The earliest growth factors found were the nerve growth factor (NGF) and epidermal growth factor (EGF) . The neurotrophic factor nerve growth factor (NGF) is active in its precursor form (proNGF) outside space. It is here that maturation and degradation occur . NGF and other neurotrophic factors generate and release energy in target tissues . They activate receptors on presynaptic components innervating neurons, transmitting signals regulating survival and differentiation . NGF precursor translocates into the ER lumen, transporting via the exocytotic route. Then it undergoes proteolytic cleavage to change into a physiologically active mature form. Nerve growth factor (NGF) is a protein that governs the development and responsiveness of sensory nerves and the inflammatory, immunological response . NGF can pass the blood-brain barrier when it binds to transferrin receptor antibodies .