Abstract Malfunction of the brain’s waste clearing glymphatic system has been shown to play a key role in cerebral small vessel disease the most common cause of vascular cognitive impairment prevalent with chronic hypertension in the aging population. Cerebral small vessel disease (cSVD) affects 750 million people worldwide, causes up to 45% of all dementias, and accounts for ~20% of all stroke cases, yet the underlying pathophysiology - even in the setting of hypertension - remains incompletely understood. Remarkably, the status of the lymphatic system (LS) has not been investigated in cSVD. We have novel data showing functional impairment of the LS a cSVD rat model with chronic hypertension (spontaneously hypertensive stroke prone (SHRSP) rat strain). Here we posit the entirely novel idea that alterations of the lymphatic system including meningeal lymphatics and lymph nodes draining brain waste in the setting of chronic hypertension contribute to cSVD. Specifically, we will test the main hypotheses that, cSVD with chronic hypertension is associated with uncoupling of the glymphatic and lymphatic systems and that systemic impairment of lymphatic drainage contributes to the pathogenesis of cSVD. We will apply our novel imaging approaches and computational analysis tools to characterize lymphatic drainage concurrently with glymphatic transport in a comprehensive series of experiments involving SHRSP rats with normotensive Wistar Kyoto (WKY) rats serving as controls. In Aim 1, we will determine the role of hypertension on glymphatic-lymphatic coupling. Lymphatic system function will be measured concurrently with glymphatic transport in untreated SHRSP rats and in SHRSP rats treated with antihypertensive medication (amlodipine) to reduce small vessel pathology at the whole-body level. We hypothesize that decreased glymphatic transport in SHRSP rats with chronic hypertension will be associated with glymphatic-lymphatic uncoupling. Furthermore, we expect amlodipine treatment will restore LS function in SHRSP rats. In Aim 2, we hypothesize that the pathogenesis of cSVD with chronic hypertension may be caused by a defect in lymphatic drainage that impairs glymphatic waste clearance over time. This assumption will be tested by gain-of-function (increasing the lymphatic vasculature with Vascular Endothelial Growth Factor C (VEGF-C)) and loss-of-lymphatic drainage (blocking drainage to the dcLN) experiments. In Aim 3 the goal is to generate a molecular and biochemical platform which will drive the understanding of which changes in the lymphatic system are associated with chronic hypertension. We will first conduct a comprehensive “omic” analysis of the CSF collected from WKY and SHRSP rats in Aims 1 & 2, since our scientific premises indicate that CSF is a reliable mirror of the ongoing brain activities. Next, we will move towards the anatomical, cellular and biochemical characterization of the lymphatics draining to the deep cervical node, since prelimin...