The Characterization and Regulation of Benzodiazepine Binding Sites in the Mammalian Retina, Cerebral Cortex and Kidney

The binding of [JH]flunitrazepam (FLU) to membranes prepared from mammalian brain, retina and kidney was investigated by means of conventional filtration assay techniques. In the mouse brain a study of the ontogeny of [ H]FLU binding was conducted. Specific [ H]FLU binding was present early in development and there was a rapid increase in receptor density (Bmax) during the first 2 weeks of neonatal life. This increase could be described by the function, 1/ y 1 a'e , where a = 1.8 pmol/brain, k = 0.23 weeks and x = time O in weeks (r = 0.98). By 3-4 weeks of age, adult levels of [ H]FLU binding were reached (~115 fmol/mg tissue). Notable changes in the equilibrium dissociation constant (K^) during development were not observed. Y-Aminobutyric acid (GABA) has previously been shown to increase the affinity of [ H]FLU binding in the adult rat brain; in the present studies this effect was shown to be present throughout the development of the mouse brain. Kinetic analyses of the GABA enhancement of [ H]FLU binding indicated that the change in was due to a decrease in the rate constant of dissociation (k_^). [ H]FLU binding has been shown to occur in the mammalian retina and it has all the characteristics of cerebral [ H]FLU binding. Monosodium glutamate (MSG) is toxic to retinal neurons and it was used to ascertain the putative cellular localization of retinal BZD binding sites. Nine weeks following neonatal MSG administration,