Previous exposure to cocaine enhances cocaine self-administration in an alpha 1-adrenergic receptor dependent manner.
Noradrenergic transmission is implicated in the biochemical and behavioral effects of cocaine. Recently, we demonstrated that the alpha 1-adrenergic receptor antagonist prazosin attenuates cocaine-induced reinstatement of drug-seeking behavior. We now assessed whether prazosin could counter the effect of previous exposure to cocaine to enhance subsequent self-administration behavior. Rats were pre-exposed to systemic injections of either saline, prazosin (0.3 mg/kg), saline+cocaine (10 mg/kg), or prazosin+cocaine for 5 days. Starting 15-18 days after the last pre-exposure injection, rats were trained to self-administer cocaine (0.5 mg/kg/infusion) under a fixed ratio 3 (FR3) schedule of reinforcement. Several tests were conducted. First, responding for cocaine under an FR3 schedule was assessed across several doses (0.125-1.0 mg/kg/infusion). Second, responding for cocaine (0.5 mg/kg/infusion) under a progressive-ratio (PR) schedule was examined for 6 consecutive days. Finally, responding for cocaine (0, 0.5, and 1.0 mg/kg/infusion) was determined under the PR schedule of reinforcement. Results showed that cocaine pre-exposed rats self-administer more cocaine compared to saline pre-exposed rats when tested under both the FR and PR schedules. Rats pre-exposed to cocaine plus prazosin did not show enhanced cocaine self-administration. These rats, as well those pre-exposed to prazosin alone, showed levels of cocaine self-administration similar to saline pre-exposed rats. Thus, previous exposure to cocaine enhanced cocaine self-administration, an effect that appears to involve activation of alpha 1-adrenergic receptors. These data, along with several recent studies, show further support for the contribution of noradrenergic transmission in the behavioral effects of cocaine.
Zhang
Xiang-Yang
XY
Division of Substance Abuse, Yale University School of Medicine, VA-CT Hospital System, West Haven, CT 06516, USA.
Kosten
Therese A
TA
D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D000831:Animals, Newborn; D001522:Behavior, Animal / Q000187:drug effects; D003042:Cocaine / Q000494:pharmacology*; D003216:Conditioning, Operant / Q000187:drug effects*; D018765:Dopamine Uptake Inhibitors / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D008297:Male; D011224:Prazosin / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D018340:Receptors, Adrenergic, alpha-1 / Q000502:physiology*; D012055:Reinforcement Schedule; D012646:Self Administration / Q000379:methods
D000317:Adrenergic alpha-Antagonists; D018765:Dopamine Uptake Inhibitors; D018340:Receptors, Adrenergic, alpha-1; D003042:Cocaine; D011224:Prazosin