Furthermore, OECs are able to secrete high level of growth factors, such as nerve growth factor (NGF), basic fibroblast growth factor (bFGF), brain derived neurotrophic factor (BDNF), glial derived neurotrophic factor (GDNF), ciliary neurotrophic factor (CNTF), neurotrophins NT4, NT5 and neuregulins, which exhibit important functions as neuronal supporting elements 14, 15, 16, 17, 18, 19.