Immunohistochemical localization of (neuro)peptide hormones in endocrine cells and nerves of the gut of a stomachless teleost fish, Barbus conchonius (Cyprinidae)

Antigen sampling in the fish intestine

Antigen uptake in the gastrointestinal tract may induce tolerance, lead to an immune response and also to infection. In mammals, most pathogens gain access to the host though the gastrointestinal tract, and in fish as well, this route seems to be of significant importance. The epithelial surface faces a considerable challenge, functioning both as a barrier towards the external milieu but simultaneously being the site of absorption of nutrients and fluids. The mechanisms allowing antigen uptake over the epithelial barrier play a central role for maintaining the intestinal homeostasis and regulate appropriate immune responses. Such uptake has been widely studied in mammals, but also in fish, a number of experiments have been reported, seeking to reveal cells and mechanisms involved in antigen sampling. In this paper, we review these studies in addition to addressing our current knowledge of the intestinal barrier in fish and its anatomical construction.

Autonomic control of gut motility: a comparative view

Gut motility is regulated to optimize food transport and processing. The autonomic innervation of the gut generally includes extrinsic cranial and spinal autonomic nerves. It also comprises the nerves contained entirely within the gut wall, i.e. the enteric nervous system. The extrinsic and enteric nervous control follows a similar pattern throughout the vertebrate groups. However, differences are common and may occur between groups and families as well as between closely related species. In this review, we give an overview of the distribution and effects of common neurotransmitters in the vertebrate gut. While the focus is on birds, reptiles, amphibians and fish, mammalian data are included to form the background for comparisons. While some transmitters, like acetylcholine and nitric oxide, show similar distribution patterns and effects in most species investigated, the role of others is more varying. The significance for these differences is not yet fully understood, emphasizing the need for continued comparative studies of autonomic control.

Enteric co-innervation of esophageal striated muscle fibers: a phylogenetic study

Enteric co-innervation of striated muscle fibers in the esophagus occurs in several mammalian species including humans. However, the functional significance is still unknown. Phylogenetic data may be instrumental in gaining further insight. We examined the bat Glossophaga soricina and the shrew Suncus murinus as representatives for phylogenetically old mammals. As ruminants the antelope Tragelaphus imberbis, the he-goat Capra falconeri and the sheep Ovis aries were selected. As non-mammals the clawed frog Xenopus laevis as representative for the taxon amphibian and the rainbow trout Oncorhynchus mykiss as representative for the taxon fish were included. Histochemistry for nicotinamide adenine dinucleotide phosphate-diaphorase and acetylcholinesterase as well as immunofluorescence for vasoactive intestinal peptide and alpha-bungarotoxin were used to demonstrate enteric nerve fibers and motor endplates, respectively. Motor endplates were associated with enteric nerve fibers in all species investigated, although the rates of co-innervation varied from approximately 10 to 20% in shrew, antelope, he-goat, frog and fish, approximately 40% in bat to nearly 90% in sheep. These results demonstrate that enteric co-innervation, in spite of varying co-innervation rates, is conserved through vertebrate evolution, and underline the significance of this newly discovered innervation component.

Immunohistochemical study on the neuroendocrine system of the digestive tract of turbot, Scophthalmus maximus (L.), infected by Enteromyxum scophthalmi (Myxozoa)

In recent years a new parasite, causing severe losses, has been detected in farmed turbot, Scophthalmus maximus (L.), in Northwestern Spain. Dead fish showed emaciation and cachexia caused by severe necrotizing enteritis, which affected all areas of the digestive tract. The parasite was classified as a myxosporean and named Enteromyxum scophthalmi. This study was designed to assess the response of the turbot neuroendocrine system against E. scophthalmi infection. Immunohistochemical tests were applied to sections of the gastrointestinal tract of uninfected and E. scophthalmi-infected turbot, and the presence of cholecystokinin (CCK-8), serotonin (5-HT), substance P (SP), calcitonin gene-related peptide (CGRP) and vasoactive intestinal peptide (VIP) were documented. A higher abundance of both endocrine epithelial cells (ECs) and nerve cell bodies and fibres for CCK-8, 5-HT and SP were recorded in the gastrointestinal tract of infected turbot, whereas VIP-like substance decreased. The results indicate that E. scophthalmi infection in turbot induced changes in the neuroendocrine system, which may cause alterations in gut motility, electrolyte and fluid secretion, and vascular and immune functions.

