Date of this Version
Published in final edited form as: Behavioral Pharmacology 2014 August ; 25(4): 277–286. doi:10.1097/FBP.0000000000000047.
Previous studies have reported that context can powerfully modulate the inhibitory effect of an antipsychotic drug on phencyclidine (PCP)-induced hyperlocomotion (a behavioral test used to evaluate putative antipsychotic drugs). The present study investigated the experimental conditions under which environmental stimuli exert their influence through associative conditioning processes. Experiment 1 examined the extent to which prior antipsychotic treatment in the home cages affected a drug’s ability to inhibit PCP-induced hyperlocomotion in a novel motor activity test apparatus. Five days of repeated haloperidol (0.05 mg/kg, sc) and olanzapine (2.0 mg/kg, sc) treatment in the home cages still potentiated their inhibition of PCP-induced hyperlocomotion (i.e. sensitization) assessed in a new environment, whereas the clozapine (10.0 mg/kg, sc) treatment enhanced the development of clozapine tolerance, indicating a lack of environmental modulation of antipsychotic efficacy. Experiment 2 assessed the impact of different numbers of antipsychotic administrations in either the home environment or test environment (e.g. 4, 2 or 0) on a drug’s ability to inhibit PCP-induced hyperlocomotion. Repeated administration of clozapine (5.0 mg/kg, sc) or olanzapine (1.0 mg/kg, sc) for 4 consecutive days, regardless of where these treatments occurred, caused a similar level of inhibition on PCP-induced hyperlocomotion. However, 4-day haloperidol (0.03 mg/kg, sc) treatment in the test apparatus caused a significant higher inhibition than 4-day home cage treatment. Thus, more exposures to the test environment under the influence of haloperidol (but not clozapine or olanzapine) cause a stronger inhibition than fewer exposures, indicating a strong environmental modulation. Collectively, these findings suggest that prior antipsychotic treatment in one environment could alter later antipsychotic-like response assessed in a different environment under certain test conditions. Therefore, whether the circumstances surrounding antipsychotic drug administration exert a powerful control of the expression of antipsychotic-like efficacy is dependent on specific experimental and drug treatment factors.