Co-localization of NADPH-diaphorase and myomodulin in synaptic glomeruli of Aplysia

We used NADPH-diaphorase staining as a marker for nitric oxide synthase to identify neurons and synapses in the nervous system of the mollusc Aplysia californica in which nitric oxide may be used as a transmitter. About 30 bilaterally paired neurons in the cerebral ganglion and a few neurons in other major ganglia were stained, as well as specific fiber tracts, neuropil and the lateral terminus, a synaptic glomerulus of the optic tract. The glomerulus was also stained by antisera to myomodulin, a peptide co-transmitter. The co-localization of myomodulin immunoreactivity and NADPH-diaphorase staining in the synaptic glomerulus, and the staining of select neurons and synaptic structures strongly suggests that nitric oxide functions in interneuronal communication.