Conditioned taste aversion and operant behavior in rats: effects of cocaine, apomorphine and some long-acting...

Apomorphine and cocaine and their long-acting derivatives, diisobutyrylapomorphine and Win 35,428 (a fluorine-substituted phenyltropane analog of cocaine), were compared for their effects in producing conditioned taste aversions and altering schedule-controlled behavior in rats. The drugs had qualitatively similar effects in both types of experiments; suitable doses of each drug produced marked decreases in consumption of flavored solutions associated with their injection and suppressed key-press responding maintained under a 30-response fixed-ratio scheduled of food presentation. Potency ratios for apomorphine and cocaine relative to their long-acting derivatives were similar in both experiments; Win 35,428 was approximately 34 times more potent than cocaine, whereas apomorphine and diisobutyrylapomorphine did not differ appreciably in potency. Extending the duration of action of cocaine by administering an initial dose of 53 micromol/kg of cocaine followed by two additional doses of 26.5 micromol/kg at 30-min intervals failed to produce a greater degree of taste aversion than administration of only a single dose of 53 micromol/kg of cocaine. The observations with Win 35,428 and diisobutyrylapomorphine confirm previous work with these compounds and extend its generally to other species of animal and types of behaviors. None of the findings support the view that the potency of a drug in producing conditioned taste aversions is correlated with its duration of action.