NMDA TREATMENT AND K-INDUCED DEPOLARIZATION SELECTIVELY PROMOTE THE EXPRESSION OF AN NMDA-PREFERRING CLASS OF THE IONOTROPIC GLUTAMATE RECEPTORS IN CEREBELLAR GRANULE NEURONS()

Growth conditions which promote the survival of cerebellar granule cel ls in culture, such as high K+ or N-methyl-D-aspartate (NMDA) treatmen t, also promote the functional expression of an NMDA-preferring subtyp e alone of the ionotropic glutamate receptors. The selective regulatio n of NMDA receptors detected electrophysiologically in individual cell s, using the whole cell patch clamp technique, is characteristic of gr anule cells in general: NMDA-induced Ca-45(2+) influx increased severa l-fold in cultures treated with either high K+ or NMDA. The increase i n NMDA receptor activity was correlated with an increase in the expres sion of an NMDA receptor protein. Since the effect of these 'trophic' conditions is mediated through Ca2+, the induced increase in the densi ty of NMDA receptors (which gate a Ca2+ conductance) provides a positi ve feedback for strengthening the trophic influences.