ABSTRACT
Two experiments investigated the mechanism for changes in measures of behavioral arousal inhibition in rats following administration of atropine. In Experiment 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 both together increased dorsal immobility durations. In Experiment 2, rats were given atropine, the beta-adrenergic antagonist propranolol, the alpha-adrenergic antagonist phentolamine, or a combination of two of the drugs. Propranolol blocked atropine-induced increases in transport response, and phentolamine was without effect. Phentolamine, when combined with atropine, increased dorsal immobility durations. Results are discussed with respect to aspects common to both transport response and dorsal immobility.
Subject(s)
Adrenergic alpha-Antagonists/pharmacology , Adrenergic beta-Antagonists/pharmacology , Arousal/drug effects , Atropine/pharmacology , Animals , Drug Synergism , Labetalol/pharmacology , Motor Activity/drug effects , Phentolamine/pharmacology , Propranolol/pharmacology , Rats , Rats, Sprague-DawleyABSTRACT
Forty-day-old rats were given varying doses (0.0, 7.5, or 15.0 mg/kg/5 ml) of atropine sulfate or atropine methylnitrate and then were tested for levels of behavioral arousal-inhibition. Behavioral measures included transport response intensity, vertical cling catalepsy duration, and dorsal immobility duration. Atropine sulfate produced large increments in transport response intensities, and atropine methylnitrate produced intermediate effects, compared with saline-treated control rats. No drug effect was reported for the measures of vertical cling catalepsy or dorsal immobility. Intraclass correlations among the various behavioral measures in this study revealed a reliable relationship between dorsal immobility duration and transport response intensity in the saline group. Administration of either the methylnitrate or sulfate solution negated this relationship. Results are discussed with respect to (a) possible mechanisms relating dorsal immobility and transport response and (b) reasons for the loss of relationship between the two measures with administration of atropine solutions.
