Shivering is one mechanism by which heat is produced in the body. Heat production is called thermogenesis. Another mechanism is through nonshivering thermogenesis regulated by brown fat (i.e. adipose). This second type of heating mechanism kicks in when we need extra heat production such as a postnatal infant, someone developing a fever, an animal arousing from hibernation, eating, or in the case of the current study, stress.
A recent study published in the American Journal of Physiology provides evidence that during stressful events brown adipose tissue can elevate body temperature through nonshivering thermogenesis. Prior to this study the role of brown adipose tissue in regulating emotional hyperthermia was uncertain.
Dr. William Blessing and colleagues at Flinders University in Adelaide, South Australia exposed "resident" Sprague-Dawley rats to a sudden intrusion by another rat for 30 mins while simultaneously measuring core body temperature along with brown adipose tissue and brain temperatures in addition to tail blood flow to examine whether brown adipose tissue can contribute to the production of emotional hyperthermia (elevated body temperatures with stress). They observed increased temperatures in the brown adipose tissue, core body and brain of the resident rats, although the rate of increase in temperature as well as overall temperatures in the brown adipose tissue were significantly (p<0.01) greater than the other sites. These findings suggest that brown adipose tissue can contribute significantly to the development of emotional hyperthermia during stress.
This type of fever has a different mechanism from fever that develops during a cold. Thus, hyperthermia due to stress is not truly “fever” but it has been historically called “fever.” I think that stress-induced hyperthermia is a better term. Stress-induced hyperthermia is a term often used for a temporary increase in body temperature caused by acute stress. However, there is no appropriate term for hyperthermia from chronic low fever.