Sources and targets of nitric oxide signalling in insect nervous systems

Nitric oxide (NO) is a membrane permeant signalling molecule which activate s soluble guanylyl cyclase and leads to the formation of cyclic GMP (cGMP) in target cells. In the nervous system, NO/cGMP signalling is thought to pl ay essential roles in synaptic plasticity during development and also in th e mature animal. This review summarizes neurochemical, cell biological, and physiological investigations of NO/cGMP signalling in the nervous system o f insects. The anatomical localization of donor and target cells suggests f unctions in olfaction, vision, and mechanosensation. Behavioural as says ha ve uncovered contributions of NO signalling in oxygen sensing, habituation to chemosensory stimuli, and associative memory formation. During developme nt, NO regulates cell proliferation, axonal outgrowth, and synaptic maturat ion. The cellular distribution of NO-responsive cells suggests that NO can serve as a retrograde synaptic messenger, as an intracellular messenger, an d as a lateral diffusible messenger irrespective of conventional synaptic c onnectivity.