Cambier, S., Gonzalez, P., Mesmer-Dudons, N., Brèthes, D., Fujimura, M., and Bourdineaud, J.P. (2012) Effects of dietary methylmercury on the zebrafish brain: histological, mitochondrial, and gene transcription analyses. Biometals : an international journal on the role of metal ions in biology, biochemistry, and medicine. 25(1):165-180.
The neurotoxic compound methylmercury (MeHg) is a commonly encountered pollutant in the environment, and constitutes a hazard
for wildlife and human health through fish consumption. To study the neurotoxic impact of MeHg on piscivorous fish, we contaminated
the model fish species Danio rerio for 25 and 50 days with food containing 13.5 μg/g dry weight (dw) of MeHg (0.6 μg MeHg/fish/day), an environmentally relevant
dose leading to brain mercury concentrations of 30 ± 4 μg of Hg g1 (dw) after 25 days of exposure and 46 ± 7 μg of Hg g1 (dw) after 50 days. Brain mitochondrial respiration was not modified by exposure to MeHg, contrary to what happens in skeletal
muscles. A 6-fold increase in the expression of the sdh gene encoding the succinate dehydrogenase Fe/S protein subunit was detected in the contaminated brain after 50 days of exposure.
An up regulation of 3 genes, atp2b3a, atp2b3b, and slc8a2b, encoding for calcium transporters was noticed after 25 days of exposure but the atp2b3a and atp2b3b were repressed and the slc8a2b gene expression returned to its basal level after 50 days, suggesting a perturbation of calcium homeostasis. After 50 days,
we detected the up regulation of glial fibrillary acidic protein and glutathione S-transferase genes (gfap and gst), along with a repression of the glutathione peroxidase gene gpx1. These results match well with a MeHg-induced onset of oxidative stress and inflammation. A transmission electron microscopic
observation confirmed an impairment of the optical tectum integrity, with a decrease of the nucleal area in contaminated granular
cells compared to control cells, and a lower density of cells in the contaminated tissue. A potential functional significance
of such changes observed in optical tectum when considering wild fish contaminated in their natural habitat might be an impaired
vision and therefore a lowered adaptability to their environment.