Suriclone is a potent non-benzodiazepine anxiolytic belonging to the cyclopyrrolone family. This study examines the distribution and properties of [ Unlike benzodiazepine (BZ) agonists, [3H1-suriclone binding to rat brain sections was not increased in the presence of GABA, and unlike imidazopyridines such as alpidem, suriclone was unable to discriminate between the BZ, and BZ, phenotype of the GABA, receptor. The autoradiographic distribution of [3H]-suriclone binding sites in the rat brain was heterogeneous and relatively similar to that previously described for GABA, receptors labelled by benzodiazepines; some regions, however, such as certain cortical areas, displayed a different labelling.The highest densities were found in frontal, occipital, parietal, and cingulate cortices (layers I, II, Ill, IV), in the molecular layer of the cerebellum, in the superior colliculus and in the hippocampus. Moderate binding densities appeared in numerous areas such as the inferior colliculus, the central grey, the dorsal raphe, and the hypothalamus whereas caudate putamen, globus pallidus, and thalamic nuclei displayed a low density of [3H]-suriclone binding sites.(0 1995 Wiley-Liss, Inc.