Influence of spinal and hypothalamic warming on metabolism and sleep in pigeons

Animals were prepared with electrooculogram (EOG), cortical electroencephalogram (EEG), and electromyogram (EMG) electrodes and with spinal and/or hypothalamic thermodes. Experiments were run at a cold and a neutral ambient temperature (T(a)) during the dark portion of a 24-h light-dark cycle. Metabolic rate, temperatures, EEG, EMG, and EOG were measured continuously for 4-h periods with hypothalamic or spinal temperature unmanipulated or warmed to the level measured during the light. The cold T(a) increased metabolic rate over the neutral T(a), but did not influence total sleep time (TST) or rapid-eye-movement sleep (REM) as precent TST. At the cold T(a), spinal warming resulted in reduction in REM as a percent TST. Spinal warming frequently caused a fall in body temperature (T(a)). A plot of REM as a percent TST vs. the fall in T(b), including data for all animals and all conditions, revealed a clear correlation between fall in T(b) and reduction in REM. Hypothalamic warming had no influence on metabolic rate, T(b), or distributions of arousal states. Cold thermal stimuli caused by a fall in T(b) can inhibit REM in birds as it can in mammals independently of thermoregulatory drive.