NGF and intervertebral disk degenerative disorder: The degenerating disc releases growth factors, such as bFGF and TGF-beta1; together with increased levels of tumour necrosis factor-α, interleukin-1β, Nerve Growth Factor, NGF and Brain Derived Neutrophic Factor, BDNF leads to increase production of macrophages and mast cells which might play a key role in the repair of the injured annulus fibrosus and subsequent disc degeneration [83].