Early Development of the Cardio-Respiratory System in the Model Animals Zebrafish (Danio rerio) and Xenopus laevis analysed with Non-Invasive Computer Assisted Image Analysis
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Beschreibung
Independent of species, the cardiovascular system is the first functioning component of
the developing vertebrate embryos. In the studies presented here the cardiovascular and
respiratory responses to environmental, genetic and epigenetic perturbations have been
examined in detail to understand the relationships between cardiac and respiratory
performance, haematopoiesis for embryonic or larval stages in the popular model animals
zebrafish and Xenopus.
In contrast to mammalian embryos, which largely depend on convective oxygen
transport, zebrafish and Xenopus larvae because of their small body mass obtain
sufficient amounts of oxygen via bulk diffusion during the first part of their development.
This permits to study genetic mutants even with extreme defective phenotypes of the
cardio-respiratory system. Due to the tiny size of the animals new non invasive
techniques had to be used and developed in order to perform all the measurements
necessary for the characterization of the functional development of the cardio-respiratory
system. Most of these techniques are based on the use of microscopic video imaging
methods combined with a digital data analysis with custom designed software individually
developed for the different experiments.
The experiments clearly revealed that almost all of the components of the circulatory
system start working very early during development. While sympatho-vagal control of
heart rate could only be demonstrated at 12 dpf in zebrafish larvae, ventilation as well as
heart rate became sensitive to hypoxic stimulation as early as 4 dpf. Accordingly, in the
early stages, in which sympatho-vagal control of the circulatory system was not yet
established, peripheral resistance and cardiac activity was under hormonal control, and
responsiveness to adrenaline or acetylcholine was established already at 4 day post
fertilization (dpf). Nitric oxide induced vasoactivity was observed on 7 dpf.
With respect to ventilatory control the combination of classical blocking experiments and
immunohistochemistry gave strong evidence for a late onset of NMDA receptor-mediated
ventilatory control in zebrafish larvae. The chemoreflex became MK801 sensitive at 8 dpf,
but did not completely rely on a glutamatergic transmission until 13 dpf.
Hypoxia induced stimulation of angiogenesis was not observed until 15 dpf, while chronic
swim training increased the vascularization indexes at this stage of development. On the
other hand, red cell concentration was elevated in hypoxic animals at 15 dpf, but not in
trained animals. Swim training also increased mitochondrial density of muscle cells.
Experiments with different parental feeding regimes revealed that cardiovascular
parameters are very sensitive to be affected by maternal influences. As a consequence
breeding and feeding protocol has to be carefully standardized for animals which serve
for physiological measurements.
The microtechniques developed for the studies presented here have the capability to be
upscaled for high throughput screening of cardiovascular parameters i.e. for industrial
drug screening.
Autor*in
Thorsten Schwerte
Themen in »Early Development of the Cardio-Respiratory System in the Model Animals Zebrafish (Danio rerio) and Xenopus laevis analysed with Non-Invasive Computer Assisted Image Analysis«
Bildanalyse Herzkreislaufphysiologie Zebrafisch cardiovascular physiology zebrafish