Ketamine NMDA receptor-independent toxicity during zebrafish (Danio rerio) embryonic development

Concerns have been raised that the effect of anaesthetic drugs on the central nervous system may result in long-term impairment, namely when ketamine is used during embryogenesis. In addition, the cell and molecular basis of anaesthetics teratology and toxicity are still uncertain and its implications in the development remain to be clarified. More recently, the potential risks for human, and animal, exposure through environmental contamination also became an important question. In this study, the effects of sub- and over anaesthetic doses of ketamine were investigated during zebrafish (Danio rerio) embryonic development by exposing zebrafish embryos to ketamine concentrations (0.2, 0.4 and 0.8 mg mL(-1)) for a period of 20 min during the blastula stage. Ethanol 2% was used as a positive control. Morphological parameters, the overall pattern of cell death using acridine orange and overall degree of oxidative stress levels by 2,7-dichlorodihydrofluorescein-diacetate were determined. Lethality and/or developmental anomalies were measured based on specific time endpoints until 144 h post fertilisation. Results showed a concentration-dependent increase in anomalies and mortality. Cephalic disorders, enlarged organs and tail/spine anomalies were the most prominent deformities observed at 144 hpf. Acridine orange images revealed no differences in cellular death pattern in exposed embryos at 24 hpf. At the same time point, the cellular redox processes were found to be similar among groups. In summary, this study shows that ketamine is teratogen and toxic, interfering with the normal developmental pathways of embryogenesis, suggesting that ketamine exerts an independent NMDA receptor action during the zebrafish blastula stage.