Since neurotransmitters are not consumed in the synaptic process, what are the mechanisms to decrease their concentrations in the synaptic cleft after they have been used?

As the binding of neurotransmitters to the postsynaptic receptors is reversible, after these neurochemicals perform their role they must be eliminated from the synaptic cleft. Neurotransmitters can then bind to exact proteins that keep them back to the axon they came from in a process known as neurotransmitter re-uptake. They can also be destroyed by exact enzymes, such as acetylcholinesterase, an enzyme that destroys acetylcholine. Or they can simply disperse out of the synaptic cleft.