Biphasic nature of the effects of Δ9-tetrahydrocannabinol on body temperature and brain amines of the rat

Abstract

The effect of i.v. injected Δ 9-tetrahydrocannabinol ( Δ 9-THC) on behaviour, body temperature and levels of brain monoamines, measured spectrophotofluorimetrically, of the rat were determined. Doses of Δ 9-THC in the range of 0.05–5.0 mg/kg produced biphasic changes in behaviour, body temperature and levels of 5-hydroxy-indoleacetic acid (5-HIAA). The whole brain levels of dopamine (DA), noradrenaline (NA) and 5-hydroxytryptamine (5-HT) were not altered by Δ 9-THC. The subjective behavioural biphasic responses did not appear to be dose related, whereas the biphasic changes in body temperature and brain levels of 5-HIAA were dose-related. Low dose of Δ 9-THC (0.05 and 0.1 mg/kg) caused hyperthermia, while doses of 1.0, 2.0 and 5.0 mg/kg induced hypothermia. On the other hand, 0.05 mg/kg Δ 9-THC significantly reduced, whereas doses of 1.0, 2.0 and 5.0 mg/kg significantly increased the 5-HIAA level in a dose-related manner. It is concluded that an inverse relationship exist between Δ 9-THC-induced changes in body temperature and alterations in brain 5-HIAA levels.