Remodeling of Ventricular Catecholaminergic Axons Following Chronic Intermittent Hypoxia in Mice

Chronic intermittent hypoxia (CIH) is a widely employed model for sleep apnea. The imbalance of autonomic control may contribute to CIH-induced cardiovascular diseases. Previously, we demonstrated that CIH increases sympathetic innervation of the atria. In this study, we determined whether CIH remodels peripheral cardiac tyrosine hydroxylase (TH, a marker for sympathetic efferent axons) innervation in the whole ventricles. The two challenges here were: 1) labeling the entire TH-IR axon innervation in the full thickness (~500 μm) of whole flat-mount ventricles. 2) Quantifying the topographical distribution of TH-IR axons through the thick ventricular walls at the single axon/varicosity scale. In this study, C57BL/6J mice (male, 2 months old, n=7/group) were exposed to room air (RA, 21% O 2 ) or CIH (alternating between 21% and 5.7% O 2 every 6 minutes for 10 hours/day) for 8-10 weeks. We prepared flat-mounts of the whole ventricles and septum and processed them with immunohistochemical labeling for TH. Using the Zeiss M2 Imager, confocal microscope, Zeiss Arivis Vision 4D, and Neurolucida system, we traced and digitized the TH-IR axons. We found that: 1) In RA and CIH mice, several large TH-immunoreactive (TH-IR) bundles from the base area entered the ventricles and septum. These large bundles branched into numerous smaller bundles as they traveled downward toward the apex and finally developed into fine varicose axons and terminals in the epicardial and myocardial layers. 2) Using Vision 4D, we were able to accurately detect, trace, and digitize all TH-IR axons in the ventricle walls with high accuracy. 3) CIH increased overall TH-IR axon density and network complexity of the whole ventricles and septum. 3) Abnormal CIH TH-IR axon terminal structures were frequently seen. 4) We geometrically and precisely registered the tracing data into a scaffold map for presentation and comparison in 3D. Altogether, CIH increased sympathetic innervation of the heart which may contribute to the augmented sympathetic drive. Our success in mapping data in the 3D heart scaffold will establish a heart-brain connectome/atlas. Supported by NIH 1 U01 NS113867-01 NIH R15 1R15HL137143-01A1, 2R01HL137832-05 and Carl Zeiss. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.