Efeitos da melatonina sobre os parâmetros bioquímicos e comportamentais em zebrafish (Danio rerio) submetidos ao estresse agudo e crônico

Abstract

The objective of this study was to evaluate hematological, hormonal (cortisol), enzymatic, and behavioral parameters of zebrafish subjected to melatonin administration followed by acute or chronic stress. Wild type zebrafish were divided into five groups: naïve control (N), negative control (C-), positive control treated with diazepam (C+), melatonin treatment dose 1 (Melt. 1), and melatonin treatment dose 2 (Melt. 2). Exposure to treatments in groups C+ (0.16 mg/L diazepam), Melt. 1 (6800 nM) and Melt. 2 (13600 nM) was performed prior to stress protocols. Acute stress was unleashed by the chase with a net for 5 minutes followed by exposure to the air for 1 minute, and the chronic protocol was performed in which different stress sources were carried at different times during 8 days. Blood cells were counted, enzyme activity were quantified and body cortisol levels were measured, as well as oxidative stress parameters (substances reactive to thiobarbituric acid – TBARS, reactive oxygen species – ROS, and antioxidant activity – SOD and CAT). For behavioral analysis, all animals were subjected to the open field test. Melatonin was able to modulate acute stress effects on zebrafish by promoting lymphocytosis, inhibiting the increase of cortisol levels, reducing locomotor parameters, inducing a state of sleep, reducing lipid peroxidation, and stimulating antioxidant enzymatic activity. In fish chronically stressed, exposure to diazepam promoted effects associated with hematological profile (thrombocytopenia), reduction of TBARS levels and increased SOD activity. Chronic exposure to melatonin at both concentrations reduced TBARS levels and promoted an increase in activity status and locomotor activity.