Once is too much: conditioned changes in accumbens dopamine following a single saccharin-morphine pairing.
The present study tested whether presentation of a taste cue would support conditioned suppression of dopamine in the nucleus accumbens (NAcc) following a single taste-drug pairing. Nondeprived male Sprague-Dawley rats were given 20-min access to a 0.15% saccharin conditioned stimulus (CS). Immediately thereafter, experimental rats were injected with morphine (15 mg/kg ip); standard controls were injected with saline; and explicitly unpaired controls were injected with morphine, but approximately 24 hr later. All rats were then given one 20-min CS-only test. Microdialysis samples from the NAcc were measured over 20-min intervals before, during, and after CS access on the conditioning and test trial. The results showed that a single saccharin-morphine pairing led to a marked reduction in CS intake, and the reduction in intake was accompanied by a conditioned blunting of the accumbens dopamine response to the saccharin reward cue. In turn, a single exposure to the saccharin cue also blunted the unconditioned dopamine response to morphine. Reward comparison effects, then, are cross-modal, bidirectional, and immediate, resulting in both unconditioned and conditioned changes in brain and behavior.
Grigson
Patricia Sue
PS
Department of Neural and Behavioral Sciences, Pennsylvania State University College of Medicine, Hershey, PA 17033, USA. psg6@psu.edu
Hajnal
Andras
A
D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects; D003213:Conditioning, Psychological / Q000187:drug effects* / Q000502:physiology; D004298:Dopamine / Q000378:metabolism*; D008297:Male; D017551:Microdialysis / Q000379:methods; D009020:Morphine / Q000494:pharmacology*; D009294:Narcotics / Q000494:pharmacology*; D009714:Nucleus Accumbens / Q000187:drug effects*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012439:Saccharin / Q000008:administration & dosage*; D013549:Sweetening Agents / Q000008:administration & dosage*; D013997:Time Factors
D009294:Narcotics; D013549:Sweetening Agents; D009020:Morphine; D012439:Saccharin; D004298:Dopamine