Hypothermia produced in mice by histamine acting on the central nervous system.

1. In mice 1-10 mug histamine injected intraventricularly produces hypothermia.2. This hypothermia was not antagonized by chlorcyclizine administered subcutaneously or intraventricularly, but chlorcyclizine injected intraventricularly was effective in antagonizing the hypothermia produced by a subcutaneous injection of histamine.3. Pretreatment with atropine was without effect on the hypothermia produced by an intraventricular injection of 10 mug histamine.4. Amphetamine and tranylcypromine not only effectively reduced the intensity of, or abolished, the hypothermia but also reversed the response to an intraventricular injection of 10 mug histamine so that hyperthermia was produced. Pargyline was without effect.5. Tolazoline strongly potentiated the hypothermia produced by the intraventricular injection of 10 mug histamine, but phentolamine did not.6. It is concluded that at least part of the hypothermia produced by a subcutaneous injection of histamine arises as a result of an action on the central nervous system.7. The possible mechanisms by which histamine acting on the central nervous system produces hypothermia and the suggestion that histamine may have a physiological role in thermoregulation are discussed in the light of these findings.