Cannabinoid agonism via WIN 55,212-2 did not impair auditory discrimination in rats. Twenty-two rats were trained to press a lever for sucrose in response to either a pure tone or white noise, with correct responses reinforced and incorrect ones punished. After reaching criterion, they received 1.2 mg/kg, 3 mg/kg, or saline. On day 3, active lever-pressing was higher in both dose groups compared to saline, but overall pressing decreased over time in the high-dose group. No effects on discrimination or errors were observed, indicating that cannabinoid agonism did not negatively affect auditory discrimination, contrary to some previous findings.
Nicotine and phencyclidine (PCP) each separately increased rats' lever-pressing for a brief visual stimulus, indicating a reinforcement-enhancement effect. The effect was dose-dependent for nicotine (0.2 or 0.4 mg/kg) and present with PCP (2.0 mg/kg) across increasing fixed-ratio schedules. Adding PCP to nicotine did not further increase lever-pressing, possibly due to a ceiling effect. PCP's effect appeared driven largely by locomotor stimulation, whereas nicotine's effect was independent of locomotor activity. This dissociation suggests that different pharmacological properties underlie the reinforcement-enhancement effects of these substances.