Retinal ganglion cell response to axotomy and nerve growth factor in the regenerating visual system of the newt (Notophthalmus viridescens): an ultrastructural morphometric analysis.

Nerve growth factor (NGF) treatment, given as a single 200 BU intraocular injection at the time of optic nerve transection, was found to significantly accelerate the retinal ganglion cell response to axotomy in the newt (Notophthalmus viridescens). In the control series the per cent of neurons in the retinal ganglion layer demonstrating nuclear reactivity (i.e. chromatin changes) reaches a peak by 14 days post axotomy (14 DPA), plateaus through 21 DPA and falls thereafter, returning to control levels by 90 DPA. NGF treatment is shown to significantly accelerate the entrance of responding retinal ganglion cells into the reactive nuclear phase between 1 and 7 DPA, and by 7 DPA nuclear reactivity has reached a peak, in contrast to 14 DPA for control values. Consequently, NGF treatment causes retinal ganglion cells to be in the nuclear reactive state a week longer than controls but reactivity diminishes after 21 DPA as in controls. Electron microscopic morphometric analysis further substantiates these observations by demonstrating that NGF treatment can elicit certain cellular organelle changes a week earlier (i.e. at 7 DPA) than they would normally occur (i.e. at 14 DPA) in response to axotomy. In addition to eliciting cellular hypertrophy at 7 DPA, NGF treatment significantly increases Golgi field densities in the neuronal perikaryal cytoplasm as well as a doubling of the number of nucleoli per nucleus and stimulating a significant increase in nucleolar cross-sectional areas. A dose-response relationship exists between the per cent of retinal ganglion cells demonstrating nuclear reactivity at 7 DPA and various NGF concentrations which compares favorably with the dose response study involving the number of regenerating axons per nerve cross-section at 14 DPA. Studies to determine if the NGF mediated responses were a specific effect elicited by this protein molecule or whether they are also produced by other peptides which share some properties in common with NGF demonstrate that only NGF is capable of eliciting these responses.