Ultrastructural and protein synthetic changes in embryonic brain: cells aggregated at 0 degree C.

Cells dissociated from brains of 16 to 18 day-old mice embrya were rotated at 37 degrees C and 0 degree C for 7--8 days. While cells aggregated at 37 degrees C formed compact aggregates, cells aggregated at 0 degree C were found in clusters or were randomly distributed. Cells aggregated in the cold did not differ markedly from the controls in their ultrastructural organisation till the 2--3 day in vitro (DIV). Later, significant structural changes, such as distention of cytoplasmic membranes, destruction of mitochondrial membranes, disappearance of ribosomes, shrinkage of nuclei and disturbance of cytoplasmic membranes were apparent. On the 6--7 DIV, groups of cells were separated by a distance of 100 nm and more, and large parts of their cytoplasm disappeared and outside cell perikarya fragments of membranes appeared forming dense debris. However, even at this period some cells were found which did not show signs of degeneration. Protein synthetic activity in aggregated cells increased linearly at 37 degrees C till 7 DIV, whereas in cells aggregated at 0 degree C an inhibition of about 34% was found at 4 DIV and at 7 DIV the curve of 14C leucine incorporation declined almost to zero. It is thus evident that cells aggregated at 0 degree C maintain an almost normal ultrastructural pattern during the first days of cultivation and only protein synthetic activity is lowered. Cellular membranes, damaged during the dissociation partly regenerated even at 0 degrees C and membraneous contacts were formed between several cells.