Introduction: Besides intense renin-angiotensin system activation and sympathoexcitation, heart failure (HF) is accompanied by marked autonomic dysfunction. We showed previously in hypertensive rats that blood-brain barrier (BBB) dysfunction in preautonomic areas aggravated the autonomic dysfunction but is corrected by aerobic training (T). There is no information in HF Hypothesis: We hypothesized that BBB dysfunction within the paraventricular hypothalamic nucleus (PVN) contributes to the autonomic imbalance, which may be ameliorated by T Methods: Wistar rats were submitted to anterior descending coronary artery occlusion or Sham surgery and echocardiography. Four weeks later, HF (ejection fraction≤40%) and Sham rats underwent a T (55% of maximal exercise capacity) or sedentary (S) protocol for 8 weeks and were chronically cannulated for hemodynamic/autonomic recordings and determination of BBB permeability (intra-arterial injection of fluorescent dyes with high and low molecular weight). To investigate the mechanisms underlying HF- and T-induced BBB changes, the PVN was harvested and processed for transmission electron microscopy Results: HF-S exhibited reduced arterial pressure (AP, -10%), increased sympathetic activity to vessels and heart (+45% on average), decreased spontaneous baroreflex sensitivity (BrS, -19%), large increase in systolic AP variability (+53%), and 4-fold increase in PVN BBB leakage (11.3±1.4 vs. 2.8±0.2 %area in Sham-S). HF-S also exhibited increased transcytotic vesicles (+80%) in PVN capillaries’ endothelium, without any change in tight junctions’ expression, capillary diameter, and pericytes’ coverage. These changes were completely normalized in HF-T rats. In Sham rats T only caused resting bradycardia, increased BrS, and a mild reduction of transcytotic vesicles and PVN leakage. There were significant correlations between the number of transcytotic vesicles x PVN BBB leakage (Y=0.82x -1.74, r 2 =0.843, P<0.001) and BBB leakage x sympathetic activity (Y=0.66x +4.37, r 2 =0.415, P<0.001) Conclusions: HF courses with PVN BBB dysfunction, which is due to increased transcytosis without changes in the paracellular pathway. Training ameliorates HF’s autonomic control by normalizing transcytosis

Heart failure (HF) is characterized by reduced ventricular function, compensatory activation of neurohormonal mechanisms and marked autonomic imbalance. Exercise training (T) is effective to reduce neurohormonal activation but the mechanism underlying the autonomic dysfunction remains elusive. Knowing that blood-brain barrier (BBB) lesion contributes to autonomic imbalance, we sought now to investigate its involvement in HF- and exercise-induced changes of autonomic control. Wistar rats submitted to coronary artery ligation or SHAM surgery were assigned to T or sedentary (S) protocol for 8 weeks. After hemodynamic/autonomic recordings and evaluation of BBB permeability, brains were harvesting for ultrastructural analysis of BBB constituents, measurement of vesicles trafficking and tight junction’s (TJ) tightness across the BBB (transmission electron microscopy) and caveolin-1 and claudin-5 immunofluorescence within autonomic brain areas. HF-S rats vs. SHAM-S exhibited reduced blood pressure, augmented vasomotor sympathetic activity, increased pressure and reduced heart rate variability, and, depressed reflex sensitivity. HF-S also presented increased caveolin-1 expression, augmented vesicle trafficking and a weak TJ (reduced TJ extension/capillary border), which determined increased BBB permeability. In contrast, exercise restored BBB permeability, reduced caveolin-1 content, normalized vesicles counting/capillary, augmented claudin-5 expression, increased TJ tightness and selectivity simultaneously with the normalization of both blood pressure and autonomic balance. Data indicate that BBB dysfunction within autonomic nuclei (increased transcytosis and weak TJ allowing entrance of plasma constituents into the brain parenchyma) underlies the autonomic imbalance in HF. Data also disclose that exercise training corrects both transcytosis and paracellular transport and improves autonomic control even in the persistence of cardiac dysfunction.