Apomorphine-induced flavor-drug associations: a dose-response analysis by the taste reactivity test and the...

Apomorphine is a positively reinforcing drug at low to moderate doses, but appears to lose its reinforcing properties at higher doses. In Experiment 1, across a range of doses (0.5-15.0 mg/kg, intraperitoneally), apomorphine produced a CTA over 5 conditioning/testing trials which was not dose-dependent by a single bottle test. The rejection taste reactivity responses of chin rubbing and gaping, however, only occurred at the highest dose of apomorphine (15 mg/kg). In Experiment 2, a CTA test which was designed to more effectively discriminate among the different drug dose conditions indicated that the doses of 2.5, 7.5 and 15 mg/kg of apomorphine produce CTAs of equivalent strength. Our results support the contention that CTAs produced by positively reinforcing drugs are not accompanied by a palatability shift.