哺乳类小脑皮质中异位的樸坎业氏细胞及其发生的意義

HETEROTOPIC PURKINJE CELLS IN THE MAMMALIAN CEREBELLAR CORTEX AND THEIR GENETIC SIGNIFICANCE

觀察了食蟲、齧齒、食肉、貧齒、偶蹄、靈長各目的成長動物,以及年齡不同的正常和病態的人類小腦切片,在皮質淺部都見異位的樸氏細胞。在皮質中層正列以上,樸氏細胞可附貼皮質的外緣,甚至落入軟膜下腔。在分子層中,它們可孤處、團聚、間隔平排、在正位行伍錯亂、也可漫佈分子全層。異位的細胞多屬稚型:形體渾圓、胞核大、胞漿少、方向複雜樹突細直。它們也顯病態:胞體狹長、形相枯竭、有時多核、多仁。樸氏細胞的異位照例伴有應自表層沉居深部的顆粒細胞,這表示它們同是出於邊緣顆粒。說樸氏細胞源出室壁生發層不能解釋它們留居皮質的淺部。異位的事實指證它們來自邊緣顆粒層,出於二級的生發,下沉定居中層。初型的樸氏細胞受了惡性因素的影響,減低了遷移、分化的能力,以致留居原產地點,隨軟膜落入下腔,下沉時隨地中止-孤處、團聚、成排、漫散。在病理小腦中,皮質的團塊可孤處深部,這表示二級的生發細胞永達淺面而在深部增殖,也生出樸氏細胞。受了發生的遏制,成長以後,分子層中部可長久殘存横延的“外”顆粒層;此時深方即無有或少有樸氏細胞。此層稀疏或中斷的地點,在下方樸氏細胞就分化很好。這暗示樸氏細胞是通過此層從淺面移來的。樸氏細胞在淺部的異位指證它們至少有一部分(若非全部)是出自早期的邊緣顆粒層。

Heterotopic Purkinje cells are found in the superficial cerebellar cortex in various microscopic sections of the cerebellum of adult representatives of the mammalian orders including insectivores,rodents,carnivores,artio-dactyls and primates,as well as normal and pathological human beings of different ages.Superficial to the middle layer of the cerebellar cortex the heterotopic Purkinje cells are hung on the outermost margin of the cortex or even slipped into the subpial space.Within the molecular layer they subsist in isolation,in groups,in rarefied file,in tortuous alignment,or in wholesale displacement.The heterotopic Purkinje cells are largely hypotrophic with roundish bodies,large nuclei,little cytoplasm,and slender and straight dendrites.Their orientation is multifarious.They are,again,often pathological,being elongated,withered,or with multiple nuclei or nucleoli.They are frequently accompanied by primitive granules which geneti-cally descend from the superficial to the deep planes,thus hinting at their common source.The theory of ventrieular origin fails to explain the aberration of the Purkinje cells to the superficial parts,whereas the facts of heterotopy reflect their origination from the margin and their descent towards the middle level as products of a secondary germination.Under adverse conditions,the primordial Purkinje cells are affected in their capacity of migration and differentiation and,consequently,remain in the original ger-minal bed or slip into the subpial cavity with the crumpling pia mater.They may,again,halt midway singly,collectively,in interrupted file,in sinuous row formation,or in dispersion throughout the whole molecular layer.Cortical patches occasionally present in the interior of pathological cerebellum testifies to the capacity of the potential germinal cells coming from the ventricular matrix to proliferate Purkinje and other cortical cells in the deep as well as in the superficial portions.The retention at adult age of the’external’granular or Kirschhof’s layer together with simulta-neous reduction or absence of Purkinje cells below implies the derivation of the latter cells normally from the margin through a stage corresponding to such granules.The heterotopy of Purkinje cells in the superficial cortex signifies that a part(if not whole)of them at least originate from the marginal granular layer of the early stage.