Neurons involved in nitric oxide-mediated cGMP signaling in the tobacco hornworm, Manduca sexta

Recently, both nitric oxide synthase (NOS), and nitric oxide (NO)-sensitive guanylyl cyclase were cloned in Manduca sexta and implicated in several ce llular, developmental, and behavioral processes (Nighorn et al. [1998] J Ne urosci 18:7244-7255). However, NO is a highly diffusive gas, and little is known about the range and specificity of its actions on neurons. To begin e xamining the role of NO as a neurotransmitter in the central nervous system (CNS) of larval Manduca, we have mapped potential NO-producing neurons usi ng fixation-resistant NADPH-diaphorase staining and antisera that recognize a NOS-specific epitope. In addition, to detect NO-responsive neurons, we t reated the CNS with NO donors and used antibodies that recognize elevated l evels of cyclic 3',5'-guanosine monophosphate (cGMP). Many potential NO-pro ducing neurons were mapped, including the ventral unpaired median cells and three pairs of lateral cells in each abdominal ganglion. Additional neuron s in the dorsal midline of ganglia A5-7 (PM2) appear to express NOS in a se gment-specific manner. At the larval-to-pupal transition, this staining pat tern changes; the PM2 neurons stain weakly or are undetectable and there is novel expression of NOS in cell 27. In response to NO donors, a small numb er of neurons produce detectable cGMP accumulation in a segment-specific pa ttern. These include a pair of posteriodorsally positioned interneurons (IN 505) in all the abdominal ganglia, PM2 neurons in A5, and PM1 and PM2 neuro ns in A7. Hence, PM2 neurons in A5 and A7 are potentially capable of produc ing and responding to NO. These identified NO-producing and responding neur ons provide a tractable model system for studying the dynamics and specific ity of NO signaling in the CNS. J. Comp. Neurol. 419: 422-438, 2000. (C) 20 00 Wiley-Liss, Inc.