Enrichment of specific GABAergic neuronal types in the mouse perirhinal cortex
GABAergic neurons represent 10-15% of the neuronal population of the cortex but exert a powerful control over information flow in cortical circuits. GABAergic neurons show an extraordinary diversity in their morphology, physiology, molecular markers and connectivity. This diversity allows GABAergic neurons to participate in a wide variety of microcircuit motifs. The diversity of GABAergic neurons has been shown to be conserved across cortical regions. The GABAergic population can be broadly divided in three major classes parvalbumin, somatostatin and 5HT3aR groups. The largest GABAergic class in the cortex is represented by the parvalbumin-expressing fast-spiking neurons, which provide powerful somatic inhibition to their postsynaptic targets. Recently, the density of parvalbumin-expressing neurons has been shown to be lower in associative areas of the mouse cortex, including the perirhinal cortex, as compared to sensory and motor areas. In the present study we investigated whether this reduction in parvalbumin-expressing neurons leads to a decreased GABAergic population, or to an enrichment of other GABAergic cell-types. We found that the GABAergic population of the perirhinal cortex is comparable to that of a primary sensory area, and it is enriched of neurons belonging to the 5HT3aR group. We also demonstrate that, despite the low density of parvalbumin-expressing neurons, the perirhinal cortex contains a comparable population of fast-spiking neurons, most of which do not express parvalbumin. Our results demonstrate a yet uncharacterized diversity within the fast-spiking population across cortical regions.