Differential effects of intra-accumbens and systemic amphetamine on latent inhibition using an on-baseline,within-subject conditioned suppression paradigm

Latent inhibition (LI) is a phenomenon in which repeated, non-reinforced presentation of a stimulus retards subsequent conditioning to that stimulus. Several recent experiments have suggested that LI is abolished following acute, low doses of amphetamine given during pre-exposure and conditioning, and this effect has been attributed to amphetamine-induced changes in dopamine levels in the nucleus accumbens. Experiments 1 and 2 examined the effects of two doses of intra-accumbensd-amphetamine (10 µg/µl and 3 µg/µl) on LI in an on-baseline, within-subject conditioned suppression paradigm. There was no effect of either dose on LI, but a significant disinhibition of conditioned suppression resulted in a retardation of learning. In experiment 3 the effects of a low dose of systemicd-amphetamine (0.5 mg/kg) on latent inhibition were examined. The results replicated the abolition of LI found in previous studies, and demonstrated enhanced post-shock suppression in amphetamine-treated animals. These data provide no evidence for the involvement of the mesolimbic dopamine system in LI.