Distribution of extrinsic enkephalin-containing nerve fibers in the rat rectum and their origin in the major pelvic ganglion

The distribution of nerve fibers containing enkephalin (ENK)-like immunoreactivity was examined in the rectum of aganglionosis rats (AGRs) which completely lack the intramural ganglion cells in the large intestine, and was compared with that of their normal littermates. Furthermore, Met5-enkephalin-Arg6-Gly7-Leu8 (MEAGL)-like immunoreactive neurons projecting to the rectum were examined using retrograde tracing combined with immunohistochemistry in the major pelvic ganglion of normal male rats. In the intermuscular space of the aganglionic rectum of AGRs, unlike the pattern of the normal intermuscular plexus, moderate numbers of ENK-like-immunoreactive fibers were arranged in an irregular, coarse network; greatly diminished numbers of immunoreactive fibers were found in the submucosa. No ENK-like-immunoreactive fibers were seen in the circular muscle layer and mucosa. In the normal rat rectum, ENK-like-immunoreactive fibers were seen throughout all layers, and immunoreactive nerve cells were found predominantly in the myenteric plexus of colchicine-treated animals. Fluoro-Gold injected into the upper rectum labelled numerous principal ganglion neurons in the major pelvic and inferior mesenteric ganglia. Less than 10% of tracer-labelled neurons were positive for fluorescein immunolabelling of MEAGL in the major pelvic ganglion; no immunoreactive neurons were found in the inferior mesenteric ganglion. In the major pelvic ganglion of the colchicine-treated normal rats, about 5% of principal ganglion neurons were immunoreactive for MEAGL. Comparison of serial paraffin sections of the major pelvic ganglion stained for tyrosine hydroxylase (TH), MEAGL and vasoactive intestinal polypeptide (VIP), respectively, revealed that more than half of MEAGL-like immunoreactive neurons were also positive for TH; there was no case showing co-existence of MEAGL with VIP in the principal neurons. These results indicate that a small number of enkephalin-containing neurons in the major pelvic ganglion project to the rectum, and that more than half of these neurons are postganglionic sympathetic. They may terminate mainly in the myenteric ganglia in the rectum.

Immunohistochemistry and nerve lesion experiments on the methionine-enkephalin immunopositive neurons in the small intestine of the bullfrog (Rana catesbeiana)

Nerve elements in the small intestine of the bullfrog. Rana catesbeiana, were studied by immunohistochemistry with anti-methionine enkephalin antisera and by nerve lesion experiments, using laser irradiation. Methionine-enkephalin immunopositive nerve fibers occur in the myenteric plexus, circular muscle layer, submucosa, and mucosa. Immunopositive nerve cell bodies in the myenteric plexus have dendrite-like and a long axon-like processes. In the froglet (3 months after metamorphosis), these axon-like processes lead posteriorly in the nerve strand of the myenteric plexus. Some bifurcate, one branch continuing posteriorly, the other doubling back to lead anteriorly; both form terminal varicose fibers in the circular muscle layer. Nerve lesion experiments, in the adult bullfrog, resulted in accumulations of methionine-enkephalin immunoreactivity at the oral and hinder edges of the laser-irradiated necrotic area; there were sprouting and nonsprouting immunopositive stumps. It is suggested that bidirectional flow of methionine-enkephalin in the myenteric plexus is mediated via the anterior and posterior branches of the axon-like process. The difference in sprouting behavior of immunopositive nerve fiber stumps, after nerve lesion, is discussed with reference to regional differences of the axon-like process.

