Context determines the type of sensitized behaviour: a brief review and a hypothesis on the role of environment in behavioural sensitization

Behavioural sensitization to psychostimulants may develop context-dependenc y in certain circumstances. Animals given a stimulant repeatedly in a test cage but not in other environments may show enhanced drug-induced behaviour in the test cage. Conditioning mechanisms have been claimed to be responsi ble for these phenomena. However, several recent findings are not properly accounted for by conditioning. In addition, growing evidence supports the h ypothesis that behavioural sensitization reflects neural changes induced by repeated exposure to psychostimulants (the pharmacological hypothesis). Ho wever, the pharmacological hypothesis itself fails to account for environme ntal influences. In this paper, we propose a hypothesis on the role of envi ronment that is complementary to the pharmacological hypothesis. According to our hypothesis, environment does not have a causal role in the developme nt of sensitization, but it modifies the mode of expression of the sensitiz ed behaviour. Sensitization primarily reflects a neuroadaptive change induc ed by repeated exposure of the neural system to psychostimulants. However, psychostimulants are known to induce different behaviours in different envi ronments. Therefore, repeated administration of a psychostimulant in differ ent environments would result in augmentation of different behaviours. Our hypothesis potentially accommodates various previous observations. We brief ly review the literature and present our hypothesis. (C) 2000 Lippincott Wi lliams & Wilkins.