髄鞘形成とグリア

Biological Response on Neuron aid Neuroglia in Relation to Myelination

　髄鞘形成は神経成長の過程に存在するさまざまな神経グリア相関の一つであるが，今回は髄鞘形成時におこる諸因子を細胞生物学の領域より考察したい。

　一般に神経障害がおきるとき，とくに末梢性の場合にはそれが組織所見のうえでWaller変性であろうと脱鞘現象であろうといずれにしろ髄鞘myelinがそこなわれる。しかし神経機能障害の初期と平行するmyelinの変化を光学顕微鏡所見でうることはむずかしい。

Myelination is the process by which a nerve fiberin the developing nervous system becomes sur-rounded by a myelin sheath arised from thespiraling invagination of the oligodendrocyte- orSchwann cell-plasma membrane. The purpose ofthis report was to clarify the glio-neural correlation,especially biological response of oligodendrocyte andSchwann cell before and on myelination, usingtissue culture technique and observation of re-generating nerve in vivo with fluorescence micro-scopy.

With the aid of a microspectrophotometer,fluorescence value on myelin sheath is determinedat 625 mμ stained by protoporphyrine Ⅲ. Themyelin fluorescence on spinal cord of 15-18 dayschick embryo could be observed but no sheathstructure (premyelinating stage). After 19 dayschick embryo, nerve fibers are acquired the myelin ofsheath structure. It suggested that the phospholipidsconcerned with myelination were remarkably bio-synthesized in premyelinating stage.

Oligodendrocytes and Schwann cells cultivated invitro presented themselves to be characteristic inpremyelinating stage. Aside from stretching andcontracting movements of these processes or oc-casional emergence of membranous processes, snail-like movements were observed. Furthermore, thesecells indicated potent neurotropic affinity, whichwas witnessed by the adhesion of their processeson the nerve fibers. Periaxillar protoplasm wasfilled with dense aggregation of mitochondrias.

Some biochemical evidence from the test tube indicates that the action of chlorpromazine is onoxidative phosphorylation, and morphologicallyapplied chlorpromazine localized to the mitochondria' area of the neuron soma and to the myelin sheathin vitro; it did not bind so permanently to the myelinas to elements of the perikaryon. If using thetreatment of chlorpromazine on premyelinatingstage, the satellite glias were mostly stained, not-withstanding the prevention of the drug penetratesinto the neuron. The results support the assumptionthat oligodendrocyte and Schwann cell are kept toincrease the oxidative phosphorylation in pre-myelinating stage.

On the other hand, nerve growth promotingprotein prepared from bovine and porcine sub-maxillary gland in our laboratory, accelerates theaxon growth in vitro and in vivo. Using thisprotein on nerve regenerating animals, myelinformation was found to occure after the primaryaxon growth began to be promoted. These findingslead to the conclusion that the initiative of myelinformation take on neuron itself and satellite gliasare help to accelerate the lipids biosynthesis.