Heterogeneous responses of neostriatal neurons to amphetamine in freely moving rats

Single-unit activity was recorded from the neostriatum of unrestrained, behaving rats. Neuronal discharges were found to vary with specific motor responses, general changes in motor activity, or the presentation of orienting stimuli. In each case, however, 1.0 mg/kg D-amphetamine produced approximately equal numbers of excitations and inhibitions. A subsequent injection of a higher dose (5.0 mg/kg) either produced a greater change in firing rate in the same direction or reversed the direction of the low-dose response. Amphetamine, therefore, does not produce uniformly excitatory effects in the neostriatum of ambulant animals. In fact, the neuronal response to amphetamine appears to reflect a complex interaction of several factors, including ongoing behavior and drug dose.