Light microscopic autoradiographic localisation in rat brain of the binding sites for the GABAA receptor antagonist [3H]SR 95531: comparison with the [3H]GABAA receptor distribution.

Quantitative receptor autoradiography has been employed to determine the binding distribution of [3H]SR 95531 (2'-(3'-carboxy-2',3'-propyl)-3-amino-6-p-methoxyphenylpyrazinium bromide), a GABAA receptor antagonist, in the rat brain. The location showed good correspondence, in most areas, with the binding of [3H]GABA to GABAA receptors. The major exceptions were binding to cerebellum and hippocampus. We also describe here a non-GABA-associated [3H]SR 95531 binding site which is found at its highest level in the hippocampal CA1 region but also in CA2, CA3, dentate gyrus and cerebral cortex. The results support the localisation of [3H]SR 95531 sites to the GABAA receptor complex.