DISTRIBUTION OF FIBROBLAST GROWTH-FACTOR IN CULTURED DORSAL-ROOT GANGLION NEURONS AND SCHWANN-CELLS .2. REDISTRIBUTION AFTER NEURAL INJURY

The localization of fibroblast growth factor was examined in both immature (<20 days in vitro) and mature (>30 days in vitro) dorsal root ganglion neuron-glial cell co-cultures as a function of time after in vitro crush injury of the neurites. In the 20 day cultures, neuritic membrane vesicles were seen adhering to Schwann cells following neurite injury. Fibroblast growth factor was not detected on the surface of these membrane vesicles when they were associated with either the degenerating neurites or the surface of Schwann cells. However, the cytoplasm of the Schwann cells demonstrated fibroblast growth factor immunoreactivity at all times. In contrast, injury to neurites after 30 days in vitro resulted in demonstrable fibroblast growth factor immunoreactivity on the surfaces of the neuritic membrane vesicles both before and after their association with the Schwann cells. Furthermore, there was a change in the pattern of fibroblast growth factor immunoreactivity on the surface of Schwann cells after injury: initially the staining was patchy but with increasing time it became more uniform and more intense. A similar pattern of staining was noted on the surface of oligodendrocytes co-cultured with dorsal root ganglion neurons. However, astrocytes which were co-cultured with dorsal root ganglion neurons did not show any fibroblast growth factor immunoreactivity. Also, after injury at 30 days in vitro, the neuronal cell bodies began to express fibroblast growth factor immunoreactivity on their extracellular surfaces and the regenerating neurites exhibited fibroblast growth factor immunoreactive material on the surface of their plasma membranes. This redistribution of fibroblast growth factor via degenerating neuritic membrane vesicles to the plasma membrane of Schwann cells may be involved in neuronal signalling to glial cells after neuronal injury.