Changes in regional brain temperature induced by increase in neuronal activity in rats

The brain temperature largely depends on the metabolic activities of brain tissues and blood flow in the brain. However the physiological significance of brain temperature and its regulation remain unclear. To elucidate the relationship among regional brain temperatures (rBT), blood flow and brain activity, we simultaneously recorded brain temperature, blood flow and electrophysiological neuronal activities in the gustatory cortical area (GC) of rats, in response to somatosensory stimuli (electrical stimuli, L-menthol and capsaicin) or taste stimuli to the tongue. The temperature in the GC rose by 0.01 ~ 0.05°C after the neuronal activation by electrical and taste stimuli (0.5 M NaCl, 0.5 M sucrose, or 0.1 M citric acid). The effect was stronger with L-menthol and capsaicin than that with electrical and taste stimuli. The increase of temperature in the GC was correlated with the increase of neuronal activity, but not in other area, such as the visual cortex. Furthermore, the stimulation-induced increases in spike frequency of a small neuronal ensemble in the GC were co-localized with increases in blood flow. The increases in the blood flow were showed soon before or the almost same time as the changes in the rBTs. These results suggest that the changes in the rBTs are directly related to the brain activities including the stimulation-induced neuronal activity and blood flow.