The effects of apomorphine on the acquisition of schedule-induced polydipsia in rats.

Injections of the dopamine agent, apomorphine, at the doses of 0.05, 0.50 and 1.0 mg/kg were given to three different groups of rats while a fourth group received an injection of the drug vehicle. The injections preceded each of 15 schedule-induced polydipsia (SIP) acquisition sessions in which the subjects bar-pressed for food pellets on a fixed interval 60-sec schedule of reinforcement. The vehicle-injected group developed SIP over sessions while each dose of apomorphine suppressed the acquisition of SIP. Bar-press rates were also depressed at the higher doses, while response patterning was affected at the lower dose. The results support the contention that a normally functioning dopamine system is necessary for the acquisition of SIP, but they do not support the view that this neurotransmitter system is specifically involved in the generation of SIP.