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Biomedical subjects

A Andrew

Publications and source records attributed to A Andrew.

At least 37 records · Page 2Linked to original sources
PubMed1989

Differentiation of endocrine cells in chick allantoic epithelium combined with pancreatic mesenchyme.

Allantoic endoderm of 3-day chick embryos was combined with pancreatic mesenchyme of 5-day embryos and cultured as chorio-allantoic grafts for a total of 14 days. Recombinations of endoderm and mesenchyme of the pancreas and of the allantois served as controls. The usual types of endocrine cells differentiated in the pancreatic controls, none in the allantoic controls. In experimental grafts simple columnar epithelium with goblet cells and a sucrase-positive brush border developed; a few insulin cells and endocrine cells typical of the intestine differentiated. Hence allantoic endoderm has endocrine potentiality not realised in vivo, where its own mesenchyme may be inhibitory.

Allantois↗
PubMed1988

Differentiation of intestinal and ectopic endocrine cells from avian gastric and pancreatic endoderm.

The chorio-allantoic grafts analysed were prepared from avian proventricular endoderm combined with its own or pancreatic mesenchyme and from re-associated pancreatic layers. Intestine developed ectopically in some grafts: in these, endocrine cells typical of intestine differentiated irrespective of the source of the endoderm or mesenchyme. In addition, endocrine cells inappropriate for the surrounding histology were detected in small numbers in grafts of all categories. Clearly it is not the mesenchyme that is responsible but perhaps some aspect of the procedure, which may relate to stressful stimuli thought to provoke intestinal metaplasia. The differentiation of inappropriate cells aids in understanding the occurrence of ectopic endocrine tumours.

Animals↗
PubMed1988

Can proventricular mesenchyme promote differentiation of endocrine cells in gizzard endoderm?

Previous findings prompted the suggestion that avian proventricular mesenchyme might induce differentiation of endocrine cells with gastrin-releasing peptide (GRP)-like immunoreactivity in endoderm from an organ which, at hatching, is deficient in such cells. Therefore gizzard endoderm and proventricular mesenchyme from chick embryos of 5 days' incubation were combined and grown as chorio-allantoic grafts. Controls comprised re-associated endoderm and mesenchyme of the gizzard and of the proventriculus. In the experimental grafts, as in proventricular controls, immunocytochemistry revealed not only GRP cells, but also the other endocrine cell types characteristic of proventriculus. All these cell types were either absent or very rare in gizzard controls.

Animals↗
PubMed1987

The effect of pancreatic mesenchyme on the differentiation of endocrine cells from gastric endoderm.

To determine whether mesenchyme plays a part in the differentiation of gut endocrine cells, proventricular endoderm from 4- to 5-day chick or quail embryos was associated with mesenchyme from the dorsal pancreatic bud of chick embryos of the same age. The combinations were grown on the chorioallantoic membranes of host chick embryos until they reached a total incubation age of 21 days. Proventricular or pancreatic endoderm of the appropriate age and species reassociated with its own mesenchyme provided the controls. Morphogenesis in the experimental grafts corresponded closely to that in proventricular controls, i.e. the pancreatic mesenchyme supported the development of proventricular glands from proventricular endoderm. Insulin, glucagon and somatostatin cells and cells with pancreatic polypeptide-like immunoreactivity differentiated in the pancreatic controls. The latter three endocrine cell types, together with neurotensin and bombesin/gastrin-releasing polypeptide (GRP) cells, developed in proventricular controls and experimental grafts. The proportions of the major types common to proventriculus and pancreas (somatostatin and glucagon cells) were in general similar when experimental grafts were compared with proventricular controls but different when experimental and pancreatic control grafts were compared. Hence pancreatic mesenchyme did not materially affect the proportions of these three cell types in experimental grafts, induced no specific pancreatic (insulin) cell type and allowed the differentiation of the characteristic proventricular endocrine cell types, neurotensin and bombesin/GRP cells. However, an important finding was a significant reduction in the proportion of bombesin/GRP cells, attributable in part to a decrease in their number and in part to an increase in the numbers of endocrine cells of the other types. This indicates that mesenchyme may well play a part in determining the regional specificity of populations of gut endocrine cells.

Animals↗
PubMed1987

The embryonic origin of connective tissue mast cells.

To find out whether mast cells are derived from the neural crest or from mesoderm, explants of avian blastoderm, from which the neural crest was excluded, were grown on the chorio-allantoic membrane of chick hosts. The grafts were fixed in aldehyde fixatives and stained to demonstrate metachromatic connective tissue mast cells. In grafts of chick endoderm and mesoderm, mast cells were present despite the absence of neural crest derivatives. To ascertain whether these mast cells were perhaps of host origin, in a second experiment quail embryos were used as donors; explants included all three germ layers and were delimited so as to exclude neural crest cells. The proportion of the mast cells present that showed very large nucleoli such as are characteristic of quail cells was far in excess of that observed in mast cells of a young chick and much closer to that seen in these cells in a young quail. The same was true for grafts in which quail mesoderm had been combined with chick endoderm. Taken together, the results show that connective tissue mast cells are mesodermal rather than neural crest in origin.

Animals↗
PubMed1984

The distribution of endocrine cell progenitors in the gut of chick embryos.

