TRPV1+ Sensory Fibers in the Mouse Renal Cortex ‐ Juxtaglomerular Anatomy and Optogenetic Stimulation

Hypertension is the leading contributor to cardiovascular-related deaths worldwide. To overcome obstacles presented by traditional drug-based therapies for hypertension, clinical trials are currently underway investigating the efficacy of catheter-based renal denervation (CBRDN) for the treatment of hypertension. While recent clinical trials support CBRDN as efficacious, this method is nonspecifically destructive in nature, ablating both sympathetic (efferent) and sensory (afferent) renal nerves. Previous publications from our group showed, via afferent-specific renal denervation, that sensory nerves drive the development and maintenance of the DOCA-salt hypertension in rats. However, the physiological roles that specific types of sensory renal nerves play in regulating cardiovascular function is not known. With this objective in mind, we used large volume tissue clearing and imaging techniques, as well as kidney-targeted optogenetic stimulation of TRPV1+ sensory fibers, to investigate the anatomy and function of sensory nerves in the renal cortex of the mouse. We investigated the anatomical relationship between renal glomeruli and sensory fibers using transgenic mouse lines and tissue clearing techniques. Approximately half of the glomeruli analyzed are in close proximity to CGRP+ and/or TRPV1+ sensory fibers. These fibers often follow a periglomerular path and are closely apposed to Bowman's capsule, contrasting the arteriolar interactions describing sympathetic fibers. Sensory fiber density is similar across superficial, midcortical, and juxtamedullary cortical areas, and glomeruli are equally likely to be accompanied by a nearby sensory fiber regardless of which cortical depth they reside in. Based on these observations, and the expression profiles of these sensory fibers, our working hypothesis is that they sense changes in glomerular function, such as glomerular pressure. Further ongoing experiments will directly test this hypothesis. The quantification of the anatomical distribution of sensory fibers near mouse renal glomeruli is significant in that cortical sensory fibers have not been studied in detail. Their presence in the renal cortex is consistent with a role of these neurons in the regulation of renal function. We subsequently investigated the roles of TRPV1+ sensory fibers in regulation of renal function in isoflurane anesthetized mice using a custom-designed optogenetic kidney cup. LED stimulation was applied to the renal cortex in transgenic mice that express channelrhodopsin in TRPV1+ nerve fibers. Arterial pressure and cortical blood flow were measured before, during and after optogenetic stimulation. Optogenetic stimulation of cortical sensory nerves decreased renal resistance and this response was absent in mice that had previously undergone RDN surgery. Based on these results, we hypothesize that juxtaglomerular TRPV1+ renal sensory fibers function in a novel sympathoexcitatory reflex that regulates renal vascular resistance.