Neurotransmitter receptors in the avian brain. III. GABA-benzodiazepine receptors.

GABA/benzodiazepine (BZ) receptors were localized in the pigeon brain by in vitro receptor autoradiography using [3]flunitrazepam as ligand. Highest densities of binding sites were observed in the optic tectum, in the nucleus pretectalis, the nucleus intercollicularis and the substantia gelatinosa of the spinal cord. Intermediate densities were found in the forebrain, particularly the paleostriatum primitivum, the nucleus rotundus and the cerebellum. Low densities were detected in the midbrain and brainstem. The paleostriatum primitivum and cerebellum were enriched in receptors of the BZ type I, as indicated by their high affinity for compound CL 218872. The addition of GABA resulted in an enhanced binding of the ligand in all brain regions. All these results indicate that GABA/BZ receptors in the pigeon brain present similar pharmacological properties and comparable anatomical distribution to those in mammalian brain.