Immunohistochemical and ultrastructural studies on the endocrine polypeptide (APUD) cells of the avian gastrointestinal tract

An immunocytochemical study of the endocrine cells in the stomach and duodenum of Zonotrichia capensis subtorquata (Passeriformes, Emberizidae)

The main purpose of this study was to evaluate the regional distribution pattern and relative frequency of some endocrine cells in the three portions of the gastrointestinal tract (GIT)--the proventriculus, gizzard and duodenum- of the rufous-collared sparrow (Zonotrichia capensis subtorquata), by immunohistochemical methods using six types of polyclonal antisera, specific for serotonin (5-HT), somatostatin (D cells), glucagon, motilin, polypeptide YY (PYY) and insulin. In the proventriculus, endocrine cells immunoreactive for all of these markers were observed. The somatostatin-immunoreactive cells were found with greater frequency, with the presence of cytoplasmic processes. In the gizzard, endocrine cells secreting somatostatin, 5-HT and PYY were detected, while those secreting glucagon and insulin were not. In the final part of the gizzard, endocrine cells secreting 5-HT were more frequent, and cells secreting somatostatin and insulin were not detected. All of the cell types studied were observed in the duodenum in different frequencies, except for cells immunoreactive for glucagon and insulin. The somatostatin-positive (D cells) were the most numerous, being more prevalent in the intestinal glands. The other endocrine cells were identified in smaller numbers, some of them located in the intestinal villi and Lieberkuhn glands. The finding of these cell types in the duodenum confirms their preferential location in the final portions of the principal segments of the digestive system and suggests control by feedback of its functions. In conclusion, some interesting distributional patterns of gastrointestinal endocrine cells were found in this species of sparrow.

Immunolocalisation of serotonin, gastrin, somatostatin and glucagon in entero-endocrine cells of the goose (Anser anser)

The processes of digestion in the avian gastrointestinal tract depend on sophisticated control systems that co-ordinate secretion of digestive juices and movement of the luminal contents. In the current study, the distribution of serotonin-, gastrin-, glucagon- and somatostatin-immunoreactive endocrine cells was investigated by immunocytochemical methods in the intestinal tract of the goose. The number of cells immunoreactive for each antiserum was evaluated in different regions of the intestinal tract. Serotonin-, glucagon- and somatostatin-immunoreactive endocrine cells were seen throughout the intestinal tract, but somatostatin-immunoreactive cells were not detected in the colon of the goose. Gastrin-immunoreactive cells were detected only in the duodenum, jejunum and colon mucosa. It is concluded that the distribution pattern of the entero-endocrine cells in the goose is similar to that of most of the mammalian and other poultry species.

Gut endocrine cells in birds: an overview, with particular reference to the chemistry of gut peptides and the distribution, ontogeny, embryonic origin and differentiation of the endocrine cells

This review deals with gut endocrine cells in birds. It focuses on both morphological and developmental aspects of these cells, which were included members of Pearse's APUD series. They comprise many cell types, which, in birds as in mammals, produce serotonin and a range of regulatory peptides. The chemical structure of most avian gut peptides has been established. These peptides and their functions are outlined here. The types and distribution of avian gut endocrine cells are detailed and compared with the situation in mammals. In birds, ultrastructural work has been limited to certain types of gut endocrine cell and not as widely applied as in mammals. However, immunocytochemistry has found widespread application in studies on birds: the hatching chick and also the adult chicken and certain other species such as the quail and duck have been studied. Gut endocrine cells showing immunoreactivity for the following peptides/serotonin have been identified: somatostatin, pancreatic polypeptide (PP), peptide YY, glucagon, secretin, vasoactive intestinal peptide, gastrin, cholecystokinin (CCK), neurotensin, motilin, gastrin-releasing peptide, substance P, enkephalin and serotonin. The colocalization of different peptides (including chromogranins) and of peptides and serotonin in the same gut endocrine cells is reviewed: notable amongst such associations are glucagon with PP and gastrin/CCK with neurotensin in the same cells. On morphological grounds cells have been identified as endocrine in avian gut from at least 9 days of incubation. Immunocytochemical studies show the majority of the various types first to appear between 12 to 14 days of incubation, with substantial numbers being recorded from 17 days onwards. Experimental studies on chicken and quail embryos have determined the embryonic origin of gut endocrine cells: evidence is unequivocal that such cells arise from the endoderm, not the neural crest, other ectoderm or the mesoderm. Studies on avian embryos have also contributed to our knowledge of mechanisms controlling the differentiation of gut endocrine cells: evidence shows that gut mesenchyme plays an important role in provoking (or inhibiting) the development of gut endocrine cells and there are indications that the endocrine cell pattern in gut is established early and that an axially-derived factor may be important in this process. The kinds of genetic mechanism possibly involved are mentioned but full elucidation of the processes concerned is awaited. A better understanding of the formation of endocrine tumours of the gut should result from the findings.

