Comparative neurotoxicity study of mercury-based inorganic compounds including Ayurvedic medicines Rasasindura and Kajjali in zebrafish model

Zebrafish behavioral model is a powerful tool for neuroscience research. Behavioral changes in the zebrafish are studied by administering drugs. With the aid of automated and open-source MATLAB program, high-accuracy tracking of zebrafish can be achieved, and the important behavioral parameters can be calculated. Although mercury is accepted as a potent neurotoxin, used as a key element for preparing certain Ayurvedic medicines. In this work, mercury-based inorganic compounds, including HgCl2, HgS, and Ayurvedic medicines (Rasasindura and Kajjali) were administrated in zebrafish, and the effects on various behavioral parameters and cortisol levels were studied. A significant change in the basic locomotor parameters of fish was observed including speed (43% reduction), meander (150% increment), and a number of freeze points (125% increment), during 5-day treatment of HgCl2 along with a 3-fold increase in cortisol level against the control groups. Abnormal behavior was also recorded in color preference test, and novel tank diving behavior of HgCl2-treated groups, which can be attributed to the neurotoxicity induced by the HgCl2 administration. Contrary to this, the Rasasindura-treated group showed a significant increase in speed by 33%, decrease in meander by 20%, decrease in freeze points by 30%, and insignificant alteration in cortisol levels, which can be related to the rejuvenating nature of the Ayurvedic medicine Rasasindura. Additionally, Kajjali treated group did not show any substantial changes in zebrafish cortisol level and behavioral parameters except one in the diving test that indicates lowering stress. Similarly, HgS group showed normal behaviors except two irregular motor behaviors identical with the HgCl2 group. From these results, it can be concluded that the mercury-based Ayurvedic Rasasindura and Kajjali did not show any adverse effect or toxicity on zebrafish behavior model