Cardiac morphology and blood pressure in the adult zebrafish

Abstract

Zebrafish has become a popular model for the study of cardiovascular development. We performed morphologic analysis on 3 months postfertilization zebrafish hearts (n Ն 20) with scanning electron microscopy, hematoxylin and eosin staining and Masson's trichrome staining, and morphometric analysis on cell organelles with transmission electron photomicrographs. We measured atrial, ventricular, ventral, and dorsal aortic blood pressures (n Ն 5) with a servonull system. The atrioventricular orifice was positioned on the dorsomedial side of the anterior ventricle, surmounted by the single-chambered atrium. The atrioventricular valve was free of tension apparati but supported by papillary bands to prevent retrograde flow. The ventricle was spanned with fine trabeculae perpendicular to the compact layer and perforated with a subepicardial network of coronary arteries, which originated from the efferent branchial arteries by means of the main coronary vessel. Ventricular myocytes were larger than those in the atrium (P Ͻ 0.05) with abundant mitochondria close to the sarcolemmal. Sarcoplasmic reticulum was sparse in zebrafish ventricle. Bulbus arteriosus was located anterior to the ventricle, and functioned as an elastic reservoir to absorb the rapid rise of pressure during ventricular contraction. The dense matrix of collagen interspersed across the entire bulbus arteriosus exemplified the characteristics of vasculature smooth muscle. There were pressure gradients from atrium to ventricle, and from ventral to dorsal aorta, indicating that the valves and the branchial arteries, respectively, were points of resistance to blood flow. These data serve as a framework for structure-function investigations of the zebrafish cardiovascular system.

PDGF signaling is required for epicardial function and blood vessel formation in regenerating zebrafish hearts

“…Interestingly, epicardium-specific pdgfrβ knock-outs in mice show abnormal clustering of endothelial cells, absence of epicardial-derived smooth muscle cells, and defective coronary artery formation (22), indicating an essential role for PDGF signaling in coronary vessel development. Therefore, despite the fact that pericytes rather than smooth muscle cells surround the endothelial cells of blood vessels in zebrafish (14), molecular events in the developing mouse heart are very similar to what we observed during zebrafish heart regeneration. For instance, some tbx18-positive cells have been shown to express pdgfrβ in embryonic mouse hearts, indicative of the epicardial contribution of pdgfrβ-marked vascular support cells (10).…”

“…Zebrafish coronary blood vessels do not have smooth muscle cells. Instead, blood vessels are surrounded by pericyte-like mural cells (14). If epicardial cells undergo EMT during zebrafish heart regeneration, they most likely contribute to mural cells and fibroblasts of the coronary vessels.…”

High-Resolution Tissue Doppler Imaging of the Zebrafish Heart During Its Regeneration

“…The diameter of the adult zebrafish bulboventricular annulus is typically 100-150 lm, as measured by scanning electron microscopy. 15 A bulboventricular annulus of similar size was observed by echocardiography, and even better dynamic blood flow information was obtained using this modality. Figure 5b shows a typical CMI image of a normal zebrafish heart and its corresponding anatomical measurement locations.…”

“…The human heart comprises separate discrete chambers, whereas the ventricle of the zebrafish heart is filled with muscular trabeculae to form a spongy network and the atrium was mainly composed of pectinate muscle. 15 The long and slender trabecular network creates many tiny intertrabecular lacunae in the ventricle, which increases the contractile efficiency in pumping the blood into the bulbus arteriosus. However, this spongy network of the ventricle may increase the resistance to blood inflow or decrease the pressure gradient between the two chambers during early diastole.…”

“…Although such an array system can provide a high imaging frame rate for the cardiac imaging of small animals, the use of higher frequency ultrasound would improve the image resolution. 14 The heart of the adult zebrafish is smaller than 1.5 · 1.5 · 1.5 mm 3,15 and so the ultrasound frequency needs to be higher than 75 MHz to provide sufficient resolution for imaging the detailed heart structures according to the suggestions from previous studies. 14,16 Array transducers operating at frequencies higher than 50 MHz are not available, but a singleelement transducer system based on mechanical scanning is still an option for zebrafish heart imaging.…”