Effects of raclopride in the nucleus accumbens on ethanol seeking and consumption

Background: Nucleus accumbens dopamine has been shown to play a role in the processing of behaviorally relevant stimuli and to mediate ethanol-reinfor ced responding. Previous research that used a fixed-ratio schedule of respo nding maintained by the presentation of small dippers (0.1 ml) of ethanol d emonstrated that the dopamine D-2 antagonist, raclopride, decreased total r esponding for ethanol by both delaying the onset of responding and causing the early termination of lever-press behavior. Because these studies requir ed animals to continuously respond to obtain access to small amounts of eth anol over a period of self-administration, this procedure assessed a combin ation of appetitive (seeking) and consummatory (drinking) behavior. The par adigm used in the present study separated the appetitive or seeking respons e from the consummatory response to assess the effects of raclopride on bot h types of ethanol-related behaviors. Methods: Male Long-Evans rats were trained to emit a fixed number of lever- press responses that resulted in access to a drinking tube that contained 1 0% ethanol for 20 min, once each day. We measured the effects of microinjec tions of raclopride (1.0, 3.0, and 10.0 mug/subject) into the nucleus accum bens, before the sessions, on appetitive and consummatory responding. Results: Raclopride delayed the onset of ethanol-seeking (appetitive respon ding) at all doses and decreased the number of responses made at the low an d high doses. The rate of responding, however, was unaffected. Raclopride h ad no effect on the latency to begin consuming ethanol or on any of the cha racteristics of the initial bout of ethanol intake at all doses tested. Tot al ethanol intake was decreased, after an initially "normal" pattern of sel f-administration, following only the highest dose of raclopride. Mean ethan ol intake (g/kg) was 0.54 (+/-0.03) after no injection, 0.51 (+/-0.04) afte r sham treatment, and 0.38 (+/-0.05) after 10 mug of raclopride. Conclusions: The procedural separation of the seeking and intake responses used in this experiment allowed us to assess the effects of dopamine recept or antagonism in the nucleus accumbens on these two different behaviors. Ov erall, appetitive responding that preceded the delivery of an ethanol solut ion was more sensitive to raclopride treatment than was consummatory respon ding. These findings are consistent with a stimulus-processing function of the mesolimbic dopamine system.