Thermosensitive neurons in the brain.

Abstract

Experimental methods commonly used in brain research, such as transection, ablation, focal lesion, and stimulation of the higher nervous structures have disclosed not only hypothalamic control of body temperature but also temperature sensitivity of the hypothalamus per se. Several classical studies clearly demonstrated that local warming or cooling of the hypothalamus produced appropriate thermoregulatory responses. The existence of thermosensitive neurons in the preoptic and anterior hypothalamic area (POAH) was first reported in the early 1960s [44,45], paving the way for neurophysiological studies on thermoregulation.A neuron that increases its steady discharge frequency at higher or lower local temperature is called a warm-sensitive or cold-sensitive neuron, respectively. The former type is encountered more frequently during microelectrode exploration. POAH thermosensitive neurons have been found not only in mammals, but also in birds, reptiles, and fish. More recent studies have revealed a wide distribution of thermosensitive neurons in the nervous system, including the midbrain, medulla oblongata, and spinal cord.Almost all cell activities in living organisms are, of course, more or less temperature dependent. At least two tests are required to distinguish whether a particular thermosensitive neuron is involved in temperature regulation. One is whether thermal stimulation of the region containing the particular neuron evokes appropriate thermoregulatory responses. From this point of view, the midbrain is the only exception among the areas mentioned above. Another point to be examined is whether a particular neuron is specifically sensitive to local temperature. Various criteria have been proposed to classify neurons into thermosensitive and non-thermosensitive types. Neurons having thermosensitivity of at least 0.8 imp/sec °C are considered warm-sensitive and those with at least -0.6 are considered cold-sensitive [5]. Furthermore, in a brain with complex neural networks, deciding whether a neuron is a true thermoreceptor or a thermosensitive interneuron is difficult even if the neuron shows a relatively high Q1° value. These difficulties led investigators undertake in vitro studies on neuronal thermosensitivity that clearly demonstrated the presence of true thermally sensitive neurons

Rhythmic aftereffects in the osmotic stimulation-induced spike activity of thermosensitive neurons of the preoptic region

“…Thermosensitive neurons demonstrating similar responses to temperature increases or decreases in the RPO itself were described earlier in vivo [11,12] and in vitro, in RPO and anterior hypothalamus slices [1,13,14 ]. Generally similar responses were recorded in cats and rats at temperature increases or decreases in different skin regions [12,15].…”

Modes of action of local hypothalamic and skin thermal stimulation on salivary secretion in rats.

“…Sensitive sites for salivary secretion by local brain warming are restricted to the anterior part of the hypothalamus, where thermosensitive neurones are located (Nakayama, 1985). Rats with lesions in the preoptic area do not salivate in response to heat as intact rats do (Hainsworth & Stricker, 1970;Toth, 1973).…”

Cortical, thalamic, and hypothalamic responses to cooling and warming the skin in awake humans: A positron-emission tomography study

“…Almost all the cells described in these studies increase their level of activity in concert with increases in temperature. Cells responsive to cooling of the hypothalamus have been described only infrequently (2).…”