MODULATORY INFLUENCE OF PUTATIVE INHIBITORS OF NITRIC-OXIDE SYNTHESISON VISUAL PROCESSING IN THE CAT LATERAL GENICULATE-NUCLEUS

1. Using an in vivo preparation we have examined the actions of two in hibitors of nitric oxide synthase (NOS), NG-nitro-L-arginine (L-NOArg) and N-G-methyl-L-arginine (L-MeArg), in the feline dorsal lateral gen iculate nucleus(dLGN). We compared the responses obtained to iontophor etic application of these substances during visual stimulation with th ose elicited by visual stimulation alone. The effects of concurrent ej ection of L-arginine (L-Arg), the normal physiological substrate of NO S, and D-arginine, the inactive isomer, were tested on these responses . 2. Extracellular application of L-NOArg and L-MeArg produced clear a nd repeatable effects, consisting of substantial reduction in discharg e rate without affecting response selectivity, on 94% of tested cells. These effects were prevented by simultaneous application of L-Arg, wh ich when ejected alone produced no change on visual evoked responses. 3. The data suggest that nitric oxide (NO) is necessary for the transm ission of the visual input under normal visual stimulation and show a direct involvement of NO in visual information processing at the level of dLGN, suggesting that its contribution to brain mechanisms is more profound that previously thought.