Bromocriptine enhancement of responding for conditioned reward depends on intact D1 receptor function.
It has been suggested that reward-related learning may require intact functioning at the dopamine D1 receptor. The present experiment tested this hypothesis by challenging the reward-enhancing effects of the D2 agonist, bromocriptine, with a D1 antagonist, SCH 23390. For comparison, the effects of the D2 antagonist, pimozide, were also evaluated. Male rats (n = 240) were pre-exposed to a chamber with two levers, one producing a 3-s lights-off stimulus and the other a 3-s tone stimulus. Four conditioning sessions followed, during which levers were absent and presentations of the lights-off stimulus were paired with food. Testing consisted of comparing presses on each lever after conditioning to before conditioning for each rat. Control groups showed a significantly greater increase in responding for lights-off than tone, indicating that the lights-off stimulus had become a conditioned reward. Results showed that bromocriptine (0.25-10.0 mg/kg, IP, 60 min before test session) enhanced responding at doses of 2.5 and 5.0 mg/kg significantly more on the conditioned reward lever than on the other lever. The lowest dose of SCH 23390 (1.0 microgram/kg, SC, 2 h before testing) eliminated the bromocriptine-produced enhancement at 2.5 mg/kg and a significant enhancement was seen at 10.0 mg/kg. The higher doses of SCH 23390 (5.0 and 10.0 micrograms/kg) eliminated the bromocriptine effect and the conditioned reward effect itself, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)
Ranaldi
R
R
Department of Psychology, Queen's University, Kingston, Ontario, Canada.
Beninger
R J
RJ
D000704:Analysis of Variance; D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects*; D001971:Bromocriptine / Q000494:pharmacology*; D003216:Conditioning, Operant; D004305:Dose-Response Relationship, Drug; D007858:Learning; D008297:Male; D051381:Rats; D017208:Rats, Wistar; D017447:Receptors, Dopamine D1 / Q000187:drug effects* / Q000502:physiology
D017447:Receptors, Dopamine D1; D001971:Bromocriptine