The aim of this experiment was to find out whether or not, at early stages of development, progenitors of the various types of gut endocrine cells are localized to one or more specific regions of the gastrointestinal tract. Transverse strips of blastoderm two to four somites in length were excised between the levels of somites 5 and 27 in chick embryos at 5- to 24-somite stages and were cultured as chorioallantoic grafts. The distribution of endocrine cells in the grafts revealed confined localization of progenitor cells only in the case of insulin-immunoreactive cells. The progenitors of cells with somatostatin-, pancreatic polypeptide-, glucagon-, secretin-, gastrin/CCK-, motilin-, neurotensin- and serotonin-like immunoreactivity were distributed along the length of the presumptive gut at the time of explantation; indeed, in many cases they were more widespread than are their differentiated progeny in normal gut of the same age. This finding indicates that conditions in grafts must differ from those that operate in the intact embryo. Also it may explain the occurrence of ectopic gut or pancreatic endocrine cells in tumours of the digestive tract.

Animals↗
PubMed1981

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.

Animals↗
PubMed1980

The ultrastructural identity of pancreatic polypeptide cells in chicks.

A very similar ultrastructure has been attributed to pancreatic polypeptide and somatostatin cells in chickens. In order to characterize any possible differences between them, cells shown to be immunoreactive for these hormones in semi-thin sections of chick pancreas were identified in adjacent thin sections prepared for conventional electron microscopy. In this way the ultrastructural features of the immunoreactive cells could be determined. In general, in somatostatin-immunoreactive cells, granule profiles are almost exclusively round, whereas in pancreatic polypeptide cells there are elongate as well round profiles. Within cells of both types the electron density of the granule matrix varies from one granule to another, but the range of density is greater in pancreatic polypeptide granules. The latter are slightly smaller than somatostatin granules.

Animals↗
PubMed1980

Is there a ventral neural ridge in chick embryos? Implications for the origin of adenohypophyseal and other APUD cells.

Two- to ten-somite chick embryos were studied in order to ascertain whether, as has been proposed, there exists a 'ventral neural ridge' which gives rise to the hypophyseal (Rathke's) pouch. Serial sections and stereo-microscopy were used. The neural ridges arch around the rostral end of the embryo onto the ventral surface of the head, but no evidence was found for their extension to form a 'ventral neural ridge' reaching the stomodaeum: in fact a considerable expanse of non-thickened surface ectoderm was seen to separate the ventral portions of the neural ridges from the stomodaeum. The thickening of neural ectoderm which does appear on the ventral surface of the head results from apposition and fusion of the opposite neural ridges flanking the neural plate and thus the tip of the anterior neuropore--the classically accepted mode of closure of the neuropore. These findings are in accord with the generally accepted concept of the origin of the hypophyseal pouch rather than with its derivation from a 'ventral neural ridge'. No sign of neural crest formation was encountered ventrally; this observation excludes the possibility that endocrine cells of the APUD series could originate from neural crest in this region.

APUD Cells↗
PubMed1979

An immunocytochemical study of the distribution of pancreatic endocrine cells in chicks, with special reference to the relationship between pancreatic polypeptide and somatostatin-immunoreactive cells.

Araldite sections of formalin-fixed pancreas from chicks at hatching were treated by an indirect immuno-enzyme technique to reveal cells containing APP, somatostatin, glucagon and insulin. APP cells were found scattered in the exocrine parenchyma. A few were associated with insulin-containing B islets and occasional cells occurred in and around glucagon-containing A islets. Somatostatin-immunoreactive cells were distributed peripherally in A and B islets and were dispersed in the exocrine tissue. APP cells were roughly as numerous in the exocrine parenchyma as somatostatin-immunoreactive cells. Since certain published observations point to the possible occurrence of APP and somatostatin in the same cells, consecutive sections were stained for these hormones. In no case did the two peptides occur in the same cell. Sections subjected to double-staining confirmed this result. Therefore it is likely that the described differences between APP and somatostatin-immunoreactive cells are valid.

Animals↗
PubMed1979

An experimental investigation into the possible origin of pancreatic islet cells from rhombencephalic neurectoderm.

To determine whether or not any pancreatic islet cell type arises from rhombencephalic levels of neurectoderm, lengths of presumptive rhombencephalon (containing potential neural crest) of Black Australorp chick embryos at 6- to 9-somite stages were replaced isotopically and isochronically by neural tube of Japanese quail embryos. Some transplants included mesencephalic regions. In some cases various levels of the rhombencephalon were deleted and not replaced. The quail nuclear marker was detected in cranial ganglia in operated embryos sacrificed at 3 3/4 days of incubation and in enteric ganglia and cells accompanying some pancreatic nerves, in embryos killed at 7 days of incubation. This provided evidence of normal migration of crest cells from the grafts. Dopa was administered to the younger embryos, which were submitted to the formaldehyde-induced fluorescence procedure to demonstrate APUD (Amine Precursor Uptake and Decarboxylation) cells. No pancreatic APUD cells exhibited the quail nuclear marker. In 9- to 11-day embryos, A and B cells were identified by specific light and electron microscopic features. None showed the quail marker. The marker was also absent from those D cells seen and from cells of an as yet unidentified type, but not enough of these were found to warrant a conclusion. All islet cell types were found in embryos from which various levels of the rhombencephalon had been deleted. It is concluded that at least A and B islet cells are not derived from the rhombencephalic neurectoderm and probably not from mesencephalic levels. Their most likely origin remains the endoderm, which was the accepted source until recently.

APUD Cells↗