Survival of isolated axonal segments in culture: Morphological, ultrastructural, and physiological analysis

Some transected distal axons survive for months in vivo, generate new neurites, and reconnect to proximal segments before degenerating. To determine the factors regulating these phenomena, we studied the behavior of transected axons in cultured metacerebral neurons (MCn) of Aplysia. The neurons were isolated from the ganglia and cultured at 18°C. The morphology, ultrastructure, and electrophysiological properties of the transected axons, as well as their ability to synthesize protein, were examined at different times postaxotomy. Follow-up studies revealed that cultured isolated axonal segments can preserve their morphological integrity for up to 14 days, maintain their passive and active membrane properties for at least 10 days, and extend new neurites and form electrotonic junctions with their proximal segments and intact MCns. De novo protein synthesis is an unlikely mechanism to account for the survival of the isolated axons since they did not incorporate [³⁵S]methionine. We conclude that the viability of transected axons in culture devoid of other cells depends on pools of proteins synthesized prior to the transection and energy stores sufficiently large to maintain neuronal homeostasis.