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The serotonin neurons in nucleus raphe dorsalis of adult rat: A light and electron microscope radioautographic study
Author(s) -
Descarries Laurent,
Watkins Kenneth C.,
Garcia Sylvia,
Beaudet Alain
Publication year - 1982
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.902070305
Subject(s) - biology , nucleus , serotonergic , cytoplasm , electron microscope , organelle , serotonin , cell bodies , anatomy , free nerve ending , monoamine oxidase , population , apposition , synaptic vesicle , vesicle , biophysics , microbiology and biotechnology , endocrinology , biochemistry , central nervous system , membrane , receptor , physics , demography , sociology , optics , enzyme
The serotoninergic nerve cell body population of nucleus raphe dorsalis (RD) was identified by radioautography following cerebroventricular instillation of tritiated serotonin ([ 3 H]5‐HT) in adult rats pretreated with a monoamine oxidase inhibitor. Series of histological sections taken throughout the midbrain and upper pons exhibited a similar distribution and number of labeled nerve cell bodies in RD after prolonged administration ofeither 10 −5 or 10 −4 M [ 3 H]5‐HT or 10 −4 M [ 3 H]5‐HT and 10 −3 M nonradioactive noradrenaline. This allowed systematic mapping and quantification of serotoninergic nerve cell bodies at various levels of the RD. Their extrapolated total number averaged 11,500. Twice as many unreactive (nonserotoninergic) neurons were present within the same region. In electron microscope radioautographs, the labeled cells were usually larger (17.9 μm mean diameter) than their unlabeled congeners (13.1 μm), but stereological sampling of their perikarial organelle content failed to reveal any difference in cytoplasmic composition. Few [ 3 H]5‐HT‐labeled axonal varicosities were observed in RD and none were found in close apposition or in synaptic junction with labeled nerve cell bodies, dendrites, or unreactive perikarya. A detailed statistical analysis of silver grain distribution in both labeled and “unlabeled” nerve cell bodies indicated that in the former, but not in the latter, dense bodies had a relatively high affinity for [ 3 H]5‐HT. Mitochondria and the cytoplasmic membrane were the only other organelles to show higher labeling indices in labeled than in unlabeled cells. Other sites of[ 3 H]5‐HT localization could be ascribed to artefactitious cross‐linkage of the tracer by the fixative, since they had the same relative affinity in the two cell populations. These results provide new insights into the morphology and cytofunctional properties of the 5‐HT neurons of rat RD.