Distribution of serotonin-immunoreactive gut endocrine cells in chicks at hatching. Examination of possible co-localisation with peptides reveals unexpected cross-reactivity of substance P antiserum with serotonin

Serotonin-immunoreactive, i.e. enterochromaffin (EC) cells were found to be widely distributed in the intestine of the newly hatched chick but sparse in the stomach, and being particularly abundant in the duodenum, upper ileum and rectum. Although in birds, as in mammals, EC cells are most abundant in the intestine, in the stomach they are far sparser than in mammals. Comparison of adjacent sections immunostained for serotonin and a peptide provided no evidence that EC cells in the hatching chick contain motilin or substance P, and that at least the great majority of bombesin-immunoreactive cells contain no serotonin: it is apparent that the mammalian pattern of distribution of peptides in EC cells does not occur in the chick, at least at hatching. Cross reaction of an antiserum to substance P with serotonin was discovered, suggesting the need for a review of existing evidence for co-localisation of this peptide with serotonin.

Immunohistochemical differentiation of gastrin and cholecystokinin in gastrointestinal tract of chickens

The presence of cholecystokinin (CCK) in the gastrointestinal tract of chickens has not been well demonstrated, although immunological and chromatographic techniques have shown the presence of intestinal gastrin-CCK-like factors. Recently, a new peptide, structurally related to mammalian CCK, but with a gastrin-like activity, has been isolated from the digestive tract of chickens. The objective of this work has been: 1) to study the presence of gastrin-CCK-like immunoreactivity (IMR) in the digestive tract of chickens; 2) to distinguish chicken gastrin from CCK; and 3) to establish their distribution using specific antibodies. Tissue specimens from the proventriculus, gizzard, pylorus, duodenum, jejunum, ileum, ceca, and rectum were studied using indirect immunofluorescence procedures. The antibodies used were: 1) an antibody specific against the C-terminal pentapeptide common to gastrin and CCK; 2) one specific against CCK-33; and 3) one specific against chicken gastrin. Their use allowed the differentiation of two cellular populations which showed different affinities for the antibodies, indicating the presence of a gastrin-like peptide in the antrum and another CCK-like peptide in the small intestine, with the highest concentration in the proximal ileum. Immunoreactivity was not found in any other studied area. Two different peptides of the gastrin-CCK family are present in the chicken's gastrointestinal tract. However their differentiation and identification are more difficult than in mammals due to the greater structural similarities of these peptides in birds.

