Concepts to utilize in describing thermoregulation and neurophysiological evidence for how the system works

Abstract

We would like to emphasize about the system involved with homeostatic maintenance of body temperature. First, the primary mission of the thermoregulatory system is to defend core temperature (T (core)) against changes in ambient temperature (T (a)), the most frequently encountered disturbance for the system. T (a) should be treated as a feedforward input to the system, which has not been adequately recognized by thermal physiologists. Second, homeostatic demands from outside the thermoregulatory system may require or produce an altered T (core), such as fever (demand from the immune system). There are also conditions where some thermoregulatory effectors might be better not recruited due to demands from other homeostatic systems, such as during dehydration or fasting. Third, many experiments have supported the original assertion of Satinoff that multiple thermoregulatory effectors are controlled by different and relatively independent neuronal circuits. However, it would also be of value to be able to characterize strictly regulatory properties of the entire system by providing a clear definition for the level of regulation. Based on the assumption that T (core) is the regulated variable of the thermoregulatory system, regulated T (core) is defined as the T (core) that pertains within the range of normothermic T (a) (Gordon in temperature and toxicology: an integrative, comparative, and environmental approach, CRC Press, Boca Raton, 2005), i.e., the T (a) range in which an animal maintains a stable T (core). The proposed approach would facilitate the categorization and evaluation of how normal biological alterations, physiological stressors, and pathological conditions modify temperature regulation. In any case, of overriding importance is to recognize the means by which an alteration in T (core) (and modification of associated effector activities) increases the overall viability of the organism.

Role for kisspeptin/neurokinin B/dynorphin (KNDy) neurons in cutaneous vasodilatation and the estrogen modulation of body temperature

“…These findings are similar to other studies showing that E 2 treatment improved the ability to maintain core temperature when exposed to high ambient temperatures (36,39). Because the primary function of hypothalamic thermoregulation is to defend T CORE across a wide range of T AMBIENT (49), these data indicate that ovariectomy induces thermoregulatory dysfunction, which is corrected by E 2 treatment. Interestingly, OVX KNDy-ablated rats exposed to the high T AMBIENT were able to maintain their body temperature closer to normal than OVX control rats.…”

The Involvement of Brain Monoamines in the Onset of Hyperthermic Central Fatigue

“…With an elevation in body temperature to values over 42°C, there is an eminent risk of protein denaturating with subsequent cellular death. However, despite being more tolerant to hypothermia than to hyperthermia (see above) when the former is severe, i.e., when body temperature falls below 32°C, there are critical risks for life maintenance that include the loss of motor coordination, cardiac arrhythmias and even death by cardiac arrest (Kanosue, 2010). Body temperature is the net result of the heat produced by metabolic actions and the heat dissipated to the environment.…”

Physiological benefits likely underlie the systematic recruitment of thermoeffectors

“…Thermoeffectors that are physiologically 'cheap' are activated before more 'expensive' (i.e., resource consuming) responses are evoked. Thus, in humans, changes in skin blood flow are observed prior to the initiation of sweating in the heat (a body water consuming response) and increases in metabolism in the cold (an energy consuming response) [1]. It is likely that this is an evolutionarily conserved phenomenon, providing the benefit of regulating body temperature without the use of physiological resources.…”

“…However, temperature regulation is not dependent on time. Rather, thermoeffectors are initiated by afferent thermosensory feedback [1]. However, the recruitment of autonomic and behavioral thermoeffectors relative to changes in body temperature had not been quantified in humans.…”

“…Finally, the mechanisms underlying this apparent orderly recruitment remain unknown. While the neurophysiological mechanisms contributing to orderly recruitment of autonomic thermoeffectors are becoming more understood [1], it is less known how thermal behavior directly fits into this arrangement.…”