Ultrastructural evidence for diffuse transmission by monoamine and acetylcholine neurons of the central nervous system

Abstract

Publisher Summary Wealth of evidence has accumulated to confirm the reality and heuristic value of the volume transmission paradigm. In its largest acceptance, this diffuse mode of transmission may now be considered to apply not only to neuronal populations characterized by a paucity of synaptic junctions, but also to wholly junctional ones, such as the glycine-, GABA- and glutamate-containing neurons, which display spillover of their transmitter. Using immunoelectron microscopy, many of the receptors for these aminoacidergic transmitters, as well as for monoamines, ACh and neuropeptides, have been visualized in extrasynaptic membrane locations, on neuronal somata, dendrites, axons and axon terminals, as well as glia and endothelial cells, often remote from the corresponding release sites. The ambient level hypothesis has provided a framework for explaining some of the sustained and regulatory, as well as trophic-like effects of transmitters on a prolonged time scale.