| Summary: | In each experiment an adult male albino mouse was placed in an apparatus consisting of two narrow semi-circular tunnels joined together to form a complete circle. The apparatus was either mounted in a pressure vessel or a glass vessel. The tunnels were kept at different temperatures (usually 21.6 and 27.5 <SUP>o</SUP>C) and behavioural, thermoregulation was monitored by measuring the length of time spent in each tunnel. It was found that general anaesthetics (N<SUB>2</SUB>O, CHCIF<SUB>2</SUB>, CHCI<SUB>3</SUB>, N<SUB>2</SUB> and Ar) induced changes in behaviour directed at lowering deep body temperature. The following occurred: a) Dose related falls in rectal temperature. Tr was maintained at temperatures above the ambient temperature. b) Effects of anaesthetics on behavioural thermoregulation were reversible. c) Effects of different anaesthetics on behavioural thermoregulation were additive. d) At pressures above 11.33 atm the effects of N<SUB>2</SUB> and Ar are greater than predicted. This response is a two component response; "anaesthetic" and "pressure" component. e) Effects of anaesthetics were not pressure reversed, but showed an additive effect. f) Pressure induces a change in behaviour directed at lowering deep body temperature at pressures of either Ne or He greater than 11.33 atm. In conclusion it was thought general anaesthetics induced changes in the optimal "set-point", which down regulated deep body temperature. The sites of action of pressure and anaesthetic are different, but as yet unknown. Further mechanistic experiments are required to uncover those anatomical sites affected.
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