A hypoxia-sensitive medullary nucleus modulates cerebral blood flow via a disynaptic pathway to cortex

The RVLM (rostral ventral lateral medulla) region of the brainstem is implicated as a controller of both systemic and cerebral blood flow (CBF). Past studies leave open the question of how the RVLM stabilizes CBF in awake animals. Here, we focus on CBF regulation by the adenergic subpopulation of RVLM neurons (RVLM_Dβh). Hypoxic challenge increases the variability of the activity of RVLM_Dβh neurons along with increased CBF. Experimental photoactivation of RVLM_Dβh neurons leads to rapid vasodilation of pial arterioles across the cortical mantle and increased CBF, which is only then followed by an increase in cortical activity. No significant changes in systemic physiology are observed. Virus tracing establishes disynaptic pathways from the RVLM to neocortex with predominant relays involving the lateral hypothalamus and the zona incerta subthalamic nuclei. Chemogenetic inhibition of those nuclei led to a 70 % reduction in the ability of photoactivated RVLM_Dβh neurons to induce cortical vasodilation and increase CBF. In toto, these findings reveal a major RVLM subcortical pathway to drive transcortical increases in CBF and represent an adaptive mechanism to inform the cerebral vasculature about environmental shifts in pO₂.