A Novel Flp Reporter Mouse Shows That TRPA1 Expression Is Largely Limited to Sensory Neuron Subsets.

Transient receptor potential ankyrin 1 (TRPA1) is a polymodal cation channel that is activated by electrophilic irritants, oxidative stress, cold temperature, and GPCR signaling. TRPA1 expression has been primarily identified in subsets of nociceptive sensory afferents and is considered a target for future analgesics. Nevertheless, TRPA1 has been implicated in other cell types including keratinocytes, epithelium, enterochromaffin cells, endothelium, astrocytes, and CNS neurons. Here, we developed a knock-in mouse that expresses the recombinase FlpO in TRPA1-expressing cells. We crossed the TRPA1Flp mouse with the R26ai65f mouse that expresses tdTomato in a Flp-sensitive manner. We found tdTomato expression correlated well with TRPA1 mRNA expression and sensitivity to TRPA1 agonists in subsets of TRPV1 (transient receptor potential vanilloid receptor type 1)-expressing neurons in the vagal ganglia and dorsal root ganglia (DRGs), although tdTomato expression efficiency was limited in DRG. We observed tdTomato-expressing afferent fibers centrally (in the medulla and spinal cord) and peripherally in the esophagus, gut, airways, bladder, and skin. Furthermore, chemogenetic activation of TRPA1-expressing nerves in the paw evoked flinching behavior. tdTomato expression was very limited in other cell types. We found tdTomato in subepithelial cells in the gut mucosa but not in enterochromaffin cells. tdTomato was also observed in supporting cells within the cochlea, but not in hair cells. Lastly, tdTomato was occasionally observed in neurons in the somatomotor cortex and the piriform area, but not in astrocytes or vascular endothelium. Thus, this novel mouse strain may be useful for mapping and manipulating TRPA1-expressing cells and deciphering the role of TRPA1 in physiological and pathophysiological processes.

Action potential conduction in the mouse and rat vagus nerve is dependent on multiple voltage-gated sodium channels (NaV1s).

Action potential (AP) conduction depends on voltage-gated sodium channels, of which there are nine subtypes. The vagus nerve, comprising sensory afferent fibers and efferent parasympathetic fibers, provides autonomic regulation of visceral organs, but the voltage-gated sodium channels (NaV1) subtypes involved in its AP conduction are poorly defined. We studied the A- and C-waves of electrically stimulated compound action potentials (CAPs) of the mouse and rat vagus nerves with and without NaV1 inhibitor administration: tetrodotoxin (TTX), PF-05089771 (mouse NaV1.7), ProTX-II (NaV1.7), ICA-121341 (NaV1.1, NaV1.3, and NaV1.6), LSN-3049227 (NaV1.2, NaV1.6, and NaV1.7), and A-803467 (NaV1.8). We show that TTX-sensitive NaV1 channels are essential for all vagal AP conduction. PF-05089771 but not ICA-121341 inhibited the mouse A-wave, which was abolished by LSN-3049227, suggesting roles for NaV1.7 and NaV1.2. The mouse C-wave was abolished by LSN-3049227 and a combination of PF-05089771 and ICA-121341, suggesting roles for NaV1.7 and NaV1.6. The rat A-wave was inhibited by ProTX-II, ICA-121341, and a combination of these inhibitors but only abolished by LSN-3049227, suggesting roles for NaV1.7, NaV1.6, and NaV1.2. The rat C-wave was abolished by LSN-3049227 and a combination of ProTX-II and ICA-121341, suggesting roles for NaV1.7 and NaV1.6. A-803467 also inhibited the mouse and rat CAP suggesting a cooperative role for the TTX-resistant NaV1.8. Overall, our data demonstrate that multiple NaV1 subtypes contribute to vagal CAPs, with NaV1.7 and NaV1.8 playing predominant roles and NaV1.6 and NaV1.2 contributing to a different extent based on nerve fiber type and species. Inhibition of these NaV1 may impact autonomic regulation of visceral organs.NEW & NOTEWORTHY Distinct NaV1 channels are involved in action potential (AP) initiation and conduction from afferent terminals within specific organs. Here, we have identified the NaV1 necessary for AP conduction in the entire murine and rat vagus nerve. We show TTX-sensitive channels are essential for all AP conduction, predominantly NaV1.7 with NaV1.2 and NaV1.6 playing lesser roles depending on the species and fiber type. In addition, we show that NaV1.8 is also essential for most axonal AP conduction.