Nitric oxide synthase, choline acetyltransferase, catecholamine enzymes and neuropeptides and their colocalization in the anterior pelvic ganglion, the inferior mesenteric ganglion and the hypogastric nerve of the male guinea pig

Abstract

By the indirect immunofluorescence method, the distribution of nitric oxide synthase (NOS)-like immunoreactivity (LI) and its possible colocalization with neuropeptide immunoreactivities, with two enzymes for the catecholamine synthesis pathway, tyrosine hydroxylase (TH) and dopamine β-hydroxylase (DBH), as well as the enzyme for the acetylcholine synthesis pathway, choline acetyltransferase (ChAT) were studied in the anterior pelvic ganglion (APG), the inferior mesenteric ganglion (IMG) and the hypogastric nerve in the male guinea pig. The analyses were performed on tissues from intact animals, as well as after compression/ligation or cut of the hypogastric nerve. In some cases the colonic nerves were also cut. Analysis of the APG showed two main neuronal cell populations, one group containing NOS localized in the caudal part of the APG and one TH-positive group lacking NOS in its cranial part. The majority of the NOS-positive neurons contained ChAT-LI. Some NOS-positive cells did not contain detectable ChAT, but all ChAT-positive cells contained NOS. NOS neurons often contained peptides, including vasoactive intestinal peptide (VIP), neuropeptide tyrosine (NPY), somatostatin (SOM) and/or calcitonin gene-related peptide (CGRP). Some NOS cells expressed DBH, but never TH. The second cell group, characterized by absence of NOS, contained TH, mostly DBH and NPY and occasionally SOM and CGRP. Some TH-positive neurons lacked DBH. In the IMG, the NOS-LI was principally in nerve fibers, which were of two types, one consisting of strongly immunoreactive, coarse, varicose fibers with a patchy distribution, the other one forming fine, varicose, weakly immunoreactive fibers with a more general distribution. In the coarse networks, NOS-LI coexisted with VIP- and DYN-LI and the fibers surrounded mainly the SOM-containing noradrenergic principal ganglion cells. A network of ChAT-positive, often NOS-containing nerve fibers, surrounded the principal neurons. Occasional neuronal cell bodies in the IMG contained both NOS- and ChAT-LI. Accumulation of NOS was observed, both caudal and cranial, to a crush of the hypogastric nerve. VIP accumulated mainly on the caudal side and often coexisted with NOS. NPY accumulated on both sides of the crush, but mainly on the cranial side, and ENK was exclusively on the cranial side. Neither peptide coexisted with NOS. Both substance P (SP) and CGRP showed the strongest accumulation on the cranial side, possibly partly colocalized with NOS. It is concluded that the APG in the male guinea-pig consists of two major complementary neuron populations, the cholinergic neurons always containing NOS and the noradrenergic neurons containing TH and DBH. Some NOS neurons lacked ChAT and could represent truly non-adrenergic, non-cholinergic neurons. In addition, there may be a small dopaminergic neuron population, that is containing TH but lacking DBH. The cholinergic NOS neurons contain varying combinations of peptides. The noradrenergic population often contained NPY and occasionally SOM and CGRP. It is suggested that NO may interact with a number of other messenger molecules to play a role both within the APG and IMG and also in the projection areas of the APG.