Immunohistochemical study on distribution of endocrine cells in gastrointestinal tract of flower fish (Pseudophoxinus antalyae)

AIM: To detect distribution and relative frequency of endocrine cells in gastrointestinal tract of flower fish (Pseudophoxinus antalyae).

METHODS: The intestinal tract of flower fish was divided into four portions from proximal to distal; the enlarged area after oesophagus and anterior, middle and posterior intestine. Immunohistochemical method using the peroxidase anti-peroxidase complex was employed. All antisera between four portions of flower fish were compared using ANOVA.

RESULTS: Eleven types of gut endocrine cells were determined; they were immunoreactive for calcitonin gene related peptide, substance P, vasoactive intestinal peptide, bombesin, somatostatin-14, secretin, TrkA, TrkB, TrkC, neurotensin, neuropeptide Y, which were found in almost all portions of the gastrointestinal tract.

CONCLUSION: The regional distribution and relative frequency of immunoreactive cells in the flower fish, Pseudophoxinus antalyae, are essentially similar to those of other fish.

Immunohistochemical study on the endocrine cells in gut of the stomachless teleost, Zacco platypus (Cyprinidae)

The regional distribution and relative frequency of neurohormonal peptides-producing cells were demonstrated in the gut of the stomachless teleost, Zacco platypus (Temminck et Schegel), using 10 types of specific antisera raised against mammalian regulatory peptides. The gut of Z. platypus was divided into five portions from proximal to distal (segment I-V). Most of immunoreactive cells in the epithelial lining portion, between epithelial cells, were generally spherical or spindle shape having long cytoplasmic process that was reached via the lumen while cells round in shape were found in the basal portions of epithelial lining occasionally. Serotonin-, somatostatin-, glucagon-, cholecystokinin (CCK)-8 and pancreatic polypeptide (PP)-immunoreactive cells were observed in this study. However, no chromogranin A-, secretin-, vasoactive intestinal peptide (VIP)-, substance P- and bombesin-immunoreactive cells were found. Serotonin-immunoreactive cells were demonstrated throughout the entire gut tract and occurred more frequently than other cells. Somatostatin-immunoreactive cells were restricted to proximal segments of the gut (segment I-III) with rare frequencies, and glucagon-immunoreactive cells were demonstrated in the proximal segments of the gut (segment I, II) with moderate to few occurrences. CCK-8-immunoreactive cells were found throughout the whole intestinal tract except for most proximal segment (segment I) with moderate to few frequencies and PP-immunoreactive cells were demonstrated in the proximal to middle segments, segment I-III, with a few, rare and rare frequencies, respectively.

Occurrence of ACTH- and enkephalin-like peptides in the developing gut of Dicentrarchus labrax L

We carried out immunohistochemical tests in the developing gut of the sea bass Dicentrarchus labrax to follow the appearance and distribution of the immunoreactivity (IR) to antibodies against POMC-derived, adrenocorticotropic hormone (ACTH), alpha-melanocyte stimulating hormone (alpha-MSH) and beta-endorphin (beta-End), and against two enkephalins, with the aim to study a possible involvement of these molecules in the early neuro-immune-endocrine integration. Our data show that IR to antibodies against some molecules involved in the stress response, such as ACTH and enkephalins, are present in the sea bass gut from an early larval stage (4 days after hatching), before transition to the exotrophic feeding. Moreover, the present study demonstrates for the first time the presence of ACTH-like immunoreactive material in developing gut of a fish. The possible roles of tested molecules are discussed.

Identification, localization and morphology of APUD cells in gastroenteropancreatic system of stomach-containing teleosts

