SUBCHRONIC MORPHINE INCREASES AMPHETAMINE-INDUCED POTENTIATION OF BRAIN-STIMULATION REWARD - REVERSAL BY DNQX

The ability of morphine and amphetamine to potentiate brain stimulatio n reward was studied in rats with monopolar electrodes in the medial f orebrain bundle. Animals received seven daily injections of morphine ( 3 mg/kg, s.c.) or saline followed 10 min later by either DNQX (100 mg/ kg, i.p.) or its vehicle. On the 8th day the self-stimulation (SS) res ponse was examined 60 min or 30 min after the administration of either morphine (3 mg/kg, s.c.) or amphetamine (1.5 mg/kg, s.c.), respective ly. It was found that the subchronic administration of morphine sensit izes animals to subsequent amphetamine-, but not morphine-induced acti vation of SS, which may be prevented by the coadministration of DNQX, an antagonist of the non-NMDA subtype of glutamate receptors.