Warm Cells

by Guy McKhann, M.D.

October 11, 2016

This is a column from Dana's print publication, Brain in the News

About 10 years ago, my family joined my youngest son for a Florida vacation. We went to a beach south of Miami that was promoted as one of the best on the East Coast. (As a Cape Codder, I didn’t think it qualified, but that is irrelevant.) Upon entering the water, I suddenly realized that my right side hurt. It was quite tingly, in a very unpleasant way. I came out of the water and it was fine. I went back in several times and each time it was the same, though only from my neck down; my face was fine. That night I experimented in the shower, and determined that I had an abnormal response to cold, with quite a sharp cut-off in temperature.

On returning to Baltimore, where I was heading The Krieger Mind/Brain Institute, I recruited several of its system-oriented neuroscientists to determine my exact temperature parameters. I reported the findings to my wife, who suggested that I shouldn’t treat myself as merely a laboratory animal but should see a neurologist. I did, and he and I decided that something was up either in the spinal cord, at the level of my neck because my face was not involved, or it might be in my thalamus, a region where sensory inputs merge. The next day I subjected myself to some imaging studies, and sure enough I had a small area of injury in my spinal cord, right where the sensory tracts run. Somehow, it had disrupted only those carrying messages of “cold.”

Since then I have had my eye out for reports of the central perception of temperature. There aren’t many, but in this issue, Pete Farley outlines a recent report from the University of California San Francisco. It has been known for some time that there were nerve cells in a small area of the brain, the preoptic hypothalamus, that responded to temperature. But things were complicated by the fact that this small area also included nerve cells involved in sleep, hunger, and sexual arousal. It was not clear which cells were limited to hot and cold.

Using the most modern genetic techniques, the UCSF group identified two groups of nerve cells that responded to warmth. They did this by showing that two specific genes were turned on, or made active, when the environment was made warmer. They also proved this neuronal response was very rapid, thus not dependent on the body being warmer. It turns out there were direct signals from the heat-sensitive cells in the skin, indicating that there are direct connections from these cells to these nerve cells in the brain. These heat-activated brain cells send connections to other parts of the brain that activate multiple responses, such as sweating, panting, moving to colder areas, or dilatation of blood vessels.

These cells in the preoptic hypothalamus did not respond to cold. Presumably there are similar cold-sensitive cells that function in a similar fashion.

As for my own abnormal response to cold, known as dysesthesia, it has never changed; I’ve just gotten used to it. I am trying to use it as leverage to put a heater in our pool, but have yet to succeed.