Age-related changes in binding to excitatory amino acid uptake sites in human cerebellum.

In vitro autoradiography and test-tube assay of the sodium-dependent binding of D-[3H]aspartate were used to localize and quantify the uptake site for the excitatory amino acid neurotransmitters glutamate and aspartate in the cerebellar cortex of human cerebellar hemispheres. Autoradiograms revealed a pronounced heterogeneity in the distribution of D-[3H]aspartate binding in cortex from adult brains, with the highest binding density corresponding to the Purkinje cell layer, high binding in molecular layer and low binding in granule cell layer. In contrast, cerebellar cortex from infants at term (40 weeks gestation) had only low binding of the ligand in both the molecular and the Purkinje cell layers. Both methods employed for measuring D-[3H]aspartate binding showed that the number of binding sites in Purkinje and molecular layers increased rapidly from term to 20 weeks postnatal age and achieved levels higher than those found in adult cerebellum. It is concluded that a substantial increase in the numbers of glutamate/aspartate uptake sites takes place in the human cerebellum during the early postnatal period. It is deduced that the excess uptake sites are eliminated as the cerebellum matures.