Immunoreactivity for the GABAA Receptor 1 Subunit, Somatostatin and Connexin36 Distinguishes Axoaxonic, Basket, and Bistratified Interneurons of the Rat Hippocampus

A. Baude, C. Bleasdale, Y. Dalezios, P. Somogyi, T. Klausberger
2006 Cerebral Cortex  
Parvalbumin (PV)-expressing interneurons synchronize cortical neurons through g-aminobutyric acidergic (GABAergic) synapses. Three types of PV-containing interneurons populate stratum pyramidale of the hippocampal CA1 area: basket cells targeting somata and proximal dendrites, axoaxonic cells innervating axon initial segments, and bistratified cells targeting the dendrites of pyramidal cells. We tested whether this axonal specialization is accompanied by a differential expression of molecules
more » ... volved in neuronal signaling. Immunofluorescence evaluation of interneurons labeled by neurobiotin in vivo shows that axoaxonic cells express significantly less GABA A receptor a1 subunit in the plasma membrane than basket and bistratified cells. Electron microscopic immunogold labeling reveals that this subunit contributes heavily to extrasynaptic receptors providing a substrate for tonic inhibition. Results from additional immunofluorescence experiments were consistent with the finding that only bistratified cells express the neuropeptide somatostatin. From the molecular profiles, we estimate that basket, bistratified, and axoaxonic cells represent about 60%, 25%, and 15%, respectively, of PV-containing cells in CA1 stratum pyramidale. In addition, all 3 interneuron classes form connexin36immunopositive dendrodendritic gap junctions. The differential expression of signaling molecules and the relative frequency of cells reflect the specialized temporal contribution of the 3 types of PV-positive interneurons to GABA release in the network.
doi:10.1093/cercor/bhl117 pmid:17122364 fatcat:5noql2rvlffqbiiiykfcz3knoy