Premium
Anatomically heterogeneous populations of CB 1 cannabinoid receptor‐expressing interneurons in the CA3 region of the hippocampus show homogeneous input–output characteristics
Author(s) -
Szabó Gergely G.,
Papp Orsolya I.,
Máté Zoltán,
Szabó Gábor,
Hájos Norbert
Publication year - 2014
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.22330
Subject(s) - neuroscience , inhibitory postsynaptic potential , gabaergic , axon , cannabinoid receptor , postsynaptic potential , hippocampal formation , mossy fiber (hippocampus) , biology , interneuron , hippocampus , perforant path , excitatory postsynaptic potential , receptor , dentate gyrus , biochemistry , agonist
A subpopulation of GABAergic cells in cortical structures expresses CB 1 cannabinoid receptors (CB 1 ) on their axon terminals. To understand the function of these interneurons in information processing, it is necessary to uncover how they are embedded into neuronal circuits. Therefore, the proportion of GABAergic terminals expressing CB 1 and the morphological and electrophysiological properties of CB 1 ‐immunoreactive interneurons should be revealed. We investigated the ratio and the origin of CB 1 ‐expressing inhibitory boutons in the CA3 region of the hippocampus. Using immunocytochemical techniques, we estimated that ∼40% of GABAergic axon terminals in different layers of CA3 also expressed CB 1 . To identify the inhibitory cell types expressing CB 1 in this region, we recorded and intracellularly labeled interneurons in hippocampal slices. CB 1 ‐expressing interneurons showed distinct axonal arborization, and were classified as basket cells, mossy‐fiber‐associated cells, dendritic‐layer‐innervating cells or perforant‐path‐associated cells. In each morphological category, a substantial variability in axonal projection was observed. In contrast to the diverse morphology, the active and passive membrane properties were found to be rather similar. Using paired recordings, we found that pyramidal cells displayed large and fast unitary postsynaptic currents in response to activating basket and mossy‐fiber‐associated cells, while they showed slower and smaller synaptic events in pairs originating from interneurons that innervate the dendritic layer, which may be due to dendritic filtering. In addition, CB 1 activation significantly reduced the amplitude of the postsynaptic currents in each cell pair tested. Our data suggest that CB 1 ‐expressing interneurons with different axonal projections have comparable physiological characteristics, contributing to a similar proportion of GABAergic inputs along the somato‐dendritic axis of CA3 pyramidal cells. © 2014 Wiley Periodicals, Inc.