THERMOSENSITIVITY OF CENTRAL NERVOUS SYSTEM IN PIGEONS AND ITS INFLUENCE ON BODY TEMPERATURE REGULATION

1. In unanesthetized pigeons the vertebral canal was selectively cooled or heated with thermodes chronically implanted into the peridural space. Changes of spinal cord temperature induced in this way caused distinct thermoregulatory responses without changes of hypothalamic temperature. 2. At neutral ambient temperature (27-30° C) and normal core and skin temperatures, a decrease of spinal cord temperature induced cold shivering. During cooling periods of 20 min, the oxygen consumption was elevated, in the average, for 60% of its resting rate. Core temperature rose for 1.0-1.5° C. The skin temperatures of the trunk also rose. The skin temperature of the feet, however, showed a distinct fall (Fig. 1). 3. In the range of thermally indifferent ambient conditions, the threshold temperature of shivering was investigated by slowly lowering vertebral canal temperature (0.1° C per min). As indicated by electromyographical recordings, an average fall of peridural temperature for 1.6° C at 25° C air temperature and for 2.8° C at 30° C air temperature was necessary to evoke shivering (Fig. 5). 4. Under cold external conditions (10° C), when the animals were shivering and consequently had increased their heat production, oxygen consumption was increased and decreased respectively by slightly lowering or elevating vertebral canal temperature (±0.5 to 1.0° C). A linear correlation between oxygen consumption and vertebral canal temperature was found in this situation (Fig. 12). 5. Selective heating of the spinal cord at neutral ambient temperatures evoked thermal panting and cutaneous vasodilatation in the feet, which resulted in a considerable fall of core temperature. The threshold temperature of panting fell with ambient temperature (Fig. 10). 6. Under hot external conditions (36-37° C), when the animals were panting, spinal cord cooling could lower the increased respiratory rate to normal values (Fig. 11). 7. The experiments give evidence for the existence of thermosensitive structures in the vertebral canal of pigeons. These structures are most likely localized within the spinal cord. Spinal cord thermosensitivity must be considered as an important factor involved in body temperature regulation of birds. © 1969 Springer-Verlag.