The southern grasshopper mouse is notable for its resistance to venom as it routinely kills and eats Arizona bark scorpions, a species with a highly venomous sting.
The southern grasshopper mouse is notable for its resistance to venom as it routinely kills and eats Arizona bark scorpions (Centruroides sculpturatus), a species with a highly venomous sting.
In the arid regions inhabited by the southern grasshopper mouse, the Arizona bark scorpion is plentiful and avoided by most predators because of the very painful sting it can inflict. The grasshopper mouse can feed on this scorpion with impunity even when the scorpion stings it repeatedly in the face.
Researchers have found that a neural mechanism is involved that blocks the sending of pain messages to the brain. This mouse can normally feel pain from other sources, but can be temporarily insensitive to these stimuli after a dose of venom from a bark scorpion. This pain modulation is activated soon after the scorpion sting. For a moment, the mouse feels pain, but then the scorpion venom binds to the transmembrane channel otNav1.8. Specifically, the venom binds to a glutamic acid residue located within the channel protein. This prevents neuron action potentials from firing, and acts as a type of temporary anesthetic and pain reliever for the mouse. When this glutamic acid was replaced with hydrophilic glutamine residue, the venom did not bind with the protein, and the pain modulation ability was lost.