Effects of cholecystokinin and gastrin on gastroduodenal motility and coordination in chickens

Cholecystokinin (CCK) has not been isolated from chicken gut yet and there has been no study on the effects of chicken gastrin (CG), the only gastrin/CCK peptide isolated from avian gut, on gastrointestinal motility. The main objective was to study the effects of CCK and CG on gastroduodenal motility and coordination in chickens. Electrodes for electromyography were implanted in the stomach and proximal and distal duodenum of 4 wk old chickens. Sulphated CCK-octapeptide (CCK8) (10(-10) to 10(-8) moles/kg), CCK-tetrapeptide (CCK4) (2 x 10(-10) to 2 x 10(-8) moles/kg) and CG (3 x 10(-10) to 10(-8) moles/kg) were given in a 10 min i.v. infusion. All these peptides induced a dose-dependent inhibition of gastric motility. CCK8 induced a duodenal hyperactivity whereas CCK4 and CG induced a duodenal inhibition. Neither the CCK-A receptor antagonist L364,718 nor the CCK-B receptor antagonist L365,260 (10(-9)-10(-7) moles/kg) antagonized CCK8 actions. From these results we suggest that the receptors mediating CCK effects are different from those of mammals. The site of action for these peptides is the same in the stomach whereas in the duodenum there are two different ones, one mediating excitation and the other inhibition. These results suggest a physiological role for CCK regulating gastroduodenal motility in birds.

Gastrointestinal hormones in birds: morphological, chemical, and developmental aspects

Historically, the enterochromaffin cell was the first endocrine cell type detected in avian gut; subsequently, a number of types of such cells were distinguished on the basis of the ultrastructural features of the secretory granules. More recently, immunocytochemical procedures have revealed somatostatin-, pancreatic polypeptide (PP)-, polypeptide YY-, glucagon-, secretin-, vasoactive intestinal peptide (VIP)-, gastrin-, cholecystokinin-, neurotensin-, bombesin-, substance P-, enkephalin-, motilin-, and FMRFamide-like immunoreactivity in avian gastrointestinal endocrine cells. Most endocrine cells are located in the antrum; there are a number in the proventriculus and small intestine but few in the gizzard, cecum, and rectum. Several avian gastroenteropancreatic hormones, including glucagon, VIP, secretin, bombesin, neurotensin, and PP, have been isolated and sequenced. They resemble the equivalent mammalian peptides in terms of molecular size but differ in amino acid composition and sequence; some (e.g., VIP) differ only in minor respects, others (e.g., secretin) more radically. Gastrointestinal endocrine cells appear late in development; available data indicate that few types are recognized by either immunocytochemistry or electron microscopy before 16 days of incubation. Experimental evidence has shown that at least the majority of gut endocrine cells are of endodermal origin and are not derived from the neural crest or neuroectoderm as earlier proposed. In early embryos, the progenitors of gastrointestinal endocrine cells are more widespread than are the differentiated cells in chicks at hatching. This, along with other observations, raises the question of factors that might influence the differentiation of gut endocrine cells.

An immunocytochemical survey of endocrine cells in the gastrointestinal tract of chicks at hatching

The distribution of gastrin-, cholecystokinin-, glucagon-, secretin-, vasoactive intestinal polypeptide-, substance P-, bombesin-, neurotensin-, motilin-, somatostatin- and avian pancreatic polypeptide-like cells, demonstrated by indirect immunocytochemistry, was studied in samples from the following regions: proventriculus, gizzard, pylorus, duodenum, upper and lower ileum, caeca and rectum. The pylorus is particularly rich in gastrin-, neurotensin- and somatostatin-like cells. No cells immunoreactive for gastric inhibitory polypeptide or insulin were detected. In a number of instances the same cells were found to stain with antisera raised to different gut peptides. This happened with antisera detecting gastrin- and neurotensin-like cells, with secretin, vasoactive intestinal polypeptide, glucagon and substance P. The possibility that antigenic determinants to more than one peptide are contained in certain endocrine-like cells is considered.

