Rate-dependent effects of bupropion on nicotine self-administration and food-maintained responding in rats

Bupropion has been found to be a useful pharmaceutical agent in furthering smoking abstinence. Preclinical research investigating the effects of bupropion on nicotine self-administration has indicated bupropion has selective effects on nicotine self-administration. However since response rates maintained by nicotine were significantly lower than rates of response maintained by the non-drug reinforcers, bupropion may have resulted in rate-dependent effects. The current experiments attempted to decrease the high response rate maintained through non-drug reinforcers in order to have more comparable control rates when investigating the selectivity of bupropion for nicotine self-administration. The effects of bupropion on nicotine self-administration (0.03 mg/kg/inf) were compared to food-maintained responding at two levels of food deprivation (deprived and satiated). Rats were satiated prior to the experimental session in order to decrease the overall response rates maintained through food reinforcement. Bupropion increased nicotine intake, but dose-dependently decreased food intake, when rats were food-deprived. However, when more comparable rates of behavior in the food-satiated group were investigated, bupropion had similar effects on nicotine and food-maintained responding. The data indicate that the effects of bupropion can be influenced by the control rate of responding. The results from these experiments also indicate that bupropion may not exert a selective effect on nicotine self-administration, since low rates of food and drug maintained responding were increased by the drug. These results indicate the importance of controlling for differences in response rates when attempting to assess the effects of drugs on responding maintained by different reinforcers. Furthermore, the results from the present study suggest that motivational variables (i.e. food deprivation) may be used to control for response rate differences maintained by drug and non-drug reinforcers.