Morphology and projections of myenteric neurons to colonic fiber bundles of the cat

Regulation of colon function depends on the location of nerve cell bodies and the distribution of intrinsic nerve fibers in the myenteric plexus. The morphology and projections of myenteric neurons through colonic fiber bundles in cat colon were determined using in vivo retrograde transport of HRP and Fast blue. Myenteric neurons were found to project from at least 5 to 59 mm orad (mean: 42 mm) or aborad (mean: 54 mm) through colonic fiber bundles. Approximately 73% of labelled cells were in ganglia within 2.8 mm of colonic fiber bundles in the axis of circular muscle fibers; none was beyond 7.7 mm. There were 2 soma morphologies. One type (Dogiel type I) had a mean soma diameter of 40.5 microns and had a rough somal surface. There were few if any short, broad dendrites, but its one long process extended to a branch point of an adjacent colonic fiber bundle. The other type (Dogiel type III) had a mean soma diameter of 26.4 microns, had a smooth somal surface and had few if any fine dendrites. It also projected a single long axon to colonic fiber bundles. There were twice as many Dogiel type III neurons. We conclude that myenteric neurons in the cat colon project both orad and aborad over relatively long distances through colonic fiber bundles where they form another intrinsic neuronal connection for the myenteric plexus.

Distinct distribution of CGRP-, enkephalin-, galanin-, neuromedin U-, neuropeptide Y-, somatostatin-, substance P-, VIP- and serotonin-containing neurons in the two submucosal ganglionic neural networks of the porcine small intestine

In addition to differences between the two submucosal ganglionic neural networks, i.e., the plexus submucosus externus (Schabadasch) and the plexus submucosus internus (Meissner), with respect to the occurrence and distribution of serotonin as neurotransmitter, immunocytochemistry also revealed a distinct distribution for various neuropeptides in these two plexuses. Immunoreactivity for galanin, vasoactive intestinal polypeptide, calcitonin gene-related peptide, substance P, neuromedin U, enkephalin, somatostatin and neuropeptide Y was found in varicose and non-varicose nerve fibres of both submucosal ganglionic plexuses, albeit with a distinct distributional pattern. The difference in neurotransmitter and/or neuromodulator content between both neural networks became even more obvious when attention was focussed on the immunoreactivity of the nerve cell bodies for these substances. Indeed, neuropeptide Y, enkephalin- and somatostatin-immunoreactive neuronal perikarya as well as serotonergic neuronal cell bodies appear solely in the plexus submucosus externus. Neuromedin U-immunoreactive perikarya, mostly coexisting with substance P, are observed in large numbers in the plexus submucosus internus, whilst they are rare in the plexus submucosus externus. Double-labelling immunostaining for substance P with CGRP and galanin revealed a different coexistence pattern for the two submucosal ganglionic plexuses. The differing chemical content of the neuronal populations supports the hypothesis that the existence of the two submucosal ganglionic plexuses, present in most large mammals including man, not only reflects a morphological difference but also points to differentiated functions.

[Met]enkephalin-Arg6-Gly7-Leu8-immunoreactive nerves in guinea-pig and rat lungs: distribution, origin, and co-existence with vasoactive intestinal polypeptide immunoreactivity

[Met]Enkephalin-Arg6-Gly7-Leu8 is an endogenous opioid peptide, first isolated from the bovine adrenal medulla. Because this octapeptide is specifically contained in the amino acid sequence of preproenkephalin A but not in other opioid precursors like preproopiomelanocortin or preproenkephalin B, [Met]enkephalin-Arg6-Gly7-Leu8 has been regarded as a specific marker for preproenkephalin A and its derivatives. In this study, we examined the occurrence and origin of [Met]enkephalin-Arg6-Gly7-Leu8-immunoreactive nerves in the guinea-pig and rat lung by immunohistochemical techniques, using a specific antiserum against this peptide. In addition, we investigated the possible co-existence of [Met]enkephalin-Arg6-Gly7-Leu8 and vasoactive intestinal peptide immunoreactivity in neuronal elements of the respiratory tract. In both species, [Met]enkephalin-Arg6-Gly7-Leu8 immunoreactivity was localized in nerve fibers chiefly distributed to the trachea and major bronchi, where they were prevalent in smooth muscle bundles, in the lamina propria, around airway glands, and in the walls of pulmonary vessels, but were absent in airway epithelium. Slight differences in the distribution pattern of immunoreactive nerve fibers were noted between the two species: immunoreactive nerve fibers in the smooth muscle bundles were much more abundant in guinea-pigs than in rats, while those in the mucous glands were richer in rats than in guinea-pigs. Neither chemical sympathectomy by 6-hydroxydopamine, nor chemical sensory denervation by capsaicin, changed the density or distribution of [Met]enkephalin-Arg6-Gly7-Leu8-immunoreactive nerve fibers in the airway, suggesting an intrinsic source for these nerve fibers. Colchicine injection into the tracheal wall, to promote the accumulation of neuropeptides in nerve cell bodies, led to the visualization of [Met]enkephalin-Arg6-Gly7-Leu8 immunoreactivity in some neuronal cell bodies within airway ganglia. Immunostaining for [Met]enkephalin-Arg6-Gly7-Leu8 and for vasoactive intestinal polypeptide on serial adjacent sections of airway ganglia obtained from colchicine-treated tracheae, demonstrated the co-existence of these immunoreactivities in a population of nerve cell bodies in these ganglia. The immunohistochemical localization of immunoreactive [Met]enkephalin-Arg6-Gly7-Leu8 in nerve elements in guinea-pig and rat lungs provides a morphological basis for the possibility that preproenkephalin A-related opioid peptides may have a neuromodulatory role in mammalian airways and pulmonary vessels.

