The neural circuit required for the behavior of searching for a comfortable temperature environment (thermoregulatory behavior) exists separately from the circuit that senses temperature and transmits it to the brain. A research group at Nagoya University has compiled these research results and recently published them in the electronic version of the English scientific journal. The research group has made it possible to contribute to the elucidation of the mechanism of heat stroke.
The research group led by Professor Kazuhiro Nakamura of the Graduate School of Medicine, Nagoya University obtained this research data in a rat experiment. In the experiment, two metal plates were placed side by side, one with a heat of 38 degrees and the other with a suitable temperature (neutral temperature) of 28 degrees. The space between the two plates was not separated, and the rats were placed in the space and allowed to move freely for 20 minutes. The experiment was divided into a group of normal rats and a group of rats in which the part (thalamus) that recognizes temperature sensations such as heat and cold in the brain was destroyed.
As a result, normal rats stayed on the 28 degree plate for a long time. Attention was paid to the behavior of rats that destroyed the thalamus, but they also stayed at 28 degrees for a long time, similar to normal rats. Even in an experiment in which a hot plate of 38 degrees was replaced with a plate of cold 15 degrees, both groups preferred 28 degrees. From this, it was found that it is not necessary to feel the temperature through the circuit that conveys the sensation of temperature for the body temperature regulation behavior.
According to the research group, the paraventricular nucleus of the outer arm has a function in the brain that controls body temperature, such as sweating to release heat when it is hot and shaking muscles to generate heat when it is cold. Has already been located. This time, we administered a drug that suppresses the action of that part, made a rat with the thalamus as it was, and conducted an experiment on this rat in which two metal plates with different temperatures were arranged side by side. Then, it was found that the rats on the plate of 38 degrees Celsius in the heat and 15 degrees Celsius in the cold did not move and stayed on the plate and could not take thermoregulatory behavior. Rats that remained above 38 degrees have become hyperthermic, which can be called a “heat stroke state.”
From these results, Professor Nakamura et al. Have found that the paraventricular nucleus of the lateral arm is connected to the circuit necessary for the action of seeking a more comfortable temperature environment by feeling the ambient temperature as comfortable or unpleasant, and feeling the temperature in the brain. It has become clear that there is a circuit necessary for thermoregulatory behavior in addition to the circuit that conveys it (spinothalamic tract). If this interferes with the circuit required for thermoregulatory behavior, for example, even if you consciously feel “hot” in a hot environment, you may not be able to take thermoregulatory behavior that matches that sensation. That means that it is possible that such a case could lead to heat stroke.
Regarding heat stroke, many cases of elderly people who stay in a hot and humid room for a long time and worsen their symptoms and die are reported.
This research was conducted as part of the Japan Science and Technology Agency (JST) Strategic Creative Research Promotion Project Individual Research (PRESTO).