M ethod for Measuring Cervical Vagus Nerve Activity in Conscious and Freely Moving Rats

Abstract

The vagus nerve innervates most of the organs in the thoracic and abdominal cavity and plays a central role in inter‐organ networks through afferent and efferent vagal nerve activity. However, few attempts have been made to measure vagal nerve activity in the conscious state; thus, the nature of vagal nerve activity remains unclear. In this study, we attempted to develop a method to measure cervical vagal nerve activity in conscious, freely moving rats. Using male Wistar rats, the right cervical vagus nerve was dissected approximately 1 mm under anesthesia, and a bipolar electrode made of twisted stainless‐steel wire was hooked onto the vagus nerve and fixed with silicone gel. A microcatheter for administering a long‐acting local anesthetic (levobupivacaine hydrochloride 0.75%) was placed at least 5 mm peripherally from the electrode. Measurements were recorded under conscious and free‐living conditions. The right cervical vagal nerve activity (rcVNA) showed continuous activity of approximately 20 μV at peak‐to‐peak potential. The rcVNA was reduced by approximately 80% after administering 30 μL of levobupivacaine through the microcatheter. This allowed us to block the afferent VNA and selectively measure the efferent VNA. Using this method, we observed that efferent rcVNA decreased during REM sleep compared with NREM sleep. Moreover, we succeeded in measuring rcVNA and renal SNA simultaneously and continuously in conscious rats.