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Synthetic cathinones, such as 3,4-methylenedioxypyrovalerone (MDPV), are recreational drugs of abuse often identified in 'bath salts' preparations. Humans report compulsive patterns of bath salts use, and previous work suggests that a subset of rats develop unusually high levels of MDPV self-administration. This study aims to test the hypothesis that high levels of impulsivity (e.g., inability to withhold responding for a sucrose reward) will predispose rats to high levels of MDPV self-administration relative to rats with lower levels of impulsivity. The 1-choice serial reaction time task (1-CSRTT) was used to assess impulsivity (i.e., premature responding) in 10 female and 10 male Sprague Dawley rats. Rats were then allowed to self-administer 0.032 mg/kg/inf MDPV or 0.32 mg/kg/inf cocaine, after which full dose-response curves for MDPV (0.001-0.1 mg/kg/inf) or cocaine (0.01-1 mg/kg/inf) were generated under a FR5 schedule of reinforcement. After a history of self-administering MDPV or cocaine, impulsivity was reassessed under the 1-CSRTT, prior to evaluating the acute effects of MDPV (0.032-0.32 mg/kg) or cocaine (0.1-1 mg/kg) on impulsivity. Level of impulsivity was not correlated with subsequent levels of either MDPV or cocaine self-administration, and level of drug self-administration was also not correlated with subsequent levels of impulsivity, although acute administration of MDPV and cocaine did increase premature responding. In failing to find direct relationships between either impulsivity and subsequent drug-taking behaviour, or drug-taking behaviour and subsequent assessments of impulsivity, these findings highlight the complexity inherent in the associations between impulsive behaviour and drug-taking behaviour in both animal models and humans. [ABSTRACT FROM AUTHOR]

Recent estimates suggest increased popularity of the concurrent use of opioids and stimulants, with over 50% of treatment-seeking opioid users reporting regular stimulant use. The goal of the current study was to determine how opioid dependence and withdrawal affect the reinforcing effects of fentanyl, cocaine, and methamphetamine. Male Sprague-Dawley rats were allowed to self-administer fentanyl under a progressive ratio (PR) schedule of reinforcement. Baseline evaluations of reinforcing effectiveness of fentanyl, cocaine, and methamphetamine were determined. Opioid dependence was then established by administering escalating doses of morphine (10-40 mg/kg) twice-daily for four days and subsequently maintained by once-daily injections of 40 mg/kg morphine. To evaluate the impact of opioid dependence and withdrawal on the self-administration of fentanyl, cocaine, and methamphetamine, sessions occurred either 12 or 20 h after the morphine, respectively. During opioid withdrawal, the fentanyl dose-response curve was shifted rightward with an increase in maximal effectiveness, whereas it was shifted rightward with a reduction in maximal effectiveness when evaluated in rats currently dependent on opioids, relative to baseline. The reinforcing effects of cocaine and methamphetamine were unchanged by either condition. The current studies provide direct evidence that the reinforcing effects of fentanyl are increased in opioid-withdrawn rats and reduced in opioid-dependent rats, relative to rats that are not physically dependent on opioids. These findings suggest that motivations to use opioids are dependent on the state of the individual whereas stimulants retain their reinforcing effects regardless of whether the individual is in an opioid-dependent or withdrawn state., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2021 Seaman Jr and Collins.)