full expression of NSE and synapsin I/synaptophysin immunoreactivities. In adulthood, peptide distribution is similar to that described in other mammals, although a relative absence of immunoreactive cell bodies was observed in the spinal cord.     

Effects of ketamine on the cholecystokinin,somatostatin, substance P,and thyrotropin releasing hormone in discrete regions of rat brain

Intraperitoneal injection of ketamine (100 mg/kg body weight) significantly reduces the levels of cholecystokinin (CCK) somatostatin (SRIF), and substance P (SP)-like immunoreactivity in various regions of rat brain. No significant change in thyrotropin releasing hormone (TRH)-like immunoreactivity was observed. Neuropeptide systems may be involved in the neuropharmacologic effects of ketamine.     

Neuropeptides and retinal development

Different peptidergic systems have been investigated with some detail during retinal development, including substance P (SP), vasoactive intestinal polypeptide (VIP), pituitary adenylate cyclase activating polypeptide (PACAP) and somatostatin (SRIF). Concerning possible developmental actions of neuropeptides, VIP and PACAP exert protective and growth-promoting actions that may sustain retinal neurons during their development. In addition, the presence of transient SRIF expressing cells and recent observations in SRIF receptor knock out mice indicate variegated roles of this peptide in the development of the retina and of retinofugal projections. Finally, recent studies have shown that, in the developing rabbit retina, changes in the expression pattern of SP receptors are accompanied by modifications of SP physiological effects, indicating that retinal circuits where SP is involved are likely to function in a substantially different manner before the retina becomes involved in the processing of visual stimuli. SP neurotransmission in the immature retina may subserve developmental events, and SP is likely to represent an important developmental factor for the maturation of retinal neurons and circuitries.     

Purification, characterization, and localization of neuropeptides in the cornea

The immunologically detected neuropeptides methionine enkephalin (ME), substance P (SP), beta-endorphin (beta-End), and alpha-melanocyte stimulating hormone (alpha-MSH) were purified from bovine corneal extracts by gradient, followed by isocratic, reversed phase-high performance liquid chromatography (RP-HPLC) and characterized, after both chromatographic steps, by radioimmunoassay (RIA). Immunologically detected ME and SP were purified from canine corneal extracts by gradient RP-HPLC and characterized by RIA. An anatomical study of the bovine cornea separated the cornea into an epithelium-enriched and a stroma-enriched portion. After gradient RP-HPLC, RIA demonstrated that all the ME-like immunoreactivity was located in the corneal epithelium, whereas the SP-like immunoreactivity was distributed between the stroma and epithelium in an approximate two-to-one ratio.     

Immunohistochemical Localization of Cardio-Active Neuropeptides in the Heart of a Living Fossil, Nautilus pompilius L. (Cephalopoda, Tetrabranchiata)

Neuropeptides play an important role in modulating the effects of neurotransmitters such as acetylcholine and noradrenaline in the heart and the vascular system of vertebrates and invertebrates. Various neuropeptides, including substance P (SP), vasoactive intestinal polypeptide (VIP) and FMRFamide, have been localized in the brain in cephalopods and the neurosecretory system of the vena cava. Previous studies involving cephalopods have mainly focussed on the modern, coleoid cephalopods, whereas little attention was paid to the living fossil Nautilus. In this study, the distributions of the peptides related to tachykinins (TKs) and the high affinity receptor for the best characterized TK substance P (tachykinin NK-1), VIP, as well as FMRFamide were investigated in the heart of Nautilus pompilius L. by immunohistochemistry. TK-like immunoreactivity (TK-LI) was seen associated to a sub-population of hemocytes, VIP-LI glial cells in larger nerves entering the heart, whereas FMRFamide immunoreactivity was distributed throughout the entire heart, including the semilunar atrioventricular valves. The pattern of FMRFamide immunoreactivity matched that of Bodian silver staining for nervous tissue. The NK-1-LI receptor was located on endothelial cells, which were also positive for endothelial nitric oxide synthase-LI (eNOS). The results indicate that neuropeptides may be involved in the regulation of the Nautilus heart via different mechanisms, (1) by direct interaction with myocardial receptors (FMRFamide), (2) by interacting with the nervus cardiacus (VIP-related peptides) and (3) indirectly by stimulating eNOS in the endothelium throughout the heart (TK-related peptides).     

