PROJECT 4 (ladecola): Forebrain Mechanisms of Neurovascular Dysfunction in Hypertension The brain is a major target of the end-organ damage produced by hypertension, an effect linked to the disruption of vital cerebrovascular regulatory mechanisms that threatens the cerebral blood supply and increases the brain's susceptibility to stroke and dementia. The long-term goal of Project 4 is to unravel the mechanisms by which hypertension exerts its deleterious effects on the brain. Angll plays a key role in the pathophysiology of hypertension. Systemic administration of Angll at concentrations not sufficient to elevate arterial pressure induces hypertension if the administration is sustained in time (slow pressor hypertension). Synaptic adaptations (neuroplasticity) in the subfornical organ (SFO), one of the forebrain circumventricular organs, and in the paraventricular nucleus of the hypothalamus (PVN) are critical for the development of the neurohumoral dysfunction underiying the hypertension. These adaptive changes, turned maladaptive, are triggered by Angll through activation of ATI receptors in the SFO and consequent production of reactive oxygen species (ROS). The SFO, in turn, activates NMDA receptors in the PVN, which contribute to the hypertension by increasing sympathetic outflow and releasing hormones, including vasopressin (AVP). Circulating Angll and AVP increase the vascular expression of endothelin-1 (ET1), a potent vasoconstrictor that is upregulated in arteries of patients with essential hypertension. Project 4 will test the hypothesis that slow pressor hvpertension elicits cerebrovascular dvsfunction, which is mediated by the SFO-PVN pathway through neurohumoral effects on cerebral blood vessels involving Anall, AVP and ET1. Experiments will be conducted in mice in which cerebrovascular regulation will be studied using cranial window preparations. Both pharmacological and genetic approaches will be used to achieve the stated goals. We will test the following hypotheses: (1) Slow pressor Angll administration disrupts key homeostatic responses of the cerebral circulation, an effect that may precede the development of hypertension;(2) The central signaling mechanisms of the cerebrovascular dysfunction involve AT1 receptors and ROS production in the SFO, and NMDA receptors in the PVN;(3) PVN-derived AVP and circulating Angll induce cerebrovascular dysfunction through upregulation of ET1 in cerebral blood vessels;(4) Angll and ET1 act synergistically to induce cerebrovascular dysfunction via NADPH-oxidase derived ROS.
Hypertension is the leading cause of stroke and vascular cognitive impairment. However, the mechanisms of these effects are pooriy understood. The proposed studies represent the first exploration of the role of the SFO-PVN axis in the cerebrovascular dysfunction induced by slow pressor hypertension. The results will provide novel insights into the fundamental mechanisms by which hypertension alters the cerebral circulation and may suggest new therapies to protect the brain from the devastating effects of hypertension.
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