Sensory systems are integral to an animal’s behavioral repertoire (i.e., searching for food, habitats and mates while avoiding predators). Survival depends on the ability to detect, interpret and respond appropriately to external stimuli, particularly painful (tissue damaging) stimuli. This is critical when foraging or hunting for food – animals must distinguish beneficial from potentially harmful food items. Chemosensation or “chemical sense” is the process by which sensory systems distinguish beneficial from harmful chemicals. Transient Receptor Potential (TRP) channels are a group of membrane proteins that transduce both innocuous and nociceptive (painful) chemical, thermal and mechanical stimuli. TRPA1 (ankyrin family) and TRPV1 (vanilloid family) are particularly interesting because they are expressed in the trigeminal ganglia (TG) of sensory neurons that innervate the eyes, nose, mouth and upper airways, and in the dorsal root ganglia (DRG) of sensory neurons that innervate the lower airways. These polymodal receptors initiate pain signals in response to a number of noxious chemicals, extreme temperatures, changes in pH and tissue damage. Activation of TRPA1 and TRPV1 is also associated with initiation of inflammatory and immune responses. However, TRPA1 and TRPV1 expression patterns, molecular mechanisms of polymodal activation, and role in inflammatory and immune responses are not completely understood.

Darkling beetles (Eleodes longicollis) and their predators, scorpion mice (Onychomys torridus) provide an unprecedented opportunity to examine the molecular physiology of TRPA1 and TRPV1 pain signaling, and to ask how changes in TRP channel structure, function and expression impact predatory behavior and species interactions. Darkling beetles, when threatened, stand on their head and spray a chemical cocktail in the face of their predator. One chemical, benzoquinone, activates TRPA1 while the acidic pH activates TRPV1 causing irritation of the eyes, nasal and oral membranes in sensitive animals. Inhalation of the noxious spray can also cause irritation of the lower airways. Scorpion mice (carnivores) prey on darkling beetles, while opportunistic insectivores (Cactus mice, Peromyscus eremicus) avoid the beetles. Scorpion mice show little response to beetle sprays. Hind-paw injections suggest that scorpion mice TRPA1 and TRPV1 channels are less sensitive to noxious chemicals (formalin, capsaicin) compared to house mice.