Rationale Dopamine D2-like agonists maintain responding when substituted for cocaine in laboratory animals. However, these effects appear to be mediated by an interaction with stimuli that were previously paired with cocaine reinforcement (CS). Objectives To evaluate the extent to which the pramipexole-maintained and -induced responding are influenced by cocaine-paired stimuli. Methods Rats were trained to nosepoke for cocaine under fixed ratio 1 (FR1) or progressive ratio (PR) schedules of reinforcement. In FR1-trained rats, pramipexole was substituted for cocaine with injections either paired with CSs, or delivered in their absence. The capacity of experimenter-administered pramipexole to induce FR1 and PR responding for CS presentation was evaluated. The effects of altering stimulus conditions, as well as pretreatments with D2- (L-741,626) and D3-preferring (PG01037) antagonists on pramipexole-induced PR responding were also evaluated. Results When substituted for cocaine, pramipexole maintained responding at high rates when injections were paired with CSs, but low rates when CSs were omitted. Similarly, experimenter-administered pramipexole induced dose-dependent increases in FR1 or PR responding, with high rates of responding observed when the CS was presented, and low rates of responding when CS presentation was omitted. D2 and D3 antagonists differentially affected pramipexole-induced PR responding, with L-741,626 and PG01037 producing rightward, and downward shifts in the dose-response curve for CS-maintained responding, respectively. Conclusions These data indicate that pramipexole is capable of enhancing the reinforcing effectiveness of conditioned stimuli, and raise the possibility that similar mechanisms are responsible for the increased occurrence of impulse control disorders in patients being treated with pramipexole.

Recent mutagenesis studies have identified a mutant G4C/S10C/T172R/G173Q cocaine esterase (CCRQ CocE) with an in vitro duration of action of 440 days. Although the in vivo duration of CCRQ CocE's action was o24 h, modification of this enzyme with polyethylene glycol (PEG) polymers resulted in a CocE (PEG-CCRQ CocE) capable of preventing cocaine-induced lethality for up to 72 h. The current studies were aimed at providing a detailed characterization of the effectiveness, selectivity, and duration of PEG-CCRQ CocE's actions in cocaine self-administration and discrimination assays in rats. Pretreatment with PEG-CCRQ CocE produced dose-dependent rightward shifts in the dose-response curves for cocaine self-administration and discrimination, with the highest dose of PEG-CCRQ CocE capable of producing an initial shift of cocaine's reinforcing and interoceptive effects of 430-fold to the right, with significant inhibition of these effects observed for up to 72 h. Although PEG-CCRQ CocE also produced slight reductions in the rates of methylphenidate-and foodreinforced responding, these effects were short-lived, lasting o24 h. Finally, when taken together with the finding that PEG-CCRQ CocE failed to alter the cocaine-like interoceptive effects of either methylphenidate or d-amphetamine, these results suggest that PEG-CCRQ CocE possesses a high degree of pharmacologic specificity for cocaine and a prolonged in vivo duration of action. In conclusion, these studies provide strong evidence to support the further development of long-lasting, highly efficient CocEs, such as PEG-CCRQ CocE, as a potential therapeutic option for the treatment of cocaine abuse in humans.

Background A longer acting, double mutant bacterial cocaine esterase (CocE T172R/G173Q; DM CocE) has been shown to protect mice from cocaine-induced lethality, inhibit the reinforcing effects of cocaine in rats, and reverse cocaine’s cardiovascular effects in rhesus monkeys. The current studies evaluated the effectiveness of DM CocE to protect against, and reverse cocaine’s cardiovascular, convulsant, and lethal effects in male and female rats. Methods Pretreatment studies were used to determine the effectiveness and in vivo duration of action for DM CocE to protect rats against the occurrence of cardiovascular changes, convulsion and lethality associated with acute cocaine toxicity. Posttreatment studies were used to evaluate the capacity of DM CocE to rescue rats from the cardiovascular and lethal effects of large doses of cocaine. In addition, male and female rats were studied to determine if there were any potential effects of sex on the capacity of DM CocE to protect against, or reverse acute cocaine toxicity in rats. Results Pretreatment with DM CocE dose-dependently protected rats against cocaine-induced cardiovascular changes, convulsion and lethality, with higher doses active for up to 4 hrs, and shifting cocaine-induced lethality at least 10-fold to the right. In addition to dose-dependently recovering rats from an otherwise lethal dose of cocaine, post-treatment with DM CocE also reversed the cardiovascular effects of cocaine. There were no sex-related differences in the effectiveness of DM CocE to protect against, or reverse acute cocaine toxicity. Conclusions Together, these results support the development of DM CocE for the treatment of acute cocaine toxicity.