Visualizing oxidative stress-induced depression of cardiac vagal baroreflex by MRI/DTI in a mouse neurogenic hypertension model

A clinical hallmark of hypertension is impairment of the cardiac vagal baroreflex, which maintains stable blood pressure and heart rate under physiological conditions. There is also evidence that oxidative stress in the brain is associated with neurogenic hypertension. We tested the hypothesis that an augmented superoxide level in the nucleus tractus solitarii (NTS), the terminal site of baroreceptor afferents, contributes to the depression of cardiac vagal baroreflex by disrupting the connectivity between the NTS and the nucleus ambiguus (NA), the origin of the vagus nerve, during neurogenic hypertension. An experimental model of neurogenic hypertension that employed intracerebroventricular infusion of angiotensin II in male adult C57BL/6 mice was used. Based on tractographic evaluations using magnetic resonance imaging/diffusion tensor imaging of the medulla oblongata in the brain stem, we found that the connectivity between the NTS and NA was disrupted in neurogenic hypertension, concurrent with impairment of the cardiac vagal baroreflex as detected by radiotelemetry. We further found that the disrupted NTS-NA connectivity was reversible, and was related to oxidative stress induced by augmented levels of NADPH oxidase-generated superoxide in the NTS. We conclude that depression of the cardiac vagal baroreflex induced by oxidative stress in the NTS in the context of neurogenic hypertension may be manifested in the form of dynamic alterations in the connectivity between the NTS and NA.