Localization of cGMP immunoreactivity and of soluble guanylyl cyclase in antennal sensilla of the hawkmoth Manduca sexta

The intracellular messenger cGMP (cyclic guanosine monophosphate) has been suggested to play a role in olfactory transduction in both invertebrates an d vertebrates, but its cellular location within the olfactory system has re mained elusive. We used cGMP immunocytochemistry to determine which antenna l cells of the hawkmoth Manduca sexta are cGMP immunoreactive in the absenc e of pheromone. We then tested which antennal cells increase cGMP levels in response to nitric oxide (NO) and to long pheromonal stimuli, which the ma le encounters close to a calling female moth. In addition, we used in situ hybridization to determine which antennal cells express NO-sensitive solubl e guanylyl cyclase. In response to long pheromonal stimuli with NO donors p resent, cGMP concentrations change in at least a subpopulation of pheromone -sensitive olfactory receptor neurons. These changes in cGMP concentrations in pheromone-dependent olfactory receptor neurons cannot be mimicked by th e addition of NO donors in the absence of pheromone. NO stimulates sensilla chaetica type I and II, but not pheromone-sensitive trichoid sensilla, to high levels of cGMP accumulation as detected by immunocytochemistry. In sit u hybridizations show that sensilla chaetica, but not sensilla trichodea, e xpress detectable levels of mRNA coding for soluble guanylyl cyclase. These results suggest that intracellular rises in cGMP concentrations play a rol e in information processing in a subpopulation of pheromone-sensitive sensi lla in Manduca sexta antennae, mediated by an NO-sensitive mechanism, but n ot an NO-dependent soluble guanylyl cyclase.