Continuous monitoring of hypothalamic neurotransmitters and thermoregulatory responses in exercising rats

The purpose of the present study was to investigate the relationship between thermoregulation and catecholamine release in the preoptic area and anterior hypothalamus (PO/AH) during incremental treadmill running in the rat. To this aim, we combined in vivo brain microdialysis, biotelemetry and metabolic measurements for continuous monitoring of core body temperature (T(core)), neurotransmitters and thermoregulatory responses. The animals were exercised for 1h at 23°C. Treadmill speed was increased every 20 min (10, 20 and 26 m min⁻¹). T(core), oxygen consumption (V˙O₂, an index of heat production) and tail skin temperature (T(tail), an index of heat loss) were simultaneously measured. Brain microdialysis samples were collected every 10 min, and these samples were analyzed for noradrenaline (NA), dopamine (DA) and serotonin (5-HT). T(core) and V˙O(2)₂ significantly increased during treadmill and were exercise intensity dependent. After an initial drop T(tail) increased significantly during exercise. Both NA and DA levels in the PO/AH increased significantly during exercise. There was no effect on serotonin release. T(core), V˙O₂ and T(tail) were positively correlated with the levels of NA and DA. Our data suggest that thermoregulatory responses are dependent on the intensity of the exercise and that these responses are associated with changes in NA and DA release, but not in 5-HT release in the PO/AH.