Directional blood flow within a shared capillary network links the nucleus of the solitary tract and area postrema in rats

Capillary networks are classically viewed as passive conduits that supply energy to active neural tissue. Whether microvascular organization can also contribute to functional communication between adjacent brain regions remains largely unexplored. The nucleus of the solitary tract (NTS) and area postrema (AP) form a brainstem complex that coordinates homeostatic regulation; however, the organization and functional significance of their shared microcirculation remain unknown.

Previous anatomical studies identified direct capillary connections between the NTS and AP, demonstrating a continuous microvascular network between two anatomically distinct regions. Here, we used in vivo two-photon microscopy, combined with fluorescent vascular labeling and analysis of red blood cell dynamics, to investigate the blood flow within the shared NTS-AP microvasculature. Blood flow across these junctions is predominantly unidirectional, flowing from the NTS towards AP.

Morphometric analyses reveal that AP capillaries are significantly larger than those in the NTS, providing a structural basis for this flow asymmetry. Despite these geometric differences, capillary flow velocities are preserved across regions, indicating active regulation of perfusion within the shared network. These findings reveal directional blood flow within a shared AP-NTS capillary network, identifying a potential vascular route by which diffusible signals generated in one region may preferentially reach the other.

Preprint is available at https://doi.org/10.1101/2025.11.22.689934. This work was supported by NHLBI 162575 (J.E.S.) and by the Office of the Director, National Institutes of Health and National Institute of General Medical Sciences under Award Number S10OD032336-01. Neuroscience Institute, Georgia State University, Atlanta, GA, USA Kaitlin E.

Carson, Ranjan Roy & Javier E. Stern Center for Neuroinflammation and Cardiometabolic Diseases, Georgia State University, Atlanta, GA, USA The authors declare no competing interests. Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

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