Caspase Lesions of PVN-Projecting MnPO Neurons Blocks the Sustained Component of CIH-Induced Hypertension in Adult Male Rats

Purpose: Obstructive Sleep Apnea (OSA) is characterized by cessations in respiration that leads to development of hypertension and persists into the waking period even during normal respiratory patterns. Previous studies show that experimental models of chronic intermittent hypoxia (CIH) produces sustained hypertension similar to that with OSA. It has been proposed that peripheral and CNS renin-angiotensin systems contribute to hypertension associated with CIH. Our working hypothesis is that increased circulating angiotensin II feeds into the forebrain, increasing excitatory signaling through the hypothalamus and hindbrain, creating a vicious cycle. The median preoptic nucleus (MnPO) is an integrative forebrain region that contributes to blood pressure regulation. The MnPO has projections to the paraventricular nucleus (PVN) of the hypothalamus, which contains pre-autonomic centers that project to regions in the hindbrain and regulate sympathetic outflow. We hypothesize that lesioning pathway specific projections from the MnPO to the PVN could attenuate CIH hypertension. Methods: Adult male Sprague-Dawley rats (250-300g) were anesthetized with isoflurane and stereotaxically injected bilaterally in the PVN with a retrograde AAV containing Cre (AAV9.CMV.HI.eGFP-Cre.WPRE.SV40) and with the caspase-3 (AAV5-flex-taCasp3-TEVp) or control virus (AAV5-hSyn-DIO-mCherry) in the MnPO. After 1-week recovery, rats were instrumented with aortic radio telemetry and allowed an additional week recovery. Rats were then moved to new homecages and underwent baseline recording before undergoing our 7-day CIH protocol. Results: The control group exposed to CIH developed chronic hypertension, however, caspase lesions blunted the sustained hypertension. Brain tissue processed for FosB immunohistochemistry showed decreased expression with caspase-induced inhibition in the MnPO and downstream autonomic regulating nuclei. CIH significantly increased plasma advanced oxidative protein products (AOPP) levels in controls. This increase in AOPP levels was blocked in caspase-lesioned rats comparable to normoxic control concentrations. In situ hybridization experiments indicate a reduction in angiotensin type 1a receptors (AT1aR) expression in the caspase-lesioned group exposed to CIH compared to CIH controls. Conclusion: The results indicate that MnPO neurons that project to the PVN play a significant role in blood pressure regulation and in the development of persistent CIH hypertension.