Immunohistochemical localization of parvalbumin in rat and monkey autonomic ganglia

The cellular distribution of parvalbumin-like immunoreactivity in autonomic ganglia such as superior cervical sympathetic ganglia, paravertebral sympathetic chain ganglia (T6), ciliary ganglia and enteric ganglia was investigated by immunohistochemical peroxidase-antiperoxidase methods using an antiserum against rat skeletal muscle parvalbumin. We detected parvalbumin-like immunoreactivity in almost all neurons of rat superior cervical sympathetic ganglia and other paravertebral sympathetic chain ganglia, where the antigen was located in the cytoplasm but the nuclei were not labelled. No neurons positive for parvalbumin-like immunoreactivity were observed in rat ciliary ganglia or enteric ganglia. In monkey, almost all neurons of the superior cervical sympathetic ganglia contained parvalbumin-like immunoreactivity, but none of the neurons of the ciliary ganglia were labelled with the antiserum to parvalbumin. These results suggest that parvalbumin-like immunoreactivity exists in a specific subpopulation of the neurons of the autonomic nervous system.

Distribution of nerves containing vasoactive intestinal polypeptide-like immunoreactivity in rats with congenital aganglionosis of the colon

The distribution of nerves containing vasoactive intestinal polypeptide-like immunoreactivity was examined immunohistochemically in whole-mount specimens of the colons of mutant rats, which completely lacked intramural nerve cells in the colon, and of their normal littermates. In the aganglionic colon, greatly diminished numbers of vasoactive intestinal polypeptide-like immunoreactive nerve fibers were found in the circular muscle layer, lamina propria of the mucosa, and in the submucosa. In the intermuscular space of the aganglionic colon, unlike the pattern of the normal Auerbach's plexus, vasoactive intestinal polypeptide-like immunoreactive nerve fibers were arranged in an irregular, coarse network. These findings suggest the existence of extrinsic nerves containing vasoactive intestinal polypeptide in the aganglionic colon of the hereditary aganglionic rat.

Effect of chemical ablation of myenteric neurons on neurotransmitter levels in the rat jejunum

We have quantified neurotransmitter changes in the rat jejunum in which the myenteric neurons were ablated by serosal application of benzalkonium chloride. Within 2 days after benzalkonium chloride treatment, there was a 40% reduction in the activity of choline acetyltransferase, a specific marker for cholinergic neurons, and a 25% reduction in the amount of vasoactive intestinal peptide per centimeter length of jejunum. By 15 days, levels were comparable to those in control segments, and by 45 days after myenteric neuronal ablation, levels in treated tissues were twice those in controls. In contrast, we observed no reduction in the amount of leucine-enkephalin per centimeter length of jejunum at early times after benzalkonium chloride treatment, although by 45 days, levels of this neurotransmitter in treated segments of jejunum were more than twice those in controls. Significant increases in muscle thickness and tissue weight were also observed at 15, 30, and 45 days after myenteric neuronal ablation. Thus we have observed that in response to chemical ablation of myenteric neurons in the rat jejunum, there is a thickening of the smooth muscle layers and a compensatory increase in the production of certain neurotransmitters by the surviving neuronal elements in the gut.

