Multiple motor patterns in the stomatogastric ganglion of the shrimp Penaeus japonicus

Motor patterns of the cardiac sac, the gastric and the pyloric network in t he stomatogastric nervous system of the shrimp Penaeus japonicus, the most primitive decapod species, were studied. Single neurons can switch from the gastric or the pyloric pattern to the cardiac sac pattern. Some of the pyl oric neurons fire with the gastric pattern. All of the gastric neurons fire with the pyloric pattern, unlike those in reptantians. Proctolin activates and modulates the cardiac sac and the pyloric rhythm, and promotes reconfi guration of the networks. Neurons of the three networks have so many interc onnections that they construct a multifunctional neural network like those in Cancer. This network may function in different configurations under the appropriate conditions. Several modes of interactions between the networks found in different reptantian species can apply to the penaeidean shrimp. S uch interactions are general features of the stomatogastric nervous system in decapods. Phylogenetic differences among the decapod infraorders are see n in the number and orientation of muscles and the innervation pattern of m uscles. The multifunctional networks have existed in the most primitive dec apod species, and types of configurations of the networks would have evolve d to produce a wide range of motor patterns as the foregut structure has be come complex.