Transient increase in ligand binding to quisqualate and kainate sites in cerebral cortex of immature rats.

The postnatal changes in the specific binding of [3H]kainate and [3H]AMPA (RS-alpha-amino-3-hydroxy-5-methyl-4-isoxasolopropionic acid, an agonist of quisqualate receptors) were studied in cerebral cortex of rats, aged 2-360 days. The binding of the two ligands was assayed in whole-tissue homogenates. Similar developmental time courses were found for kainate and AMPA binding, characterized by high perinatal levels, a further increase during the first few days after birth, an early maximum value around the age of one week, and a gradual decrease to adult values which were attained at an age of 3-4 weeks. As revealed by Scatchard analysis, the transient elevation of ligand binding was derived from an increased density of binding sites, which, in the case of AMPA, was accompanied also by an increase in binding affinity. The results indicate that, in the immature cerebral cortex, kainate and quisqualate receptors may play a role other than in synaptic transmission.