Richardson, M. K. | bioRxiv Science

bioRxiv2021

Developmental neuroanatomy of the Rosy Bitterling Rhodeus ocellatus (Teleostei: Cypriniformes)--A microCT study

Bitterlings are a group of teleost fish (Cyprinifromes: Acheilanathidae) notable for their brood parasitic lifestyle. Bitterling embryos develop as parasites inside the gill chamber of their freshwater mussel hosts. However, little is known about brain development in this species. Here, we have imaged the development of the brain of the Rosy Bitterling (Rhodeus ocellatus) at four embryonic stages (165, 185, 210, 235 hours post-fertilization) using micro-computed tomography (microCT) with special emphasis on developmental regionalization and brain ventricular organization. We provide a detailed neuroanatomical account of the development of the brain divisions with reference to The Atlas of Early zebrafish Brain Development and the updated prosomeric model. Segmentation and three-dimensional visualization of the ventricular system were performed in order to clarify changes in the longitudinal brain axis as a result of cephalic flexure during development. During early embryonic and larval development, we find that histological differentiation, tissue boundaries, periventricular proliferation zones, and ventricular spaces are all recognizable using microCT. Importantly, our approach is validated by the fact that the profile of CT values displayed here in the bitterling brain are consistent with genoarchitecture identified in previous studies. We also find developmental heterochrony of the inferior lobe in the Rosy Bitterling compared to the zebrafish. Our study provides a foundation for future studies of the brain development in the Rosy Bitterling, a valuable model species for studying the evolutionary adaptations associated with brood parasitism.

neuroscience↗

bioRxiv2020

Effect of pesticides and metals on zebrafish embryo development and larval locomotor activity

The zebrafish has been widely used as a predictive model in safety and toxicology. Low cost high-throughput screening can be achieved with this model, and the genome contains orthologues of the majority of human disease genes. However, previous studies indicate that the predictivity of the zebrafish model in toxicology varies between compound and compound class. We examined this issue by screening 24 compounds from two different compound classes, metals and biocides (pesticides/insecticides) for toxicity in the zebrafish model and looked at the effects on hatching, morphology and predictivity for mammalian toxicity. Wild-type zebrafish embryos were exposed to test compounds in 96-well plates for 96 hours starting at 24 hours post fertilization. Hatching was either delayed or accelerated depending on the compound. Three types of alteration in behavioural responses were noted: (i) hypoactivity; (ii) hyperactivity; and (iii) biphasic response (a dose-dependent shift between hypo- and hyperactivity). LC50 of compounds was calculated and compared to published LD50 values in rodents. The zebrafish-rodent values were poorly correlated for both metals and biocides. We conclude that, although the zebrafish is a good model for some aspects of toxicology, its predictivity for mammalian toxicity needs to be determined per compound class.

pharmacology and toxicology↗