Origin and distribution of VIP (vasoactive intestinal polypeptide)-nerves in the genito-urinary tract

VIP (Vasoactive Intestinal Polypeptide)-immunoreactive nerves were found throughout the genito-urinary tract of the cat; they were less numerous in the guinea pig and in the rat. In the cat, VIP nerves were particularly numerous in the neck of the urinary bladder and proximal urethra, in the uterine cervix and in the prostate gland. The nerves were found in smooth muscle, around blood vessels and in the connective tissue immediately beneath the epithelium. Ganglia were found below the trigonum area of the bladder, in the wall of the proximal urethra, and in paracervical tissue. VIP-immunoreactive nerve cell bodies occurred in all these ganglionic formations. These ganglia probably represent the origin of the VIP nerves of the genital tract since their removal in the female cat greatly reduced the VIP nerve supply. Transection of the hypogastric nerves had no overt effect. Transection of the cervix eliminated the VIP nerves above the level of the lesion, except those in the ovaries, supporting the view that the VIP nerves of the uterus and the oviduct are derived from a paracervical source.

Cholecystokinin-like peptides in avian brain and gut

Extracts of turkey brain and jejunum contain a factor closely resembling the COOH-terminal octapeptide of porcine cholecystokinin (CCK). Turkey antral extracts contain factors distinguishable in immunochemical and gel filtration properties from the mammalian forms of gastrin and CCK.

[Development and function of endocrine cells in the proventriculus of the chicken (author's transl)]

An argyrophil endocrine cell type with typical intraepithelial development is seen initially on the 8th day of incubation in the epithelium of the main lumen of the chicken-proventriculus. During the embryonic period, rapid development of these cells can be observed with a quantitative maximum on the 13th day of incubation. At this time increased digestive efficiency is necessary for the chicken embryo with the start of gastric secretion combined with the first swallowing of albumen. There is a subsequent decrease in the number of endocrine cells in the main lumen epithelium, their function in hatched or adult specimens is largely taken over by cells which appear in the epithelium of the glands of the proventriculus on the 16th and later days of incubation. On the 2nd day after hatching the adult distribution pattern of endocrine cells in the proventriculus is attained.

Intestinal endocrine cells of chicks around the time of hatching

The duodenum of 16-day Black Australorp chick embryos, and the duodenum, ileum, large intestine and caeca of 18-day embryos and of chicks within 30 h of hatching, have been studied by electron microscopy. Cells were found with secretory granules resembling those in mammalian EC, S, A-like, EG and D cells (terminology of Solcia et al., 1973), and were on this basis tentatively identified accordingly. The distribution and frequency of the chick cells in different parts of the tract correspond well to the situation in mammals.

Endocrine cells of the stomach of chicks around the time of hatching

The proventriculus, gizzard and pyloric antrum (region between the gizzard and the duodenum) of 18-day Black Australorp chick embryos and of chicks within 30 h of hatching have been studied by electron microscopy. D and EC cells, and putative G, D1 and A-like cells were identified (terminology of Solcia et al., 1973) but no ECL cells. No endocrine cells of any kind were revealed in the gizzard.

Vasoactive intestinal polypeptide: abundant immunoreactivity in neural cell lines and normal nervous tissue

Vasoactive intestinal polypeptide immunoreactivity is present in high concentrations in clonal lines of neuronal and glial origin. The central nervous system and sympathetic ganglia are also rich in the peptide. The findings suggest that this peptide, hitherto thought limited to the gastrointestinal tract, is widely distributed in neural tissue and may have broad physiological significance.

Growth-hormone release-inhibiting hormone in gastrointestinal and pancreatic D cells

The normal pancreatic D cell has been well recognised since 1931, but its secretory product has not been identified with certainty. Combined immunocytochemical methods, and histological methods for endocrine granules, have demonstrated that it contains a product with G.H.-R.I.H.-like immunoreactivity. G.H.-R.I.H. has also been localised in the upper gastrointestinal tract, tentatively in the morphologically similar D cell of the Wiesbaden classification. The potent actions of this peptide on pancreatic and gastrointestinal function suggest that it may play an important role in digestive physiology.