Most people who have performed in front of an audience can attest to the physiological response the body has to stress. Sometimes, stress can make your heart rate increase, your palms start sweating, your blood pressure rises, and some people even hyperventilate. These responses, sometimes referred to as “fight or flight” are meant to protect us. Another physiological response that people may not be aware of is that stress can give you a fever, but what controls this response has been largely unknown until recently.
Since 2004, researchers from Nagoya University in Japan have been trying to find the neural circuit that triggers the body to increase in temperature in response to stress. To do this, they used brown fat tissue, which is a “good fat” that generates heat when needed. The researchers found that if they blocked the β3-adrenergic receptor proteins in brown fat, which allows the tissue to respond to signals from neurons and cause a stress-induced fever.
The scientists injected viral retrograde tracers into the brown fat cells of rats. Tracers allow the researchers to see in which brain regions the neurons project to the fat. They found that the neurons in the rostral medullary raphe (rMR), clusters of nuclei in the brain stem, connect to brown fat. They also discovered that the dorsomedial hypothalamus (DMH) was upstream of the rMR, and when the scientists artificially activated this DMH-rMR pathway, they saw an increase in neuronal activity and heat production in brown fat. They also found that when they activated this pathway, the rats had an increased blood pressure and heart rate, which suggests that this pathway could be responsible for various physiological responses to stress.
The researchers wanted to find out which cortical regions in humans could send these same instructions to the DMH. Again, they used retrograde tracers, but this time they were injected into the DMH. They found that one small region called the dorsal peduncular cortex and dorsal taenia tecta (DP/DTT) contained the tracers. The scientists impaired the connection to DMH in three ways to study the response that the DP/DTT had to stress. In all three cases, they were able to induce hyperthermia. The researchers’ most recent study on stress-induced hyperthermia is published in the journal, Science.