The dry mass of the cerebellar cortex of the rat and rabbit. Results and methodological problems of determining the dry mass with the use of the interference microscope

Abstract

1. To measure the value of the dry mass of Purkinje cerebellar cells, two methods of cell isolation were chosen (‘free hand dissection’ and tissue imprints). The cells isolated by the modified technique of smears with the aid of polyvinyl foil, had a smaller degree of damage. The authors report their own modification of the isolation method. 2. The technique used for measuring the dry mass in fresh and fixed sections with the aid of the interference microscope has been described. The results of measurements obtained by the method of two media and by measuring sections mounted in saline are given. 3. In the dry mass of fixed and unfixed sections different values were found. The value of the dry mass concentration increased both in the nucleus and in the cytoplasm. In unfixed sections, the value of the concentration of the dry mass in the nucleus approached that of the plasma. In fixed tissue, the concentration of the dry mass in the plasma was 1.85 times higher than in the nucleus. This difference was probably caused by a larger reduction in the volume of the cytoplasm, due to fixation, than in that of the nucleus, so that the dry mass was more condensed. 4. The highest value of the dry mass was found in the nucleolus (0.45 pg/cu.μ) and next to that, in the granular layer islets and the thickened area of the nuclear membrane (0.43 pg/cu.μ). The dendrites of the Purkinje cells had a low dry mass which decreased in the distal direction. 5. The curve of the dry mass fluctuation of isolated Purkinje cells and of various intracellular components showed a uniform tendency which does not suggest the incidence of different cell types. The individual deviations of the dry mass values of the entire neuron, of its nucleus, nucleolus, cytoplasm, nuclear membrane and of the dendrites fluctuated round the mean value. 6. A very close relation was found between the dry mass value of the intracellular components and that of the nucleolus. Except for the dry mass in the distal dendrites, the value of the nuclear dry mass, and of the dry mass of the nuclear membrane, the cytoplasm and the proximal part of the dendrite, depended on the dry mass of the cell nucleolus. 7. In unfixed cryostat sections, the molecular layers in the homogenous field of the interference microscope appeared as a homogenous formation where only single cell elements were visible. In specimens embedded in paraffin, the density of the dendrites clearly differed from that of the medium. Owing to the treatment of the tissue there probably occured an elimination of soluble substances the concentration of which was higher in the dendrites.