Subdiaphragmatic vagal nerve stimulation attenuates the development of hypertension and alters nucleus of the solitary tract transcriptional networks in the spontaneously hypertensive rat

Augmented vagal signaling may be therapeutic in hypertension. Most studies to date have used stimulation of the cervical vagal branches. Here, we investigated the effects of chronic intermittent electric stimulation of the ventral subdiaphragmatic vagal nerve branch (sdVNS) on long-term blood pressure, immune markers, and gut microbiota in the spontaneously hypertensive rat (SHR), a rodent model of hypertension characterized by vagal dysfunction, gut dysbiosis, and low-grade inflammation. We evaluated the effects of sdVNS on transcriptional networks in the nucleus of the solitary tract (NTS), a major cardioregulatory brain region with direct gut vagal projections. Male juvenile SHRs were implanted with radiotelemetry transmitters and vagal nerve cuffs for chronic intermittent electric sdVNS, applied three times per day for 7 consecutive weeks followed by 1 wk of no stimulation. Blood pressure was measured once a week using telemetry in the sdVNS group as well as age-matched sham-stimulated SHR controls. At the endpoint, colonic and circulating inflammatory markers, corticosterone, and circulating catecholamines were investigated. Bacterial 16 s sequencing measured gut bacterial abundance and composition. RNA sequencing evaluated the effects of sdVNS on transcriptional networks in the NTS. SHRs that received sdVNS exhibited attenuated development of hypertension compared with sham animals. No changes in peripheral inflammatory markers, corticosterone, or catecholamines and no major differences in gut bacterial diversity and composition were observed following sdVNS, apart from decreased abundance of Defluviitaleaceale bacterium detected in sdVNS SHRs compared with sham animals. RNA sequencing revealed significant sdVNS-dependent modulation of select NTS transcriptional networks, including catecholaminergic and corticosteroid networks.NEW & NOTEWORTHY We show that stimulation of the ventral subdiaphragmatic vagal nerve branch may be a promising potential approach to treating hypertension. The data are especially encouraging given that rodents received only 30 min per day of intermittent stimulation therapy and in view of the potential of long-term blood pressure effects that are not stimulus-locked.

Abstract P188: Electrical Stimulation of Sub-Diaphragmatic Vagal Trunk Alleviates Hypertension in the SHR

Introduction: The vagus facilitates a bidirectional gut-brain communication. Low vagal tone is shown in conditions marked by inflammation and dysbiosis, including hypertension (HTN). However, the role of gut-projecting vagal nerve branches in blood pressure (BP) control is unexplored. Supplementing the potentially impaired gut vagal tone using electrical vagal nerve stimulation (vns) may restore homeostasis of the microbiota-gut-brain axis in HTN.

Methods: Male 8 week-old Wistar-Kyoto (WKY, N=6) and spontaneously hypertensive rats (SHR, N=10) were used. Rats were implanted with radiotelemetric BP transducers. WKY rats received either a unilateral surgical vagotomy of the ventral sub-diaphragmatic vagal trunk (vgnx, N=3) or sham surgery (SHAM, N=3). SHR were implanted with either a silicone cuff electrode (500μm, Microprobes for Life Sciences, Gaithersburg, MD) (vns, N=5) or a sham cuff (SHAM, N=5) on same vagal trunk. SHR were connected to an IZ2H current controlled stimulus generator (Tucker-Davis Technologies, Alachua, FL), and subjected to biphasic, 600μA, 0.5s/phase, 25Hz vns for 10 minutes per session, three sessions per day, 5 days per week. 24-hour BP recordings were made once per week for seven weeks in all rats. Relative abundance of gut bacterial phyla ( Firmicutes, Bacteriodetes, Actinobacteria ) was determined in fecal DNA of all rats using qPCR.

Results: Compared with SHAM, WKY vgnx showed a significant elevation in systolic BP (SBP) at week 7 post-vgnx (WKY SHAM: 148±4 mm Hg vs. WKY vgnx: 177±4 mm Hg; p <0.05). After 7 weeks of vns, SHR STIM group exhibited a significant dampening in SBP rise from baseline (SHR SHAM: ΔSBP=44±5 mm Hg vs. SHR vns: 22±3 mm Hg; p <0.05) and in mean BP (MBP) rise from baseline (SHR SHAM: ΔMBP=38±4 mm Hg vs. SHR vns: 14±3 mm Hg; p <0.05) compared to SHAM. No difference was observed in relative abundance of major bacterial phyla between the WKY vgnx and SHR vns rats and their respective controls.

Conclusions: Bioelectric restoration of gut vagal tone is beneficial in restitution of neural gut-brain axis in control of BP in HTN. Considering no changes were observed in major gut bacterial phyla following WKY vgnx and SHR vns, the observed BP responses may be due to perturbations in gut vagal afferent rather than efferent signaling.