Morphological and ultrastructural alterations in the retina of Danio rerio after exposition to cadmium.

Cadmium is one of the most harmful heavy metal present in aquatic systems since its toxic effects are exerted on many animal species, including teleosts. Damages interest a plethora of organs and tissues including the visual system. For teleosts, the sense of sight is important both for hunting and for escape and, therefore, a damage at this level alters behavior and reduce the fitness. In this study, we describe the ultrastructural alterations produced by cadmium on the photoreceptors and ganglion cells in retina of adult zebrafish, a model organism. To check whether the effects are dose-related, we tested two different concentrations of CdCl2: 0,3mg/L mouth of the river Sarno, Italy and 3mg/L. Results indicate that cadmium exposure induces a moderate retinal disorganization, in particular, that it induces apoptosis among photoreceptors and ganglion cells. This event activates a regenerative response by the Müller glial cells, stem cells, present in the inner nuclear layer. They differentiate and then migrate as, neuronal cells progenitors, thus regenerating the damaged retina.