Effects of scopolamine and unilateral lesions of the basal forebrain on T-maze spatial discrimination and alternation in rats

Abstract

Cholinergic systems are thought to play a role in memory. It has been suggested that cholinergic neurons, possibly the cortically projecting cells of the nucleus basalis magnocellularis, are differentially involved in working and reference memory. To evaluate this hypothesis the effects on memory of scopolamine (0, 0.3, 0.6 mg/kg) or unilateral kainic acid (4.7 nmoles in 1 microliter) lesions of the basal forebrain of rats were tested. Working memory, the recall of recent events of transient importance that is vulnerable to interference, was tested using a T-maze alternation task; reference memory, information stored over the long term that is relatively resistant to interference, was evaluated using a spatial discrimination task in the T-maze. The differential sensitivity of the two tasks to interference effects was confirmed by the finding that the insertion of a 30-sec delay between trials significantly reduced performance in the alternation but not the spatial discrimination task. Furthermore, scopolamine or the lesions significantly impaired alternation but not spatial discrimination performance. Biochemical assays of the kainate-injected brains confirmed that the cortical cholinergic marker, choline acetyltransferase, was significantly reduced. These results support the hypothesis that working and reference memory may be differentially controlled by cholinergic systems.