Morphological and behavioral responses of zebrafish after 24h of ketamine embryonic exposure

Ketamine, one anesthetic used as an illicit drug, has been detected both in freshwater and marine ecosystems. However, knowledge of its impact on aquatic life is still limited. This study aimed to test its effects in zebrafish embryos by analyzing its time- and dose-dependent developmental toxicity and long-term behavioral changes. The 24h-LC₅₀ was calculated from percent survival using probit analysis. Based on the 24h-LC₅₀ (94.4mgL^-1), embryos (2hour post-fertilization - hpf) were divided into four groups, including control, and exposed for 24h to ketamine concentrations of 50, 70 or 90mgL^-1. Developmental parameters were evaluated on the course of the experimental period, and anatomical abnormalities and locomotor deficits were analyzed at 144hpf. Although the portion of ketamine transferred into the embryo was higher in the lowest exposed group (about 0.056±0.020pmol per embryo), the results showed that endpoints such as increased mortality, edema, heart rate alterations, malformation and abnormal growth rates were significantly affected. At 144hpf, the developmental abnormalities included thoracic and trunk abnormalities in the groups exposed to 70 and 90mgL^-1. Defects in cartilage (alcian blue) and bone (calcein) elements also corroborated the craniofacial anomalies observed. A significant up-regulation of the development-related gene nog3 was detected by qRT-PCR at 8 hpf. Early exposure to ketamine also resulted in long-term behavioral changes, such as an increase in thigmotaxis and disruption of avoidance behavior at 144 hpf. Altogether, this study provides new evidence on the ketamine teratogenic potential, indicating a possible pharmacological impact of ketamine in aquatic environments.