Motor activation by amphetamine infusion into nucleus accumbens core and shell subregions of rats differentially sensitive to dopaminergic drugs

Selective breeding based on activity in a swim test has been used to produc e lines of rats that show a high level of activity in the swim test (Swim H igh-active (SwHi) rats) and a low level of activity in the swim test (Swim Low-active (SwLo) rats). Previous studies have indicated that dopamine (DA) function is enhanced in SwHi rats and reduced in SwLo rats; a principal fi nding was that SwLo rats showed much smaller increases in ambulatory activi ty after systemic administration of amphetamine than did SwHi or non-select ed rats. In light of the importance of the nucleus accumbens (NAC) in amphe tamine-induced activity, the present study investigated whether DA function in NAC differs in SwHi and SwLo rats. Amphetamine was infused bilaterally into either the core or shell subregion of NAG, and ambulation or swim test activity was then measured. In SwLo rats, infusion of amphetamine (0.2-2.0 mu g) into either NAC core or shell produced moderate increases in ambulat ion. In SwHi rats, infusion of amphetamine into NAC shell produced similar moderate increases in ambulation, but infusion into the core produced marke dly larger dose-related increases in ambulation. In the swim test, infusion of amphetamine (1.0 mu g) increased activity by affecting the dominant beh avior of each line; i.e. struggling increased in SwHi rats and floating dec reased in SwLo rats, with large effects seen in both lines with infusion in to either NAC core or shell. These results support the idea that the distin ct behavioral characteristics of SwHi and SwLo rats are mediated in part by differences in NAC-DA function. (C) 1999 Elsevier Science B.V. All rights reserved.