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Contribution of brainstem GABAergic circuitry to descending antinociceptive controls: II. Electron microscopic immunocytochemical evidence of gabaergic control over the projection from the periaqueductal gray to the nucleus raphe magnus in the rat
Author(s) -
Reichling David B.,
Basbaum Allan I.
Publication year - 1990
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.903020214
Subject(s) - nucleus raphe magnus , periaqueductal gray , gabaergic , neuroscience , serotonergic cell groups , dorsal raphe nucleus , raphe nuclei , biology , axon , nucleus , serotonergic , inhibitory postsynaptic potential , anatomy , midbrain , central nervous system , serotonin , receptor , biochemistry
Abstract Pharmacological, physiological, and behavioral studies suggest that inhibitory GABAergic neurons influence the projection from the midbrain periaqueductal gray matter to the medullary nucleus raphe magnus. The present study used electron microscopic immunocytochemical techniques to examine the morphology and synaptic relationships of GABA‐immunoreactive terminals in the ventrolateral periaqueductal gray. These putative GABAergic terminals comprise almost 40% of all axon terminals in the periaqueductal gray. GABA‐immunoreactive terminals contain small, clear, pleomorphic or round, vesicles, and 46% also contain some dense‐cored vesicles. In some experiments we also used a colloidal gold‐conjugated retrograde tracer to label periaqueductal gray neurons that project to the nucleus raphe magnus. About half of the synaptic inputs onto the cell bodies and proximal dendrites of retrogradely labeled neurons are GABA‐immunoreactive; these putative GABAergic synapses, which directly control activity in neurons projecting from the periaqueductal gray to the nucleus raphe magnus, might mediate the antinociception‐related effects of exogenous GABAA receptor ligands.