Serotonin release in the preoptic area and anterior hypothalamus is not involved in thermoregulation during low-intensity exercise in a warm environment

The aim of the present study was to assess the response of serotonin (5-hydroxytryptamine; 5-HT) in the preoptic area and anterior hypothalamus (PO/AH) to thermoregulation during exercise in a warm environment. In addition, it was investigated whether a rapid increase in extracellular 5-HT levels in the PO/AH modifies the thermoregulatory response under the same exercise conditions. Rats were made to run for 120 min at 10 m min⁻¹ on a treadmill at the ambient temperature of 30 °C. Body core temperature (T_core) was monitored using a biotelemetry system, and tail skin temperature (T_tail) was simultaneously measured as an index of heat loss response. Microdialysis in combination with HPLC was used to measure concentrations of monoamines in the PO/AH. Both T_core and T_tail increased during the first 20 min of exercise and remained stable until the end of the exercise period. Low-intensity exercise did not induce any changes in 5-HT release in the PO/AH, although the levels of norepinephrine and dopamine were increased. Moreover, increased extracellular 5-HT by local perfusion of 1 μM citalopram (selective 5-HT reuptake inhibitor; SSRI) in the PO/AH had no effect on the thermoregulatory response during acute low-intensity exercise in a warm environment. These results suggest that enhanced release of only 5-HT in the PO/AH may not intervene thermoregulation during exercise in a warm environment.