They don't, the neurotransmitters stay on either side of the synapse. Neurotransmitters are released when the synaptic vesicles fuse with the presynaptic neuron's membrane, so as to release them into the synaptic cleft.
Sodium ions
Presynaptic neurons release the neurotransmitter in response to an action potential. Postsynaptic neurons receive the neurotransmitter (and can however become presynaptic to the next nerve cell, if the neurotransmitter has stimulated the cell enough).
Yes, Autoreceptors are located at the receptor site on the presynaptic neuron. They provide feedback on the amount of neurotransmitter release in the synaptic cleft in order to regulate its level through the activity of G proteins and second messengers.
endocannabinoids
An action potential travels down the neuron and reaches the presynaptic knob. This causes the Calcium ion channels to open and allow an influx of calcium into the knob. The increased concentration of calcium causes the secretory vesicles within the knob to bind to the outer membrane and release their neurotransmitter (e.g. ACh) into the synaptic cleft.
Leaves the presynaptic neuron, activates ion channel
blocking the dopamine or monoamine reuptake into the presynaptic axon ending
Botulinus toxin blocks the release of acetylcholine from the presynaptic terminal. This is a total blockage of neuronal transmission.
a neuron
Facilitation
Calcium triggers synaptic vesicles to discharge the neurotransmitter into the synaptic cleft.