Voluntary consumption of amphetamine, cocaine, ethanol and morphine by rats as influenced by a preceding period of forced drug intake and clozapine.

Forced nicotine intake was previously found to decrease a subsequent free choice selection, whereas clozapine (CL) caused a marked increase in its consumption. Here these findings are extended to ethanol, cocaine, morphine and amphetamine. Forced intake of ethanol, cocaine, morphine and amphetamine had no major effect on a subsequent voluntary intake. CL, a dopamine D4 antagonist, increased the voluntary consumption of amphetamine and morphine with no effects on ethanol or cocaine intake. Only for cocaine was it found that low-consuming rats increased but high-consuming rats decreased their voluntary cocaine intake by CL. Thus, forced drug exposure per se does not lead to subsequent enhancement of voluntary intake; CL exerts differential effects on intake of these drugs, and a specific dopaminergic set point may govern the voluntary intake of cocaine by individual rats.