Effect of Anesthesia and Diurnal Variation on Chronic Vagus Nerve Activity in Rats

The vagus nerve, serving as a pivotal link between the brain and vital organs, regulates crucial physiological functions. It plays a central role in maintaining homeostasis within the body and must dynamically adapt to changing conditions such as anesthesia or sleep. While vagal tone, typically estimated indirectly from heart rate variability, has been extensively studied, direct measurement of vagal activity during sleep and anesthesia remains unreported to date. Recent technological advancements have facilitated the recording of vagus nerve activity in freely moving rodents using small, highly flexible carbon nanotube yarns. Consequently, it is now feasible to directly investigate vagal activity during events known to impact homeostasis, such as diurnal variations and anesthesia. In this study, we explore the relationship between anesthesia and vagus nerve activity by comparing the effects of 2% isoflurane anesthesia with activity in freely moving male Sprague Dawley rats. The findings reveal that 2% isoflurane anesthesia significantly suppresses vagus nerve activity, and normal activity levels do not resume until 2 h after the termination of the anesthesia supply. Additionally, we examine the influence of diurnal variations on vagus nerve activity and observe a notable presence of diurnal variations in vagal activity patterns. These results provide insights into the interaction among anesthesia, diurnal variations, and vagal tone, offering valuable understanding of the autonomic nervous system during critical physiological states.