Previous experience disrupts atropine-induced stereotyped "trapping" in rats

Three experiments were conducted to investigate the phenomenon of atropine-induced stereotypic trapping in rats reported by Schallert, De Ryck, and Teitelbaum (1980). The first two showed that such trapping was disrupted by previous experience with the specific trapping task or the test context alone. The third showed that, in response to the test context, specific behaviors were altered in rats experienced with the context. Inexperienced atropine-treated animals moved slowly and showed a strong thigmotaxis to surfaces with the body and particularly the snout. The hindquarters did not cooperate well with the movements of the forequarters. In contrast, atropine-treated animals familiar with the context moved with medium-speed, coordinated movements, were independent of surface contact with body and snout, and the hindquarters cooperated fully with forequarter movements. These reactions of drugged animals were exaggerated forms of those of undrugged animals to the unfamiliar and familiar context, respectively. Thus, atropine enhances the reactions of the rat to both a novel and a familiar environment. The enhanced reactions to a novel environment appear as stereotyped behaviors that trap the animal in particular configurations of surfaces. The enhanced reactions to a familiar environment abolish the stereotypic trapping normally produced by atropine. This pattern of results indicates that it is not atropine per se that leads to trapping. Rather, stereotypic trapping develops as a consequence of an interaction between the adaptive responses of the rat to a novel environment and atropine.