Differential effects of d,l-amphetamine on licking maintained by electrical hypothalamic stimulation and/or water in rats.

The role of the reinforcer as a determinant of the behavioural effects of amphetamine was assessed with a procedure under which response requirements were equated. Eight rats were trained to lick on fixed-ratio schedules of rewarding lateral hypothalamic stimulation and water delivery, respectively. The effects of d,l-amphetamine (0.2-2.0 mg/kg) were investigated in the lateral hypothalamic stimulation condition and compared with the effects of the drug at 1.0 mg/kg in the water condition. Licking maintained by hypothalamic stimulation was increased after amphetamine administration to approximately 200% of control performance at 1.0 mg/kg. At this dose amphetamine administration resulted in a decrease in water maintained licking. A computer analysis of the temporal patterning of licking in both water and stimulation conditions was carried out. This analysis revealed that amphetamine may attenuate the disruptive effects of hypothalamic stimulation on the lick-interrupt cycle. The differential effects of amphetamine on licking maintained by the two events may reflect either unequal participation of catecholaminergic circuits in the two types of reward, or anti-inhibitory motor effects of amphetamine.