The Roles of Transient Receptor Potential Vanilloid 1 and 4 in Olfactory Regeneration.

Olfactory disorders, which are closely related to cognitive deterioration, can be caused by several factors, including infections, such as COVID-19; aging; and environmental chemicals. Injured olfactory receptor neurons (ORNs) regenerate after birth, but it is unclear which receptors and sensors are involved in ORN regeneration. Recently, there has been great focus on the involvement of transient receptor potential vanilloid (TRPV) channels, which are nociceptors expressed on sensory nerves during the healing of damaged tissues. The localization of TRPV in the olfactory nervous system has been reported in the past, but its function there are unclear. Here, we investigated how TRPV1 and TRPV4 channels are involved in ORN regeneration. TRPV1 knockout (KO), TRPV4 KO, and wild-type (WT) mice were used to model methimazole-induced olfactory dysfunction. The regeneration of ORNs was evaluated using olfactory behavior, histologic examination, and measurement of growth factors. Both TRPV1 and TRPV4 were found to be expressed in the olfactory epithelium (OE). TRPV1, in particular, existed near ORN axons. TRPV4 was marginally expressed in the basal layer of the OE. The proliferation of ORN progenitor cells was reduced in TRPV1 KO mice, which delayed ORN regeneration and the improvement of olfactory behavior. Postinjury OE thickness improved faster in TRPV4 KO mice than WT mice but without acceleration of ORN maturation. The nerve growth factor and transforming growth factor ß levels in TRPV1 KO mice were similar to those in WT mice, and the transforming growth factor ß level was higher than TRPV4 KO mice. TRPV1 was involved in stimulating the proliferation of progenitor cells. TRPV4 modulated their proliferation and maturation. ORN regeneration was regulated by the interaction between TRPV1 and TRPV4. However, in this study, TRPV4 involvement was limited compared with TRPV1. To our knowledge, this is the first study to demonstrate the involvement of TRPV1 and TRPV4 in OE regeneration.

The Role of Anatomical Imaging and Intraoperative Neuromonitoring (IONM) for Successful Prediction of a Nonrecurrent Laryngeal Nerve.

A nonrecurrent laryngeal nerve (NRLN) is a rare anatomical variant of laryngeal nerves that branches directly from the vagus nerve. The anatomical abnormality makes it difficult to identify the NRLN and results in high incidence of accidental nerve injury during surgery. A 76-year-old woman complained of swelling in the right side of her neck and visited our university hospital for further examination. Ultrasonography showed a right thyroid lobe mass with calcification and fine needle aspiration biopsy was classified as class III. Computed tomography revealed that the right subclavian artery branched directly from the descending aorta without branching from the brachiocephalic artery and ran behind the esophagus. Since it was afraid that the accidental injury of NRLN was likely to occur, a right thyroid lobe dissection using intraoperative neuromonitoring (IONM) was performed. After separating the connective tissue on the thyroid capsule from the right side of the trachea to the inferior pole laterally, the NRLN running across the level of the inferior margin of the cricoid cartilage was identified by using IONM 0.5 mA stimulation. After complete dissection of right thyroid lobe, we again stimulated the NRLN by 0.5 mA and the electromyographic response was confirmed. The pathological analysis confirmed nodular hyperplasia without malignancy; the condition was diagnosed as an adenomatous goiter. There was no vocal cord dysfunction and hoarseness after the surgery. IONM contributed to the prevention of NRLN injury during the surgery. We believe that it is important to confirm the presence or absence of an aberrant subclavian artery on preoperative imaging, and that IONM should be considered to identify the NRLN to prevent vocal cord paralysis if its presence is suspected.