text: <unk> s, also called "neurotrophic factors", are a family of protein which induce the survival of neurons. They belong to a family of growth factors, secreted proteins usually found in the blood stream which are capable of signaling particular cells to survive, differentiate, or grow.<unk>  factors are secreted by target tissue and act by preventing the associated neuron from initiating programmed cell death - thus allowing the neurons to survive.<unk> s also induce differentiation of progenitor cells, to form neurons.
  The<unk>  family includes nerve growth factor (NGF), brain-derived<unk>  factor (BDNF),<unk> -1 <unk> -1),<unk> -3 <unk> -3), and<unk> -4 <unk> -4).
option_0: Neurotrophin
option_1: Glutelin
option_2: Triptans
option_3: Bryostatin
option_4: Retapamulin
option_5: Myotilin
option_6: Insulin-like growth factor
option_7: Menotropins