We have utilized transmission electron microscopy to study oligodendrocyte-enriched cell cultures established from dissociated neonatal rat cerebra by the method of McCarthy and de Vellis [1980]. Cells were examined after 14 and 26 days in vitro. The overall morphology of the cells from cultures at both time periods was similar and consistent with previous reports of light (immature) oligodendrocyte fine structure. The cells contained an eccentrically located nucleus, prominent Golgi regions, numerous free ribosomes, and microtubules. Large numbers of processes with varying diameter were also observed. There was some indication of cytoplasmic maturation from the younger to the older cultures. The most important feature of the 26-day cultures was the large quantity of intercellular membranes which were shown to be continuous with oligodendrocyte processes. These membranes often exhibited the appearance of "loose myelin" and were therefore not normally compacted. Layers of membrane with the morphologic appearance of compact myelin were observed on an occasional oligodendrocyte perikaryon or process. This finding necessitates a reevaluation of the widely held theory that oligodendrocytes are not able to elaborate myelin in the absence of neurons.

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Four infants with the clinical and pathological findings of the cerebro-hepato-renal syndrome of Zellweger are reported. They were the children of two sets of parents who were healthy and unrelated. In each family the occurrence of one affected sibling of each sex adds further evidence to the autosomal recessive nature of this disorder.

The ultrastructure of one spinal and five cerebral neoplasms diagnosed by light microscopy as primitive neuroectodermal tumors supports a cell population consisting largely of poorly differentiated neuroepithelial cells. The most unique ultrastructure feature was the presence of annulate lamellae in four of the six cases. Glial cells in the neoplasm were not unequivocally of neoplastic origin and were possible reactive. There was no evidence of neuroblastic or neuronal elements, although there was frequently focal early neuroblastic differentiation by light microscopy. Although we have seen neoplasms which are clearly neuroblastic, these particular tumors are not purely neuroblastic and should not be classified as neuroblastomas.

We measured the activity of several acid hydrolases in oligodendrocyte and mixed glial (predominantly astrocytic) cell cultures prepared from neonatal rat cerebra. When compared with the mixed glial cultures, the cultured oligodendrocytes exhibited higher levels for all the hydrolases when activities were normalized to protein content. When enzymic activities were examined as a function of DNA content, oligodendrocytic alpha-L-fucosidase, beta-D-glucuronidase, arylsulfatase, and N-acetyl-beta-D-glucosaminidase were higher than in mixed glial cultures, whereas the activities of alpha-D-glucosidase, beta-D-galactosidase and acid phosphatase were not elevated. These differences could not be accounted for by the fetal bovine serum present in the culture medium. The enrichment in acid hydrolase specific activities in the oligodendrocytes may be associated with a rapid turnover of at least some of the extensive myelin-like membrane formed by these cultured cells. Alternatively, the enrichment of acid hydrolase activity in the oligodendrocytes may be associated with intracellular vesicles of lysosomal origin which may play a role in myelin-like membrane assembly. Exactly which of the above two processes, or possible combinations thereof, is responsible for the present finding is not known.

Summary.A specimen from a patient with an ectopic pinealoma located in the third ventricle was investigated by light and electron microscopy.The study has demonstrated many small membrane-limited electron-dense granules in the pinea]ocyte-like principal tumor cells. They were similar to those found in the normal pineal body of mammals and probably represent granules of biogenic amines.The literature of biochemical studies on the secretion of the pineal body and the pinealoma was reviewed as supportive evidence of our ultrastructural findings.Zusammen/assung. Eine Gewebsprobe aus eincm ektopischen Pinealom des 3. Ventrikels wurde licht-und elektronenmikroskopisch untersucht. In den Pinealocyten-~hnlichen Hauptzellen des Tumors wurden viele kleine membranbegrenzte elektronendichte Granula nachgewiesen. Sie waren tLhnlich denen in normalen Pblealiszellen der S~uger und entspreehen wahrscheinlich Granu]a biogener Amine. _&us der Literatur fiber biochemische Untersuchungen fiber die Sekretion der Pinealis und des Pinealoms ergeben sich unterstfitzendc Argumente zu der Deutung der eigenen ultrastrukturellen Befunde.