Sex differences in the subcellular distribution of angiotensin type 1 receptors and NADPH oxidase subunits in the dendrites of C1 neurons in the rat rostral ventrolateral medulla

Abstract

The rostral ventrolateral medulla (RVLM), a region critical for the tonic and reflex control of arterial pressure, contains a group of adrenergic (C1) neurons that project to the spinal cord and directly modulate pre-ganglionic sympathetic neurons. Epidemiological data suggest that there are gender differences in the regulation of blood pressure. One factor that could be involved is angiotensin II signaling and the associated production of reactive oxygen species (ROS) by NADPH oxidase, which is emerging as an important molecular substrate for central autonomic regulation and dysregulation. In this study dual electron microscopic immunolabeling was used to examine the subcellular distribution of the angiotensin type 1 (AT1) receptor and two NADPH oxidase subunits (p47 and p22) in C1 dendritic processes, in tissue from male, proestrus (high estrogen) and diestrus (low estrogen) female rats. Female dendrites displayed significantly more AT1 labeling and significantly less p47 labeling than males. While elevations in AT1 labeling primarily resulted from higher levels of receptor on the plasma membrane, p47 labeling was reduced both on the plasma membrane and in the cytoplasm. Across the estrous cycle, proestrus females displayed significantly higher levels of AT1 labeling than diestrus females, which resulted exclusively from plasma membrane density differences. In contrast, p47 labeling did not change across the estrous cycle, indicating that ROS production might reflect AT1 receptor membrane density. No significant differences in p22 labeling were observed. These findings demonstrate that both sex and hormonal levels can selectively affect the expression and subcellular distribution of components of the angiotensin II signaling pathway within C1 RVLM neurons. Such effects could reflect differences in the capacity for ROS production, potentially influencing short term excitability and long term gene expression in a cell group which is critically involved in blood pressure regulation, potentially contributing to gender differences in the risk of cardiovascular disease.