PRESYNAPTIC RECEPTORS AND THE CONTROL OF GLUTAMATE EXOCYTOSIS

When a typical glutamate-containing neurone fires, an action potential is propagated down the branching axon through more than a thousand va ricosities. At each of these release sites the probability that a syna ptic vesicle will be exocytosed into the synaptic cleft is individuall y controlled by means of presynaptic receptors: autoreceptors respondi ng by positive or negative feedback to previously released transmitter , or heteroreceptors under the influence of other neurotransmitters or modulators. The simplest system in which to investigate presynaptic m odulation is the isolated nerve terminal or synaptosome; studies with this preparation have revealed a complex interplay of signal-transduct ion pathways.