Microscopic photoplethysmography-based evaluation of cardiotoxicity in whitefish larvae induced by acute exposure to cadmium and phenol.

Toxic environmental pollutants pose a health risk for both humans and animals. Accumulation of industrial contaminants in freshwater fish may become a significant threat to biodiversity. Comprehensive monitoring of the impact of environmental stressors on fish functional systems is important and use of non-invasive tools that can detect the presence of these toxicants in vivo is desirable. The blood circulatory system, by virtue of its sensitivity to the external stimuli, could be an informative indicator of chemical exposure. In this study, microscopic photoplethysmography-based approach was used to investigate the cardiac activity in broad whitefish larvae (Coregonus nasus) under acute exposure to cadmium and phenol. We identified contamination-induced abnormalities in the rhythms of the ventricle and atrium. Our results allow introducing additional endpoints to evaluate the cardiac dysfunction in fish larvae and contribute to the non-invasive evaluation of the toxic effects of industrial pollutants on bioaccumulation and aquatic life.

Optical transparency and label-free vessel imaging of zebrafish larvae in shortwave infrared range as a tool for prolonged studying of cardiovascular system development.

Optical techniques are utilized for the non-invasive analysis of the zebrafish cardiovascular system at early developmental stages. Being based mainly on conventional optical microscopy components and image sensors, the wavelength range of the collected and analyzed light is not out of the scope of 400-900 nm. In this paper, we compared the non-invasive optical approaches utilizing visible and near infrared range (VISNIR) 400-1000 and the shortwave infrared range (SWIR) 900-1700 nm. The transmittance spectra of zebrafish tissues were measured in these wavelength ranges, then vessel maps, heart rates, and blood flow velocities were calculated from data in VISNIR and SWIR. An increased pigment pattern transparency was registered in SWIR, while the heart and vessel detection quality in this range is not inferior to VISNIR. Obtained results indicate an increased efficiency of SWIR imaging for monitoring heart function and hemodynamic analysis of zebrafish embryos and larvae and suggest a prolonged registration period in this range compared to other optical techniques that are limited by pigment pattern development.

Influence of hypomagnetic field on the heartbeat in zebrafish embryos.

The magnetic environment may influence the functioning of the cardiovascular system. It was reported that low-frequency and static magnetic fields affect hemodynamics, heart rate, and heart rate variability in animals and humans. Moreover, recent data suggest that magnetic fields affect the circadian rhythms of physiological processes. The influence of the magnetic environment on heart functionating during early development has been studied insufficiently. We utilized transparent zebrafish embryos to evaluate the effect of the hypomagnetic field on the characteristics of cardiac function using a noninvasive optical approach based on photoplethysmographic microscopic imaging. The embryos were exposed to the geomagnetic and hypomagnetic fields from the second to the 116th hour post fertilization under a 16 h light/8 h dark cycle or constant illumination. The exposure of embryos to the hypomagnetic field in both lighting modes led to increased embryo mortality, the appearance of abnormal phenotypes, and a significant increase in the embryo's heartbeat rate. The difference between maximal and minimal heartbeat intervals, maximal to minimal heartbeat intervals ratio, and the coefficient of variation of heartbeat rate were increased in the embryos exposed to the hypomagnetic field under constant illumination from 96 to 116 h post fertilization. The dynamics of heartbeat rate changes followed a circadian pattern in all studied groups except zebrafish exposed to the hypomagnetic field under constant illumination. The results demonstrate the importance of natural magnetic background for the early development of zebrafish. The possible mechanisms of observed effects are discussed.

Single-shot Mueller-matrix imaging of zebrafish tissues: In vivo analysis of developmental and pathological features.

Zebrafish is a well-established animal model for developmental and disease studies. Its optical transparency at early developmental stages allows in vivo tissues visualization. Interaction of polarized light with these tissues provides information on their structure and properties. This approach is effective for muscle tissue analysis due to its birefringence. To enable real-time Mueller-matrix characterization of unanesthetized fish, we assembled a microscope for single-shot Mueller-matrix imaging. First, we performed a continuous observation of 48 species within the period of 2 to 96 hpf and measured temporal dependencies of the polarization features in different tissues. These measurements show that hatching was accompanied by a sharp change in the angle and degree of linearly polarized light after interaction with muscles. Second, we analyzed nine species with skeletal disorders and demonstrated that the spatial distribution of light depolarization features clearly indicated them. Obtained results demonstrated that real-time Mueller-matrix imaging is a powerful tool for label-free monitoring zebrafish embryos.

Blood Vessel Imaging at Pre-Larval Stages of Zebrafish Embryonic Development.

The zebrafish (Danio rerio) is an increasingly popular animal model biological system. In cardiovascular research, it has been used to model specific cardiac phenomena as well as to identify novel therapies for human cardiovascular disease. While the zebrafish cardiovascular system functioning is well examined at larval stages, the mechanisms by which vessel activity is initiated remain a subject of intense investigation. In this research, we report on an in vivo stain-free blood vessel imaging technique at pre-larval stages of zebrafish embryonic development. We have developed the algorithm for the enhancement, alignment and spatiotemporal analysis of bright-field microscopy images of zebrafish embryos. It enables the detection, mapping and quantitative characterization of cardiac activity across the whole specimen. To validate the proposed approach, we have analyzed multiple data cubes, calculated vessel images and evaluated blood flow velocity and heart rate dynamics in the absence of any anesthesia. This non-invasive technique may shed light on the mechanism of vessel activity initiation and stabilization as well as the cardiovascular system's susceptibility to environmental stressors at early developmental stages.

Imaging photoplethysmography and videocapillaroscopy enable noninvasive study of zebrafish cardiovascular system functioning.

We report on the noninvasive method for in vivo study of fish's cardiovascular system, that is, the heart and the structure of vessels that carry blood throughout the body. The proposed approach is based on combined photoplethysmographic and videocapillaroscopic microscopic imaging and enables noncontact two-dimensional mapping of blood volume changes. We demonstrate that the obtained data allows precise measurements of heartbeat, blood flow velocity and other important parameters (see Videos S1 and S2). To validate the developed image processing technique, we have carried out multiple experiments on zebrafish-a well-proven informative model organism widely used to understand cardiac development. The proposed approach may be effective for the study of cardiovascular system formation and functioning as well as the impact of various influencing factors on them.