Modification of novelty preferences in rats by current and prior treatment with scopolamine and methylscopolamine.

Two experimental paradigms were adopted to compare effects of scopolamine and its quaternary derivative, methylscopolamine, on the behaviour of albino rats in an exploration box comprising novel and familiar halves. Subjects tested with the first paradigm were exposed to one of the halves, injected and then observed 20 min later. Although both drugs reduced preferences for the previously inaccessible novel half, only scopolamine decreased rearing and increased ambulation. With the second paradigm, behaviour was assessed without any current drug influence. On the 2 days prior to testing the rats had been exposed to one half of the apparatus while drugged. Prior treatment with both scopolamine and methylscopolamine reduced novelty preference to the extent that the familiar half of the apparatus was preferred. Both drugs also reduced rearing (for females only) and ambulation. It was concluded that the results with both paradigms provided some support for the view that reductions in novelty preference by anticholinergic drugs arise from their aversive peripheral actions.