Neuron division or enucleation.

The classical Bielschowsky-Gross neurohistological method was used to reproduce all the morphological phenomena interpreted by many authors as signs of neuron division, budding, and fission. It is suggested that these signs are associated with the effects of enucleation, which occurs in many cells of other tissue types in response to a variety of chemical and physical treatments. Studies were performed using neurons isolated from the mollusk Lymnaea stagnalis and exposed in tissue culture to the actin microfilament inhibitor cytochalasin B. Phase contrast time-lapse video recording over periods of 4-8 h demonstrated nuclear displacement, ectopization, and budding, to the level of almost complete fission of the neuron body. This repeats the pattern seen in static fixed preparations in "normal" conditions and after different experimental treatments. Budding of the cytoplasm was also sometimes seen at the early stages of the experiments. Control experiments in which cultured neurons were exposed to the solvent for cytochalasin B, i.e., dimethylsulfoxide (DMSO), did not reveal any changes in neurons over a period of 8 h. We take the view that the picture previously interpreted as neuron division and fission can be explained in terms of the inhibition of actin microfilaments, sometimes developing spontaneously in cells undergoing individual metabolic changes preventing the maintenance of cytoskeleton stability.