Irradiation-induced effects on the innervation of rat salivary glands: Changes in enkephalin- and bombesin-like immunoreactivity in ganglionic cells and intraglandular nerve fibers

When treating head and neck for cancer with the use of radiotherapy the salivary glands are usually within the treatment volume with ensuing dryness and discomfort. Since the autonomic nervous system is of pivotal importance for the salivary gland function and integrity, the irradiation-induced effects may involve an influence on the innervation of salivary glands. Therefore, the rat submandibular gland, including the submandibular ganglionic cells, has been subjected to immunohistochemical examination with respect to expression of neuropeptides following fractionated irradiation with high energy photons. A markedly enhanced expression of bombesin- and leu-enkephalin-(ENK)-like immunoreactivities (LI) in the ganglionic cells and a pronounced increase in the number of nerve fibers showing these immunoreactivities in the submandibular gland tissue following irradiation were observed 10 days after treatment. On the other hand, no changes in the patterns of VIP (vasoactive intestinal polypeptide)- and NPY (neuropeptide Y)-immunoreactivities occurred. Thus, the present study shows that alterations in the expression of certain neuropeptides take place in the submandibular gland and its associated ganglionic cells in response to irradiation of the head and neck region. These changes may add further explanation to the inherent radiosensitivity of salivary glands.     

The distribution of putative neurotransmitters in the nervous system of the dipteran Chironomus tentans insect larva: An immunohistochemical study using antisera to 5-hydroxytryptamine,tyrosine hydroxylase,methionine-enkephalin,proctolin and bombesin

Using the indirect immunofluorescence technique, the localization and distribution of transmitters, transmitter-related enzymes and neuropeptides was studied in the larvae of the dipteran species Chironomus tentans. Immunoreactivity could be seen for 5-hydroxytryptamine, tyrosine hydroxylase (the rate-limiting enzyme in the catecholamine synthesis), and the neuropeptides methionine-enkephalin (met-enk), proctolin and bombesin. The immunoreactivity was confined both to cell bodies as well as to nerve fibers within ganglia and along the alimentary canal. Furthermore, tyrosine hydroxylase immunoreactivity could also be seen in epithelial cells locally distributed along a short, middle part of the alimentary tract. These latter cells were regarded as endocrine-like cells. No immunoreactivity could be found with certainty for the enzyme phenylethanolamine-N-methyltransferase (PNMT) nor for the peptides vasoactive intestinal polypeptide (VIP), dynorphin, substance P, somatostatin, thyrotropin releasing hormone (TRH), neuropeptide Y (NPY), peptide histidine isoleucine amide (PHI), neurotensin, galanin and cholecystokinin (CCK).     

Distribution of vasoactive intestinal peptide and calcitonin gene-related peptide immunoreactive nerve fibers and binding sites in the hamster seminal vesicle during post-natal development.

The distribution of vasoactive intestinal peptide (VIP)- and calcitonin gene-related peptide (CGRP)-immunoreactive nerves and 125I-labeled VIP- and CGRP-binding sites was studied in the hamster seminal vesicle of 12-, 30- and 60-day-old animals. In addition, the general innervation of the seminal vesicle was examined using the general neuronal marker synaptophysin. Our results show that the densities of the overall (synaptophysin immunoreactive) and CGRP-immunoreactive innervation is constant during the post-natal development of the gland. However, a significant decrease in VIP-containing nerves is observed at the end of puberty. The autoradiographic study revealed that in 12-day-old animals, the epithelium presents VIP binding sites. However, in 30-day-old animals, VIP binding sites are observed in the epithelium of only a few clumps of acini. In 60-day-old animals, the gland is composed of acini with dilated lumina where VIP binding sites are not detected. In all groups studied the epithelium does not exhibit CGRP binding sites. The seminal vesicle muscle layer displays specific binding sites for both VIP and CGRP at all post-natal developmental times, but the density of VIP binding sites is higher in 12- than in 30- and 60-day-old animals. Our results, showing the presence of specific VIP and CGRP binding sites during the development of the hamster seminal vesicle, suggest that these neuropeptides may be involved in the growth and differentiation of the gland.     

Depletion of neuropeptides in rat parotid glands and declining atropine-resistant salivary secretion upon continuous parasympathetic nerve stimulation

In rats the parasympathetic auriculo-temporal nerve on one side was continuously stimulated at 40 Hz for 20-80 min in the presence of adrenergic blockers (dihydroergotamine and propranolol) +/- atropine. During the first 10 min this gave rise to a flow of saliva from the parotid gland that in the atropinized rats amounted to 35% of that found in rats not treated with atropine, while the protein and amylase outputs were 75% of those in non-atropinized rats. The atropine-resistant secretion of fluid and proteins declined to 5-10% of the initial value within 40 min but did not cease completely even after 80 min. The marked reduction in secretory responses was not due to desensitization or exhaustion of the gland cells. The nerve stimulation reduced the parotid gland content of vasoactive intestinal peptide (VIP) and substance P (SP) to approximately 60 and 25% of that of contralateral glands after 20 and 60 min, respectively. The probable explanation for the decline in secretory response seems to be depletion of non-adrenergic, non-cholinergic transmitter(s). The present results suggest that neuropeptides are involved in the regulation of salivary secretion but provide no direct evidence that either VIP or SP is responsible for the atropine-resistant salivary secretion.     

