The effects of atropine and adrenergic antagonists on behavioral arousal in rats

Two experiments investigated the mechanism for changes in measures of behav ioral arousal inhibition in rats following administration of atropine. In E xperiment 1, 40-day-old rats were given administrations of atropine sulfate , the alpha-, beta-adrenergic blocker labetalol, or both. The drugs, either alone or in combination, increased transport response intensity, whereas b oth together increased dorsal immobility durations. In Experiment 2, rats w ere given atropine, the beta-adrenergic antagonist propranolol, the a-adren ergic antagonist phentolamine, or a combination of two of the drugs. Propra nolol blocked atropine-induced increases in transport response, and phentol amine was without effect. Phentolamine, when combined with atropine, increa sed dorsal immobility durations. Results are discussed with respect to aspe cts common to both transport response and dorsal immobility.