Manganese(II) chloride alters behavioral and neurochemical parameters in larvae and adult zebrafish

Manganese (Mn) is an essential metal for organisms, but high levels can cause serious neurological damage. The aim of this study was to evaluate the effects of MnCl2 exposure on cognition and exploratory behavior in adult and larval zebrafish and correlate these findings with brain accumulation of Mn, overall brain tyrosine hydroxylase (TH) levels, dopamine (DA) levels, 3,4-dihydroxyphenylacetic acid (DOPAC) levels and cell death markers in the nervous system. Adults exposed to MnCl2 for 4 days (0.5, 1.0 and 1.5 mM) and larvae exposed for 5 days (0.1, 0.25 and 0.5 mM) displayed decreased exploratory behaviors, such as distance traveled and absolute body turn angle, in addition to reduced movement time and an increased number of immobile episodes in larvae. Adults exposed to MnCl2 for 4 days showed impaired aversive long-term memory in the inhibitory avoidance task. The overall brain TH levels were elevated in adults and larvae evaluated at 5 and 7 days post-fertilization (dpf). Interestingly, the protein level of this enzyme was decreased in larval animals at 10 dpf. Furthermore, DOPAC levels were increased in adult animals exposed to MnCl2. Protein analysis showed increased apoptotic markers in both the larvae and adult nervous system. The results demonstrated that prolonged exposure to MnCl2 leads to locomotor deficits that may be associated with damage caused by this metal in the CNS, particularly in the dopaminergic system.