Effect of acute exposure of triazophos on histological structure and apoptosis of the brain and liver of zebrafish (Danio rerio)

Triazophos (TAP) has become a part of widespread pollutant of the aquatic environment due to its residue. Current study was designed to investigate the toxic effect of TAP at different doses (0.06, 0.3 and 1.5 mg/L) to the model organism of zebrafish (Dario rerio) by using multi-endpoint analysis in a 96 h acute exposure test. The direct observation that histological and ultrastructural alteration of zebrafish brain and liver were carried out via paraffin section in hematoxylin and eosin (H&E) staining and transmission electron microscopy (TEM), respectively. In addition, a series of methods were applied for exploring the physiological parameters related to cellular apoptosis. Results indicated that vacuolar structure after 96 h treatment with TAP were appeared in the molecular and granular layers of cerebellum. A large number of nuclear retraction, tissues vacuolation and cytoplasmic loss were observed in liver at histological level. From the fine structural level, the mitochondrial vacuolation and membrane damage of brain cells were found and the cristae of mitochondria disintegrated partly in hepatocytes. Onset of such histological structure alterations were one of the most intuitive reflection to TAP exposure, which needs to analyze biochemical alterations for further study. The mitochondrial membrane potential (MMP) showed a downward trend in the brain and liver of zebrafish. Simultaneously, the activity of caspase-3 and caspase-9 increased after 96 h exposure with a concentration-dependent manner, which could be served as a suitable indicator of cellular apoptosis. Furthermore, apoptosis-related genes (Apaf-1, p53, Bax, Bcl-2, caspase-3 and caspase-9) transcription showed different alterations in response to the TAP treatment. These results indicated that TAP exposure led to apoptosis in zebrafish brain and liver and it was speculated that the apoptosis may occur through mitochondrial pathway. The present study demonstrated that the exposure of zebrafish to the insecticide TAP led to observe its effects at both histological structure and apoptosis level in liver and brain.