PV-containing neurons in the medial prefrontal cortex. Brain slices adjacent to those stained for GAT-1-IR were immunostained for PV and counterstained for Nissl. The photomicrographs shown here do not have the Nissl counterstain for clarity. A, PV-IR in the shallow regions of the medial prefrontal cortex showing cell bodies and PV-IR fibers. The roman numeral identifies the approximate start of the cortical layer. B, A photomicrograph of a bipolar PV-IR cell in the medial prefrontal cortex. Scale bar, 10 μm.