Nitric oxide and cyclic GMP induce vesicle release at Drosophila neuromuscular junction

Nitric oxide (NO) diffuses as short-lived messenger through the plasma memb rane and serves, among many other functions, as an activator of the cGMP sy nthesizing enzyme soluble guanylyl cyclase (sGC). In view of recent genetic investigations that postulated a retrograde signal from the larval muscle fibers to the presynaptic terminals, we looked for the presence of an NO/cG MP signaling system at the neuromuscular junction (NMJ) of Drosophila melan ogaster larvae. Application of NO donors induced cGMP immunoreactivity in t he presynaptic terminals but not the postsynaptic muscle fibers at an ident ified NMJ. The NO-induced cGMP immunoreactivity was sensitive to a specific inhibitor (ODQ) of the sGC. Since presynaptic terminals which were surgica lly isolated from the central nervous system are capable of synthesizing cG MP, we suggest that an NO-sensitive guanylyl cyclase is present in the term inal arborizations. Using a fluorescent dye that is known to stain recyclin g synaptic vesicles, we demonstrate that NO donors and membrane permeant cG MP analogues cause vesicle release at the NMJ. Moreover, the NO-induced rel ease could be blocked by the specific inhibitor of the sGC. A destaining of synaptic terminals after NO exposure in Ca2+-free solution in the presence of cobalt chloride as a channel blocker suggested that NO stimulates Ca2+- independent vesicle release at the NMJ. The combined immunocytochemical and exocytosis imaging experiments imply the involvement of cGMP and NO in the regulation of vesicle release at the NMJ of Drosophila larvae. (C) 1999 Jo hn Wiley & Sons, Inc.