AIM:To identify the type localization and morphology of APUD endocrine cells in the gastroenteropancreatic (GEP) system of stomach-containing teleosts, and study APUD endocrine system in the stomach, intestine and pancreas of fish species.METHODS:Two kinds of immunocytochemical (ICC) techniques of the streptavidin biotin-peroxidase complex (SABC) and streptavidin-peroxidase (S-P) method were used. The identification, localization and morphology of APUD endocrine cells scattered in the mucosa of digestive tract, intermuscular nerve plexus and glandular body of northern snakehead (Channa argus), ricefield eel (Monopterus albus), yellow catfish (Pelteobagrus fulvidraco), mandarinfish (Siniperca chuatsi), largemouth bass (Micropterus salmoides),oriental sheatfish (Silurus asotus), freshwater pomfret (Colossoma brachypomum) and nile tilapia (Tilapia nilotica) were investigated with 8 kinds of antisera.RESULTS:The positive reaction of 5-hydroxytryptamine (5-HT) immunoreactive endocrine (IRE) cells was found in the digestive tract and glandular body of 8 fish species in different degree.Only a few gastrin (GAS)-IRE cells were seen in C.argus,M.albusand P.fulvidraco. Glucagon (GLU)IRE cells were not found in the digestive tract and glandular body but existed in pancreatic island of most fish species. The positive reaction of growth hormone (GH)IRE cells was found only in pancreatic island of S. Chuatsi and S. Asotus, no positive reaction in the other 6 fish species. Somatostatin (SOM), calcitonin (CAL), neurofilament (NF) and insulin (INS)-IRE cells in the stomach, intestine and pancreas of 8 kinds of fish were different in distribution and types. The distribution of all 8 APUD cells was the most in gastrointestinal epithelium mucosa and then in digestive glands. The positive reaction of SOM and 5-HT-IRE cells was found in intermuscular nerve plexus of intestine of P.fulvidraco and S.chuatsi. Only GH-IRE cells were densely scattered in the pancreatic islands of S.chuatsi and S. asotus, and odd distribution in the pancreas of S. asotus.SOM-IRE cells were distributed in the pancreatic islands of S. asotus, C. Brachypomumand T. nilotica. There were INS-IRE cells in the pancreatic islands of S. chuatsi and S. asolus. Eight kinds of APUD cells had longer cell body and cytoplasmic process when they were located in the gastrointestinal epithelium, and had shorter cell body and cytoplasmic process in the gastric gland, and irregular shape in the esophagus and pancreatic island.CONCLUSION:Eight kinds of IRE cells were identified in the GEP system of stomach-containing teleosts. These endocrine cells were scattered in gastrointestinal mucosa, intermuscular nerve plexus, gland body, pancreatic gland and islands under APUD system. CAL and GH-IRE cells in the pancreatic islands of fishes showed functional diversity for these two hormones. Their morphological feature provides evidence of endocrine-paracrine and endocrine-exocrine acting mode. This research can morphologically prove that the GEP endocrine system of fish (the lowest vertebrate) is almost the same as of mammal and human.

Glucagon- and NPY-related peptide-immunoreactive cells in the gut of sea bass (Dicentrarchus labrax L.): a light and electron microscopic study

Glucagon and peptide of the neuropeptide Y (NPY) family immunoreactivities were studied in the gut of sea bass (Dicentrarchus labrax) using antisera against bovine/porcine glucagon, porcine glucagon, glicentin (10-30), bovine pancreatic polypeptide (PP), peptide tyrosine tyrosine (PYY), salmon PYY (sPYY), and NPY. Glucagon-, glicentin-, PYY-, and NPY-immunoreactive (ir) cells were detected in the stomach, and glucagon-, PP-, PYY-, sPYY-, and NPY-ir cells in the intestine. PP, PYY, and NPY immunoreactivities coexisted in intestinal endocrine cells (NPY-like peptide containing cells), in some of which there was also glucagon immunoreactivity. Preabsorption tests indicated that different products of the glucagon gene(s) are probably expressed in the stomach and intestine of sea bass and that the peptides belonging to the NPY family in the endocrine cells of the intestine are more similar to NPY than to other peptides of this family. Glucagon-ir cells in the stomach, and glucagon/NPY-like containing cells in the intestine, were characterized by conventional and immunogold electron-microscopic techniques. The glucagon cells had secretory granules with a clotted content, the gold particles being observed in both the core and the halo. Glucagon/NPY-like cells showed two types of secretory granules differing in size, both of which were immunogold labeled with anti-NPY and anti-sPYY; the smaller granules were weakly immunogold labeled with anti-glucagon.

