In the preceding chapters, it was emphasized that paraneuronal hormones and neurotransmitters overlap and are continuous with each other both in their chemical nature and in the route and range of their transport to the target cells. The continuity is also recognized between the responses of various target cells to paraneuronal hormones and to a variety of chemical substances released from neurons, but this continuity cannot easily be expressed following the rigid criteria of classic neurotransmitters and hormones. In this chapter, by amending the classic criteria of neurotransmitters, a new mode of chemical transmission of information will be proposed to unify a large variety of actions of messenger substances released from neurons and paraneurons. The term “messenger substance” is thus used to deal collectively with the chemical substances released from neurons and paraneurons, including the systemic, local, and paracrine hormones, neurotransmitters, and neuromodulators.
KeywordsSympathetic Ganglion Classic Neurotransmitter Cytoplasmic Receptor Inferior Mesenteric Ganglion Intercalate Duct Cell
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