THE NITRIC OXIDE-CGMP PATHWAY MAY MEDIATE COMMUNICATION BETWEEN SENSORY AFFERENTS AND PROJECTION NEURONS IN THE ANTENNAL LOBE OF MANDUCA-SEXTA

The nitric oxide (NO)-cGMP signaling system is thought to play importa nt roles in the function of the olfactory system in both vertebrates a nd invertebrates. One way of studying the role of NO in the nervous sy stem is to study the distribution and properties of NO synthase (NOS), as well as the soluble guanylyl cyclases (sGCs), which are the best c haracterized targets of NO. We study NOS and sGC in the relatively sim ple and well characterized insect olfactory system of the hawkmoth, Ma nduca sexta. We have cloned Manduca sexta nitric oxide synthase (MsNOS ) and two sGCs (MsGC alpha 1 and MsGC beta 1), characterized their bas ic biochemical properties, and studied their expression in the olfacto ry system. The sequences of the Manduca genes are highly similar to th eir mammalian homologs and show similar biochemical properties when ex pressed in COS-7 cells. In particular, we find that MsGC functions as an obligate heterodimer that is stimulated significantly by NO. We als o find that MsNOS has a Ca2+-sensitive NO-producing activity similar t o that of mammalian neuronal NOS. Northern and in situ hybridization a nalyses show that MsNOS and the MsGCs are expressed in a complementary pattern, with MsNOS expressed at high levels in the antennae and the MsGCs expressed at high levels in a subset of antennal robe neurons. T he expression patterns of these genes suggest that the NO-sGC signalin g system may play a role in mediating communication between olfactory receptor neurons and projection neurons in the glomeruli of the antenn al lobe.