Abstract 085: Loss of Microglia Enhances Neuronal Activity in the Sympathetic Paraventricular Nucleus

Abstract

Microglia, the primary immune cells in the CNS, are critical in the maintenance of brain homeostasis such as participating neurogenesis and pruning synapses. Our previous work indicates that microglia are activated in hypertension; depletion of microglia in different activation status have opposite effects on blood pressure regulation, which could be due to tuning sympathetic outflow. To further delineate the mechanism how microglia modulate sympathetic nerve activity, we investigated the effect of microglial depletion on sympathetic neuronal activity in the hypothalamic paraventricular nucleus (PVN). In transgenic CD11b-DTR mice, intracerebroventricular (ICV) infusion of diphtheria toxin resulted in over 90% loss of microglia in the brain. Using the transgenic mouse brain slices, we examined the excitability of RVLM-PVN neurons by electrophysiological technique. Patch-clamp recordings obtained from the RVLM-projecting PVN neurons showed significant increases in firing frequency (3.59±0.72 vs. 1.56±0.51; P<0.05 by t-test) and half-width of action potential (2.53 ± 0.11 vs. 1.65 ± 0.07; P<0.001 by t-test); and a dramatic reduction in the outward K currents (I A and I k ) in the absence of microglia compared to control. Single-cell RNA sequencing analysis of RVLM- PVN neurons revealed a significant decreased expression of I A (Kcnd2 abd Kcnd3) and I k (kcna2, Kcna3 and Kcnc2) subunits in neurons without microglia vs. the controls. These results indicate that loss of microglia increases PVN sympathetic neuronal activity, which could be mediated, at least in part, by the inhibition of outward K currents. Collectively, this study suggests a critical role of microglia in the maintaining the homeostasis of sympathetic PVN neurons in normal condition.