Non-synaptic transmission at autonomic neuroeffector junctions.
Non-synaptic transmission is characteristic of autonomic neuroeffector junctions. The structure of the autonomic neuromuscular junction is described. The essential features are that: the terminal portions of autonomic nerve fibers are varicose and mobile, transmitters being released 'en passage' from varying distances from the effector cells; while there is no structural post-junctional specialization on effector cells, receptors for neurotransmitters accumulate on cell membranes at close junctions; muscle effectors are bundles rather than single smooth muscle cells, that are connected by gap junctions which allow electrotonic spread of activity between cells. A multiplicity of transmitters are utilized by autonomic nerves, and cotransmission occurs often involving synergistic actions of the cotransmitters, although pre- and post-junctional neuromodulation of neurotransmitter release also take place. It is suggested that autonomic neural control of immune, epithelial and endothelial cells also involves non-synaptic transmission.
Burnstock
Geoffrey
G
Autonomic Neuroscience Centre, Royal Free and University College School of Medicine, Rowland Hill Street, London NW3 2PF, United Kingdom. g.burnstock@ucl.ac.uk
D000818:Animals; D006801:Humans; D008855:Microscopy, Electron, Scanning; D009451:Neuroeffector Junction / Q000502:physiology*; D009435:Synaptic Transmission