title: Effects of dopamine D1-like and D2-like agonists in rats trained to discriminate cocaine from saline: influence of experimental history.
abstract: Effects of D1-like and D2-like agonists were compared in rats (Rattus norvegicus) with differing levels of experience (24 or 9 mo) in a cocaine discrimination procedure (5.6 mg/kg cocaine; fixed-ratio 20 schedule of food presentation). Cocaine, d-amphetamine, and D2-like agonists (quinelorane, 7-OH-DPAT) dose-dependently substituted for cocaine in both groups of rats. In contrast, D1-like agonists (SKF 82958, SKF 77434) substituted for cocaine only in rats with less discrimination experience. Pretreatment with D2-like agonists increased the stimulus effects of low cocaine-doses in both groups, whereas D1-like agonists produced these effects only in rats with less discrimination experience. The data suggest that the stimulus effects of cocaine overlap with those of D2-like agonists across a broader range of conditions than with those of D1-like agonists. Thus, D2-like receptors may play an especially important role in cocaine's behavioral effects.
authors.affiliation: Alcohol and Drug Abuse Research Center, McLean Hospital--Harvard Medical School, Belmont, Massachusetts 02478, USA.
authors.forename: S B
authors.initials: SB
authors.lastname: Caine
authors.forename: S S
authors.initials: SS
authors.lastname: Negus
authors.forename: N K
authors.initials: NK
authors.lastname: Mello
authors.forename: J
authors.initials: J
authors.lastname: Bergman
mesh_terms: D015647:2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-benzazepine / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D001552:Benzazepines / Q000494:pharmacology; D003042:Cocaine / Q000494:pharmacology*; D003913:Dextroamphetamine / Q000494:pharmacology; D004193:Discrimination Learning / Q000187:drug effects; D004192:Discrimination, Psychological / Q000187:drug effects*; D018491:Dopamine Agonists / Q000494:pharmacology*; D018765:Dopamine Uptake Inhibitors / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D017447:Receptors, Dopamine D1 / Q000819:agonists*; D017448:Receptors, Dopamine D2 / Q000819:agonists*; D013764:Tetrahydronaphthalenes / Q000494:pharmacology
chemical_list: D001552:Benzazepines; D018491:Dopamine Agonists; D018765:Dopamine Uptake Inhibitors; D017447:Receptors, Dopamine D1; D017448:Receptors, Dopamine D2; D013764:Tetrahydronaphthalenes; D015647:2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-benzazepine; C071262:SK&F 82958; D003042:Cocaine; C031349:7-hydroxy-2-N,N-dipropylaminotetralin; D003913:Dextroamphetamine; C067114:SK&F 77434