Indicators of neuritis growth and retraction in tissue culture and histological specimens.

The dynamics of structural processes in cultured neurons was studied by time-lapse video recording and compared with the diversity of morphological structures in fixed preparations. Ellipsoid terminal structures indicate not the growth, but growth arrest of neurites and the start of their retraction (retraction bulbs). Only growth cones can be the indicators of neuritis growth and development. Autotomy of individual terminals is a normal process, but does not indicate neural pathology. The "neuroplasm protuberances" on fixed preparations do not indicate neuroplasm extrusion, but reflect an extreme state of retracting processes. The formation of varicosities results not from swelling, but from redistribution of the neuroplasm and often accompanies its contraction. Disruption of neural contacts and complete invagination of neurites into the cell body are not indicative of the neuron death. These cells can form new processes and make new interneuron contacts.