What about fever when you're nervous?

Author: Dayu Lin psychological stress can cause physiological reactions, including increased body temperature.the researchers have elucidated a neural circuit behind this stress-induced fever.you are going to give a speech soon, and there are a lot of audience.while you wait, your heart starts to thump, your breathing becomes short, your blood pressure rises, and your palms sweat.these physiological reactions are evolutionarily conservative mechanisms that can help your body prepare for immediate danger or escape quickly.another key reaction is increased body temperature.emotional stress causes this psychogenic fever in many mammals, from rodents to humans [1,2].so, what is the neural mechanism behind this phenomenon? A paper published in science by Kataoka et al. [3] described a key neural loop in psychogenic induced hyperthermia.since 2004, the team has been looking for neural circuits that cause heat production by taking brown adipose tissue as the breakthrough point [4]. This latest research is based on their long-term scientific research results.brown fat is a "good" fat that produces heat when needed.there are a large number of β 3-adrenergic receptor proteins in brown fat, which can make the tissue respond to neuron signals, and inhibiting the activity of β 3-adrenergic receptor protein can alleviate the stress-induced hyperthermia [5].in the 2004 study, Kataoka's team injected a virus "retrograde tracer" into the brown fat of rats; the tracer would pass through the interconnected neurons, allowing the authors to identify which brain area the neurons projected to the brown fat [4].the authors found that neurons in the brainstem area, called the rostral raphe medulla (RMR), were linked to brown fat.after that, the team found that the dorsomedial hypothalamus (DMH) was a key brain area upstream of RMR [2].after the authors artificially activated the DMH – RMR pathway, it was found that the activity of neurons increased and brown fat began to produce heat; unexpectedly, heart rate and blood pressure also increased, which indicated that DMH – RMR pathway can coordinate various physiological responses under stress conditions.for people, psychological stress often involves the understanding of complex situations, so it may need instructions from the cortex involved in cognition.in this latest study, Kataoka et al. Tried to identify the cortical regions that might transmit these instructions to DMH. as in their previous studies, the authors used retrograde tracers, but this time they injected DMH to find neurons connected to their thermogenic circuits. they found that only one cortical area that was rarely studied was clearly marked by a tracer. this area, called the dorsal peduncle cortex and dorsal tegmental zone (DP / DTT), is also highly active after social failure in rats (here social failure refers to the loss of a rat to another dominant rat in a vicious conflict). in order to study the role of this region in stress response, the author destroyed its connection with DMH in three ways: using chemical inhibitors to inhibit the activity of DP / DTT whole region; using virus to kill cells projecting from DP / DTT to DMH; and using complex genetic methods to specifically inhibit the activity of neurons projecting from DP / DTT to DMH. in either case, the author's interventions can reduce stress-induced hyperthermia. in contrast, artificial activation of neuronal projections between the two regions causes a series of responses, including increased heart rate, increased blood pressure, and increased heat production by brown fat. the team used evidence to show that DP / DTT neurons transmit excitatory signals to DMH, and that DP / DTT projections terminate near DMH cells, and DMH then projects to RMR. taken together, Kataoka et al. Supported the view that a dp / DTT – DMH – RMR – brown fat circuit produces heat under stress (Fig. 1). Figure 1 | stress connection. Kataoka et al. [3] reported that the DP / DTT brain regions of rats were involved in psychogenic fever, the rise of body temperature under social stress. stress related information will reach DP / DTT from two other brain regions: paraventricular thalamic nucleus (PVT) and thalamic dorsal medial nucleus (MD). The neurons of DP / DTT then project to DMH, activate the neurons there, and then transmit neuronal projections to RMR from there. finally, RMR neurons can indirectly connect with brown adipose tissue to produce heat. how does stress related information reach DP / DTT? Further retrograde tracing showed that the strongest input signal of DP / DTT came from the midline thalamic region of the brain, including paraventricular thalamic nucleus (PVT) and dorsal medial thalamic nucleus (MD). PVT is highly sensitive to various physiological and psychological stressors, such as predator cues and pain [6]. in contrast, MD mediates complex cognitive functions such as rule learning, abstraction, assessment and (human) imagination through interaction with the prefrontal cortex [7]. therefore, whether it's physical pain or anticipated legal disputes, every possible stressor can reach the DP / DTT in some way. however, it is not clear how different stressors are encoded in DP / DTT, whether the response of DP / DTT to stressors is affected by experience, and whether the defect of DP / DTT cells leads to physiological stress response disorder. further electrophysiological or optical recording of DP / DTT cells will help to answer these questions. philosopher and psychologist William James believes that fear is an interpretation of the physiological response to threats, not the reverse [8]. in other words, it's not because we're afraid that we're afraid because we're running away. if James is right, inhibiting the physiological response of rats to threats can make them no longer afraid. Kataoka et al. Then asked: if a rat encounters another aggressive rat that has just defeated it in a tense social interaction, can inhibition of DP / DTT – DMH pathway inhibit the fear of the former rat? Under normal conditions, the defeated animal will try to stay away from the attacker to prevent further injury. in contrast, normal animals that had never experienced social failure before showed no signs of fear and looked at the dominant rats with great interest. it is worth noting that when the authors inhibited the DP / DTT – DMH pathway in failed rats, they also showed the same behavior as normal rats. that is to say, the behavior of fear, and perhaps the cognition of fear (which can only be inferred from the behavior of rats), depends on the body's response to threat. tell us why it helps to take a deep breath before a big speech. . the data also indicate that inhibition of physiological stress response may also be an effective way to relieve mental stress. it is important here that non stress related thermoregulation, such as changes in body temperature due to infection or external temperature differences, is not mediated by DP / DTT, but is another area upstream of DMH: preoptic area [9]. therefore, inhibition of the DP / DTT – DMH pathway is not expected to affect daily thermoregulation. although it is still in the initial stage, manipulation of DP / DTT may be a way to control chronic psychological stress. < br / < br / < br / < br / < br / < br / References: 1. 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