Effect of atropine on behavioral arousal in the developing rat.

Atropine-induced changes in behavioral arousal were examined in the developing rat between 21 and 40 days of age using a single exploratory trial on an elevated T-maze. Under atropine (10 mg/kg, i.p.) spontaneous activity as measured by numbers of errors, rearing responses, and stereotyped responses was significantly decreased in animals less than 25 days of age. It was significantly increased, however, between 26 and 30 days, with maximal action on the 28th day. After 30 days the effect of atropine was negligible. These results support the hypothesis of a cholinergic inhibitory mechanism controlling behavioral arousal and becoming efficient after the 25th day of life.