Behavioral sensitization to chronic amphetamine develops in parallel with an enhancement of amphetamine-stimulated efflux of acetylcholine (ACh) in striatum. The present study investigated the role of NMDA receptors in the latter phenomenon. Rats were treated with either saline (1.0 ml/kg, i.p.) or amphetamine (4.0 mg/kg, i.p., b.i.d.) for 12 days followed by a withdrawal period of 2-3 weeks. In vivo microdialysis was employed to measure striatal ACh efflux. Amphetamine challenge (4.0 mg/kg, i.p.) evoked a significant increase in striatal ACh efflux in rats withdrawn from chronic amphetamine while having no significant effect on ACh efflux in saline-pretreated rats. Inclusion of the NMDA receptor antagonist (+/-)-2-amino-5-phoshonopentanoic acid (APV; 100 microM) in the perfusion solution blocked the amphetamine-induced increase in striatal ACh efflux observed in amphetamine-pretreated rats. In saline-pretreated animals, the presence of APV had no apparent effect on the profile of striatal ACh efflux following amphetamine challenge. Thus, the stimulatory effect of amphetamine challenge on striatal ACh efflux that selectively is observed in animals withdrawn from chronic amphetamine is dependent upon NMDA receptor activation.