AES inputs target nitrergic neurons containing GABA. To determine if nitrergic interneurons colocalized with this neurotransmitter, sections were processed for NOS (A, B; red pseudocolored) and GABA (D, E; green pseudocolored) double-labeling. The distributions of soma diameters for NOS, GABA, and double-labeled neurons are shown in C, F, and I, respectively, and their quantification is shown in I (inset). Quantification reveals that approximately half (46.07%) of the NOS-immunostained neurons are GABAergic, whereas 88.94% of the GABAergic neurons are NOS-immunostained (inset in I). Arrows in G and H denote NOS-immunostained neurons that did not colocalize with GABA. Note that GABAergic neurons, visualized with DAB (brown reaction product), receive appositions from AES fibers that were visualized with nickel-intensified DAB (black reaction product). The drawing at the top left corner in (A) indicates the approximate location of the tissue magnified in A-H. Abbreviations: stratum griseum superficiale (SGS); stratum opticum (SO), stratum griseum intermediale (SGI), stratum griseum profundum (SGP); periaqueductal gray (PAG). Scale bar = 100μm in H (also applies to A, B, D, E and G); 25μm in J (also applies to K and L).