Aversive stimulus properties of scopolamine

The drug state produced in rats by intraperitoneal injections of scopolamine hydrobromide (1.2 mg/kg) was treated as a putative aversive US. This US was paired with a distinctive spatial location in a shuttle box for 6 of 12 daily sessions by confining the subject to one side following scopolamine and to the other side following saline (6 sessions). Two groups of 8 subjects each received zero and 20 min post-injection delays respectively. Following zero delay, but not 20 min delay, subjects avoided the side associated with scopolamine in drug-free, free choice tests. This is evidence that the immediate post-injection drug state induced by scopolamine is aversive.