Summary: The ability of an organism to reduce the brain blood flow in response to sudden surges in systemic blood pressure(BP) is known as cerebral autoregulation (CAR). In contrast to term neonates preterm neonates are not able to reducecerebral blood flow (CBF) in response to increased systemic BP. In preterm neonates this exposes fragile cerebral vesselsto a significantly increased blood flow at high pressure leading to their rupture and brain damage. Our preliminary studiesdemonstrate that near-term fetuses can constrict carotid arteries and reduce CBF when systemic BP rises; however thiscapability is not developed in the preterm fetus. We also observed that the constriction of carotid arteries to reduce CBF isregulated by the adrenergic nervous system specifically by the activities of alpha-1 adrenergic receptors (1-ARs). Thesereceptors are expressed at a significantly lower number in preterm carotid arteries. Also we observed that following theremoval of adrenergic control in the near-term fetus by severing the superior cervical ganglion (SCG) made them lose theirability to reduce carotid blood flow (CaBF) to the brain with the rise in systemic BP. Thus after the removal of SCG bothpreterm and near-term fetuses cannot reduce CBF following an increase in systemic BP. During ex-vivo experiments oncarotid segments we observed that preterm arterial constriction in response to 1-ARs agonist was significantly lower thanthose from near-term lambs. Thus we concluded that reduced activities of 1-ARs play a fundamental role in regulatingCaBF with the rise in systemic BP. We also observed that the reduction in the activities of 1-ARs agonists in pretermresulted from reduced expression of 1-ARs compared to those in near-term fetal lambs. Furthermore we present evidencethat DNA hypermethylation reduces 1-ARs promoter activities by luciferase reporter assays and the involvement of histonemodifications. Thus we will test the hypothesis that promoter DNA hypermethylation and histone modifications reduce theexpression and function of 1-AR subtypes (1A- 1B- 1D) in the carotid arteries and play an essential role in the maturationof cerebral autoregulation from preterm to term fetus. We will also collect data from both sexes (male versus female) toidentify sex-related changes. The studies will be conducted ex-vivo on isolated carotid arteries and in vivo in chronicallycatheterized fetal sheep. The hypothesis will be tested with two specific aims. Aim 1: From preterm to term fetus in a sex-specific manner we will conduct an in-depth mechanistic analysis of promoter DNA methylation and histone modificationson differential expression of 1-AR subtypes in carotid arteries. Aim 2: From preterm to term fetus in a sex-specific mannerwe will determine the functional significance of differential 1-AR subtypes promoter methylation histone modificationsand gene expression on carotid artery contractility and blood flow regulation to the brain in response to an increase insystemic pressure. The measurements will be conducted in real-time in-vivo with in-utero fetal maturation every weekfrom 105 to 137 days. This will provide valuable information regarding the role of 1-AR subtypes and the epigeneticmechanisms involved in the maturation of CAR.