Besides neural circuits which can feel and convey temperature to our brain, there is another neural circuit which enables us to conduct thermoregulatory behavior. Thermoregulatory behaviors are actions we take to regulate our body temperature. The Nagoya University group announced their findings through the electronic version of a British science journal. The group says that these findings may help solve mechanisms of heat stroke.
The research group headed by Professor Kazuhiro Nakamura of Nagoya University Graduate School of Medicine obtained data through rat experiments. In the experiment, two metal plates were placed side by side. One was heated to 38 degrees Celsius and the other was set at 28 degrees, a comfortable temperature. The two plates were not separated by any partition, so that the rats could pass through the two plates freely for 20 minutes. The experiment was conducted with a group of normal rats and a group of rats with destroyed thalamus (part of the brain which senses heat)
As a result, normal rats stayed on the 28 degrees plate for a long time. The behavior of rats with destroyed thalamus attracted a lot of attention, but like the normal rats, they stayed longer on the 28 degrees plate. The 38 degrees plate was later exchanged with a plate cooled to 15 degrees, but rats of both groups preferred the 28 degrees plate. From this, the group found that rats’ thermoregulatory behavior did not root from conventional temperature-sensing circuits that convey temperature.
Previously, the group had already discovered that there is a site called "lateral parabrachial nucleus” (LPB) in the human brain which regulates body temperature. In hot weather, it allows us to sweat and release heat. In cold weather it allows us to shiver our muscles to create heat. This time, the group administered drugs to rats to create rats with suppressed function of the LPB nucleus. The thalamus was not manipulated and was left in its original state. Then, the abovementioned experiment with the two plates of different temperature was conducted again with these rats. Ultimately, it was found that the rats which gathered to the plated heated to 38 degrees or cooled to 15 degrees did not bother to move and stayed on the plate, not being able to regulate their body temperature. Particularly, the body temperature of rats which stayed on the 38 degrees plate recorded high temperature which can be diagnosed as an abnormal state caused by heat disturbance.
From these results, Professor Nakamura and colleagues reveal that apart from the temperature-perception circuit (spinothalamocortical pathway), there is another neural circuit prompting behavior to seek comfortable temperature in the "lateral parabrachial nucleus” (LPB) which senses temperature around us. When one’s neural circuit needed for thermoregulatory behavior is damaged, one may still feel “hot” in the gruesome heat, but may not be able to conduct appropriate behavior to regulate body temperature. Such cases may lead to heat strokes.
Regarding heat stroke, many elderly people who stay in hot and humid rooms for long hours tend to worsen their symptoms, sometimes leading to death.
This research was conducted as part of Japan Science and Technology Agency (JST)’s individual strategic creative research promotion project PRESTO.