The BDNF/TrkB system in the zebrafish retina under normal and ex-perimental conditions

The BDNF/TrkB system regulates different features of neuronal development and, particularly, plays a key role in the molecular mechanisms underlying the development, differentiation and maturation of photoreceptors and retinal nerve circuits. Therefore, the aim of this study was to analyze the role of the BDNF/TrkB system in the biology of the zebrafish retina used as an experimental model. The expression levels and the cellular local-ization of BDNF and TrkB in the zebrafish retina under normal conditions and after exposure to different light-ing conditions, natural photoperiod (control), continuous exposure to different wavelengths (white light, white blue-and blue), and darkness for 10 days have been analyzed using qRT-PCR, Western blot and immunohisto-chemistry techniques. The results demonstrated that the expression of BDNF and TrkB in the retina of zebraf-ish remains constant from the first stages of development to adulthood, while the exposure to different wave-lengths causes a decrease of BDNF mRNA and of BDNF immunostaining. On the contrary the expression of TrkB mRNA was upregulated and TrkB immunoreactivity increased. The exposure to continuous darkness de-termines a decrease of the expression levels of mRNAs for BDNF and TrkB and the absence of the immunore-action for BDNF but not for the TrkB. The results, taken together, demonstrate that light regulates the expres-sion of the BDNF/TrkB system in the zebrafish retina and might contribute to better understand different as-pects of the complex pathophysiology of retinopathies induced by light.