Effects of dopamine depletion from the caudate-putamen and nucleus accumbens septi on the acquisition and performance of a conditional discrimination task.

Three experiments compared the effects of dopamine depletion from the caudate-putamen (CAUD; dorsal striatum) or nucleus accumbens septi (NAS; ventral striatum), or a systemically administered dopamine receptor antagonist (alpha-flupenthixol) on the acquisition and performance of a conditional discrimination task involving temporal frequency. In Expt. 1, rats receiving 6-hydroxydopamine (6-OHDA) lesions of the CAUD were impaired in the acquisition of a visual version of the task, and rats with 6-OHDA lesions of the NAS were not reliably impaired. Even when the rats with CAUD lesions had acquired the discrimination, they were still significantly slower to collect earned food pellets. Both CAUD and NAS lesions reduced a bias to respond to the faster of the two discriminative stimuli. In Expt. 2, rats with 6-OHDA lesions of CAUD were markedly impaired in their accuracy and speed of responding when they had been trained to criterion preoperatively. These effects could not be mimicked in controls by prefeeding (which had only minor effects on performance). Rats with 6-OHDA-induced lesions of the NAS were unimpaired in either visual or auditory discrimination performance, but were slower to extinguish responding than controls. In Expt. 3, alpha-flupenthixol (0.1-0.56 mg/kg, i.p.) produced dose-dependent impairments in both latency to respond and choice accuracy in visual and auditory versions of the task. In conjunction with other results, these data suggest that (1) dopamine receptor blockade and central dopamine depletion can impair discrimination performance under certain conditions (2) dopamine depletion from the ventral and dorsal striatum, respectively, have dissociable effects on behaviour controlled by conditioned reinforcers and discriminative stimuli and (3) the disruption of discrimination performance by dorsal striatal dopamine depletion is probably attributable to several factors.