A new method for quantifying effects of cannabinoid withdrawal in mice

Abstract

People using ?9-tetrahydrocannibinol (THC) or other cannabinoids often complain about difficulty stopping, suggesting they have become cannabis dependent. Studies in humans and nonhuman primates have documented spontaneous cannabinoid withdrawal symptoms for days to weeks following prolonged exposure to THC. In mice, however, symptoms of dependence are only seen by precipitating withdrawal with a cannabinoid antagonist. The present studies sought to validate a rapid method for quantifying cannabinoid withdrawal in mice and use these novel procedures to evaluate precipitated cannabinoid withdrawal at different time points. Mice were injected for 5 days with THC or AM2389 (a novel cannabinoid agonist) once or twice daily. The cannabinoid antagonist, rimonabant, was injected at 4- to 48-hrs after the last agonist injection and behaviors were digitally recorded in 5-min intervals at 15-, 30-, and 45-min after rimonabant injection. Scratching, paw tremors, head shakes, grooming, and rearing were scored from the recordings at 0.67x speed. 10 mg/kg rimonabant increased scratching in untreated mice, but did not affect other behaviors. In mice treated daily with THC or AM2389, the effects of rimonabant changed as it no longer induced scratching behavior, but did increase paw tremors. Additionally, the increase in paw tremors was observed even in the absence of rimonabant at 24 hrs after AM2389; representing the first observation of spontaneous cannabinoid withdrawal in mice. In summary, our results demonstrate that cannabinoid precipitated withdrawal can be evaluated in 5-min epochs and, under some experimental conditions, mice show evidence of spontaneous withdrawal.