Somatostatin neurons in the small intestine of the guinea pig: a light and electron microscopic immunocytochemical study combined with nerve lesion experiments by laser irradiation

Somatostatin-like immunoreactive neurons are present in both the myenteric and the submucous plexuses of the small intestine of the guinea pig. Dense varicosities of immunopositive nerve fibres surround the ganglionic cells, some of which also display somatostatin-like immunoreactivity. Immunoelectron microscopy demonstrated axo-somatic synapse formation between the somatostatin immunoreactive neuronal elements. Nerve lesion experiments using argon laser irradiation showed that most of the somatostatin-like immunoreactive fibres of the myenteric plexus were directed anally, whereas those of the submucous plexus had no directional polarity.

An immunohistochemical study of methionine-enkephalin-Arg6-Gly7-Leu8-like immunoreactivity-containing liquor-contacting neurons (LCNs) in the rat spinal cord

The localization of methionine-enkephalin-Arg6-Gly7-Leu8 (Met-Enk-Arg-Gly-Leu)-like immunoreactivity in the medullospinal liquor-contacting neurons (LCNs) of the rat was immunohistochemically investigated using a modified Sternberger's PAP method. In this study, we also examined the distribution of Met-Enk-Arg-Gly-Leu-like immunoreactive LCNs in the entire length of the medulla oblongata and spinal cord. The immunoreactive LCN possessed an oval, polygonal or rod-shaped perikaryon which protruded an axon-like process and a CSF-contacting process. In the entire length of the medulla oblongata and spinal cord, 60-70 immunoreactive LCNs were observed. They were sparsely distributed along the central canal. The ratio of the number of immunoreactive LCNs in each segment/total number of immunoreactive LCNs in the medulla oblongata and whole spinal cord was as follows: medulla oblongata, 0%; cervical segments, 28.1%; thoracic segments, 56.8%; lumbar segments, 12.0%; sacral segments, 3.0%; and coccygeal segments, 0%. When the immunoreactivity of perikarya of LCNs was weak, a few nerve terminals with a strong Met-Enk-Arg-Gly-Leu-like immunoreactivity were noticed on them. These findings suggest that preproenkephalin A-related opioid peptides including Met-Enk-Arg-Gly-Leu may be secreted into the cerebrospinal fluid (CSF) through the terminal portions of axon-like processes and/or CSF-contacting processes of LCNs. Enkephalin-containing nerve terminals on the LCNs may represent modulating afferents aiding the receptive and/or secretory functions of the neurons.

Ultrastructural demonstration of calcitonin in osmium-fixed human medullary carcinoma of thyroid by the protein A-colloidal gold technique

In two medullary carcinomas of the thyroid gland two types of secretory granules were found electron microscopically in the cytoplasm of the tumour cells. The sizes of the granules in one case ranged 103-345 nm in diameter; they were round in shape, and they co-existed in the same tumour cell. They could not, therefore, be distinctively subdivided into two types. In another case, secretory granules in the cytoplasm closely resemble EC granule in morphology. Using the protein A-colloidal gold (PAG) technique the content of secretory granules could be identified as calcitonin irrespective of their sizes or morphology. Immunoreactivity at the ultrastructural level was fairly well preserved even in the osmium-fixed tumour cells. The labelling index, expressed as a mean number of gold particles per unit square area of the secretory granule, was higher in the non-osmium-fixed tumour cells than in the osmium-fixed. Non-osmium-fixed tumour cells embedded either in epoxy or methacryl resin were almost equally labelled with gold particles. The result indicates that the PAG method is practicable to demonstrate the ultrastructural localization of calcitonin even in the osmium-fixed, epoxy resin embedded material.