The effects of a single exposure to uncontrollable stress on the subsequent conditioned place preference responses to oxycodone, cocaine, and ethanol in rats
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Acute stress has been shown to facilitate the rewarding effects of a number of commonly abused drugs, although the stressor typically must be administered either immediately before or during drug administration and often in the same environment. We have previously reported that a single session of an uncontrollable (inescapable tailshock, IS), but not controllable (escapable tailshock, ES), stressor can enhance the conditioned place preference (CPP) response to morphine, even when stressor and drug administration are separated temporally and spatially. However, this persistent, trans-situational enhancement did not occur to amphetamine CPP.
The following experiments were conducted to determine whether the long-term effects of IS on drug reward are specific to opioids.
Materials and methods
Adult, male Sprague–Dawley rats were exposed to a single session of IS or remained in their home cages (HC). Twenty-four hours later, using an unbiased procedure, CPP conditioning was conducted with either oxycodone (0, 2, or 5 mg/kg, sc), cocaine (0, 1, 5, or 10 mg/kg, ip), or ethanol (0.3, 1, or 2 g/kg, ip). Another group of rats were exposed to IS, ES, or HC treatment and conditioned with oxycodone (5 mg/kg, sc) 24 h later.
IS enhanced the subsequent CPP response to oxycodone, but not cocaine or ethanol. This enhancement was dependent on the controllability of the stressor, as ES did not affect oxycodone CPP.
These results indicate that the long-term, trans-situational enhancing effect of uncontrollable stress on drug reward is specific to opioids.
KeywordsReward Uncontrollable stress Oxycodone Opioid Cocaine Psychostimulant Ethanol CPP Sensitization Rat
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