Effect of prior sensitization of stereotypy on the acquisition and retention of tolerance to amphetamine hypophagia

The purpose of this study was to determine whether prior sensitization of stereotypy interferes with the development and retention of tolerance to amphetamine-induced hypophagia. Rats were given intermittent injections of either amphetamine to induce sensitization of stereotypy, or saline. Both sensitized and nonsensitized groups became tolerant to drug-induced hypophagia to the same degree. Such tolerance was accompanied by a decrease in the frequency of stereotyped movements while milk was available. After a 4 wk drug withdrawal period, both groups lost tolerance and displayed more intense stereotypy than they had prior to drug withdrawal. Therefore, sensitization of stereotypy did not retard the development of tolerance. However, the loss of tolerance following drug withdrawal may have been due to the development of more intense stereotypy and/or the "unlearning" of previously acquired strategies for suppressing stereotypy.