Non-synaptic intercellular communication: presynaptic inhibition.

Synapse is the most common and generally accepted structural basis for the interaction between neurons. It provides a "one-to-one" communication system between neurons. However, there is another possibility for interneuronal communication: when one neuron communicates with many others without making synaptic contact. In the past few years neurochemical, morphological and pharmacological evidence has been obtained that some neurotransmitters may be released from non-synaptic sites, for diffusion to target cells more distant than those seen in conventional synaptic transmission. The non-synaptic interneuronal communication between neurons plays a physiological role in the presynaptic modulation of chemical neurotransmission. This would be a transitional form between the classical neurotransmission and the broadcasting of neuroendocrine secretion.