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Principal cells are the postsynaptic targets of supramammillary afferents in the hippocampus of the rat
Author(s) -
Maglóczky Zsófia,
Acsády László,
Freund Tamás F.
Publication year - 1994
Publication title -
hippocampus
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.767
H-Index - 155
eISSN - 1098-1063
pISSN - 1050-9631
DOI - 10.1002/hipo.450040316
Subject(s) - neuroscience , dentate gyrus , postsynaptic potential , inhibitory postsynaptic potential , hippocampal formation , entorhinal cortex , hippocampus , subiculum , anterograde tracing , population , chemistry , biology , nucleus , medicine , biochemistry , receptor , environmental health
Neurons of the supramammillary nucleus are known to fire phase‐locked to hippocampal theta rhythm. Stimulation of this area induces theta activity in the hippocampus via the medial septum and facilitates perforant pathway stimulation‐evoked population spikes in the dentate gyrus even if the medial septum is inactivated. This latter effect was suggested to be due to a direct inhibitory input from the supramammilary nucleus to hippocampal nonpyramidal cells resulting in disinhibition. In the present study, using anterograde tracing with Phaseolus vulgaris leucoagglutinin, we aimed to identify the types of neurons innervated by the supramammillary projection in the dentate gyrus and Ammons horn, with particular attention to the presumed postsynaptic inhibitory neurons, which may mediate the proposed disinhibitory action. Double‐immunostaining for the tracer and different neuropeptides (somatostatin, cholecystokinin, neuropeptide Y) or calcium binding proteins (calretinin, parvalbumin, calbindin D 28k ) present in different subpopulations of interneurons revealed no multiple contacts between supramammillary afferents and labeled inhibitory cells at the light microscopic level. Furthermore, postembedding immunostaining of electron microscopic sections for GABA demonstrated that none of the 68 PHAL‐labeled supramammillary boutons examined and none of their postsynaptic targets were immunoreactive for the inhibitory neurotransmitter. We conclude, therefore, that most if not all postsynaptic targets of the supramammillary projection are principal cells both in the dentate gyrus and in the CA2‐CA3a subfields. This suggests that a mechanism other than disinhibition is responsible for the facilitatory effect of this pathway on hippocampal evoked activity. © 1994 Wiley‐Liss, Inc.