Neurons with multiple messengers--distribution and possible functional significance.

Publisher Summary This chapter presents some studies that have been carried out in the peripheral nervous system, where some tissues contain well-defined neuronal inputs that are favorable for experimental analysis of the significance of coexistence of classical transmitters and peptides. The chapter elaborates the two central coexistence systems: dopamine (DA) neurons containing a cholecystokinin (CCK)-like peptide and 5-HT neurons containing substance P-and thyrotropin releasing hormone (TRH)-like immunoreactivities. The chapter focuses on some neuronal systems containing both a classical transmitter and a peptide (or more than one peptide), and analyzes the present status with respect to the functional significance of this coexistence phenomenon. Starting with a peripheral system, the cat salivary gland, where the parasympathetic and sympathetic innervation both represent coexistence systems, evidence is presented that a classical transmitter and a peptide act postsynaptically in a cooperative way to induce a certain physiological response. In contrast, the peptide may inhibit the release of the classical transmitter in the vas deferens of the rat, another peripheral system. Two central systems are discussed: dopamine neurons containing a CCK-like peptide and bulbospinal 5-HT neurons containing substance P and TRH-like immunoreactivities. Several studies have attempted to investigate the physiological significance of coexistence, and apparently, meaningful interactions have been observed.