Timber rattlesnake; Taken by Tad Arensmeier from St. Louis, MO, USA |
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Hikers in Maryland are repeatedly warned at trailheads about the presence of venomous snakes. According to the Maryland DNR, there are over 27 species and subspecies of snakes in Maryland, including two venomous pit vipers, the copperhead and timber rattlesnake. Pit vipers are named for their large specialized pit organs located between the nostril and eye on each side of their face. These organs allow pit vipers to sense infrared radiation, detecting warm-blooded prey at temperatures above ~30°C and distances of up to one meter.
The pit organ is composed of a thin membrane suspended in a hollow chamber. This membrane, serving as an infrared antenna, is packed with mitochondria (cellular power plants) and linked to many nerve fibers. These fibers send signals from the pit organs to the brain. The sensitivity of detection is dependent on the anatomical and molecular characteristics of the pit organ.
This week in a Nature advance online publication, scientists reveal the identity of the molecular sensor used by pit vipers and describe how these sensors convey information to the snake brain. Rather than “seeing” in infrared, the pit organ actually heats up due to the ion channel TRPA1. Researchers found TRPA1 in nerve endings leading to the pit organ at levels 400x that in other nerve endings. Humans and other mammals also have TRPA1 (63% similar to pit viper) which is activated by the pungent agent from wasabi and mustard plants. Unlike our TRPA1, the pit viper receptor is not only activated by the mustard agent but also by heat above 28°C. The heat activation of these channels provides an infrared map to the snake brain.
Interestingly, the researchers found no activation of TRPA1 channels in cooler temperatures, although it is known that snakes can respond to temperatures well below 28°C, perhaps to locate cooler areas in which to rest. Is there another receptor that can detect cooler climes? Or maybe the anatomy of the pit organ tunes TRPA1 in a way we haven’t yet explored.
According to the Maryland DNR, only 2-5 people get bitten by a venomous snake in the state each year. If you happen to be one of the unlucky ones, just remember:
- Don’t apply ice.
- Do keep the bite immobilized and below your heart.
- Don’t apply a tourniquet.
- Do wash it with soap and water.
- Don’t make an incision.
- Do get help immediately.
