A delicate balance between dopaminergic and cholinergic activity in the ventral striatum or nucleus accumbens (N.Acc) appears to be important for optimal performance of a wide range of behaviours. While functional interactions between these systems are complex, some data suggest that acetylcholine in the N.Acc. may dampen the effects of excessive dopamine (DA) release. We proposed that a reduction in the density of cholinergic interneurons in the N.Acc would result in behavioural alterations suggestive of a hyper-responsiveness of the N.Acc DA system. The present study aimed to produce a sustainable depletion of cholinergic neurons in the N.Acc in the rat and study the effects of such lesions on DA-dependent behaviour. A novel saporin immunotoxin targeting choline acetyltransferase was microinjected bilaterally into the N.Acc of adult rats. We confirmed histologically that two weeks post-injection, animals show a local, selective depletion of cholinergic interneurons (mean cell loss of 44%). Cholinergic-depleted rats showed a marked increase in the locomotor activating effects of amphetamine. In addition, such lesions induced a disruption of sensorimotor gating processes, reflected in a reduction in the prepulse inhibition of the acoustic startle response, which was reversed by haloperidol. These data are suggestive of pronounced hyper-responsiveness of the meso-accumbens DA system which may be of relevance to the pathophysiology of schizophrenia, a condition where selective reduction in the number of ventral striatal cholinergic neurons has been demonstrated.