Dopamine effects on neuromuscular function in hyperthermia

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Our lab has a main research focus on how the human body functions during extreme temperatures. In this field, an important question is why humans cannot exercise as hard or for as long in hot compared to cooler conditions. Historically, the main idea for this is suggested to be the loss of fluid through sweating making the heart work harder. However, many other new ideas have been proposed and demonstrated over the last twenty years, including our lab showing that a hot brain is less able to recruit and activate muscles, even if the skin or muscle itself is kept cool. We have since studied this further by looking at how brain blood flow or brain blood chemistry, both of which may change with high body temperatures, can affect muscle function. Other labs have shown that higher levels of dopamine, a transmitter molecule in the brain that seems to increase mental arousal and also heat loss responses in the body, can cause fit athletes to exercise longer and harder in the heat, and also be able to tolerate higher body temperatures. However, we do not know how dopamine might affect muscle function in the heat. We also do not know whether dopamine may affect individuals differently depending on their fitness levels. Our proposal tests whether dopamine levels directly affects muscle function at high body temperatures in people with both high and low aerobic fitness, with the overall goal of better understanding how we maintain body temperature in situations of high heat stress.