Local connection patterns of parvalbumin-positive inhibitory interneurons in rat primary auditory cortex.

In the auditory cortex (AC), GABAergic neurons constitute approximately 15-25% of all neurons. GABAergic cells are present in all sensory modalities and essential for modulating sensory receptive fields. Parvalbumin (PV) positive cells represent the largest sub-group of the GABAergic population in auditory neocortex. We investigated the projection pattern of PV cells in rat primary auditory cortex (AI) with a retrograde tracer (wheat germ apo-HRP conjugated to gold [WAHG]) and immunocytochemistry for PV. All AC layers except layer I contained cells double-labeled for PV and WAHG. All co-localized PV+ cells were within 2 mm of the injection site, regardless of laminar origin. Most (ca. 90%) of the co-localized PV cells were within 500 μm of the injection site in both dorsal-ventral and rostral-caudal dimension of the auditory core region. WAHG-only cells declined less rapidly with distance and were found up to 6 mm from the deposit sites. WAHG-only labeled cells in the medial geniculate body were in ventral division loci compatible with an injection in AI. Differences in the range and direction of the distribution pattern of co-localized PV+ cells and WAHG-only cells in AI express distinct functional convergence patterns for the two cell populations.