investigating life
How do pit vipers “see” in the dark?
The pit organs of rattlesnakes are the infrared detectors that signal the presence of warm-blooded prey. In this chapter we considered how the pit organs transduce infrared radiation into neural information. Infrared is a portion of the electromagnetic radiation spectrum, as is visible light. So could the receptor cells in the pit organs be modified photoreceptors? Or have they evolved from the types of sensory neurons in the skin that sense temperature? The temperature-sensitive neuron theory seems more likely since there is no rhodopsin in the pit organs. But how did such neurons acquire an acute sensitivity to minute changes in temperature of the pit organ caused by distant infrared emitters? The experiments covered in Investigating Life: How Do Pit Vipers “See” in the Dark? identified a particular TRP channel that is highly expressed in the trigeminal ganglia but not in the dorsal root ganglia of rattlesnakes. These experiments also revealed that the TRPA1 channel is not highly expressed in the TG or DRGs of non-pit snakes, but is highly expressed in a distantly related pit snake, the python. In the online exercise to Investigating Life: How Do Pit Vipers “See” in the Dark? it was determined that expression of the TRPA1 gene in frog oocytes causes them to have a steep temperature sensitivity in the range of 36°C to 42°C. Thus we can conclude that the TRPA1 channel has evolved along with the pit organ to enable pit vipers such as the rattlesnake to detect warm-blooded prey.
The identification of specific genes that convey specific sensory capabilities—for example, identification of the different opsin genes for color vision and the TRPA1 gene for infrared detection—raise the possibility that genetic engineering efforts could be directed toward expanding the sensory capabilities of animals, and even humans. What would it be like to be able to see in the infrared and the ultraviolet ranges or to hear infrasound and ultrasound? Would the human brain be able to process and integrate that huge amount of additional information? How would our conscious perception of reality be changed?