Amphetamine inhibits behavior-related neuronal responses in substantia nigra pars reticulata of rats working for sucrose reinforcement

Changes in activity of basal ganglia neurons, especially those in the striatum, are thought to underlie the characteristic behavioral patterns produced by d-amphetamine (AMPH). To study the role of the substantia nigra pars reticulata (SNr), a major basal ganglia output nucleus, we recorded from SNr neurons before and after a behaviorally activating dose of AMPH (0.5 mg/kg) in rats trained to nosepoke for sucrose reinforcement. Before AMPH, task-related behaviors were associated primarily with increases or both increases and decreases in SNr firing. Although these same behavior-related patterns persisted after AMPH, their relative magnitude was significantly attenuated. Units unresponsive during task events were unaffected by AMPH. Thus, rather than change the overall level of SNr firing, a behaviorally active dose of AMPH exerts context-dependent effects on the activity of SNr neurons.