[Myelin formation of the dorsal root ganglion cells of the senile rat in long-term culture].

Using the dorsal root ganglia (DRG), long-term cultures were done in neonatal (control) and senile (experimental) rats. The morphological analysis on myelin sheath formation was carried out by light microscopy, electron microscopy and image analyzing apparatus. The results are as follows: The neurites of senile DRG cells appeared 7 days later than the neurites of neonatal DRG cells. While the myelinations were observed in neonatal DRG culture by the third week, myelinations of senile DRG were also formed 7 days later. The myelin sheaths in both neonatal and senile DRG cultures looked much like those which were formed in vivo, but the number of myelinations in senile DRG culture was fewer than that of the neonatal DRG culture. In observations by electron microscopy, myelin lamellae numbered about 20 in both neonatal and senile DRG cultures with normal-appearing axon structures as seen in vivo. The discontinuities in the external lamina of Schwann cells were not observed in both the neonatal and senile DRG cultures. In the morphological analysis of neonatal and senile DRG cultures, the internodal length, diameter of myelin sheath and the length of nodal gap (distance between the rounded end of the compact myelin) were measured by image analyzing apparatus (MAGISCAN-I, Joyce Loebl LTD.) with Sudan black B stain. Although the internodal length of myelin sheath in senile DRG culture (144.9 +/- 40.7 microns) proved to be significantly longer than the neonatal DRG culture (131.6 +/- 26.2 microns) (p less than 0.01), the diameter of myelin sheath showed no significant difference between neonatal (2.9 +/- 0.7 micron) and senile (2.8 +/- 0.7 micron) DRG.(ABSTRACT TRUNCATED AT 250 WORDS)