Differential effects of N-methyl-D-aspartate receptor blockade on eticlopride-induced immediate early gene expression in the medial and lateral striatum

The function of striatopallidal neurons is regulated by N-methy-D-aspartate (NMDA) and dopamine D2 receptors. Previous studies show that immediate ear ly gene induction by D2 receptor blockade is suppressed by NMDA receptor an tagonists. Because the pharmacology of NMDA receptors depends on the incorp oration of different NR2 subunits and NR2 subunits show regional and cellul ar differences in their expression in striatum, our study examined whether different NMDA receptor antagonists would have differential effects on etic lopride-induced immediate early gene expression in striatum. Male Sprague-D awley rats were pretreated with vehicle, CGS 19755, MK-801 or ifenprodil. R ats then received injections of eticlopride and were killed 40 min later. I n situ hybridization histochemistry was used to determine the expression of c-fos and zif268 in the striatum. Eticlopride increased immediate early ge ne expression in striatum, with the increase generally being greater in lat eral than in medial striatum. Pretreatment with each of the NMDA receptor a ntagonists dose-dependently decreased the expression of the immediate early genes. This suppression of eticlopride-induced gene expression was signifi cant only in the medial-central aspect of striatum. Although there was a tr end toward suppression of the gene induction in lateral striatum, it did no t reach statistical significance and was not typically dose dependent. The data suggest that different types of NMDA receptor antagonists do not exert differential effects on D2 dopamine receptor-mediated function in the stri atum. In addition, the data indicate that eticlopride-induced gene expressi on in the striatum is not uniformly dependent on NMDA receptor activation.