Topographical mapping of catecholaminergic axon innervation in the flat-mounts of the mouse atria: a quantitative analysis

Abstract

The sympathetic nervous system is crucial for controlling multiple cardiac functions. However, a comprehensive, detailed neuroanatomical map of the sympathetic innervation of the heart is unavailable. Here, we used a combination of state-of-the-art techniques, including flat-mount tissue processing, immunohistochemistry for tyrosine hydroxylase (TH, a sympathetic marker), confocal microscopy and Neurolucida 360 software to trace, digitize, and quantitatively map the topographical distribution of the sympathetic postganglionic innervation in whole atria of C57Bl/6 J mice. We found that (1) 4–5 major extrinsic TH-IR nerve bundles entered the atria at the superior vena cava, right atrium (RA), left precaval vein and the root of the pulmonary veins (PVs) in the left atrium (LA). Although these bundles projected to different areas of the atria, their projection fields partially overlapped. (2) TH-IR axon and terminal density varied considerably between different sites of the atria with the greatest density of innervation near the sinoatrial node region (P < 0.05, n = 6). (3) TH-IR axons also innervated blood vessels and adipocytes. (4) Many principal neurons in intrinsic cardiac ganglia and small intensely fluorescent cells were also strongly TH-IR. Our work provides a comprehensive topographical map of the catecholaminergic efferent axon morphology, innervation, and distribution in the whole atria at single cell/axon/varicosity scale that may be used in future studies to create a cardiac sympathetic-brain atlas.

Chronic intermittent hypoxia remodels catecholaminergic nerve innervation in mouse atria

“…11C and D), ICG neurons were clustered together following CIH compared to RA. Similar to our recent study (Bizanti et al, 2023;Zhang et al, 2023), and in contrast to vagal efferent axons, TH-IR axons were seen to travel through TH-IR neurons in the ganglia rather than tightly encircle individual neurons. TH-IR axons coursing through ICG were observed in the optical sections (Fig.…”

“…Tissue processing and immunolabelling were performed as described previously (Bizanti et al, 2023;Zhang et al, 2023;Li et al, 2014). Following dissection, the tissues were washed six times for 5 min in 0.1M PBS (pH 7.4), then immersed for 48 h in a blocking reagent (2% bovine serum albumin, 10% normal donkey serum, 2% Triton X-100, 0.008% NaN 3 in 0.1 M PBS, pH 7.4).…”

“…To quantify the regional density of TH-IR fibres in the atria, we segregated images into specific regions of interest (ROI) similar to our previous work (Zhang et al, 2023): SAN region, AVN region (the atrial region at the interatrial septum near the AVN), SVC, IVC, right auricle, left atrial -PV junction, left PV, middle PV, right PV, left auricle. Six window frames 1000 × 1000 pixels, which included all z-steps, were selected and averaged from each region of each group.…”

A Heartbeat-Interval Time Series Analysis, Modified Detrended Fluctuation Analysis, mDFA, Distinguishes between Stressed- and Happy-Heartbeats: From Invertebrate Animals to Humans

“…Either (Yi=Ii-< I >)or(Yi=<I > À Ii) can be usable. But if squared, (< I > À Ii) 2 =(Ii-< I >) 2 , both became equal.…”

“…The cardiovascular system includes the heart, intrinsic nerve ganglia, and afferent/ efferent extrinsic nerves. It maintains brain-heart health [1][2][3]. When it goes wrong, we get sick.…”