Nitric oxide synthase distribution in the goldfish Mauthner cell

NADPH-diaphorase histochemical staining was used to assess the distribution of the enzyme nitric oxide synthase (NOS) in the goldfish brain, with the emphasis on the Mauthner (M-) cell, a reticulospinal neuron, and its inputs. Labeling was specific for certain cell types, including the M-cell, which stained heavily. The reaction product in this neuron was uniformly distributed along its axon, soma, and ventral and lateral dendrites. Afferents which synapse with the M-cell were also NADPH-diaphorase positive, including an identified class of inhibitory interneurons and the large myelinated club endings (LMCE) of eighth nerve fibers. The presence of NADPH-diaphorase in a lower level brainstem circuit that undergoes activity-dependent long-term potentiation of both excitatory and inhibitory synapses and is accessible for morpho-functional correlations provides the opportunity to elucidate the mechanism and role of nitric oxide at the single cell level.