SCOPOLAMINE ADMINISTRATION AND NBM LESIONS DIFFERENTIALLY AFFECT PERFORMANCE IN AN OPERANT DISCRIMINATION TASK

Effects of cholinergic modulation on differential conditioning perform ance in rats were evaluated in four experiments. Animals were first tr ained on an operant discrimination task. In Experiment 1, performance was evaluated following different doses of physostigmine (PHY) or scop olamine (SCO). SCO impaired performance in a dose-dependent manner; do ses causing moderate impairment were selected for the remainder of the study. In Experiment 2, to test effects of PHY on SCO-impaired animal s, rats were tested with injections of SCO (0.125 mg/kg) plus saline, injections of SCO (0.125 mg/kg kg) plus PHY (0.03125 mg/kg), or two in jections of saline. SCO reduced total responding, but PHY failed to at tenuate the effect. Although SCO decreased performance, response patte rns suggested that discrimination ability per se was unaffected. In Ex periment 3, animals were given bilateral lesions of the nucleus basali s magnocellularis (NBM); performance was reassessed with or without PH Y (0.03125 mg/kg) or SCO (0.125 mg/kg). Lesions alone did not affect t otal responding; but discrimination ability was impaired, as reflected by reduced successes and increased errors. As in Experiment 2, SCO re duced responding without affecting discrimination ability, but PHY did not improve SCO-impaired task performance. Ln Experiment ii, 12 month s after lesions, nondrug performance of animals was reassessed. Contro l animals showed recovery after one session, whereas lesioned animals took four sessions to show recovery.