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Median raphe serotonergic innervation of medial septum/diagonal band of Broca (MSDB) parvalbumin‐containing neurons: Possible involvement of the MSDB in the desynchronization of the hippocampal EEG
Author(s) -
Leranth Csaba,
Vertes Robert P.
Publication year - 1999
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/(sici)1096-9861(19990809)410:4<586::aid-cne6>3.0.co;2-h
Subject(s) - parvalbumin , neuroscience , gabaergic , biology , calretinin , dorsal raphe nucleus , interneuron , hippocampal formation , diagonal band of broca , raphe nuclei , anatomy , serotonergic , inhibitory postsynaptic potential , cholinergic , basal forebrain , serotonin , receptor , biochemistry , immunohistochemistry , immunology
Activation of median raphe serotonergic neurons results in the desynchronization of hippocampal electroencephalographic (EEG) activity. This could be a direct effect, because serotonin (5‐HT) fibers terminate on a specific population of hippocampal interneurons. On the other hand, it could be an indirect action through the medial septum/diagonal band of Broca (MSDB) pacemaker cells, because, in addition to previously described inhibitory effects, excitatory actions of 5‐HT have been demonstrated on MSDB γ‐aminobutyric acid (GABA)‐containing neurons through 5‐HT 2A receptors. Electron microscopic double immunostaining for Phaseolus vulgaris ‐leucoagglutinin (PHA‐L) injected into the median raphe (MR) and parvalbumin, choline acetyltransferase, or calretinin as well as double immunostaining for 5‐HT and parvalbumin, and colocalization for parvalbumin and 5‐HT 2A receptors were done in rats. The results demonstrated that: 1) MR axons form perisomatic and peridendritic baskets and asymmetric synaptic contacts on MSDB parvalbumin neurons; 2) these fibers do not terminate on septal cholinergic and calretinin neurons; 3) 5‐HT fibers form synapses identical to those formed by PHA‐L‐immunolabeled axons with parvalbumin neurons; and 4) MSDB parvalbumin cells contain 5‐HT 2A receptors. These observations indicate that 5‐HT has a dual action on the activity of hippocampal principal cells: 1) an inhibition of the input sector by activation of hippocampal GABA neurons that terminate exclusively on apical dendrites of pyramidal cells, and 2) a disinhibition of the output sector of principal neurons. MSDB parvalbumin‐containing GABAergic neurons specifically innervate hippocampal basket and chandelier cells. Thus, 5‐HT‐elicited activation of MSDB GABAergic neurons will result in a powerful inhibition of these GABA neurons. J. Comp. Neurol. 410:586–598, 1999. © 1999 Wiley‐Liss, Inc.