Central benzodiazepine receptors in the spinal cord and other regions of the CNS of the cat

Abstract

Central benzodiazepine (BZ) receptors were looked for in the spinal cord, cerebral cortex and cerebellum of the cat. Both [ 3H]Ro 15-1788 and [ 3H]flunitrazepam bound to benzodiazepine receptors with apparent dissociation constants (K D ) in the nanomolar range and Hill coefficients near unity. The concentration of binding sites was much greater (10–40 times, depending on the ligand used) in the cortex and cerebellum than in the spinal cord. γ-Aminobutyric acid (GABA) significantly reduced the K D value of the binding of tritiated flunitrazepam in all three areas of the central nervous system (CNS). The displacement of [ 3H]Ro 15-1788 by different benzodiazepine ligands indicates a relative prevalence of BZ 1 (high affinity for β-carboline esters and the triazolopyridazine, CL 218 872) in the cerebellum, a predominance of BZ 2 (low affinity for the same agents) in the spinal cord and a mixture of both types in the cortex. The possibility that there is regional heterogeneity of receptors for benzodiazepines in CNS of the cat is discussed.