Effects of repeated morphine deprivation on operant responding in rats.

Abstract

These studies determined the effects of repeated morphine deprivation on behavior maintained by various reinforcers in the rat. A morphine dosing schedule was designed and characterized to establish and maintain dependence while allowing for repeated observation of behavior during morphine deprivation-induced withdrawal. Self-administration of the mu-opioid agonist remifentanil was assessed in nondependent (morphine-naive) rats and compared with self-administration in morphine dependent and deprived groups. Morphine deprivation was found to enhance remifentanil self-administration. The selectivity of this effect was assessed by evaluating the effects of morphine deprivation on behavior maintained by cocaine and two food reinforcers. Deprivation did not alter cocaine self-administration; however, deprivation did enhance behavior maintained by both food reinforcers. The increase in food-maintained behavior observed in the deprived group was likely due to morphine induced food deprivation and consequent weight loss throughout the experiment. Finally, to further characterize morphine deprivation-induced changes on the reinforcing effectiveness of remifentanil, economic demand was determined in dependent and nondependent groups of rats. Compared with nondependent rats, morphine-deprived rats demonstrated less elastic demand for remifentanil indicating that deprivation increased its reinforcing effectiveness. These studies provide evidence that morphine dependence and deprivation enhances the reinforcing properties of remifentanil.Ph.D.Health and Environmental SciencesPharmacologyPsychobiologyPsychologyUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/126394/2/3253247.pd