Neuropeptides and the microcircuitry of the enteric nervous system.
The discovery of neuropeptides in enteric neurons has revolutionized the study of the microcircuitry of the enteric nervous system. From immunohistochemistry, it is now clear that some individual enteric neurons contain several different neuropeptides with or without other transmitter-specific markers and that these markers occur in various combinations. There is evidence from experiments in which nerve pathways are interrupted that populations of enteric neurons with different combinations of markers have different projection patterns, sending their processes to distinct targets using different routes. Correlations between the neurochemistry of enteric neurons and the types of synaptic inputs they receive are also beginning to emerge from electrophysiological studies. These findings imply that enteric neurons are chemically coded by the combinations of peptides and other transmitter-related substances they contain and that the coding of each population correlates with its role in the neuronal pathways that control gastrointestinal function.