Adrenocorticotropin and alpha-melanotropin in the myenteric plexus of the rat duodenum: an electron microscopic study

Stress at the intestinal surface: catecholamines and mucosa-bacteria interactions

Psychological stress has profound effects on gastrointestinal function, and investigations over the past few decades have examined the mechanisms by which neural and hormonal stress mediators act to modulate gut motility, epithelial barrier function and inflammatory states. With its cellular diversity and large commensal bacterial population, the intestinal mucosa and its overlying mucous environment constitute a highly interactive environment for eukaryotic host cells and prokaryotic bacteria. The elaboration of stress mediators, particularly norepinephrine, at this interface influences host cells engaged in mucosal protection and the bacteria which populate the mucosal surface and gut lumen. This review will address growing evidence that norepinephrine and, in some cases, other mediators of the adaptation to stress modulate mucosal interactions with enteric bacteria. Stress-mediated changes in this delicate interplay may shift the microbial colonization patterns on the mucosal surface and alter the susceptibility of the host to infection. Moreover, changes in host-microbe interactions in the digestive tract may also influence ongoing neural activity in stress-responsive brain areas.

Adrenocorticotrophic hormone modulates Escherichia coli O157:H7 adherence to porcine colonic mucosa

Exposure to stress is associated with susceptibility to disease and one stress mediator, norepinephrine, has been reported to enhance the adherence of enterohemorrhagic Escherichia coli O157:H7 (EHEC) to the colonic mucosa. We tested the hypothesis that adrenocorticotropic hormone (ACTH) and other stress-related hormones may act in a similar fashion. Explants of distal colonic mucosa from young pigs were mounted in Ussing chambers and their luminal aspect was exposed to EHEC strain 700728 for 30-90 min. When added to the contraluminal, but not luminal bathing medium, ACTH increased EHEC adherence within 90 min in a concentration-dependent manner (EC50 = 1.2 nM), but did not alter tissue electrical conductance. ACTH had no effect on the adherence of a pig-adapted non-O157 E. coli strain. The effect of 0.1 microM ACTH on luminal EHEC adherence was prevented in tissues pretreated contraluminally with the type 2 melanocortin receptor antagonist ACTH7-38, the neuronal conduction blocker saxitoxin, or the muscarinic cholinergic antagonist atropine. Moreover, ACTH7-38 decreased EHEC adherence in the absence of ACTH. These results suggest that ACTH acts via melanocortin receptors located on enteric nerves to enhance mucosal adherence of EHEC.

Co-existence of the enkephalinergic system and the melanotropinergic system in the rat duodenum shown by immunohistochemistry

The immunohistochemical distribution of alpha-melanotropin (alpha-MSH) and Met-enkephalin (Met-ENK) immunoreactivities in the rat duodenum was examined by using immunofluorescence microscopy. Alternately staining of adjacent frozen serial sections with specific antisera directed to alpha-MSH or Met-ENK revealed that within a subpopulation of myenteric plexus perikarya alpha-MSH immunostaining co-exists with that of Met-ENK. Some myenteric plexus nerve fibres also contain both Met-ENK and alpha-MSH immunoreactivity. These findings might indicate that the genes encoding for the precursors of melanotropins (the pro-opiomelanocortin precursor) and enkephalin (the pro-enkephalin precursor) are generated from a common, large and single ancestor gene which remained conserved during evolution in the rat enteric nervous system.

Immunocytochemical demonstration of proopiomelanocortin- and other opioid-related substances and a CRF-like peptide in the gut of the american cockroach, Periplaneta americana L

Using the peroxidase-antiperoxidase technique, we showed the presence of peptides which are immunologically resembling mammalian corticotropin releasing hormone (CRF)-, adrenocorticotropic hormone (ACTH)-, beta-endorphin (beta-END)-, alpha-melanocyte stimulating hormone (alpha-MSH)-, methionine-enkephalin (met-ENK)- and leucine enkephalin (leu-ENK)- like immunoreactivity in hundreds to thousands of endocrine cells and nerve fibers in the midgut of the American cockroach Periplaneta americana. In the cockroach hindgut no immunoreactive cell bodies could be observed, although nerve fibers were clearly noticed to be recognized by antisera to CRF, ACTH1-24, ACTH11-24 and beta-END. Nothing is exactly known as to the function(s) of the demonstrated materials, but one can speculate that these numerous immunoreactive cells, might have important paracrine and/or endocrine functions in the insect physiology.

Endocrine cells do not exist in rat Brunner's glands. An electron microscopic study

It was revealed by light microscopic experiments that in Brunner's glands and the epithelium of the human and mammalian duodenum, cells were present, with basally lying granulations. These granules could be identified at the ultrastructural level as accumulations of pleomorphe electron-dense granules ('argentaffin', 'chromaffin' and 'osmiophilic' granules). Depending on the light and electron microscopic staining techniques used, these cells were classified as 'mucous', 'serous', or 'endocrine' ('enteroendocrine', 'paracrine' and 'enterochromaffin') cells. In the present study, the following ultrastructural morphological criteria of Brunner's gland cells were correlated: size, shape and electron density of their nuclei and nucleoli with morphological changes of their cytoplasmic and intranuclear organelles, which serve the synthesis of mucopeptides. This proved that the synthesis of mucopeptides occurred in 3 phases. The first phase served the intranuclear synthesis of organelles, which latterly were used for the cytoplasmic mucopeptide synthesis. This phase was characterized by the appearance of an electron-lucent and euchromatic nucleus, which also contained an euchromatic and electron-lucent nucleolus, and a thin electron-dense nucleus membrane (euchromatic phase). Only a few freely lying ribosomes, membrane-bound ribosomes (rough endoplasmic reticulum, RER) and mitochondria were dispersed throughout the cytoplasm. Therefore, the cytoplasm appeared electron-lucent and nearly empty. The second phase was characterized by a round but heterochromatical nucleus containing also a heterochromatic nucleolus, and the appearance of receptosome- (endosome, endocytotic vesicle) and lysosome-like structures near to the cytoplasmic membrane of the basal cell portion, as well as in the basal and lateral perinuclear region (early heterochromatic phase). The receptosome-like structures were round-oval and contained a single electron-lucent inclusion vesicle, which had an empty space or an electron-opaque granule. Both inclusion structures were located eccentrically on the inner surface of the membrane of the receptosome-like structure. Here and there, it was possible to visualize great receptosome-like structures (multivesicular bodies) containing numerous membranous electron-lucent and electron-opaque inclusion vesicles. Electron-dense pleomorphe lysosome-like structures, bearing 1-4 electron-lucent inclusion vesicles with faint grains in their spaces, were also recognized in the basal cell portion, as well as in the basal and lateral perinuclear region.(ABSTRACT TRUNCATED AT 400 WORDS)