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A1 catecholamine cell group: Fine structure and synaptic input from the nucleus of the solitary tract
Author(s) -
Chan R. K. W.,
Peto C. A.,
Sawchenko P. E.
Publication year - 1995
Publication title -
journal of comparative neurology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.855
H-Index - 209
eISSN - 1096-9861
pISSN - 0021-9967
DOI - 10.1002/cne.903510107
Subject(s) - solitary tract , axon , nucleus , biology , immunogold labelling , immunolabeling , golgi apparatus , neuroscience , soma , endoplasmic reticulum , biotinylated dextran amine , biocytin , cell bodies , anatomy , ultrastructure , microbiology and biotechnology , central nervous system , immunohistochemistry , immunology
Preembedding immunoperoxidase staining methods were used to characterize tyrosine hydroxylase‐immunoreactive (TH‐ir) elements in the caudal ventrolateral medulla, and to determine the extent to which neurons of the A1 cell group are directly innervated by projections of the nucleus of the solitary tract (NTS). TH‐ir neurons in the A1 region were medium‐sized and multipolar. They possessed rounded nuclei with infrequent invaginations, well‐developed Golgi apparati, high cytoplasmic densities of mitochondria, and a low to moderate tendency for rough endoplasmic reticulum (RER) to align in parallel stacks. A1 cell bodies were commonly juxtaposed to TH‐positive and TH‐negative neurons, myelinated profiles, glia and /or vascular elements, but close membrane appositons were only seen with glial elements. Synaptic input to A1 neurons was predominantly asymmetric, provided virtually exclusively by non‐TH‐ir terminals, and directed principally to dendritic shafts; A1 somata are relatively sparsely innervated. In a second experiment, silver‐intensified immunogold localization of TH‐ir was combined with immunoperoxidase labeling for anterogradely transported Phaseolus vulgaris‐leucoagglutinin (PHA‐L), following tracer injections in the caudal aspect of the medial division of the NTS. These experiments revealed a small proportion of PHA‐L‐labeled axon terminals that made asymmetric contacts with dendritic shafts of TH‐ir neurons. These results suggest that the fine structure and synaptic input of A1 neurons are somewhat distinct from that of rostrally situated C1 catecholamine cells. In addition, while they document a direct NTS‐A1 projection that may participate in the interoceptive control of vasopressin secretion, the bulk of ventrolaterally directed projections from the caudomedial NTS contact noncatecholaminergic elements in the A1 region, some of which may correspond to so‐called depressor neurons implicated in the baroreflex control of sympathetic outflow and vasopressin secretion. © 1995 Willy‐Liss, Inc.