Peptidergic Modulation of Synaptic Transmission in a Rhythmic Motor System

A large number of neuropeptides are present in modulatory inputs to the stomatogastric ganglion. Many of these same peptides are also released from neurosecretory structures into the hemolymph. Within the stomatogastric ganglion neuropeptides are found in some terminals that contain small classical transmitters and make synapses onto neurons of the stomatogastric ganglion. Neuropeptides are also found in neurohemal-like profiles within the neuropil of the stomatogastric ganglion. These peptides can act physiologically on target neurons within the stomatogastric ganglion to modulate their intrinsic electrical properties. Additionally, these peptides can strongly modify the strength of synaptic connections within the stomatogastric nervous system, resulting in modulation of the motor patterns. Many of these peptides also modulate the efficacy of the synaptic connections from motor neurons to muscles and the strength of muscle contraction. Studies on peptidergic modulation of the neurons and the neuromuscular junctions of the stomatogastric nervous system provide insight into a variety of mechanisms by which central pattern generating circuits are reconfigured and motor patterns transformed into movements.