An immunocytochemical study of endocrine cells in the gut of a stomachless teleost fish, grass carp, Cyprinidae

Nineteen different antisera raised against mammalian hormones were used to identify the occurrence and distribution of endocrine cells in the gut of grass carp (Ctenopharyngodon idellus). Positive reactions were obtained in gut epithelium with antisera gastrin, glucagon, gastric inhibitory peptide, leucine enkephalin, substance P, and bovine pancreatic polypeptide. No immunoreactive product was formed using antisera against somatostatin, 5-hydroxytryptamine, insulin, avian pancreatic polypeptide, motilin, cholecystokinin, secretin, neurotensin, vasoactive intestinal polypeptide, bombesin, neuron-specific enolase, prochymosin, and pepsinogen. The exact distribution mapping of six kinds of immunoreactive endocrine cells throughout the gut of grass carp (C. idellus) is presented. The morphological characteristics of immunoreactive endocrine cells is described. Their distribution characteristics and possible modes of secretion and function are discussed. Finally, the possible relationship between the transplantation of these cells in the gastro-entero-pancreatic endocrine system is discussed.

Endocrine cells and nerves in the pyloric ceca and the intestine of Oncorhynchus mykiss (Teleostei): an immunocytochemical study

The endocrine cells of rainbow trout pyloric ceca and intestine have been investigated immunocytochemically using the avidin-biotin method. Twenty-six antisera were tested and 13 endocrine cell types immunoreacted with antisera to serotonin, somatostatin-25, bombesin, C-flanking bombesin, substance P, salmon PP, NPY, PYY, PP, glucagon, GLP1, Met-enkephalin, and CCK/G. Glucagon and GLP1 immunoreactivities appear in the same cells. Nerves positive to serotonin, substance P, PHI, and VIP were also found. The presence of cells positive to somatostatin-25, C-flanking bombesin, and salmon PP are described for the first time in fish intestine.

Effects of some autonomic drugs and neuropeptides on the mechanical activity of longitudinal and circular muscle strips isolated from the carp intestinal bulb (Cyprinus carpio)

1. The mechanical responses to some autonomic drugs and neuropeptides of longitudinal muscle (LM) and circular muscle (CM) strips isolated from the carp intestinal bulb were investigated in vitro. 2. Acetylcholine and carbamylcholine caused concentration-dependent transient contraction of both LM and CM strips. Tetrodotoxin had no effect, but atropine selectively decreased the contractile responses to acetylcholine and carbamylcholine. 3. Excitatory alpha-2 and inhibitory beta adrenoceptors were present in both LM and CM strips. 4. 5-Hydroxytryptamine (5-HT) caused concentration-dependent contraction of both LM and CM strips. Tetrodotoxin, atropine and methysergide decreased the contractile responses to 5-HT. 5. Some neuropeptides (angiotensin I, angiotensin II, bombesin, bradykinin, neurotensin, somatostatin and vasoactive intestinal polypeptide) did not cause any mechanical response (contraction or relaxation) in either smooth muscle strip. 6. Substance P (SP), neurokinin A (NKA) and neurokinin B (NKB) caused contraction of both LM and CM strips. However, the time course of the contraction in LM was different from that in CM. The order of potency was NKA greater than SP greater than NKB in LM strips and NKA greater than SP much greater than NKB in CM strips. In LM strips, the contractile responses to tachykinins were unaffected by spantide and methysergide, but partly decreased by tetrodotoxin and atropine. On the other hand, the contractile responses of CM strips were unaffected by tetrodotoxin, atropine, methysergide and spantide. 7. Dynorphin (1-13) (DYN), leucine-enkephalin (L-Enk) and methionine-enkephalin (M-Enk) caused concentration-dependent contraction of both LM and CM strips. The order of potency was DYN greater than M-Enk greater than L-Enk. Naloxone selectively decreased the responses to opiate peptides. 8. The present results indicate that acetylcholine, carbamylcholine, catecholamines, 5-HT, tachykinins (SP, NKA and NKB) and opiate peptides (DYN, L-Enk and M-Enk) affect the mechanical activity of LM and CM strips isolated from the carp intestinal bulb through their specific receptors.

Immunohistochemical localization of VIP and Met-enkephalin in the rabbit submandibular and sublingual glands

The existence and distribution of vasoactive intestinal polypeptide (VIP), and Met-enkephalin pentapeptide were investigated by means of the peroxidase-antiperoxidase (PAP) technique in rabbit submandibular and sublingual glands. In the submandibular gland, VIP immunostaining was observed in some peripheral acinar cells, while in sublingual one VIP positive fibres surrounded semilunes. Ductal cells of both glands were also reactive. These findings suggested a role of VIP in regulating volume and composition of salivary secretion.

