Current understanding on the neurophysiology of behavioral thermoregulation

Abstract

Temperature influence on the physiology and biochemistry of living organisms has long been recognized, which propels research in the field of thermoregulation. With the cloning and characterization of the transient receptor potential (TRP) ion channels as the principal temperature sensors of the mammalian somatosensory neurons, the understanding, at a molecular level, of thermosensory and thermoregulatory mechanisms became promising. Because thermal environment can be extremely hostile (temperature range on earth's surface is from ∼ -69°C to 58°C), living organisms developed an array of thermoregulatory strategies to guarantee survival, which include both autonomic mechanisms, which aim at increasing or decreasing heat exchange between body, and ambient and behavioral strategies. The knowledge regarding neural mechanisms involved in autonomic thermoregulatory strategies has progressed immensely compared to the knowledge on behavioral thermoregulation. This review aims at collecting the up-to-date knowledge on the neural basis for behavioral thermoregulation in mammals in order to point out perspectives and deployment of this research field.

Keywords: grooming; operant thermoregulatory behavior; thermo-TRP; thermogradient.

Figure 1.

Schematic of different apparatus used for the study of behavioral thermoregulatory responses in the laboratory. (A) thermogradient apparatus. (B) 2-temperature choice setup. (C) operant behavior setup. In A and B, by registering the position of the animal in the apparatus either using infrared photo beams or a camera recorder (not shown in the schematics), the selected ambient temperature can be calculated. In C, the parameter analyzed is the ambient temperature. In operant behavior, animals learn to adjust its own environmental temperature by means of pressing a bar or moving to a reward area in order to receive either heat or cold air reinforcement.

Figure 2.

Infrared thermograms (unpublished observations) of a rat exposed to supraneutral ambient temperature (∼30°C, top view) engaged in a series of grooming behavior, including medial (A) and lateral body licking (B—C). Note in D the reduction in skin temperature resultant from licking (arrow). In E, a rat exposed to a warmer ambient temperature (∼36°C) is expressing prone extension behavior. To obtain this pictures, male Wistar rat (14 weeks old) was exposed individually to ∼30 or ∼36°C in a temperature-controlled chamber (Eletrolab; Sao Paulo, SP, Brazil) and the behavior of the animal was recorded by an infrared camera (Flir, A300 – Series; Portland, OR, USA) for further analysis of the video. The grooming images were taken in the first 15 min of exposure to ∼30°C and prone extension image was taken after 60 min at ∼36°C.