AMPA RECEPTOR DEVELOPMENT IN RAT TELENCEPHALON - [H-3] AMPA BINDING AND WESTERN-BLOT STUDIES

Telencephalic membranes from rats of different embryonic (E16, E19) an d postnatal (P2, P7, P14, adult) ages were assessed for alpha-[H-3] am ino-3-hydroxy-5-methylisoxazole-4-propionic acid ([H-3] AMPA) binding and for immunoreactivity levels of AMPA receptor subunits (GluR1, GluR 2/3, and GluR4). In addition, the synaptic markers synaptophysin and N CAM(140) (a neural cell adhesion molecule isoform) were examined by im munoblot. The density of [H-3]AMPA binding sites increased steadily wi th advancing age. This increase was due mainly to the development of t he large low-affinity component (K-D = 400 nM) that dominates the [H-3 ]AMPA binding profile of adult rat brain membranes. As resolved by two -site regression analysis, the high-affinity component (K-D = 15 nM) o f the [H-3]AMPA binding increased by approximately twofold from E16 to adult, whereas the low-affinity component increased by 25-fold. Stain ing for GluR1 and GluR2/3 increased steadily with increasing age at al l time points examined; synaptophysin and NCAM(140) exhibited similar ontogenic immunostaining profiles. GluR4 immunoreactivity was first ev ident at P14 and increased by adulthood. These results indicate that A MPA receptor density increases steadily during development and that th is increase is coincident with the ontogenic expression of other synap tic components. Furthermore, there is a shift toward a preponderance o f low-affinity [H-3]AMPA binding, which occurs during the period when AMPA receptors are being sorted into postsynaptic regions, suggesting that some element of the postsynaptic membrane environment modulates A MPA receptor properties.