<P> Almost all tissues that exhibit close junctional neurotransmission also show wide junctional neurotransmission . Thus, wide junctional transmission has been described in many smooth muscles such as vas deferens, urinary bladder, blood vessels, gut as well as the nervous systems including ENS, autonomic ganglia and the CNS . </P> <P> Control of gastrointestinal (GI) movements by enteric motoneurons is critical for orderly processing of food, absorption of nutrients and elimination of wastes . Neuroeffector junctions in the tunica muscularis might consist of synaptic - like connectivity with specialized cells, and contributions from multiple cell types in integrated post-junctional responses . Interstitial cells of Cajal (ICC)--non-muscular cells of mesenchymal origin--were proposed as potential mediators in motor neurotransmission . Neuromuscular junctions in GI smooth muscles may reflect innervation of, and post-junctional responses in, all three classes of post-junctional cells . Transduction of neurotransmitter signals by ICC cells and activation of ionic conductances would be conducted electronically via gap junctions to surrounding smooth muscle cells and influence the excitability of tissues . </P> <P> In the peripheral nervous system, local junctional transmission was recognized in the late 1960s and early 1970s . Until then, all chemical neurotransmission was thought to involve synapses and the innervations of tissue were considered synonymous with the existence of a synapse . Later, it was observed that at smooth muscle neuromuscular junctions in the gut and other peripheral autonomic neuroeffector junctions, neurotransmission takes place in the absence of any synapses and it was suggested that at these sites, neurotransmission involved non-synaptic transmission . Accordingly, nerve endings release their neurotransmitters in extracellular space in a manner similar to paracrine secretion . Target cells affected by a locally released transmitter even though located several hundreds to thousands of nanometers away from the release site are considered as being innervated . </P> <P> The varicose axons were first visualized for adrenergic terminals using fluorescence histochemistry described by Falck and colleagues . </P>

Drugs acting at synaptic and neuroeffector junction sites