Ontogeny of high-affinity GABA and benzodiazepine receptors in the rat cerebellum: an autoradiographic study.

High-affinity GABA and benzodiazepine receptors were localized by light microscopic autoradiography in the developing rat cerebellum. [3H]muscimol was used for the labeling of GABA receptors and [3H]flunitrazepam for benzodiazepine receptors. Very low densities of GABA sites were found during the first postnatal week. GABA receptors start increasing linearly at the end of the second week up to adult levels around the fourth postnatal week. The increase in receptor density is concentrated in the developing granule cell layer. Benzodiazepine receptors are present at birth and increases in the density of receptors were observed already during the first postnatal week. Receptor concentrations reached adult values around the third to fourth weeks postnatally. The increase in benzodiazepine receptors in concentrated in the growing molecular layer with little change in the granule cell layer. The immature cell of the external granule layer were characterized by the absence of receptor sites. At least partial association of high-affinity GABA receptors with granule cells and benzodiazepine receptor with Purkinje cell dendrites is suggested by these developmental profiles.