Dopamine on D2-like receptors "reboosts" dopamine D1-like receptor-mediated behavioural activation in rats licking for sucrose.
BACKGROUND
The analysis of licking microstructure provides measures, such as duration and number of licking bouts, which might reveal the former an evaluation process and the latter an approach response. Dopamine D2-like receptor antagonists reduce the duration of licking bouts and mimic the effect of reducing sucrose concentration, while conflicting results are reported on the effects of dopamine D1-like receptor antagonists. The aim of this study is to examine the roles of dopamine D1-like and D2-like receptors in the activation of reward-associated responses and in reward evaluation, through the study of licking microstructure.


METHODS
The effects of the dopamine D2-like receptor antagonists raclopride (0.025-0.25 mg/kg), the D1-like antagonist SCH 23390 (0.01-0.04 mg/kg) and the antipsychotic drug haloperidol (0.02-0.05 mg/kg), have been examined on the microstructure of licking for a 10% sucrose solution in rats.


RESULTS
The results confirm that dopamine D2-like receptor antagonists reduce the duration of licking bouts and reveal that while SCH 23390 reduced licking exclusively by reducing bout number, raclopride produced on this measure an extinction mimicry effect similar to that observed in instrumental responding for different rewards.


CONCLUSIONS
These results are consistent with the hypothesis that the level of activation of the responses to the reward-associated cues depends on dopamine D1-like receptor stimulation, and is updated, or "reboosted", on the basis of a dopamine D2-like receptor-mediated evaluation process occurring during the consummatory transaction with the reward.
Dipartimento di Scienze del Farmaco, Università di Sassari, Via Muroni, 23/A, 07100 Sassari, Italy. dsfpaolo@uniss.it
Paolo S
PS
D'Aquila
D000818:Animals; D001552:Benzazepines / Q000008:administration & dosage / Q000494:pharmacology; D001696:Biomechanical Phenomena; D003463:Cues; D019422:Dietary Sucrose / Q000008:administration & dosage; D004298:Dopamine / Q000378:metabolism*; D018492:Dopamine Antagonists / Q000008:administration & dosage / Q000494:pharmacology; D065127:Dopamine D2 Receptor Antagonists; D004305:Dose-Response Relationship, Drug; D004326:Drinking / Q000187:drug effects / Q000502:physiology*; D004327:Drinking Behavior / Q000187:drug effects / Q000502:physiology*; D005108:Extinction, Psychological / Q000187:drug effects / Q000502:physiology; D006220:Haloperidol / Q000008:administration & dosage / Q000494:pharmacology; D008297:Male; D009042:Motivation / Q000187:drug effects / Q000502:physiology*; D020891:Raclopride / Q000008:administration & dosage / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D017447:Receptors, Dopamine D1 / Q000037:antagonists & inhibitors / Q000378:metabolism*; D017448:Receptors, Dopamine D2 / Q000378:metabolism*; D012201:Reward; D013997:Time Factors
D001552:Benzazepines; D019422:Dietary Sucrose; D018492:Dopamine Antagonists; D065127:Dopamine D2 Receptor Antagonists; D017447:Receptors, Dopamine D1; D017448:Receptors, Dopamine D2; C534628:SCH 23390; D020891:Raclopride; D006220:Haloperidol; D004298:Dopamine