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 leve ls of behavioral arousal-inhibition. Behavioral measures included transport response intensity, vertical cling catalepsy duration, and dorsal immobili ty duration. Atropine sulfate produced large increments in transport respon se intensities, and atropine methylnitrate produced intermediate effects, c ompared with saline-treated control rats. No drug effect was reported for t he measures of vertical cling catalepsy or dorsal immobility. Intraclass co rrelations among the various behavioral measures in this study revealed a r eliable relationship between dorsal immobility duration and transport respo nse intensity in the saline group. Administration of either the methylnitra te or sulfate solution negated this relationship. Results are discussed wit h respect to (a) possible mechanisms relating dorsal immobility and transpo rt response and (b) reasons for the loss of relationship between the two me asures with administration of atropine solutions.