Effects of electrical stimulation in the lower brainstem on temperature regulation in the unanaesthetized guinea-pig.

Electrical stimulation in lower brainstem areas presumed to be parts of the ascending noradrenergic system was carried out in the unanaesthetized guinea-pig. In the same animals noradrenaline (NA) was also injected into the anterior hypothalamus. Certain points in the lower brainstem were found, the stimulation of which resulted in a rise of oxygen uptake (more than 60% over the resting level), of body temperature and of electrical muscle activity at an ambient temperature of 29-30 degrees C. Respiratory rate also rose on stimulation, while heart rate did not show a consistent change. All these changes were found to be very similar to those obtained after an intrahypothalamic injection of NA. When the electrical stimulations at the same sites were repeated several times the extent of rise in oxygen uptake became gradually smaller, amounting to only half of the initial response after four periods of stimulation. An intrahypothalamic injection of NA restored the effectiveness of electrical stimulation in the lower brainstem to the original extent. These results suggest that the thermogenesis evoked by the electrical stimulation of these lower brainstem areas may be ascribed to the activation of ascending noradrenergic pathways terminating in the hypothalamus.