ABSTRACT
It is now apparent that a general strategy used by the nervous system is to release peptides which often act in concert with conventional neurotransmitters to modify the response of the target cells. The emergence of peptides as a class of neurotransmitters has raised numerous challenging questions concerning chemical signaling in the nervous system. Often the functional significance of a neuropeptide is not known because targets are not defined or because technical difficulties prevent the physiological study of these peptidergic neurons. Little is known about molecular mechanisms underlying peptide function. Since neuropeptides often occur with conventional neurotransmitters in neurons, questions concerning mechanisms of release of multiple transmitters and the coordination of postsynaptic action of each transmitter are raised. In summary, we have little understanding of the need for the increased complexity of the nervous system that has been revealed by the discovery of peptide neurotransmitters.
