gamma-Aminobutyric acidB receptors in the rat brain: quantitative autoradiographic localization using [3H](-)-baclofen.

The light microscopic localization of gamma-aminobutyric acidB (GABAB) receptors in the rat brain has been accomplished using in vitro autoradiography with [3H]baclofen as a ligand. Initial biochemical studies indicated this compound specifically bound to slide-mounted tissue sections with high affinity in a saturable and readily reversible manner. Autoradiograms generated by labeled tissue sections demonstrated high grain densities over structures such as the interpeduncular nucleus, molecular layer of the cerebellum, superior colliculus, several thalamic nuclei and the superficial laminae of the cortex. The majority of the GABAB sites were found to exist in regions of the brain previously reported to have significant densities of GABA sites present. A few areas were noted, however, where the distribution of GABAA and GABAB sites did not overlap.