ROSTRAL-CAUDAL DIFFERENCES IN EFFECTS OF NUCLEUS-ACCUMBENS AMPHETAMINE ON VTA ICSS

The effects of amphetamine along the rostrocaudal axis of the nucleus accumbens (NAcc) on ventral tegmental area (VTA) intracranial self-sti mulation (ICSS) were studied. Eighteen rats were trained to lever pres s for ICSS in the VTA. Rate-frequency functions were determined by log arithmically decreasing the frequency of cathodal pulses in a stimulat ion train from a value that induced maximal responding to one that ind uced no responding (thresholds), After ICSS thresholds stabilized, (+) -amphetamine (20.0 mu g/0.5 mu l) or its vehicle, distilled H(2)0 (0.5 mu l), were injected directly into the rostral NAcc (n = 6) or the ca udal NAcc (n = 8) or the caudate-putamen (CP) (n = 5) just dorsal to t he caudal NAcc. Results showed that amphetamine in the caudal NAcc sig nificantly decreased ICSS thresholds without affecting asymptotic rate s of responding, indicating a potentiation of the rewarding efficacy o f VTA stimulation. Amphetamine in the rostral NAcc or CP produced smal ler, non-significant, decreases in ICSS thresholds. Further analyses r evealed a significant positive correlation (r(13) = 0.51, P < 0.05) be tween the site of injection along the rostrocaudal axis of the NAcc an d the size of the amphetamine-produced potentiation of VTA stimulation reward. Others have reported topographical differences, including dop amine terminal density and D-1 receptor density, in the NAcc. The pres ent results indicate that these anatomical and neurochemical differenc es appear to be correlated with behavioural differences.