老齢ラットの後根神経節細胞培養における髄鞘形成

MYELIN FORMATION OF THE DORSAL ROOT GANGLION CELLS OF THE SENILE RAT IN LONG-TERM CULTURE

　抄録　老齢ラットの後根神経節細胞を培養し髄鞘形成に成功した。対照とした新生仔ラットの神経節細胞の髄鞘形成と比較した場合，1）神経突起の出現が，老齢では新生仔に比べて7日遅れ，髄鞘形成も同様に7日遅れた。2）髄鞘の形態は，光顕および電顕での観察において，in vivoのものとほとんど同じであった。形成されたミエリン層数は培養日数に関係なく20層前後であった。3）培養系で形成された有髄線維の髄鞘節は，老齢神経節細胞の方が新生仔に比べ長いが，髄鞘直径，ランビエの絞輪部の長さには差がみられなかった。4）各々の髄鞘節の長さと直径との関係では，老齢，新生仔ともに髄鞘節の長短にかかわらず直径がほぼ一定であった。

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:

1) 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, myeli-nations 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 myelina-tions in senile DRG culture was fewer than that of the neonatal DRG culture.

2) In obsevations by electron microscopy, mye-lin lamellae numbered about 20 in both neonatal and senile DRG cultures with normal-appearing axon structures as seen in vivo. The discontinui-ties in the external lamina of Schwann cells were not observed in both the neonatal and senile DRG cultures.

3) In the morphological analysis of neonatal and senile DRG cultures, the internodal length, diam-eter of myelin sheath and the length of nodal gap (distance between the rounded end of the compact myelin) were measured by image analy-zing apparatus (MAGISCAN-I, Joyce Loebl LTD.) with Sudan black B stain. Although the internod-al length of myelin sheath in senile DRG culture (144.9±40.7,um) proved to be significantly longer than the neonatal DRG culture (131.6±26.2,am) (p<0. 01), the diameter of myelin sheath showed no significant difference between neonatal (2.9± O.7 pm) and senile (2.8±0.7pm) DRG. The lengthof the nodal gap in senile DRG had a tendency to narrow as the number of culture days increased. However, no significant difference existed between neonatal (3.3±1.4 inn) and senile (3.1±18,am) DRG cultures. In the relationship between the internodal length and the diameter of myelin sheath, the diameter of myelin sheath remained rather constant, regardless of the internodal length of myelin sheath. This fact seems to resemble the features of myelin sheath in aging and regener-ation.

The present study revealed for the first time the successful myelin formation in cultures of senile rat DRG. The formed myelin sheath showed similar features when compared with that of mye-lin sheath in vivo. This study suggests the pos-sibility of myelin formation in cultures of senile animals other than rats.