脳発達障害の成因と形態学的基礎

Developmental disorders of brain—Pathological and pathogenetical basis.

I．はじめに

　高度な脳障害児の剖検脳では，小脳髄症，脳回形成異常や正中構造異常（脳梁欠損，透明中隔欠損）などの粗大な異常に加え，組織学的にも皮質の細胞構築異常，異所性ニューロン集団などの存在することが多い^1〜3）。また細胞レベルでは，ニューロンの極性異常や神経突起の分岐・伸展，走行などの異常がしばしば認められる^3〜5）。このような組織あるいは細胞レベルでの異常は，従来もっぱらニューロンの生成や移動の障害に起因するものと考えられてきた^6〜8）。しかし，ニューロンの移動が障害される機序一つを取り上げてもなお不明な点が多い。また，ニューロンの極性異常や突起の走向の異常は単なる移動障害だけでは説明しがたい。

　ここでは，心身障害見の剖検脳で遭遇することの多い組織および細胞レベルでの異常の成立機序につき，われわれの実験結果を加えつつ，最近の知見を述べる。

Pathological study on the autopsied brain of mentally and physically handicapped children discloses not infrequently various abnormalities in the histological and cytological levels, such as the abnormal cytoarchitecture, heterotopic neuronal nest, abnormal orientation of neuron and tortuous dendrite. These abnormalities have generally been considered to be resulted from the disorders of neuron production and/or mechanical obstruction of neuronal migration including abnormal radial fiber.

Our experimental studies on the microcephalic mouse, which was induced either by prenatal or by postnatal administration of cytosine arabinoside, indicated that the following factors play the impotant races for above mentioned histological and cytological changes : (1) Disturbance of the neuron production following the destruction of the matrix layer. (2) Regional and incomplete regenerated of the matrix layer and delayed neuron production in the regenerated matrix layer. (3) Unbalanced and plastic synaptogensis between the remaining neurons which have been produced prior to the destruction of the matrix layer, migrating young neurons produced in the regenerated matrix layer and the afferent fiber terminals which originate from subcortical neurons.