Scopolamine increases nonreinforced behavior in an intracranial self-stimulation discrimination paradigm

The effects of several doses of systemic scopolamine administration on brain-stimulation reward from the A10 nucleus of the ventral tegmental area (VTA) were evaluated. The intracranial self-stimulation (ICSS) task involved a two-hole nose-poke procedure allowing for the assessment of both reinforced (correct) and nonreinforced (incorrect) performance levels as a function of varying current intensities. Scopolamine (0.75, 1.5, and 3.0 mg/kg) was found not to alter the rate-intensity functions derived from descending and ascending presentation of seven current levels. However, when nonreinforced behavior was considered significant increases in error responding were evident following scopolamine injection. These results are consistent with the known disinhibitory and perseverative properties of scopolamine, and indicate that the previously reported positive actions of peripheral administration of anticholinergic drugs on ICSS likely involved a drug-induced rate-enhancement of reward-unrelated performance variables.