Exercise, thermoregulation, and the brain

Abstract

Exercise increases brain neurotransmission, and during exercise with severe heat stress, a high body temperature may directly or indirectly influence endurance performance, and the existence of a “critical” core temperature has been suggested. This comes from observations in which subjects terminate exercise at the same individual core temperature, despite having started at different core temperatures and having performed different exercise times. The brain monoamines serotonin (5-HT), dopamine (DA) and noradrenaline (NA) innervate different areas of the hypothalamus, among which include the preoptic and anterior hypothalamus (PO/AH). The PO/AH is thought to be the primary locus for body temperature regulation. This brain area integrates thermal information from central and peripheral thermoreceptors, and initiates appropriate heat loss and heat production responses. It is well known that NA and DA in these hypothalamic regions play essential roles in thermoregulation. It can be expected that a shift in the concentrations of these neurotransmitters contributes to changes in thermal regulation and consequently to fatigue, specifically when exercise is undertaken in hot environmental conditions. Core temperature can obtain critical values while perception of effort is suppressed. In rat studies we showed that the increase in core and brain temperature during exercise in the heat is under dopaminergic control. The PO/AH, the thermoregulatory centre of the brain, will be ‘bypassed’ and therefore heat dissipation is disturbed.