Circadian and arousal state influences on thermoregulation in the pigeon

We report here the characteristics of spinal thermosensitivity in pigeons as a function of arousal state and time of day. At any time in the light-dark (LD) cycle, the thresholds for shivering and panting were lower during non-rapid-eye-movement (NREM) sleep than during wakefulness. These thresholds in both awake and sleeping animals were lower during D than during L. The gain of the metabolic response to spinal cooling was nearly the same in wakefulness and NREM sleep. Shivering and panting responses to spinal thermal stimulations were impaired during REM sleep compared with wakefulness and NREM sleep. The results support the idea that central nervous system mechanisms controlling arousal states and circadian rhythmicity have separate and additive influences on temperature regulation in the pigeon.