INFLUENCE OF OPIOID SYSTEM ON BEHAVIORAL SENSITIZATION INDUCED BY COCAINE IN THE RAT

In rats, repeated daily ip administrations of a low dose (10 mg/kg) of cocaine HCl (COC) produced enhanced locomotor activity; a higher dose (50 mg/kg) led to seizures (pharmacological kindling). Daily pretreat ment with naltrexone (NTX)(2 mg/kg/sc), injected 15 min prior to COC, completely antagonized COC-induced motor and convulsant activity, exce pt on the first day when a potentiation of seizures was observed. Usin g the same treatment schedule, COC 50 mg/kg failed to induce sensitiza tion to the well known local anesthetic properties evaluated through t he loss of abdominal tone; this effect was not reversed by NTX pretrea tment. These findings provide further evidence of the modulatory role of the opiate system on cocaine sensitization.