In contrast to normal DRG sensory development, which depends on a neurotrophin and its receptors for phenotypes, we found that the eDRG and aDRG NSCs were not entirely dependent on neurotrophins for sensory differentiation, as revealed by VGluT2 (sensory transmitter), TrpV1 (capsaicin receptor), and pNF200 (myelinated sensory fibers) immunostaining in control groups. This indicates that both eDRG NSC and aDRG NSC have been primed for their phenotypes at the time of procurement, and the epigenetic conditions were passed on to the daughter cells throughout the long-term culture. However, NGF did enhance the proportion of TrpV1-expressing sensory neurons; while BDNF enhanced neuronal maturation by increasing NeuN+ neurons, but did not increase the sensory differentiation. This is in agreement that BDNF accelerates the maturation of neurons in sensory ganglia during the developing period of neurotrophin independence (33,40). Neuro-trophins have been shown to regulate gene expression for NSC differentiation (18). It is likely that the differentiation of the phenotypes also depends on the expression of neurotrophin receptors such as p75 or Trk A, B, and C in the DRG NSCs (8).
