EFFECT OF 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 tolera nce to amphetamine-induced hypophagia. Rats were given intermittent in jections of either amphetamine (2.5 mg/kg) to induce sensitization of stereotypy, or saline. Subgroups from each group then received daily i njections of either amphetamine (2 mg/kg) or saline and access to milk for 30 min. Both sensitized and nonsensitized groups became tolerant to drug-induced hypophagia at about the same rate and to about the sam e extent. Such tolerance was accompanied by a decrease in the frequenc y of stereotyped movements while milk was available. The rats were the n given daily milk tests for 4 weeks without injections. Subsequent te sts with amphetamine revealed that both groups lost tolerance to drug- induced hypophagia and displayed more intense stereotypy than they had prior to drug withdrawal. We conclude that sensitization of stereotyp y produced by intermittent injections of amphetamine (2.5 mg/kg) does not retard the development of tolerance to drug-induced hypophagia and does not alter the rat's ability to suppress stereotyped movements. H owever, the loss of tolerance following drug withdrawal may have been due to the development of more intense stereotypy and/or the ''unlearn ing'' of previously acquired strategies for suppressing stereotypy.