NITRIC-OXIDE SYNTHASE INHIBITOR BLOCKS ACETYLCHOLINE-INDUCED INCREASEIN BRAIN BLOOD-FLOW IN RAINBOW-TROUT

Nitric oxide (NO) dependent regulation of blood flow has hitherto not been demonstrated in rainbow trout or other salmonid fish. Through in vivo observations of the brain surface (optic lobes) of rainbow trout (Oncorhynchus mykiss) with epi-illumination microscopy, we show that a pplication of acetylcholine (ACh) to the brain surface induces an incr ease in cerebral blood flow velocity that can be completely blocked by the NO synthase inhibitor N-G-nitro-L-arginine. Also sodium nitroprus side, which decomposes to form NO, stimulated cerebral blood flow velo city. The results indicate that NO is a vasodilator in rainbow trout b rain, mediating the effect of ACh.