Dendrites as Sites of Storage and Release of Neurotransmitter Substances, an Extension of Dale's Principle

Publisher Summary This chapter discusses dendrites as sites of storage and release of neurotransmitter substances to an extension of Dale's principle. Applying the principle that the nature of the transmitter is characteristic of a given type of neuron and that the characteristic is unchangeable, Dale has reasoned that when dealing with two different endings of the same sensory neuron, the one peripheral and concerned with vasodilation and the other at a central synapse, the identification of the chemical transmitter of the axon-reflex would give clues for the transmitter at the central synapse of the same neuron. Dendritic processes in addition to their fundamental role of receiving information via transducing receptors—sensory neurons or incoming synaptic contacts—conventional neurons may synthesize, store, and release neurotransmitter substances. From the analyses of characteristics of three models, namely, γ-aminobutyric acid (GABA), dopamine, and substance P, it is found that some neurons release neurotransmitters affecting a variety of structures, such as incoming nerve terminals and neurons of the same kind. Other neurons might release neurotransmitters in an axon-like fashion as the granule cell dendrite of the olfactory bulb. Primary sensory neurons seem to release neuroactive peptides both at free endings, in a diffuse manner in the skin, and in a synaptic or axon-like manner in the sympathetic ganglia.