The psychoactive ingredient of marijuana induces behavioural sensitization

Here we describe, for the first time, the occurrence of behavioural sensiti zation after chronic exposure to Delta (9)-tetrahydrocannabinol. Rats were treated twice a day, for five days, with increasing doses (5, 10, 20, 40, 4 0 mg/kg i.p.) of Delta (9)-tetrahydrocannabinol or its vehicle and after 20 days of withdrawal, animals were challenged with 5 mg/kg (i.p.) of the dru g and their behaviour was assessed. Contrary to the motor inhibition induce d in control rats, challenge with Delta (9)-tetrahydrocannabinol in pre-exp osed animals elicited a complex behavioural syndrome mainly characterized b y oral stereotyped items. Due to the relevance of behavioural sensitization in drug-seeking behaviour that persists long after discontinuation of drug use, our findings suggest that cannabinoids could trigger neurobiological alteration not dissimilar from those observed with more harmful abused drug s.