[Context-dependent sensitization: reconsideration and a hypothesis].

The repeated administration of amphetamine-like psychostimulants results in an augmentation of their behavioral responses, a phenomenon known as behavioral sensitization. One important factor associated with the process of behavioral sensitization is environmental influence. It has been reported that, when drug administration is paired with a particular environment, sensitization is observed only in that particular environment. This phenomenon has been known as context-dependent sensitization. However, considering recent reports and our own studies, the classical concept of context-dependent sensitization may not be satisfactory. We propose an alternative hypothesis. Psychostimulants are known to induce different behaviors in different environments. We believe that the repeated administration of a psychostimulant in different environments results in the augmentation of different behaviors. For instance, rats treated with a stimulant in a small cage did not locomote but were observed to sniff and rear. After repeated treatment, they showed sensitization not in locomotion but in stereotyped behaviors such as sniffing and rearing. This suggests that environment does not facilitate the development of sensitization, but rather modifies the pattern and character of a stimulant-induced behavior in the sensitized animals. In this paper, we briefly review various literature and present our hypothesis.