Antagonism of oxotremorine-induced behavioral suppression by antimuscarinic drugs.

The effects of benztropine, scopolamine, atropine, methylatropine, amitriptyline, phencyclidine, and meperidine were determined alone and in conjunction with a behaviorally suppressing dose (0.05 mg/kg IM) of oxotremorine in pigeons responding under a multiple fixed-ratio 30 fixed-interval 5-min schedule of grain presentation. Benztropine, scopolamine, atropine, and amitriptyline antagonized the behavioral suppressing effects of oxotremorine at doses that alone decreased responding. In contrast, methylatropine, phencyclidine, and meperidine did not antagonize the effects of oxotremorine. These results suggest that benztropine, scopolamine, atropine, and amitripytline decrease responding due to an action at central muscarinic receptors, whereas the behavioral effects of methylatropine, phencyclidine, and meperidine are due to actions other than at central muscarinic receptors.