What are neurotransmitters?

Neurotransmitters are molecules that specialize in delivering packets of information from one neuron to another, across a narrow gap called a synapse to receptors on the receiving cell. After a wave of neurotransmitters are released by the presynaptic neuron and absorbed by postsynaptic neuron, the presynaptic neuron vacuums from the synapse any remaining neurotransmitters in preparation for the next wave of neurotransmitters it will release. Two classes of antidepressants work by blocking this "reuptake" action to keep the neurotransmitters in circulation.