Abstract
The brain-derived neurotrophic factor (BDNF) was discovered in the last century, and identified as a member of the neurotrophin family. BDNF shares approximately 50% of its amino acid with other neurotrophins such as NGF, NT-3 and NT-4/5, and its linear amino acid sequences in zebrafish (Danio rerio) and human are 91% identical. BDNF functions can be mediated by two categories of receptors: p75NTR and Trk. Intriguingly, BDNF receptors were highly conserved in the process of evolution, as were the other NTs’ receptors. In this review, we update current knowledge about the distribution and functions of the BDNF-TrkB system in the sensory organs of zebrafish. In fish, particularly in zebrafish, the distribution and functions of BDNF and TrkB in the brain have been widely studied. Both components of the system, associated or segregated, are also present outside the central nervous system, especially in sensory organs including the inner ear, lateral line system, retina, taste buds and olfactory epithelium.
Highlights
Increasing brain-derived neurotrophic factor (BDNF) levels is effective in protecting retinal ganglion cell from damage and this could be reached by exogenous application of BDNF to the retina, increasing BDNF expression using viral vector systems and/or inducing BDNF expression by agents such as valproic acid
To analyze the expression of BDNF/TrkB system in the sensory organs the sections were deparaffinized and rehydrated, washed in Phosphate-Buffered Saline (PBS) 0.1 M pH = 7.4, and incubated in 0.3% H2O2 (PBS) solution for 3 min to prevent the activity of endogenous peroxidase; fetal bovine serum was added to rinsed sections
Evidence gathered in this review confirms the pivotal role of the BDNF/TrkB system in the physiopathology of sensory cells of the sensory systems and their possible interaction with calcium-binding proteins
Summary
The brain-derived neurotrophic factor (BDNF) was discovered by Barde et al [1], and identified as a member of the neurotrophin family, which includes nerve growth factor (NGF), neurotrophin (NT) 3, and NT 4/5 [2]. Trk receptors are activated by a dimerization causing an autophosphorylation of specific tyrosine residues leading to the initiation of the signaling system. This latter involves tyrosine kinase substrates interacting with key docking sites on Trk receptors. The investigation of BDNF functions, in earlier vertebrates than mammals, aims to provide additional and clearer information on BDNF physiological functions on the neurophysiology of the brain [35] Both BDNF and TrkB, associated or segregated, are present outside the central nervous system, especially in sensory organs including the inner ear [33], lateral line system [34], retina [35,36], taste buds [37], and olfactory epithelium
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