Nitric oxide in invertebrates

Nitric oxide (NO) is considered an important signaling molecule implied in different physiological processes, including nervous transmission, vascular regulation, immune defense, and in the pathogenesis of several diseases. T he presence of NO is well demonstrated in all vertebrates. The recent data on the presence and roles of NO in the main invertebrate groups are reviewe d here, showing the widespread diffusion of this signaling molecule through out the animal kingdom, from higher invertebrates down to coelenterates and even to prokaryotic cells. in invertebrates, the main functional roles des cribed for mammals have been demonstrated, whereas experimental evidence su ggests the presence of new NOS isoforms different from those known for high er organisms. Noteworthy is the early appearance of NO throughout evolution and striking is the role played by the nitrergic pathway in the sensorial functions, from coelenterates up to mammals, mainly in olfactory-like syste ms. All literature data here reported suggest that future research on the b iological roles of early signaling molecules in lower living forms could be important for the understanding of the nervous-system evolution.