Δ8-Tetrahydrocannabinol (THC)- and 8β, 9β-epoxyhexahydrocannabinol (EHHC)-tolerant mice were tolerant to the hypothermia produced by morphine while 8α,9α-EHHC-tolerant mice were not. Morphine-tolerant mice were not. Morphine-tolerant mice acquired partial tolerance to the hypothermic effect of 8α,9α-EHHC, but not to the effect of Δ8-THC and 8β,9β-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.
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