NICOTINE-INDUCED PLACE PREFERENCES FOLLOWING PRIOR NICOTINE EXPOSURE IN RATS

The motivational properties of morphine and nicotine were investigated in an automated conditioned place preference (CPP) procedure using a two-compartment apparatus. The accuracy of the photocell recording sys tem was assessed by correlation with direct observation. In a counterb alanced conditioning design, graded doses of morphine (0.1-3.2 mg/kg S C) produced dose-related CPP. Under similar conditions, a dose of nico tine (0.6 mg/kg SC) previously reported to produce CPP failed to show an effect. Increasing the number of conditioning trials from 4 to 12 d id not facilitate CPP with nicotine. After pretreatment with nicotine (0.4 mg/kg SC) daily for 7 days prior to conditioning, nicotine (0.4-0 .8 mg/kg) produced increasing magnitudes of CPP. Locomotor activity wa s assessed during both conditioning and extinction tests. During condi tioning, nicotine but not morphine decreased activity in the first con ditioning trial, but by the fourth trial, marked stimulation was appar ent following administration of either drug. Activity in the drug-pair ed compartment was not increased during tests for CPP carried out in t he undrugged state following 4 conditioning trials with either morphin e or nicotine, but there was evidence for conditioned hyperactivity af ter 12 conditioning trials with nicotine. The results suggest that mot ivational properties of nicotine can be detected in counterbalanced CP P procedures, but only in subjects with a history of nicotine exposure . The CPP produced by morphine or nicotine does not appear to be an ar tefact associated with conditioned changes in locomotor, activity.