Capsaicin, the chemical responsible for the hot in hot peppers, now has an additional newly discovered function – it can also reduce pain. In fact, a group of scientists have used chilli to gain an insight into the mechanism behind how our bodies feel pain.
Scientists Feng Qin and Jing Yao of the State University of New York at Buffalo studied how capsaicin triggers pain receptors (molecules that sense stimuli and pass then on to the nervous system) in the skin.
In a a Eureka Science News article, the scientists were quoted saying that while sensory systems in the body are known to be adaptable (like eyes adjusting to the dark in movie theatres), whether the pain receptors adapt to differing levels of pain versus de-sensitizing completely was unknown until this February 2009 study.
The team explained that capsaicin acts by binding to a receptor in the cell wall of nerve endings and triggering an influx of calcium into cells. The nervous system then interprets these events as pain or heat, depending on which nerves are stimulated.
In the Eureka Science News article, Qin said that “The receptor acts like a gate to the neurons – when stimulated it opens, letting outside calcium enter the cells until the receptor shuts down, in a process called desensitization.”
Qin believes the analgesic action of capsaicin has to do with the desensitization process. The shutting down of the receptors , would in essence also shut down the pain. Mechanisms behind the entry of calcium leads leading to the loss of sensitivity of the neurons are however not clear to the team, yet.
According to the article, capsaicin creams are over the counter drugs for a variety of pain symptoms, from minor aches to arthritis and nervous system related injuries.
The study showed that the pain receptor is fully functional after desensitization – i.e. although our bodies stop feeling pain and are de-sensitizes, if another pain triggering event occurs like if you ate more hot chillis than before, increasing the concentration of capsaici, you can feel that. In other words, the de-sensitizationis not permanent.
“What changed was the responsiveness threshold,” said Qin. “In other words, the receptor had not desensitized per se, but its responsiveness range was shifted.
According to the scientists, this property of receptors, called adaptation, allows it to continuously respond to stimuli of vvarying strengths over a large capsaicin concentration range.
The findings have important medical implications.
The team explained in the Eureka Science News article that with such an adaptive response, the receptors are essentially self-regulated without a fixed threshold of pain that they are programmed to, thus setting no limits on low or high intensity pain levels. This would mean that the intensity of the pain an individual experiences is dependent on the recent history of pain and captures the true value of the study.