The endocrine cells in the gut of Mugil saliens Risso, 1810 (Teleostei): an immunocytochemical and ultrastructural study

The endocrine cells in the gut of Mugil saliens Risso, 1810 (leaping grey mullet) were investigated by immunocytochemical and electron microscopic techniques. Gastrin-, glucagon-, and somatostatin-immunoreactive cells were identified in the cardiac and cecal stomach regions, located mainly in the lower part of the gastric folds and in the upper part of the glands. Substance P-, somatostatin-, and pancreatic polypeptide (PP)-immunoreactive cells were found between epithelial cells in the pyloric stomach region. Gastrin-, cholecystokinin (CCK)-, gastric inhibitory polypeptide (GIP)-, substance P-, Met-enkephalin- and PP-immunoreactive cells were observed throughout the intestine while only the last three of these appeared in the posterior intestine. Nine types of gastroenteroendocrine cells were ultrastructurally characterized; some of them were related to the cell types immunocytochemically identified.

Enteric neuromuscular junctions: comparison of ultrastructural features in different phylogenetic groups

The enteric neuromuscular junctions of snail (Helix pomatia), locust (Locusta migratoria migratorioides), cockroach (Periplaneta americana), carp (Cyprinus carpio) and tench (Tinca tinca) were studied by means of different light and electron microscopic methods. The nitroblue tetrazolium staining revealed that the myenteric plexuses of the above species are composed of nerve cells, a network of varicose nerves and nerve bundles. Instead of highly organized ganglia, single neurons or small groups of 2-4 cells are characteristic of the invertebrates and fish studied. Catecholaminergic fluorescence induced by glyoxylic acid was detected in the muscular layer of the entire alimentary tract in snail and the hindgut of tench. Fluorescent nerves and perikarya were frequent in the snail gut, while only nerves and no perikarya were found in tench. A close contact between enteric muscles and nerves is the most common form of enteric neuromuscular junction in both the smooth (i.e. the molluscan and fish gut) and the striated (i.e. the insect gut) musculature. The striated musculature (i.e. the insect gut, the oesophagus of carp, and the oesophagus, stomach and the midgut of tench) also receives a synaptic input. Cytochemical evidence is provided of the cholinergic character of fish motor endplates. The ultrastructural appearance and vesicle population of certain nerve terminals suggest a universal role of aminergic and peptidergic control in gut motility.

Contractile response to substance P in isolated smooth muscle strips from the intestinal bulb of the carp (Cyprinus carpio)

1. The effect of substance P on the mechanical activity of carp intestinal bulb smooth muscle was investigated in vitro. 2. Bath-applied substance P (1 nM-1 microM) caused concentration-dependent contraction of the smooth muscle. The EC50 value was 20 +/- 3 nM (N = 13). 3. Pretreatment with tetrodotoxin (780 nM) or atropine (500 nM) partially decreased the contractile response to substance P, while methysergide (3 microM) did not decrease the response. 4. The contractile response to substance P was not decreased by [D-Pro2, D-Trp7.9]-substance P or [D-Pro4, D-Trp7.9]-substance P (4-11) pretreatment (10 microM for 5 min). 5. Exposure of the intestinal bulb to substance P (100 nM and 1 microM for 15 min) decreased the response to subsequent application of substance P, physalaemin and eledoisin in a concentration dependent manner, while the contractile response to acetylcholine or methionine-enkephalin was not affected. 6. Exposure of the intestinal bulb to physalaemin and eledoisin (100 nM for 15 min) decreased the response to subsequent application of substance P. 7. The above results indicate that substance P causes the contraction of the carp intestinal bulb smooth muscle through its direct action on the smooth muscle and its indirect action through enteric cholinergic nerves. Long-term exposure to substance P causes desensitization of the preparation to substance P, physalaemin and eledoisin at the receptor level.

Effects of cholecystokinin peptides on digestive enzymes in killifish in vivo

1. The abilities of cholecystokinin-like peptides to elicit lipase secretion were examined in the stomachless killifish, Fundulus heteroclitus. 2. Cholecystokinin octapeptide, caerulein, and nonsulfated caerulein stimulated lipase secretion in vivo, with caerulein and nonsulfated caerulein being the most potent peptides tested. 3. Lipase secretion was not induced by carbachol, and peptide stimulated lipase secretion was not inhibited by atropine. 4. These data suggest digestive enzyme secretion constitutes an evolutionary primitive role for CCK.

