GABAERGIC PROJECTION FROM THE BASAL FOREBRAIN TO THE VISUAL SECTOR OFTHE THALAMIC RETICULAR NUCLEUS IN THE CAT

We examined the projection from the basal forebrain to thalamic and co rtical regions of the visual system in cats, with particular reference to the visual sector of the thalamic reticular nucleus, the lateral g eniculate nucleus, and the striate cortex. First, we made injections o f wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) into the visual sector of the thalamic reticular nucleus and found ce lls labeled by retrograde transport in the lateral nucleus basalis mag nocellularis. Injection of biocytin into the basal forebrain resulted in the anterograde labeling of a dense band of fibers and terminals wi thin the entire thalamic reticular nucleus; this labeling extended thr ough the visual sector including the perigeniculate nucleus. No orthog rade labeling was found in the lateral geniculate nucleus. Next, we ad dressed the issue of putative neurotransmitters used by this pathway u sing a variety of immunocytochemical and histochemical markers. In thi s fashion, we identified two populations of-cells in the nucleus basal is magnocellularis of the cat: large cholinergic cells that contain ch oline acetyltransferase, NADPH-diaphorase, and calbindin and that proj ect to striate cortex-and smaller cells that contain gamma-aminobutyri c acid (GABA), glutamic acid decarboxylase, and parvalbumin and that p roject to the visual sector of the thalamic reticular nucleus. We also examined at the electron microscopic level terminals in the visual se ctor of the thalamic reticular nucleus that were labeled from a biocyt in injection in the basal forebrain. Most of these terminals form symm etric contacts onto dendrites and were revealed by postembedding immun ocytochemical staining to be positive for GABA. (C) 1994 Wiley-Liss, I nc.