Changes in NADPH diaphorase expression in the fish visual system during optic nerve regeneration and retinal development

The various functions of nitric oxide (NO) in the nervous system are not fu lly understood, including its role in neuronal regeneration. The goldfish c an regenerate its optic nerve after transection, making it a useful model f or studying central nervous regeneration in response to injury. Therefore, we have studied the pattern of NO expression in the retina and optic tectum after optic nerve transection, using NADPH diaphorase histochemistry. NO s ynthesis was transiently up-regulated in the ganglion cell bodies, peaking during the period when retinal axons reach the tectum, between 20-45 days a fter optic nerve transection. Enzyme activity in the tectum was transiently down-regulated and then returned to control levels at 60 days after optic nerve transection, during synaptic refinement. To compare NO expression in the developing and regenerating retina. we have looked at NO expression in the developing zebrafish retina. In the developing zebrafish retina the pat tern of staining roughly followed the pattern of development with the inner plexiform laver and horizontal cells having the strongest pattern of stain ing. These results suggest that NO may be involved in the survival of gangl ion cells in the regenerating retina, and that it plays a different role in the developing retina. In the tectum, NO may be involved in synaptic refin ement. (C) 2001 Elsevier Science Ireland Ltd and the Japan Neuroscience Soc iety. All rights reserved.