NONHIPPOCAMPAL MUSCARINIC RECEPTORS ARE REQUIRED FOR NONSPATIAL WORKING-MEMORY

The effects of scopolamine on nonspatial working memory were examined in rats with hippocampal lesions and sham operations. Performance was examined using a continuous conditional discrimination task in an oper ant box. Choice accuracy measured nonspatial working memory. Response bias, delay interval responses, and response probability measured resp onse preference, stimulus control, motivation, and sensorimotor abilit y. Scopolamine (0.05, 0.075, 0.1, and 0.15 mg/kg) or methylscopolamine (0.1 mg/kg) was injected (IP) 15 min prior to behavioral testing. In both control and hippocampal lesioned groups, choice accuracy declined as the delay interval increased. Scopolamine, but not methylscopolami ne, produced a dose-dependent impairment of choice accuracy (interacti on of Dose x Delay) in both groups. The scopolamine-induced impairment was not different between the control and hippocampally lesioned rats . Response bias, delay interval responses, and response probability we re not affected by scopolamine except at the highest dose, which incre ased delay interval responses. The results suggest that central muscar inic receptors outside the hippocampus are important for working memor y of nonspatial stimuli. (C) 1997 Elsevier Science Inc.