Quantitative autoradiographic study of the postnatal development of benzodiazepine binding sites and their coupling to GABA receptors in the rat brain.

The postnatal development of benzodiazepine binding sites in the rat brain was studied by quantitative receptor autoradiography using [3H]flunitrazepam. The coupling of these sites to GABA receptors was assessed in 43 cerebral structures by examining the effects of in vitro addition of GABA on flunitrazepam specific binding. Benzodiazepine-specific binding was relatively high at birth and exhibited an heterogeneous distribution pattern, anatomically different from the adult one. Data showed a sequential development of benzodiazepine receptors in relation to the time course of maturation of cerebral structures. A proliferation peak which paralleled rapid brain growth was noticed. High levels of benzodiazepine sites were transiently observed in some areas, e.g. thalamus and hypothalamus, and might be related to maturational events. In every brain structure examined, benzodiazepine binding sites were linked to GABA receptors. However, enhancement of flunitrazepam specific binding by exogenous GABA differed according to the structures studied and decreased during development, suggesting some changes in the control of GABA/benzodiazepine regulation during postnatal maturation.