THE NITRIC-OXIDE CYCLIC-GMP MESSENGER SYSTEM IN OLFACTORY PATHWAYS OFTHE LOCUST BRAIN

Nitric oxide is generated by a Ca2+/calmodulin-stimulated nitric oxide synthase and activates soluble guanylyl cyclase. Using NADPH diaphora se (NADPHd) staining as a marker for the enzyme nitric oxide synthase and an antiserum against cGMP, we investigated the cellular organizati on of nitric oxide donor and target cells in olfactory pathways of the brain of the locust (Schistocerca gregaria). A small subset of neuron al and glial cells expressed cGMP immunoreactivity after incubation of tissue in a nitric oxide donor. Nitric oxide-induced increases in cGM P immunoreactivity were quantified in a tissue preparation of the ante nnal lobe and in primary mushroom body cell cultures. The mushroom bod y neuropil is a potential target of a transcellular nitric oxide/cGMP messenger system since it is innervated by extrinsic NADPHd-positive n eurons. The mushroom body-intrinsic Kenyon cells do not stain for NADP Hd but can be induced to express cGMP immunoreactivity. The colocaliza tion of NADPHd and cGMP immunoreactivity in a cluster of interneurons of the antennal lobe, the principal olfactory neuropil of the insect b rain, suggests a role of the nitric oxide/cGMP system in olfactory sen sory processing. Colocalization of NADPHd staining and cGMP immunoreac tivity was also found in certain glial cells. The cellular organizatio n of the nitric oxide/cGMP system in neurons and glia raises the possi bility that nitric oxide acts not only as an intercellular but also as an intracellular messenger molecule in the insect brain.