A quantitative analysis of effects of neurotrophins on fiber growth from spiral ganglion neurons, using a newly developed image processing technique

Abstract

Neurotrophins (NTs) have been revealed essential for the survival of spiral ganglion neurons (SGNs). However, little is known about whether they are necessary for growth of fibers from these SGNs toward the brain. Here we report that either brain derived neurotrophic factor (BDNF) or neurotrophin-3 (NT-3) are crucial for fibers growth from SGNs in culture of newborn rat cochlear explants in serum-free medium. Moreover, we introduced a new image processing technique to analyze the effects of NTs. This new technique clarified the difference between BDNF and NT-3 in quantitative manner. SGNs were dissected from cochlea of postnatal day 2-4 Wistar rats, were cut to approximately 200 μm in diameter, and were placed on a cover glass coated with poly-L-lysine in a 35 mm dish. The SGN-explants were grown in serum-free medium supplemented with neurotrophin (nerve growth factor (NGF), BDNF, or NT-3) for 3 days. The preparations were fixed with 4% paraformaldehyde and were immunostained against neurofilament (160 kD). The total neurite length per cell was estimated and the dose dependency of neurotrophin was compared with each condition. Significant effect on neurite elongation was observed with either BDNF (≥2 ng/ml dose) or NT-3 (≥10 ng/ml), while the neurite growth was poor with NGF. [Jpn J Physiol 55 Suppl:S165 (2005)]