Cardiovascular physiology and diseases of amphibians

Application of a ImageJ-Based Method to Measure Blood Flow in Adult Zebrafish and Its Applications for Toxicological and Pharmacological Assessments

Blood flow is an important physiological endpoint to measure cardiovascular performance in animals. Because of their innate transparent bodies, zebrafish is an excellent animal model for assessing in vivo cardiovascular performance. Previously, various helpful methods for measuring blood flow in zebrafish larvae were discovered and developed. However, an optimized method to measure blood flow in adult zebrafish has not been reported. In this paper, the tail fin region was selected as target for blood flow measurements using the Trackmate method, provided by ImageJ platform. Based on power statistic calculations, the aortic vessel at the tail base was selected, and other parameters, such as ambient temperature, were investigated for method standardization, in order to minimize experimental variation. The method was also validated using fenpropathrin and ponatinib, which showed some cardiac alterations in a previous zebrafish study. We also checked the versatility of this method by following the same setup in black tetra and medaka and found that this method performed well. However, our results show that heavy pigmentation, like that found in tiger barb, and overlapping vessels, like those in parrot fish, make it hard for this method to perform well. Overall, an optimized protocol was used for the first time to measure blood flow velocity in adult wild-type zebrafish without the aid of transgenic lines or fluorescent dye.

The Amphibian Heart

Currently, there are more than 8200 amphibian species described, including the orders Anura (frogs and toads), Caudata (salamanders and newts) and Gymnophiona (caecilians). Amphibians have 3 heart chambers: 2 atria and 1 ventricle. Their heart anatomy, histology, and physiology are reviewed. The basic morphology of the heart is similar in all amphibians with some differences due to their lifestyle. Blood flow, blood mixing, and blood oxygenation show variation due to interindividual and interspecific differences. Finally, different diagnostic methods to investigate the amphibian heart are described and reported amphibian heart diseases are summarized, including genetic, congenital, infectious, and neoplastic heart diseases.

Anuran heart development and critical developmental periods: a comparative analysis of three Neotropical anuran species

The heart begins to form early during vertebrate development and is the first functional organ of the embryo. This study aimed to describe and compare the heart development in three Neotropical anuran species, Physalaemus albonotatus, Elachistocleis bicolor, and Scinax nasicus. Different Gosner Stages (GS) of embryos (GS 18-20) and premetamorphic (GS 21-25), prometamorphic (GS 26-41) and metamorphic (GS 42-46) tadpoles were analyzed using stereoscopic microscopy and Scanning Electronic Microscopy. Heart development was similar in the three analyzed species; however, some heterochronic events were identified between P. albonotatus and S. nasicus compared to E. bicolor. In addition, different patterns of melanophores arrangement were observed. During the embryonic and metamorphic periods, the main morphogenetic events occur: formation of the heart tube, regionalization of the heart compartments, development of spiral valve, onset of heartbeat, looping, and final displacement of the atrium and its complete septation. Both periods are critical for the normal morphogenesis and the correct functioning of the anuran heart. These results are useful to characterize the normal anuran heart morphology and to identify possible abnormalities caused by exposure to environmental contaminants.

Microbiological and cytological characterization of coelomic fluid from three captive endangered amphibian Gastrotheca species with edema syndrome: preliminary analysis

OBJECTIVE

Edema syndrome is highly prevalent but under researched in captive frogs around the world. The objective of the present study was to characterize at a basic microbiological and cytological level of the bacteria of the edema fluid of 20 individuals of the genus Gastrotheca to determine the presence of possible anaerobic and aerobic bacteria.

RESULTS

Fourteen types of bacteria were identified in the edema fluid, 12 of them at the species level (Pasteurella haemolytica, Hafnia alvei, Enterobacter agglomerans, Aeromonas hydrophila, Pseudomonas fluorescens, Burkholderia pseudomallei, Salmonella arizonae, Enterobacter gergoviae, Enterobacter sakazakii, Yersinia enterocolitica, Klebsiella oxytoca, and Klebsiella ozaenae) and two at the genus level (Enterococcus spp. and Streptococcus spp.). The most frequently identified cells were lymphocytes (37.7% in females and 46.4% in males), erythrocytes (23.5% in females and 17.5% in males) and neutrophils (4.2% in females and 2.8% in males). Finally, no relationship was found between the data obtained and the sex of the individuals studied.

Persistent fibrosis, hypertrophy and sarcomere disorganisation after endoscopy-guided heart resection in adult Xenopus

Models of cardiac repair are needed to understand mechanisms underlying failure to regenerate in human cardiac tissue. Such studies are currently dominated by the use of zebrafish and mice. Remarkably, it is between these two evolutionary separated species that the adult cardiac regenerative capacity is thought to be lost, but causes of this difference remain largely unknown. Amphibians, evolutionary positioned between these two models, are of particular interest to help fill this lack of knowledge. We thus developed an endoscopy-based resection method to explore the consequences of cardiac injury in adult Xenopus laevis. This method allowed in situ live heart observation, standardised tissue amputation size and reproducibility. During the first week following amputation, gene expression of cell proliferation markers remained unchanged, whereas those relating to sarcomere organisation decreased and markers of inflammation, fibrosis and hypertrophy increased. One-month post-amputation, fibrosis and hypertrophy were evident at the injury site, persisting through 11 months. Moreover, cardiomyocyte sarcomere organisation deteriorated early following amputation, and was not completely recovered as far as 11 months later. We conclude that the adult Xenopus heart is unable to regenerate, displaying cellular and molecular marks of scarring. Our work suggests that, contrary to urodeles and teleosts, with the exception of medaka, adult anurans share a cardiac injury outcome similar to adult mammals. This observation is at odds with current hypotheses that link loss of cardiac regenerative capacity with acquisition of homeothermy.

Severe necrotizing myocarditis caused by serratia marcescens infection in an axolotl (Ambystoma mexicanum)

This report provides the first account of the pathological changes associated with infection by Serratia marcescens in an adult male axolotl. The infection resulted in septicaemia with severe multifocal necrotizing myocarditis. The latter lesion evolved to cardiac rupture, haemopericardium and death resulting from cardiac tamponade. This animal was exposed to higher than usual temperatures (24-25 °C) 2 weeks before the onset of disease and this may have resulted in immunocompromise and opportunistic bacterial infection. S. marcescens was isolated from the coelomic and pericardial cavity. Both isolates were identical and were resistant to β-lactam antibiotics, but not to aminoglycosides or fluoroquinolones. The production of red prodigiosin pigment by the bacterium suggested an environmental origin. Overall, the clinical and histopathological presentation suggests that S. marcescens should be included in the list of aetiological agents of the 'red-leg'/bacterial dermatosepticaemia syndrome of amphibians.