LIGHT CONTROL OF NITRIC-OXIDE SYNTHASE ACTIVITY IN THE VISUAL PATHWAYIN THE RABBIT AND MOUSE

The aim of the present study was to characterize nitric oxide synthase (NOS) activity in the retina and in relay stations of the visual path way of rabbit and mouse exposed to dark (48 hours) and light stimuli ( 5 or 10 minutes flicker light and 36 hours neon light). To this end th e conversion of [H-3]-L-arginine into [H-3]-L-citrulline has been meas ured in the homogenate of retina and specific nuclei of the brain. Ca2 +-dependent retinal NOS activity was significantly increased in mice b ut not in rabbits exposed to dark for 48 hours as compared to control (12 hours light/dark exposed) animals. Light deprivation also enhanced Ca2+-calmodulin-dependent NOS activity in the lateral geniculate nucl eus in mice and rabbits. In mice, flicker light stimulation (5 or 10 m inutes) reduced retinal NOS activity enhanced by prior exposure for 36 hours to dark. Exposure to light for 36 hours was ineffective on reti nal and brain NOS in mice. In conclusion the present data demonstrate that Ca2+-dependent NOS activity is differentily modulated by light an d dark stimuli in the visual pathway of mouse and rabbits.