Viral Targeting of Sensory Nerves of the External Ear in a Murine Model

Hypothesis: A novel adeno-associated virus (AAV) can be used to label the sensory nerves of the external ear in mice. Background: Stimulation of the auricular branch of the vagus nerve (ABVN) has been proposed as a noninvasive approach to vagus nerve stimulation. Here, we use a recently introduced AAV with enhanced tropism for peripheral sensory neurons (AAV-PHP.S) to label the somatosensory nerves of the external ear, including the ABVN. Methods: AAV-PHP.S capsids with a Cre-dependent fluorescent reporter cargo were injected retro-orbitally into 9 adult transgenic mice. Sensory ganglia for cranial nerves V, VII, IX, X, along with cervical dorsal root ganglia (DRG) and the external ear, were harvested. Immunohistochemistry was used to visualize expression of the reporter, tdTomato, in ganglion neurons and in sensory afferent nerve fibers in the external ear. Results: Eight of the 9 injected animals showed expression in all the relevant ganglia (CN V, VII, IX, X, and DRG). Expression was quantified in the jugular ganglion of the vagus nerve (which houses the cell bodies of the ABVN); 15.8%±1.3% of the neurons in this ganglion were successfully transduced with a fluorescent reporter (tdTomato). In 8 of the 9 animals, we also detected reporter expression in sensory nerve fibers in the external ear. We quantified the expression of the reporter in the external ear and found that the majority of nerve fiber area (66%±18%) strongly expressed tdTomato. Conclusion: AAV-PHP.S can be used to transduce the sensory nerves of the external ear in mice, including the ABVN.