Brain regions expressing Fos during thermoregulatory behavior in rats

Abstract

We surveyed the neural substrata for behavioral thermoregulation with immunohistochemical analysis of the expression of Fos protein in the rat brain. We used an operant system in which a rat exposed to heat (40 degrees C) could get cold air (0 degrees C) for 30 s when it moved into the reward area. Rats moved in and out of the reward area of the system periodically and thus maintained their body temperature at a normal level. In the rats performing heat escape behavior (active group), strong Fos immunoreactivity (Fos-IR) was found in the median preoptic nucleus (MnPO), parastrial nucleus (PS), and dorsomedial hypothalamus (DMH) compared with the controls. Another group of rats (passive group) were given the same temperature changes, regardless of the rat's movement, as those obtained by rats of the active group. Fos-IR in the MnPO was also seen in this group. The present results suggest that the PS and DMH play an important role in the genesis of thermoregulatory behavior, whereas the MnPO may be important for detecting changes in ambient and/or body temperatures.

AT1 receptors in the paraventricular nucleus mediate the hyperthermia-induced reflex reduction of renal blood flow in rats

“…Neurons in the PVN are activated by increases in ambient temperature, including those that influence sympathetic nerve activity (3,7,9,27), suggesting a role for the PVN in temperature regulation. The present study, together with our more recent work showing that inhibition of neuronal function within the PVN prevented the hyperthermia-induced reduction in renal and mesenteric blood flows, provides direct evidence that the PVN plays a key role in the cardiovascular thermoregulatory responses (8,10).…”

“…There are several lines of evidence supporting a role of the PVN in the cardiovascular responses elicited during thermoregulation: 1) the PVN contains neurons that project to areas important for thermoregulation, such as the brown adipose tissue, the tail (in the rat), kidney, and gut (19, 26, 30, 34 -35); 2) the PVN can influence sympathetic nerve activity and blood flow to the gut and kidney (21); 3) some PVN neurons have an intrinsic sensitivity to changes in temperature (20); and 4) neurons in the PVN are strongly activated by hyperthermia (3,9,27).…”

Central Mechanisms for Thermoregulation in a Hot Environment

“…These results may suggest that osmotic stimulation attenuates the central thermosensitivity to heat, resulting in the suppression of autonomic heat loss responses. In contrast, heat exposure increases Fos-immunoreactive neurons in the median preoptic nucleus 70) , and the combination of heat and osmotic stimuli additively augments the number of Fosimmunoreactive neurons 79) . Thus, the influence of osmotic signal on the warm-sensitive neurons may be different among the areas in the PO.…”

“…Thus, when investigating behavioral thermoregulation in animals, we must rely on instrumental response: temperature gradient and operant system. Maruyama et al 70) compared Fosimmunoreactive neurons in rats during operant heat escape behavior (0°C cold-air rewards in a 40°C environment; active protocol) with those during passive hot and cold stimuli in the same time sequence as the operant behavior in the paired rats (passive protocol). The comparison was also done with the rats that were just placed in the operant system maintained at 25°C (control protocol).…”

The median preoptic nucleus is involved in the facilitation of heat-escape/cold-seeking behavior during systemic salt loading in rats

“…In particular, neurons in the MnPO also respond to brain temperature (49). Heat exposure increases Fos expression in the MnPO (23), and the combination of heat and osmotic stimuli additively augments the Fos expression (38). Moreover, the MnPO receives the information regarding blood volume (1), which is another factor affecting thermoregulation (8,14,15).…”