GABA-immunoreactive cell bodies and processes, as well as projection neurons in the olfactory bulb.

(A) Low-power photomicrographs from a 25-μm-thick cross section of the olfactory bulb showing multiple labelings: binding of GSIB4 to olfactory primary afferents (green), GABA immunofluorescence (red), and retrograde labeling from injections in the PT and LPal (blue). (A1) The distribution of GABAergic neurons in relation to the GL. (A2) The distribution of projection neurons in relation to the GL. (A3) Merge of A1 and A2 showing some overlap in the distribution of the GABAergic and projection neurons populations. The white frames correspond to the approximate location of photomicrographs B to D. (B) High-power photomicrograph from a section just adjacent to the one illustrated in A, showing GABA processes in the medOB glomerulus. The projection neurons (blue) were labeled from an injection in the PT and are seen inside the medOB glomerulus. Arrows point at some GABA cell bodies lying outside of the glomerulus. The green fluorescence of olfactory primary afferents was omitted for clarity, but the contours of the glomerulus are indicated with a dashed line. (C) High-power photomicrograph from the section in A, showing GABA processes in the MOB GL and in the area where projection neurons (blue) are found. Those projection neurons were labeled from an injection in the LPal. Arrows point at some GABA cell bodies. The green fluorescence of olfactory primary afferents was omitted for clarity but the contours of the glomeruli are indicated with a dashed line. (D) Photomicrograph of the central region of the olfactory bulb showing numerous GABAergic neurons and processes. This thicker section was obtained from a different experiment, in which the immunofluorescence procedure was carried out on free-floating sections. Scale bars in A = 200 μm; scale bars in B-D = 50 μm. GL, glomerular layer; GSIB4, Griffonia simplicifolia isolectin B4; ICL, internal cell layer; LPal, lateral pallium; medOB, medial part of the olfactory bulb; MOB, main olfactory bulb, ONL, olfactory nerve layer; PT, posterior tuberculum.