Substance P-like immunoreactivity and the effects of tachykinins in the intestine of the Atlantic cod, Gadus morhua

The substance P (SP)-like peptides present in the intestine of the cod, Gadus morhua, were studied by immunochemical techniques. The amount of SP-like material in extracts of the intestine was quantified using radioimmunoassay (RIA). Immunohistochemistry indicated that the SP-like material detected in nerve fibres and endocrine cells of the intestine is more closely related to SP than to the other tachykinins used in the study. The excitatory response of SP on the vascularly perfused cod intestine was reduced or abolished by treatment with atropine, methysergide or tetrodotoxin. The results indicate that SP acts partly via cholinergic and serotonergic neurons and partly directly on the smooth muscle cells of the intestine. The effect of SP was compared to the effects of 5 other tachykinins. No great difference was found between the potencies of the tachykinins, suggesting that the receptors present are most similar to the SP-P type of receptor.

Substance P is a vasoactive hormone in the Atlantic hagfish Myxine glutinosa (Cyclostomata)

The in vitro effects of synthetic substance P (SP) on rings of the ventral aorta and on the systemic heart of Myxine glutinosa were investigated by the use of an organ bath. Increasing molar amounts (10(-16) to 10(-8) M) of SP were applied and the reaction of the aortic rings was recorded with isometric transducers. SP was found to contract the Myxine aorta in a dose-dependent manner starting at a threshold concentration of 10(-14) M and reaching a plateau at 10(-11) M. Therefore, the effective dose of SP seems to be in a physiological range. On the other hand, the heart was found to be insensitive to SP even in doses as high as 10(-5) M. By means of immunohistochemistry, SP-immunoreactive endocrine cells were found throughout the Myxine intestine while no SP-immunoreactive nerve fibers were detected at the Myxine aorta. Thus, under physiological conditions the observed contractile effect of SP on the ventral aorta may be raised by SP-like material released from enteroendocrine cells.

A comparative immunocytochemical study of the gastro-entero-pancreatic (GEP) endocrine system in a stomachless and a stomach-containing teleost

The gastro-entero-pancreatic (GEP) endocrine system of a stomach-containing and of a stomachless teleost, Sparus auratus and Barbus conchonius, respectively, are studied immunocytochemically using different antisera against mammalian hormones. Insulin-, glucagon-, somatostatin-, and pancreatic polypeptide (PP)-immunoreactive cells are identified in the endocrine pancreas of both species. Only the distribution of PP-immunoreactive cells differed strongly; in the principal islet of both fishes, few PP-immunoreactive cells are present, whereas in the smaller ones many of them are observed in S. auratus and none in B. conchonius. In the digestive tract of S. auratus 10 endocrine cell types can be distinguished: neurotensin-, secretin-, serotonin-, somatostatin-, and two types of substance P-immunoreactive cells exclusively in the stomach, and C-t-gastrin/CCK-, glucagon-, Met-enkephalin-, PP-, and only one type of substance P-immunoreactive cells in the intestinal epithelium. With the exception of substance P-immunoreactive cells, the other four intestinal endocrine cells, as well as an unspecific immunoreactive cell, can also be found in B. conchonius. Coexistence of glucagon- and PP-like immunoreactivity is observed in the pancreas of S. auratus and in the gut of B. conchonius. Pancreatic and gut endocrine cells showing only PP- or glucagon-like immunoreactivity are found, too.

Neurotensin in the human fallopian tube: immunohistochemical localization and effects of synthetic neurotensin on motor activity in vitro

With the use of different region-specific antisera and the peroxidase-antiperoxidase (PAP) technique, neurotensin-immunoreactivity was found in nerve fibers of the human fallopian tube. Neurotensin-immunoreactive fibers occurred at blood vessels and in contact with smooth muscle cells of the muscular stratum. In vitro experiments with helical strips of the myometrium revealed dose-dependent excitatory actions of neurotensin on resting tension as well as on amplitude and frequency of spontaneous contractions. The results may suggest a neurotransmitter function of neurotensin in the regulation of human oviductal smooth muscle activity. Thus, neurotensin may be essential in the transport of the eggs through the fallopian tube.

