Break-points on a progressive ratio schedule reinforced by intravenous cocaine increase following depletion of forebrain serotonin.
The effect of intracerebral injections of 5,7-dihydroxy-tryptamine (5,7-DHT) on cocaine self-administration behavior was assessed. Rats were tested on a progressive ratio (PR) schedule for cocaine reinforcement. The first response on the lever each day produced an IV infusion of cocaine (0.6 mg/injection) after which the requirements of the schedule escalated with each reinforcement until the behavior extinguished. The final ratio completed was defined as the breaking point. Bilateral injections of 5,7-DHT into either the medial forebrain bundle (MFB) or amygdala (AMY) significantly increased the breaking points on the PR schedule compared to vehicle-injected control animals. We interpret these data to indicate that depletion of forebrain serotonin increases the incentive value of cocaine.
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Department of Psychology, Carleton University, Ottawa, Canada.
Roberts
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D015116:5,7-Dihydroxytryptamine / Q000494:pharmacology; D000679:Amygdala / Q000187:drug effects / Q000502:physiology; D000818:Animals; D015306:Biogenic Monoamines / Q000378:metabolism; D001923:Brain Chemistry / Q000187:drug effects*; D003042:Cocaine / Q000494:pharmacology*; D003216:Conditioning, Operant / Q000187:drug effects; D007267:Injections; D007275:Injections, Intravenous; D008297:Male; D008474:Medial Forebrain Bundle / Q000187:drug effects; D051381:Rats; D011919:Rats, Inbred Strains; D012055:Reinforcement Schedule; D012701:Serotonin / Q000378:metabolism*
D015306:Biogenic Monoamines; D015116:5,7-Dihydroxytryptamine; D012701:Serotonin; D003042:Cocaine