The distribution and colocalization of neuropeptides and 5-hydroxytryptamine in pelvic nerves supplying the posterior large intestine of the toad, Bufo marinus

Projections of pelvic autonomic neurons within the lower bowel of the male rat: an anterograde labelling study

The tissues of the large intestine which receive an innervation by neurons of the major pelvic ganglia were identified following in vivo and in vitro anterograde labelling with the lipophilic tracer 1,1'didodecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate in the male rat. The primary target in the gut of major pelvic ganglion neurons is the myenteric plexus of the distal colon and the rectum. The serosal ganglia, on the surface of the most distal region of the rectum and the circular muscle of the distal colon and rectum were less densely innervated. The pelvic ganglia do not innervate the longitudinal muscle, submucosal blood vessels, submucosal plexus, or mucosa. The pelvic supply reaches the bowel via two groups of rectal nerves and branches of the penile nerves. All of these connections also carry the axons of viscerofugal neurons from the bowel, some of which have terminal axons in the major pelvic ganglia. Finally, the different nerves supplied different targets. In particular, while the rectal nerves carried pelvic axons supplying the myenteric plexus, circular muscle, and serosal ganglia, the penile nerves only innervated the serosal ganglia. In addition, the two groups of rectal nerves innervated slightly different regions of the bowel and provided different projection patterns. However, successful in vivo labelling was achieved in only 6/12 animals and while all in vitro experiments resulted in successful labelling, it was clear that only a proportion of pelvic projections in any given nerve were labelled. These studies have shown that the major pelvic ganglia are primarily involved in the control of motility, but not of vascular and secretomotor functions. Thus pelvic neurons do not innervate the same range of target tissues within the bowel as the prevertebral ganglia. This study has also shown that the different pathways to the gut from the major pelvic ganglia innervate different tissues, suggesting that the autonomic innervation of the gut is not homogeneous along its length.

Vasoconstrictor effects of galanin and distribution of galanin containing fibres in three species of elasmobranch fish

Galanin is found in perivascular sympathetic neurons in a wide range of vertebrate species. In placental mammals, galanin has either no effect on blood pressure, or weak depressor effects, but in other vertebrates it has been shown to be a potent pressor agent. To investigate how extensive the vasoconstrictor effects of galanin may be in the vertebrates, the vascular effects of galanin were tested in two species of shark, Heterodontus portusjacksoni, and Hemiscyllium ocellatum, and a ray, Rhinobatos typus. Nerve fibres showing immunoreactivity to galanin were located surrounding gut blood vessels, but were absent from branchial efferent arteries in all three species. Intravenous injection of galanin caused a significant rise in caudal arterial blood pressure in H. portusjacksoni and H. ocellatum, but no change in R. typus. Contraction of segments of pancreatico-mesenteric artery were measured in an organ bath also. Galanin (10(-6) M) caused 21-38% of the maximum K+ induced contraction in all species, but no response in efferent branchial arteries from R. typus. In conclusion, in three elasmobranchs, a galanin-like peptide is present in perivascular nerve fibres, and galanin causes differential vasoconstriction in vascular beds. These data extend the number of vertebrate groups in which galanin has been shown to be a vasoconstrictor peptide.

Projections of nitric oxide synthase- and peptide-containing neurons in the small and large intestines of the toad (Bufo marinus)

The projections of galanin (GAL)- and vasoactive intestinal peptide (VIP)-immunoreactive (IR) and nitric oxide synthase (NOS)-containing neurons in the small and large intestines of the amphibian Bufo marinus were investigated by their reactions to surgical interruption (myotomy). In the small intestine, myotomy caused accumulation of GAL- and VIP-IR and of NADPH diaphorase reaction product (revealing NOS) in cut axons on the oral side of the operation site. On the anal side there was loss of GAL-IR axons from the circular muscle and myenteric plexus and long, anally directed processes could be traced from GAL-IR nerve cell bodies. There was no significant loss of VIP-IR or NADPH diaphorase from nerve fibres in the myenteric plexus or circular muscle layer, although anally-directed axons could be traced from nerve cell bodies on the anal side of the operation sites. In the large intestine, myotomy caused accumulation of VIP-IR and of NADPH diaphorase reaction product in cut axons on the oral side of the operation site. Anal to the cut, although there was no significant loss of these fibres from the muscle or myenteric plexus, anally directed axons could be traced from nerve cell bodies. GAL-IR fibres in the large intestine are of two types: a few contain GAL-IR alone and are thought to arise from enteric neurons; many contain both GAL- and SOM-IR and are thought to arise from nerve cell bodies in the hindgut. Myotomy caused an accumulation of GAL/SOM-IR material in fibres on the anal side of the cut and a substantial decrease in the number of fibres on the oral side. There was no detectable effect of myotomy on the GAL-IR fibres, although an abnormally high density of GAL-IR nerve cell bodies was found oral to the cut. These results indicate that VIP-IR and NOS-containing enteric neurons project in an oral to anal direction in the toad small and large intestines. Some of the neurons have short anal projections to the circular muscle. GAL-IR enteric neurons have similar projections in the small intestine, but their projections could not be determined in the large intestine. GAL/SOM-IR axons in the large intestine project from anal to oral. Myotomy in the large intestine appears to induce an increased or de novo expression of GAL-IR in enteric neurons oral to the cut.

An immunohistochemical study of the innervation of the large intestine of the toad (Bufo marinus)

The distribution of intrinsic enteric neurons and extrinsic autonomic and sensory neurons in the large intestine of the toad, Bufo marinus, was examined using immunohistochemistry and glyoxylic acid-induced fluorescence. Three populations of extrinsic nerves were found: unipolar neurons with morphology and location typical of parasympathetic postganglionic neurons containing immunoreactivity to galanin, somatostatin and 5-hydroxytryptamine were present in longitudinally running nerve trunks in the posterior large intestine and projected to the muscle layers and myenteric plexus throughout the large intestine. Sympathetic adrenergic fibres supplied a dense innervation to the circular muscle layer, myenteric plexus and blood vessels. Axons containing colocalized calcitonin gene-related peptide immunoreactivity and substance P immunoreactivity distributed to all layers of the large intestine and are thought to be axons of primary afferent neurons. Five populations of enteric neurons were found. These contained immunoreactivity to vasoactive intestinal peptide, which distributed to all layers of the large intestine; galanin/vasoactive intestinal peptide, which projected to the submucosa and mucosa; calcitonin gene-related peptide/vasoactive intestinal peptide, which supplied the circular muscle, submucosa and mucosa; galanin, which projected to the submucosa and mucosa; and enkephalin, which supplied the circular muscle layer.