Paraventricular nucleus regulatory mechanisms in stress and hypertension

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6. Project Summary/Abstract It is established that the central nervous system (CNS) contributes to the long-term regulation of blood pressure in both health and disease via effects on neuroendocrine mechanisms and sympathetic outflow. Specifically, elevations in baseline and stress-induced activation of the hypothalamic-pituitary-adrenal (HPA) axis activity and sympathetic nervous system function are implicated in the etiology of hypertension in humans and in related animal models including the spontaneously hypertensive rat (SHR). However, CNS mechanisms that mediate chronic increases in baseline blood pressure and/or stress reactivity are inadequately understood. The overall goal of our research program is to elucidate mechanisms within the brain that mediate chronic changes in baseline and stress-activated blood pressure regulation. The experiments in this application focus on regulatory mechanisms within the paraventricular nucleus (PVN) of the hypothalamus. Neurons within the PVN are critical to the central regulation of both the HPA axis and the sympathetic nervous system, and angiotensin II (Ang II) acting within the PVN has emerged as one key neuropeptide that can activate both of these outputs. We have recently identified macrophage migration inhibitory factor (MIF) as an intracellular negative regulator of the excitatory actions of Ang II in normotensive rat neurons. Collectively, our studies indicate that MIF acts within PVN neurons of normotensive rats via its intrinsic thiol protein oxidoreductase (TPOR) activity to attenuate the cardiovascular actions of Ang II. However, our data indicate this regulatory mechanism is absent from PVN neurons of SHR, and that long-term replacement of MIF within SHR neurons blunts the age-related increase in baseline blood pressure observed in this model of hypertension. These results establish an important role for MIF in attenuating the excitatory effects of Ang II, acting within the PVN, to promote age-related increases in baseline blood pressure. The present application specifically investigates the role of PVN MIF in the modulation of Ang II-mediated blood pressure regulation during acute and chronic stress, and potential contributions of both the HPA axis and the sympathetic nervous system to blood pressure regulation will be determined. The overall hypothesis is that replacement of MIF within PVN neurons of SHR will attenuate the increased blood pressure reactivity to stress observed in these animals by a mechanism that requires the TPOR activity of MIF. The specific goal is to test this hypothesis by utilizing AAV2-mediated gene delivery to chronically express MIF, or a mutant MIF protein that lacks TPOR activity, selectively in PVN neurons of SHR and normotensive control rats. This goal will be achieved via the following Specific Aims: Aim 1 is to determine the effects of long-term viral-mediated expression of MIF within PVN neurons of SHR and normotensive rats on blood pressure regulation during acute and chronic stress. Aim 2 is to determine the role of the TPOR moiety of MIF in mediating the effects of MIF within PVN neurons of SHR and normotensive rats on blood pressure regulation during acute and chronic stress.