VIP and noncholinergic vasodilatation in rabbit submandibular gland

The effect of parasympathetic nerve activation on rabbit submandibular gland (SMG) blood flow and saliva secretion were studied before and after systemic administration of atropine or hexamethonium. The parasympathetic fibers were stimulated electrically (2 and 15 Hz, 10 V, 1 msec) at the plexus around the submandibular salivary duct or at the chorda lingual nerve. In untreated animals, stimulation of parasympathetic fibers caused a frequency-dependent increase of salivary secretion and blood flow in the SMG. Atropine treatment completely abolished saliva secretion at 2 Hz and 15 Hz and the increase in SMG blood flow during stimulation at 2 Hz. Although atropine significantly reduced the vasodilatory response at 15 Hz, the highest blood flow measured under such circumstances was still about 2.5 times the prestimulation value. After hexamethonium administration no blood flow increase or saliva secretion was seen upon chorda lingual stimulation. The concentration of vasoactive intestinal polypeptide (VIP)-like immunoreactivity in the venous effluent of the SMG increased during nerve stimulation. Atropine significantly reduced, and hexamethonium abolished this VIP-output elicited by parasympathetic nerve stimulation. Local infusion of VIP, peptide histidine isoleucine (PHI) and substance P all caused atropine-resistant vasodilation but no salivation. The present data suggest that VIP and possibly PHI play a role in the atropine-resistant vasodilatation in rabbit submandibular gland elicited by parasympathetic nerve stimulation. The contribution of sensory mediators such as substance P released by stimulation of afferent nerves in the chorda lingual nerve to the salivary and vasodilatory responses seems to be of minor importance in the rabbit submandibular gland.     

Expression of neuropeptides and their receptors in the developing retina of mammals

The present review examines various aspects of the developmental expression of neuropeptides and of their receptors in mammalian retinas, emphasizing their possible roles in retinal maturation. Different peptidergic systems have been investigated with some detail during retinal development, including substance P (SP), somatostatin (SRIF), vasoactive intestinal polypeptide (VIP), pituitary adenylate cyclase-activating polypeptide (PACAP), neuropeptide Y (NPY), opioid peptides and corticotrophin-releasing factor (CRF). Overall, the developmental expression of most peptides is characterized by early appearance, transient features and achievement of the mature pattern at the time of eye opening. Concerning possible developmental actions of neuropeptides, recent studies imply a role of SP in the modulation of cholinergic neurotransmission in early postnatal rabbit retinas, when cholinergic cells participate in the retinal spontaneous waves of activity. In addition, the presence of transient SRIF expressing ganglion cells and recent observations in SRIF receptor knock-out mice indicate variegated roles of this peptide in the development of the retina and of retinofugal projections. Furthermore, VIP and PACAP exert protective and growth-promoting actions that may sustain retinal neurons during their development, and opioid peptides may control cell proliferation in the developing retina. Finally, a peak in the expression of certain peptides, including VIP, NPY and CRF, is present around the time of eye opening, when the retina begins the analysis of structured visual information, suggesting important roles of these peptides during this delicate phase of retinal development. In summary, although the physiological actions of peptides during retinal development are far from being clarified, the data reviewed herein indicate promising perspectives in this field of study.     

Canine myenteric, deep muscular, and submucosal plexus preparations of purified nerve varicosities: content and chromatographic forms of certain neuropeptides

Partially purified nerve varicosities prepared from canine small intestinal myenteric, deep muscular and submucosal plexuses were found to contain, by radioimmunoassay, gastrin-releasing polypeptide (GRP), substance P, Leu-enkephalin, Met-enkephalin, vasoactive intestinal polypeptide (VIP) and neurokinin A, but did not contain detectable amounts of neurokinin B. In all three plexus preparations, VIP was present in the highest concentration. In contrast to other species, GRP and the enkephalins were found to be present in relatively high concentrations in the submucosal plexus and GRP was present in low concentrations in the deep muscular plexus. Equal concentrations of substance P and neurokinin A were found in the myenteric and deep muscular plexus preparations but greater concentrations of substance P relative to neurokinin A were found in the submucosal plexus preparations. On reverse phase HPLC, a major peak of immunoreactivity occurred at the retention times of standard preparations for all six neuropeptides measured. Significant heterogeneity was found for GRP- and VIP-like immunoreactivity, especially in the submucosal plexus preparations. These partially purified canine small intestine nerve varicosity preparations may prove of value in studying release mechanisms for, and the posttranslational processing of, neuropeptides.