Scopolamine induced changes in activity and reactions to novelty.

The behavior of hooded rats was observed in an exploration box comprising novel and familiar halves following IP injections of 0.1, 0.25, 0.5, 0.75 or 1.00 mg/kg scopolamine or isotonic saline. Drug administration occurred after, rather than before, exposure to one of the alternative halves. All doses decreased reactions to the previously inaccessible novel half but decreases were greater for the 2 lowest doses. Rearing behavior was also suppressed by each dose whereas the number of apparatus cells entered (locomotion) was decreased by low doses but increased by high. The 3 behavioral measures showed declines in frequency during the course of each experimental session. However, low doses of the drug enhanced and high doses retarded these declines for rearing and cells entered. The study illustrated the difficulty in explaining data by unitary processes (such as attenuated habituation) when several behavioral indices and drug doses are employed within a single investigation.