Biphasic effects of 7-OH-DPAT on the acquisition of responding for conditioned reward in rats.
Previous studies have shown that dopamine (DA) receptor subtype-specific agonists differentially affect responding for conditioned reward D1-like agonists impair, whereas D2-like agonists enhance responding. The present study compared the effects of the D2-like agonists bromocriptine and 7-hydroxy-N,N-di-n-propyl-2-aminotetralin (7-OH-DPAT). Food-deprived rats (N=159) were preexposed to a chamber with two levers, one producing a tone (3 s) and the other turning the house lights off (3 s), for five 40-min sessions. In four subsequent 65-min conditioning sessions with the levers removed, the lights-off stimulus was paired with food (80 presentations per session). During two 40-min test sessions, the lights-off (CR) and tone (NCR) levers were replaced and responses at each lever were recorded. Confirming previous results, bromocriptine (0.50-5.0 mg/kg) dose-dependently enhanced responding on the lever producing conditioned reward. In contrast, 7-OH-DPAT had a biphasic effect on responding for conditioned reward. Low doses (0.10-0.25 mg/kg) reduced CR lever responding, whereas a higher dose of 1.0 mg/kg enhanced such responding. An intermediate dose of 0.50 mg/kg neither impaired nor enhanced CR lever responding. The biphasic profile of 7-OH-DPAT may arise through differential actions at D3 vs. D2 receptors or presynaptic vs. postsynaptic DA receptors at low and high doses, respectively.
Sutton
M A
MA
Department of Psychology, Queen's University, K7L 3N6, Kingston, ON, Canada.
Rolfe
N G
NG
Beninger
R J
RJ
D000818:Animals; D001971:Bromocriptine / Q000494:pharmacology; D003216:Conditioning, Operant / Q000187:drug effects*; D018491:Dopamine Agonists / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D008297:Male; D051381:Rats; D017208:Rats, Wistar; D017448:Receptors, Dopamine D2 / Q000819:agonists*; D012201:Reward; D013764:Tetrahydronaphthalenes / Q000494:pharmacology*
D018491:Dopamine Agonists; D017448:Receptors, Dopamine D2; D013764:Tetrahydronaphthalenes; D001971:Bromocriptine; C031349:7-hydroxy-2-N,N-dipropylaminotetralin