1 Vol.:(0123456789) Scientifc Reports | (2020) 10:17576 | https://doi.org/10.1038/s41598-020-74257-9 www.nature.com/scientificreports Non‑invasive vagus nerve stimulation attenuates proinfammatory cytokines and augments antioxidant levels in the brainstem and forebrain regions of Dahl salt sensitive rats Madhan Subramanian 1* , Laura Edwards 1 , Avery Melton 1 , Lyndee Branen 1 , Angela Herron 1 , Mahesh Kumar Sivasubramanian 1 , Raisa Monteiro 1 , Samantha Stansbury 1 , Priya Balasubramanian 2 , Lynsie Morris 3,4 , Khaled Elkholey 3 , Monika Niewiadomska 3 & Stavros Stavrakis 3,4* The anti‑infammatory efects of vagus nerve stimulation are well known. It has recently been shown that low‑level, transcutaneous stimulation of vagus nerve at the tragus (LLTS) reduces cardiac infammation in a rat model of heart failure with preserved ejection fraction (HFpEF). The mechanisms by which LLTS afect the central neural circuits within the brain regions that are important for the regulation of cardiac vagal tone are not clear. Female Dahl salt‑sensitive rats were initially fed with either low salt (LS) or high salt (HS) diet for a period of 6 weeks, followed by sham or active stimulation (LLTS) for 30 min daily for 4 weeks. To study the central efects of LLTS, four brainstem (SP5, NAb, NTS, and RVLM) and two forebrain sites (PVN and SFO) were examined. HS diet signifcantly increased the gene expression of proinfammatory cytokines in the SP5 and SFO. LLTS reversed HS diet‑induced changes at both these sites. Furthermore, LLTS augmented the levels of antioxidant Nrf2 in the SP5 and SFO. Taken together, these fndings suggest that LLTS has central anti‑infammatory and antioxidant properties that could mediate the neuromodulation of cardiac vagal tone in the rat model of HFpEF. Heart failure with preserved ejection fraction (HFpEF) is one of the leading causes of mortality in the elderly 1 . Te prevalence of HFpEF increases from 1% at age 40 to about 10% at age 80 2 . It is the most common cause of hospitalization in patients ≥ 65 years of age and with the growing elderly population, these trends are expected to worsen 2,3 . Te prognosis for patients with HFpEF is poor (5-year mortality rate approximately 50%) 4 , and so far, no treatment has been demonstrated to achieve positive outcomes on morbidity or mortality in these patients 5 . Infammation and fbrosis are the most prominent pathophysiological mechanisms that mediate impairments of cardiac function in heart failure. Identifcation of treatment options that target these cardiac mechanisms may prove fruitful. Vagus nerve stimulation (VNS) is a non-pharmacological, device-based therapy that is currently approved by FDA for the treatment of epilepsy and depression 6 . Recent studies have indicated that low-level VNS suppresses atrial fbrillation and infammatory cytokines in humans 7–9 . In addition, several preclinical studies have yielded promising results for the use of non-invasive VNS in improving cardiac outcomes of HFpEF 10,11 . Using Dahl OPEN 1 Department of Physiological Sciences, College of Veterinary Medicine, Oklahoma State University, 277 McElroy Hall, Stillwater, OK 74078, USA. 2 Reynolds Oklahoma Center On Aging, University of Oklahoma Health Sciences Center, Oklahoma City, OK, USA. 3 Department of Medicine, Cardiovascular Section, University of Oklahoma Health Sciences Center, Oklahoma City, OK, USA. 4 Department of Medicine, Heart Rhythm Institute, University of Oklahoma Health Sciences Center, 800 Stanton L Young Blvd, Suite 5400, Oklahoma City, OK 73104, USA. * email: madhan.subramanian@okstate.edu; stavros-stavrakis@ouhsc.edu