Feel The Burn: How insights into burning have better shaped our understanding of pain
By Theodore Fisher, Behavioral Neuroscience, 2020
Think back to the last time you burned yourself. Chances are you were cooking, touching up a hairstyle, or getting the wrinkles out of that one shirt that never washes well. Ever since we were young and accidentally touched the stove, it has been a constant struggle to avoid heat-related injuries. Now think about the last spicy thing you ate. The food may or may not have been hot, but still, you feel that same burning sensation.
All types of pain have a complex neurological basis. When the body encounters what it deems to be a harmful stimulus, a sensory response known as nociception occurs that serves to give the body feedback and protection. Specialized receptors on sensory nerve endings, or nociceptors, are activated by stimuli. These neurons then transmit signals to the spinal cord which provides further information to the brain or back to skeletal muscles. In the brain, these signals cause a flood of neurotransmitters, or chemical messengers that can cause systemic behavioral and memory changes. In fact, this is really what causes you to act with caution as well as perceive pain shortly after you are hurt. In some cases, when this danger bypasses the brain through the spinal cord and goes straight to the skeletal muscle, we get a reflex reaction that serves to protect us. These reactions are quick and unavoidable, ready to protect you from further injury.
When the body encounters what it deems to be a harmful stimulus, a sensory response known as nociception occurs that serves to give the body feedback and protection.
Unlike any other sensation, burning pain is in a class of its own. Unique neurological feedback mechanisms are what set it apart from aching, tender, sharp, or stabbing pain. Only recently, David Julius, a professor at University of California, San Francisco, uncovered the true underpinnings of burning sensation. Through the careful use of the capsaicin molecule, the spicy component found in chili peppers, Julius was able to discover a new class of nociceptors. His research points to the utility of the TRPV1 nociceptor. By genetically modifying mice to lack this receptor, Julius and his researchers found something incredible. The mice showed an extreme reduction in heat sensitivity and licked their paws much less, a reflex behavior associated with pain sensation.
This family of channels sits right on the membranes of sensory neurons, which can be activated and cause electrical signaling extremely quickly. Julius discovered that not only are these nociceptors chemically activated but also are very sensitive to thermal energy. This alone may give some explanation as to why capsaicin and heat give us similar burning perceptions.
This information has exciting clinical implications. In many medical conditions, burning pain contributes to a large decrease in the quality of life. Sciatica, arthritis, and multiple sclerosis are some very serious conditions characterized by burning symptoms. Even topical infections such as sores and frostbite involve similar sensations. Because many current pain-killing methods fail to target burning pain specifically, researchers are working to engineer drugs that downregulate TRPV1 signaling. Having both heat and chemical sensitivity, the sheer utility of these nociceptors makes them a likely target for therapeutics. Targeting a specific chemical that interacts with TRPV1 could reduce its output and further signaling to the spinal cord and brain. Through better understanding the mechanisms at play when we feel pain that may in fact be helpful to us, we look to the future for better ways to treat the pain that may hurt us.
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