An immunocytochemical and ultrastructural study of endocrine cells in the gut of a teleost fish, Sparus auratus L

Endocrine cells in the gut of Sparus auratus L. (gilt-head sea bream) have been demonstrated by immunocytochemical and electron microscopic techniques. Cells showing somatostatin and gastrin-like immunoreactivity were found in the depth of the gastric folds and in the upper part of the stomach glands while substance P immunoreactive cells were present between the upper epithelial cells of the gastric folds. Cells showing gastrin, substance P, pancreatic polypeptide, cholecystokinin, and Met-enkephalin immunoreactivity were observed in the intestinal mucosa scattered between epithelial cells. Eight types of endocrine cells were ultrastructurally characterized by the shape, size, and electron density of their respective secretory granules. A tentative correlation between these diverse cell types and those identified by immunocytochemical techniques has been established.

Immunocytochemical identification and localization of peptide hormones in the gastro-entero-pancreatic (GEP) endocrine system of the mouse and a stomachless fish, Barbus conchonius

A large number of antisera mainly raised against mammalian hormones are tested immunocytochemically on the GEP-endocrine system of mouse and fish (Barbus conchonius). The endocrine pancreas of mouse and fish appeared to contain the same four endocrine cell types; insulin-, glucagon-, PP- and somatostatin-immunoreactive cells. In mouse about 13 GEP endocrine cell types are distinguished: 1. insulin-, 2. somatostatin-, 3. glucagon-, 4. PP-, 5. (entero)glucagon-/PP-like, 6. CCK-like, 7. substance P-, 8. neurotensin-, 9. VIP-, 10. gastrin-, 11. secretin-, 12. beta-endorphin-, 13. serotonin-immunoreactive cells. Based on this and a previous study at least 13 GEP endocrine cell types seems to be present in stomachless fish: 1-9 as described for mouse, 10. (entero)glucagon-like, 11. met-enkephalin, 12. VIP-like, 13. unspecific immunoreactive endocrine cells. Coexistence of glucagon and PP-like peptides is found in the gut and pancreas of mice and in the gut of B. conchonius. In mouse pancreas and fish gut, endocrine cells showing only PP- or glucagon-like immunoreactivity are found too. In mouse stomach some endocrine cells showing only PP-immunoreactivity are demonstrated. In the same region coexistence of C-t-gastrin- and FMRF-amide-immunoreactivity is found in endocrine cells. The importance of these phenomena are discussed. Enteric nerves immunoreactive with antisera raised against substance P and GRP are found in mouse, against somatostatin and met-enkephalin in both mouse and fish and against VIP in fish.

Neuropeptides and 5-HT immunoreactivity in the gastric nerves of the dogfish (Scyliorhinus stellaris)

The gastric autonomic innervation of the dogfish was examined for regulatory peptides and serotonin by immunochemical techniques. Bouin's-fixed, paraffin-embedded or benzoquinone-fixed frozen sections were used for light microscopical immunocytochemistry and glutaraldehyde-fixed resin-embedded sections for electron microscopical immunocytochemistry. Bombesin-, somatostatin-, gastrin/cholecystokinin-, substance P-, peptide histidine isoleucine-, vasoactive intestinal peptide- and serotonin-immunoreactive nerves were found in all layers of the stomach wall. Bombesin and vasoactive intestinal peptide-containing nerves were identified at ultrastructural level. Radioimmunoassay of acetic acid extracts of tissue confirmed the presence of immunoreactivity for bombesin, somatostatin, substance P, peptide histidine isoleucine and vasoactive intestinal peptide. Reverse phase high performance liquid chromatography indicated that the peptides identified were broadly similar to their mammalian counterparts.

Neuropeptide functions in the fish gut

Several neuropeptides, more or less related to their mammalian counterparts, are present in the enteric nervous system in fish, and may function as neurotransmitters, cotransmitters or neuromodulators in this system. Excitatory effects on fish gut smooth muscle are found with bombesin, substance P and neurotensin. VIP and bombesin are inhibitory in some preparations and metenkephalin and somatostatin give varying responses. Of the more closely studied neuropeptides, a bombesin-like peptide may be involved in a cofunction with acetylcholine in the excitation of gut motility. One or more tachykinins may be involved in different mechanisms controlling the gut motility, directly or indirectly via, e.g., serotonergic neurons. Bombesin, a tachykinin and VIP may control gastric secretion, and VIP may have vasodilatory functions as well as inhibitory functions on gut motility at least in some species.