Effects of delta 9-tetrahydrocannabinol, 2.4-dinitrophenol and pentolinium tartrate on behavioural thermoregulation in mice.

1 A new apparatus in which mice are allowed to shuttle between the warm and cool parts of a continuous oval tunnel has been designed for the measurement of drug effects on behavioural thermoregulation.2 The length of time that untreated mice spent in the warmer part of the apparatus (tunnel wall temperature 38 degrees C) was found to be inversely related to the temperature of the cooler part (wall temperature 18 degrees , 24 degrees or 30 degrees C).3 Mice treated with 2,4-dinitrophenol at a dose known to be hyperthermic at an ambient temperature of 32 degrees C (20 mg/kg s.c.) spent an increased length of time in the cooler part of the apparatus (wall temperature 18 degrees C) and did not exhibit any change in rectal temperature.4 Mice treated with pentolinium tartrate at a dose known to be hypothermic at room temperature (5.0 mg/kg i.v.) spent a decreased length of time in the cooler part of the apparatus (wall temperature 24 degrees C) and did not exhibit any change in rectal temperature.5 It is concluded from the above results that the apparatus can be used to measure drug effects on behavioural thermoregulation.6 In experiments of 30 min duration, mice treated with Delta(9)-tetrahydrocannabinol (Delta(9)-THC) at doses known to be hypothermic and to lower oxygen consumption at room temperature (20 mg/kg i.p. or 2.0 mg/kg i.v.) spent a longer time in the warmer part of the apparatus between 15 and 30 min after injection. Rectal temperatures measured 30 min after injection were only slightly less than those of control mice. In these experiments the wall temperature of the cool tunnel was 24 degrees C.7 In experiments of 15 min duration, mice treated with Delta(9)-THC (20 mg/kg) and then placed in the apparatus spent more time in the cooler part of the apparatus (wall temperature 24 degrees C) and exhibited a large fall in rectal temperature.8 It is concluded that immediately after injection of Delta(9)-THC the mice do not attempt to oppose drug-induced falls in deep body temperature by moving into a warm environment and that only later do the animals demonstrate a preference for a warm environment.