Department of Dental Public Health Sciences, University of Washington, Seattle, WA 98195-7475, USA.
Physiol Behav. 2011 Apr 18;103(1):79-85. doi: 10.1016/j.physbeh.2010.12.018. Epub 2010 Dec 22.
An initial administration of 60% nitrous oxide (N(2)O) evokes hypothermia in rats and if the administration continues for more than 1-2h, acute tolerance typically develops such that the initial reduction in core temperature (Tc) reverses and Tc recovers toward control values. Calorimeter studies at normal ambient temperature indicate that hypothermia results from a transient reduction in heat production (HP) combined with an elevation in heat loss. Acute tolerance develops primarily due to progressive increases in HP. Our aim was to determine whether rats provided a choice of ambient temperatures would behaviorally facilitate or oppose N(2)O-induced hypothermia. A gas-tight thermally-graded alleyway (range, 6.7-37.0°C) enabled male Long-Evans rats (n=12) to select a preferred ambient temperature during a 5-hour steady-state administration of 60% N(2)O and a separate paired control gas exposure (order counterbalanced). Tc was measured telemetrically from a sensor surgically implanted into the peritoneal cavity >7days before testing. Internal LED lighting maintained the accustomed day:night cycle (light cycle 0700-1900h) during sessions lasting 45.5h. Rats entered the temperature gradient at 1100h, and the 5-h N(2)O or control gas period did not start until 23h later to provide a long habituation/training period. Food and water were provided ad libitum at the center of the alleyway. The maximum decrease of mean Tc during N(2)O administration occurred at 0.9h and was -2.05±0.25°C; this differed significantly (p<0.0001) from the corresponding Tc change at 0.9h during control gas administration (0.01±0.14°C). The maximum decrease of the mean selected ambient temperature during N(2)O administration occurred at 0.7h and was -13.58±1.61°C; this differed significantly (p<0.0001) from the corresponding mean change in the selected ambient temperature at 0.7h during control gas administration (0.30±1.49°C). N(2)O appears to induce a regulated hypothermia because the selection of a cool ambient temperature facilitates the reduction in Tc. The recovery of Tc during N(2)O administration (i.e., acute tolerance development) could have been facilitated by selection of ambient temperatures that were warmer than those chosen during control administrations, but interestingly, this did not occur.
初始给予 60%氧化亚氮（N(2)O）会引起大鼠体温降低，如果给予时间超过 1-2 小时，通常会出现急性耐受，使得核心温度（Tc）的初始降低逆转，Tc 恢复到对照值。在正常环境温度下的量热计研究表明，体温过低是由于产热（HP）的短暂减少与热量损失的增加相结合所致。急性耐受主要是由于 HP 的逐渐增加而发展起来的。我们的目的是确定如果大鼠可以选择环境温度，它们的行为是否会促进或反对 N(2)O 诱导的体温过低。一个气密的热分级通道（范围为 6.7-37.0°C）使雄性长耳大仓鼠（n=12）能够在 60%N(2)O 的 5 小时稳态给予和单独的配对对照气体暴露期间（顺序平衡）选择一个偏好的环境温度。Tc 通过手术植入腹腔内的传感器进行遥测测量，在测试前>7 天。内部 LED 照明在持续 45.5 小时的会话期间维持习惯的日夜周期（光照周期为 0700-1900h）。大鼠在 1100h 进入温度梯度，5 小时的 N(2)O 或对照气体期直到 23h 后才开始，以提供长时间的适应/训练期。食物和水在通道中心自由供应。在 N(2)O 给予期间，平均 Tc 的最大下降发生在 0.9h，为-2.05±0.25°C；这与对照气体给予期间 0.9h 时的 Tc 变化（0.01±0.14°C）有显著差异（p<0.0001）。在 N(2)O 给予期间，平均选择的环境温度的最大下降发生在 0.7h，为-13.58±1.61°C；这与对照气体给予期间 0.7h 时选择的环境温度的相应平均变化（0.30±1.49°C）有显著差异（p<0.0001）。N(2)O 似乎诱导了一种调节性体温过低，因为选择凉爽的环境温度有助于降低 Tc。在 N(2)O 给予期间 Tc 的恢复（即急性耐受的发展）可能是通过选择比对照给予期间选择的温度更温暖的环境温度来促进的，但有趣的是，这并没有发生。
