N ‐Methyl‐ d ‐aspartate receptors mediating hippocampal noradrenaline and striatal dopamine release display differential sensitivity to quinolinic acid, the HIV‐1 envelope protein gp120, external pH and protein kinase C inhibition

NMDA receptors regulating hippocampal noradrenaline (NA) and striatal dopamine (DA) release have been compared using superfused synaptosomes prelabelled with the [ 3 H]catecholamines. Both receptors mediated release augmentation when exposed to NMDA plus glycine. Quinolinic acid (100 µ m or 1 m m ) plus glycine (1 µ m )‐elicited [ 3 H]NA, but not [ 3 H]DA release. The NMDA (100 µ m )‐evoked release of [ 3 H]NA and [ 3 H]DA was similar and concentration‐dependently enhanced by glycine or d ‐serine (0.1–1 µ m ); in contrast, the HIV‐1 envelope protein gp120 potently (30–100 p m ) enhanced the NMDA‐evoked release of [ 3 H]NA, but not that of [ 3 H]DA. Gp120 also potentiated quinolinate‐evoked [ 3 H]NA release. Ifenprodil (0.1–0.5 µ m ) or CP‐101,606 (0.1–10 µ m ) inhibited the NMDA plus glycine‐evoked release of both [ 3 H]catecholamines. Zinc (0.1–1 µ m ) was ineffective. Lowering external pH from 7.4 to 6.6 strongly inhibited the release of [ 3 H]NA elicited by NMDA plus glycine, whereas the release of [ 3 H]DA was unaffected. The protein kinase C inhibitors GF 109203X (0.1 µ m ) or H7 (10 µ m ) selectively prevented the effect of NMDA plus glycine on the release of [ 3 H]NA. GF 109203X also blocked the release of [ 3 H]NA induced by NMDA or quinolinate plus gp120. It is concluded that the hippocampal NMDA receptor and the striatal NMDA receptor are pharmacologically distinct native subtypes, possibly containing NR2B subunits but different splice variants of the NR1 subunit.