Intravenous Scopolamine Is Potently Self-Administered in Drug-Naive Mice

Scopolamine self-administration was investigated in an acute model using drug-naive mice. The mice could self-administer intravenous infusions contingent on nose poking and were tested in pairs using a contingent and a yoked control mouse. Upon nose poking of the contingent mouse, both mice received an intravenous infusion of either saline or scopolamine (fixed ratio 1). An inverted U-shaped unit dose-response curve was seen with the contingent mice. The unit dose at which nose poking of the contingent mice peaked (mean 375 per 30 min) was 0.1 mg/kg/infusion. Nose poking of yoked control mice also increased dose dependently, but it was significantly lower than that of the contingent mice. The apparent scopolamine-induced dose-dependent hyperactivity was, however, unlikely in itself to form the entire basis for the increase in nose poking of the contingent mice. The results demonstrate that scopolamine has acute and reinforcing properties in drug naive mice.