The frequency, distribution and size of coated pits along the upper and lower cell surfaces, and the cytoplasmic volume density of secondary lysosomes were studied by ultrastructural stereological methods in sparse and post‐confluent cell cultures of a human normal glial line and a human malignant glioma line. Neither the frequency of coated pits nor the volume density of secondary lysosomes showed any statistically significant changes between the normal glial cells at 2 and 14 days after subcultivation. The numerical surface density of the coated pits was significantly higher along the lower cell surface than on the upper free surface. The coated pits on the malignant glioma cells at 14 days were far more frequent than at 2 days after subcultivation, or than on the sparse and post‐confluent glial cells. The surface density of the coated pits was higher along the upper free cell surface than on the lower surface of the glioma cells, in contrast to the glial cells. The volume density of lysosomes was significantly higher in the post‐confluent glioma cells than in the sparse cells. The mean diameter of the coated pit openings on cells at 2 days after subcultivation was significantly larger than at 14 days, both in the glial and glioma cell cultures. The observed differences in frequency and distribution of coated pits between the glial and glioma cells may reflect differences in receptor‐mediated endocytosis and be related to the different growth characteristics of the normal and malignant cells. The greatly increased load of secondary lysosomes in post‐confluent cultures of the glioma cells, in contrast to the glial cells, may be due to a higher rate of autophagocytosis in the malignant cells. The larger size of the coated pit openings on isolated than on post‐confluent cells may reflect differences in surface properties between sparse and dense cells.
The neuropil of the lateral cervical nucleus (LCN) has been studied by means of ultrastructural stereological methods. Estimates of the fractional volumes of axons, glial cells (three types), extracellular space, boutons, bouton mitochondria, dendrites, dendritic mitochondria, neuronal somata and blood vessels were calculated for four normal cats and eight cats which had been subjected to spinal deafferentation 2, 4, 9, and 14 days before perfusion. 14 days after operation the fractional volume of boutons and dendrites in the nucleus was considerably lower on the operated side, corresponding to a reduction of 67% and 64% respectively. The bouton reduction was higher than could have been expected from findings in earlier qualitative studies. The reduction in dendritic volume, which was already present after 4 days, had not been detected in earlier studies of the LCN. Dark dendrites were found both in normal animals and on the normal and operated sides in operated animals. The variation from animal to animal was great but the figures for the deafferented sides were significantly higher. The general value of the stereological technique in ultrastructural neuroanatomical research is discussed and it is concluded that quantitative methods are more sensive to small and gradual changes and should give a better estimation of transneuronal effects and of the amount of degeneration than purely qualitative methods.
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