Principal cells are the postsynaptic targets of supramammillary afferents in the hippocampus of the rat

Research output: Contribution to journalArticle

99 Citations (Scopus)

Abstract

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 D28k) 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.

Original languageEnglish
Pages (from-to)322-334
Number of pages13
JournalHippocampus
Volume4
Issue number3
DOIs
Publication statusPublished - Jun 1994

Keywords

  • granule cells
  • hypothalamic projection
  • interneurons
  • pyramidal cells

ASJC Scopus subject areas

  • Cognitive Neuroscience

Fingerprint Dive into the research topics of 'Principal cells are the postsynaptic targets of supramammillary afferents in the hippocampus of the rat'. Together they form a unique fingerprint.

  • Cite this