Neuronal sprouting and synapse formation in response to injury in the mouse organ of Corti in culture.

The effect of mechanical injury on induction of regenerative phenomena within the neurosensory epithelium was investigated in cultures of neonatal mouse cochlea. The oldest examined culture in which new neuronal growth followed insult, was injured at 13 days in vitro and fixed 24 h later. By far, the most vigorous regenerative reaction was observed in a 3-day culture 4 h post-injury. The reaction included sprouting of nerve fibers injured directly, synapse formation between the surviving hair cells and sprouting neuronal growth cones, wrapping of growing nerve fibers by extending processes of hair cell cytoplasm, and collateral sprouting of synaptically-engaged nerve endings and of nerve fibers in passage.