Effects of atropine on measures of behavioral arousal in rats

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.