Weight and activity in male mice after daily inhalation of cannabis smoke in an automated smoke exposure chamber.

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Abstract An automatic smoking machine capable of delivering marihuana smoke to groups of 10 mice at a time at a constant concentration of Δ9-THC is described. In all cases the flow rate (50 ml s−1 or 100 ml s-1) of a smoke: air mixture, and the dilution factor (1:20 or 1:10 smoke:air) was adjusted to give the same equilibrium concentration of Δ9-THC in the chamber atmosphere. At a concentration of 0–123 mg Δ9-THC litre−1 of exposure chamber atmosphere (1:20 smoke: air; 100 ml s−1 flow rate), a seven day schedule of 20 min daily treatments significantly decreased activity of the marihuana-treated animals by the sixth day over both air and placebo smoke controls. This concentration and exposure schedule failed to affect weight gain during this same period. A significant decrease in activity, although not as great as in the marihuana-treated group, was also seen in the placebo control group compared with the air control animals, indicating the need for a smoke control group in all experiments involving the administration of marihuana via inhalation. An exposure period of 102 min, with marihuana smoke diluted with air 1:10 (50 ml s-1 flow rate), at the same equilibrium concentration of 0·123 mg Δ9-THC litre−1, resulted in a mortality of 90% following administration or within 48 h. 102 min of exposure to an atmosphere of placebo smoke at a smoke:air dilution of 1:10 (50 ml s-1 flow rate), resulted in no mortality.