Opioid Dependent Reductions in Selected Ambient Temperature Following Acute, Intermittent Hypoxia
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Exposure to non-lethal acute hypoxia (hypoxic conditioning - HC) increases tolerance to subsequent hypoxia in mice. Naloxone reverses this increase in tolerance, and attenuates a decrease in body temperature (Tb). We determined whether He causes a regulated drop in the thermoregulatory set point of mice, as indicated by reduced Tb's and behavioral preference for lower ambient temperatures (Ta). We also tested for naloxone reversibility. Naloxone (0.1, 1.0 mg/kg i. p.) or saline (0.3 ml i. p.) was injected 5 min prior to hypoxic or sham conditioning (Se), after which Tb and Ta were monitored in a thermal gradient for 30 min at 30 sec intervals. He decreased Tb for all time points and decreased selected Ta during the first 10 min following conditioning. Naloxone attenuated the decrease in Tb, and reversed the decrease in selected Ta. These data suggest that the HC protocol decreases thermoregulatory set-point, and that the process leading to this decrease involves endogenous opioids as indicated by naloxone reversibility.