硬膜外圧迫時の猫脳皮質の電子顕微鏡的研究—特にステロイドの効果について

An Electron Microscope Study on the Experimental Brain Edema with Reference to the Effect of the Steroid Treatment.

I．緒言

　脳外科領域の重要課題の一つに，脳容積増大の問題がある。この脳容積が病的に増大した状態は他臓器の浮腫から類推して，脳浮腫と呼ばれたのであるが，Reichardt^44）はこれを脳浮腫と脳腫脹とに分けた。すなわち彼は細胞間隙に水分の蓄溜した状態を脳浮腫，細胞内に水分の蓄溜した状態を脳腫脹とした。さらにZülch^51）52）はこのような分類を組織学的検索によつて裏付け，安保^1）も自由水と結合水の変動の実験的観察からこれを裏付けた。しかしながら光学顕微鏡（以下光顕と略す）のレベルでも脳浮腫と脳腫脹とに分類するのは妥当でないとする研究者^19）45）もあり，この問題はまだ未解決の点を多く残している。一方約10年前より電子顕微鏡（以下電顕と略す）を導入して，脳容積増大の超微細構造上の変化を観察した多くの論文が発表されてきた^{2）27）34）35）38）43）47）48）}。（Raimondi^47）およびLuse^35）以外は全て大脳皮質についての観察である。）これらの研究においては脳容積増大時の変化は，細胞が膨化するのであつて，細胞間隙の変化は認められないという点で見解が大体一致している。しかしながら，これらの見解に対して批判も無い訳ではない。すなわち殆んどの観察は，電子線に弱いmethacrylate包埋切片によるものであり，従つて電子線による細胞微細構造の破壊をきたすおそれが多分にある。

(1) The experiments were made by means of compression on the brain of adult cats thru the ba-loon inserted epidurally in order to produce brain edema. The compressed part of the brain was sta-ined macroscopically with trypan blue which was injected intraperitoneally, and this means there exi-sts the destruction of blood-brain-barrier in this part. The stained area was examined light-micro-scopically and proved the presence of edematous changes.

We made the electron microscopic examination of the edematous area; the specimens were obtained from the compressed cerebral cortex, and fixed in 2% OsO₄ and embedded in Epon epoxy resin. The results were as follows: ( a ) Pinocytotic vesicles in cytoplasm of the ca- pillary endothelial cells increased.

( b ) Some parts of the pericapillary basement membrane were separated into two sheets, and then vesicular structures of diameter 500-700Å and collagen fibrils appeared in the separated spaces of the membranes.

( c ) Astroglias were markedly swollen, and specific fine granules of 500-700Å in diameter increased considerably in these cells. These fine granules were not digested with saliva and were stained well with uranyl acetate. Also they were preserved by KMnO₄ fixation. Hen- ce these specific fine granules might be glyco- protein or glycolipid.

( d ) Mitochondria of nerve cells were vacuolated and cristae lost their normal arrangement. Ne- uronal endoplasmic reticulum and perinuclear cisternae were distended.

These results suggest that the endothelial cell of blood capillary, the pericapillary basement mem-brane, and the process of astroglia may participate in the integrity of blood-brain-barrier as it was pointed out by van Breeman & Clemente. The fu-nctinal and structural changes of blood-brain-bar-rier might be the primary step of brain edema. Of particular interest is the increase of specific fine granules in the astroglia. The exact pathogenesis of this fact is not sure, but it might reflect the di-sorder of metabolic activity in the astroglia. So the some kinds of metalolic disorders of the astroglia may play a rule in occurrence of brain edema, associated with the derangement of the capillary endothelial cell and the pericapillary basemant me-mbrane.

( 2 ) Preclonisolone was injected intraperitoneally in large doses (5-6mg/kg body weight) to the cats which were treated with the same procedure as in (1). In contrast with (1), the compressed part of the brain was neither stained with trypan blue which was injected intraperitoneally, nor revealed any kinds of edematous changes light-microscopi-cally.

Electron microscopic examinations were done also as in (1). No distinct differences were noticed be-tween two groups; predonisolone was given before the compression in one and after the compression in another. The results obtained were as follows: ( a ) The increase of pinocytotic vesicles in cy- toplasm of the capillary endothelial cells was very slight or not realized in contrast with the series (1).

( b ) The pericapillary basem.ent membrane sho- wed almost normal; neither any sign of sepa- ration of the membrane nor appearance of col- lagen fibrils.

( c ) Mitochondria had a tendency to increase, and, particulary, took a concentrated arrange- ment in some parts in the astroglia. A.stroglia did not show any tendency of swelling, and specific fine granules in these cells seemed not to increase.

( d ) Nerve cells were free from any patholo- gical changes; mitochondria, endoplasmic reti- culum and perinuculear cisternae being of nor- mal figures.

This experiment suggest that predonisolone wo-uld support blood-brain barrier from the damage of compression on the brain and prevent from the occurrence of brain edema although its chemical or metabolic mechanism in the brain is not clear at present.