Abstract

In primary cultures of rat cerebellar neurons, a brief stimulation of glutamate receptors results in coordinated activation of a programmed early gene response involving increases in the amount of c-fos, c-jun, jun-B, and zif/268 mRNAs. Each of these genes was induced to a different extent and showed a temporal pattern characterized by either a monophasic "early" response, occurring within 30 min of glutamate addition, or a biphasic response (c-jun), lasting for up to 6 to 8 hr after the initial stimulus. The early phase of the glutamate-induced gene expression was prevented by 3-(2-carboxypiperazin-4-yl)propyl-1-phosphonic acid, a highly selective isosteric antagonist of the N-methyl-D-aspartate (NMDA)-sensitive glutamate receptor (NMDA receptor). The second phase of the c-jun response was not blocked when the NMDA receptors were completely inhibited after the initial pulse of agonist or when the quisqualate-kainate receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione was added, suggesting that a brief NMDA receptor stimulation triggers a cascade of events critical for the manifestation of the delayed c-jun expression. Furthermore, gel retardation assays demonstrated that NMDA receptor activation results in a prolonged increase in nuclear DNA-binding activity specific for the AP-1 transcriptional regulatory element. Protein immunoblot analysis showed that the composition of this nucleoprotein complex changes as a function of time, reflecting a cascade that involves an increased translation of Fos and several Fos-related proteins. The coordinated induction of several different transcription factors and the variations in transcriptional complex formation initiated by NMDA receptor stimulation may be a key mechanism in the orchestration of specific target gene expression that underlies various aspects of neuronal function, including plasticity responses.