Sensory afferents and motor neurons as targets for nitric oxide in the locust

In the adult locust, nitric oxide (NO) synthase is expressed in interneuron s that innervate mechanosensory neuropils, indicating that NO may participa te in mechanosensory processing. Here, we have identified potential neurona l targets of NO by localizing the expression and activity of soluble guanyl yl cyclase (SGC), its principal molecular target in the nervous system. We used two complementary approaches, namely immunolocalization of SGC alpha-s ubunit (SGC alpha), and of cyclic GMP (cGMP) after exposure to an NO donor. The cell bodies, axons and central projections of thoracic exteroceptors, proprioceptors, auditory receptors, and chemoreceptors were strongly immuno reactive for SGC alpha. Strong SGC alpha immunoreactivity also occurred in all thoracic motor neurons, including their axon terminals. NO-donors induc ed a pattern of cGMP immunostaining that was similar to the distribution of SGC alpha, indicating that both sensory and motor neurons contain function al SGC. Therefore, NO may modulate both the input from these sensory neuron s and the output of motor neurons. Although the expression of SGC alpha was highly consistent, NO donors did not always induce cGMP-staining in SGC-co ntaining neurons, suggesting that SGC is coregulated by factors other than NO. Complementing previous reports in the visual and olfactory system, our results indicate a general role for NO-cGMP signaling in early sensory proc essing; diffusible signals may mediate a cross-adaptation or -sensitization within neural maps where similarly tuned neurons have adjacent projections , an anatomical arrangement shared by many sensory systems. (C) 2000 Wiley- Liss, Inc.