Change in hypothermia and catalepsy induced by cannabinoids or morphine in mice tolerant to these substances.

delta 8-Tetrahydrocannabinol (THC)- and 8 beta, 9 beta-epoxyhexahydrocannabinol (EHHC)-tolerant mice were tolerant to the hypothermia produced by morphine while 8 alpha, 9 alpha-EHHC-tolerant mice were not. Morphine-tolerant mice acquired partial tolerance to the hypothermic effect of 8 alpha,9 alpha-EHHC, but not to the effect of delta 8-THC and 8 beta,9 beta-EHHC. Cataleptogenic effects of all cannabinoids were enhanced in morphine-tolerant mice as compared to non-tolerant animals. It seems that morphine-tolerant mice exhibited hypersensitivity to the cataleptogenic effect of the cannabinoids without potentiation of the hypothermia. These results suggest that the morphine-tolerant mouse may acquire 'latent' cross-tolerance to the hypothermic effect of the cannabinoids.