Immunolocalization of putative neurotransmitters innervating autonomic regulating neurones of cat ventral medulla

Abstract

This study investigated possible sites of contact of nerve fibers containing a range of putative neurotransmitter substances onto neurons in the cat ventral medulla oblongata concerned with autonomic, particularly cardiovascular, regulation. The parasympathetic preganglionic neurons of the nucleus ambiguus were identified by retrograde horseradish peroxldase tracing from the vagus nerve, and the groups of neurons in the Al and C1 cell areas and the raphe nucleus by cafscholamine enzyme or 5-hydroxytryptamins (5-HT) inurnxuohistoduemistry, respectively. Immunoreactive (-ir) nerve fibers and terminals in the vicinity of these neurons were visualized by subjecting the sections to a dual-staining technique using a brown peromddase-diaminobenzidine reaction product and a blue alkaline phosphatese-Fast blue reaction product: By employing monochrome photography with combinations of blue and orange-red filters, it was possible to discriminate neural elements displaying one or the other reaction product, or colocalization of reaction products. The results revealed the presence of calcitonin gene-related peptide (CORP) and galanin (GAL)ir in some motonsurons of the nucleus ambiguus, but not in those innervating the heart via the cardiac vagus nerve. The latter group of parasympathetic efferent neurons were found to be densely innervated by fibers innnrunoreactive for dopamine β-hydroxylase (DBH, indicating noradrenalineL ghrcine (GLY), γ-aminobutyric acid (GABA), 5-HT, enkephalin (ENK, neuropeptide Y (NPY), substance P (SP), and i hormone (TRK and, to a lesser extent, by other netropep ide-ir fibers. The came cells of the rostal C1 and caudal A1 groups showed a broadly similar pattern of innervation, most noticeably by fibers immurwreactive for DBH, GABA, 5-HT, cholecystokinin (CCIQ, CGRP, ENK, GAL, NPY, and SP. The 5-HT-ir neurons of the raphe nucleus, some also containing SP, TRH, ENK, or aorticotropin-releasing factor (CRF)-ir, were most prominently innervated by terminals containing DBH, GABA, CCK, ENK, NPY, TRH, somatostatin (SRIF), and vasoactive intestinal polypeptide (VIP)-ir. Although the proof that these groups of neurons receive functional synaptic contacts from the immunoreactive fibers awaits furtis ultrastructural studies, the results do suggest that a wide range of putative transmitters may influence the activity of efferent neurons in the cat medulla controlling autonomic functions.