The effect of neurotrophic factors on spiral ganglion neurons

The current study investigates the survival and neuritogenic effects of various neurotrophic factors on rat spiral ganglion neurons (SGNs) in vitro. In particular, ciliary neurotrophic factor (CNTF), glial derived neurotrophic factor (GDNF), neurotrophin-3 (NT-3) and neurturin (NRTN) were assayed on postnatal day 4-6 SGNs. CNTF and NT-3 produced a robust survival effect while GDNF and NRTN failed to do so. A dose response revealed CNTF to be effective at promoting survival as low as 5ng/ml. In addition, CNTF promoted neurite growth in both depolarizing and non-depolarizing conditions, suggesting that CNTF can partially overcome the inhibitory effect of membrane depolarization. Lastly, the effect of NTFs was assayed between basal and apical neurons in culture. The preliminary results suggest there is no difference in response to NTFs between these two spatially distinct populations, however, it was noted that under depolarizing conditions apical neurons produce significantly shorter neurites than their basal counterparts.