Autonomic and Antihypertensive Actions of Neuronal CGRP/RAMP1 Receptors

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DESCRIPTION (provided by applicant): Calcitonin gene-related peptide (CGRP) functions as an autocrine/paracrine factor, hormone and neuro- modulator. While best known for its potent vasodilator activity, CGRP is involved in many neural processes including nociception, neurogenic inflammation, migraine and anxiety. The CGRP receptor has an obligatory requirement for a subunit called Receptor Activity-Modifying Protein 1 (RAMP1). RAMP1 enhances CGRP binding to the receptor and receptor trafficking. While the role of vascular CGRP receptors is well recognized, the role of nervous system CGRP receptors in blood pressure regulation remains unclear. T he proposed studies will test the hypothesis that nervous system CGRP/RAMP1 receptors are powerful modulators of baroreflex sensitivity and autonomic activity capable of preventing or reversing hypertension. The specific aims of the proposed research are to: (1) Determine whether selective overexpression of RAMP1 in the nervous system improves autonomic regulation and attenuates angiotensin II (Ang-II) and phenylephrine-induced hypertension, and conversely if deletion of nervous system RAMP1 impairs auto- nomic regulation and enhances hypertension; (2) Identify nervous system sites of CGRP/RAMP1 receptor expression responsible for autonomic and blood pressure phenotypes in the nervous system-targeted RAMP1 transgenic and knockout mice; and (3) Test the hypothesis that activation of nervous system CGRP/ RAMP1 receptors abrogates Ang-II induced dysautonomia and hypertension by reducing oxidative stress. Our preliminary data indicate that just a 1.5-fold overexpression of RAMP1 in the nervous system improves autonomic regulation and nearly abolishes Ang-II hypertension. We will measure autonomic and cardiovascular phenotypes in male and female RAMP1 transgenic and knockout mice using the nervous system-specific nestin Cre-recombinase to globally target the nervous system and local injections of viral vectors expressing Cre-recombinase to target specific brain regions including brainstem, subfornical organ and paraventricular nucleus. Blood pressure, heart rate, locomotor activity and an array of autonomic indices will be measured in conscious mice implanted with blood pressure and ECG telemeters, both under basal conditions and during hypertension induced by 4-week infusions of Ang-II and phenylephrine delivered by osmotic minipump. To separate effects on sensory vs. central com- ponents of the baroreflex, complementary experiments will be performed in anesthetized mice that include measurements of baroreceptor afferent nerve activity from aortic depressor nerve and reflex changes in heart rate and blood pressure during graded electrical stimulation of baroreceptor afferents. Systemic and central infusions of the antioxidant tempol and central injections of viral vectors encoding siRNAs targeted to NADPH oxidase subunits will be used to determine the role of oxidative stress in mediating autonomic dysregulation and hypertension. Gene expression of CGRP, CGRP receptor subunits, Ang-II receptors, and pro- and anti- oxidant molecules will be measured in the relevant brain regions, sensory ganglia, and peripheral arteries. The significance of identifying nervous system CGRP/RAMP1 receptors as positive modulators of autonomic control relates to their potential as therapeutic targets for treatment of dysautonomia in hyperten- sion, and other pathological states such as heart failure and diabetes. Inhibition of Ang II-mediated effects by activation of CGRP/RAMP1 receptors has widespread implications in hypertension and heart failure.