Lack of effect of choline and narcotic antagonists upon apomorphine discrimination

Rats were trained to discriminate between the stimulus properties of intraperitoneal 0.16 mg/kg apomorphine and saline in a two-lever, food-motivated operant task. Subjects were then injected with either 79 mg choline chloride, 0.02 mg/kg haloperidol, 10 mg/kg naloxone or 10 mg/kg naltrexone prior to apomorphine or saline discriminative testing. Only haloperidol pretreatment was observed to significantly alter the rats' ability to discriminate apomorphine. The results are discussed in relation to the possible mechanism(s) of action of narcotic antagonist and cholinomimetic drug effects upon dopaminergically mediated behaviors.