The effects of ibotenic acid lesions of the basal forebrain on visual discrimination performance in rats

Rats were trained to stable performance in a conditional brightness discrimination task and then received infusions of ibotenic acid or vehicle into the basal forebrain. Following 2 weeks of recovery, animals were retested in the original discrimination. Lesioned rats tended to performed badly on the first day of testing as measured by all parameters (percent correct responding, latency to respond, and missed trials) but thereafter, most rats recovered quickly to prelesion levels. In keeping with previous reports, an approximately 30% reduction in choline acetyltransferase activity was observed in the lesioned animals. Four rats showed no recovery over a period of several months; however, an analysis of the choline acetyltransferase in several brain regions revealed no obvious differences to those animals in which performance recovered. Postlesion testing with the putative nootropic beta-carboline ZK 93426 showed no major differences to the effects observed in control animals. Scopolamine had similar negative effects in both groups tested. These data indicate that deficits induced by lesions of the basal forebrain do not correlate with reductions in cholinergic activity.