Neural network partitioning by NO and cGMP

The stomatogastric ganglion (STG) of the crab Cancer productus contains sim ilar to 30 neurons arrayed into two different networks (gastric mill and py loric), each of which produces a distinct motor pattern in vitro. Here we s how that the functional division of the STG into these two networks require s intact NO-cGMP signaling. Multiple nitric oxide synthase (NOS)-like prote ins are expressed in the stomatogastric nervous system, and NO appears to b e released as an orthograde transmitter from descending inputs to the STG. The receptor of NO, a soluble guanylate cyclase (sGC), is expressed in a su bset of neurons in both motor networks. When NO diffusion or sGC activation are blocked within the ganglion, the two networks combine into a single co njoint circuit. The gastric mill motor rhythm breaks down, and several gast ric neurons pattern switch and begin firing in pyloric time. The functional reorganization of the STG is both rapid and reversible, and the gastric mi ll motor rhythm is restored when the ganglion is returned to normal saline. Finally, pharmacological manipulations of the NO-cGMP pathway are ineffect ive when descending modulatory inputs to the STG are blocked. This suggests that the NO-cGMP pathway may interact with other biochemical cascades to p artition rhythmic motor output from the ganglion.