Action of selective serotonin reuptake inhibitors (SSRIs) at a chemical synapse, computer artwork. Chemical synapses are the junctions between any two nerves (at right, blue) of the nervous system. SSRIs are a class of antidepressants used in the treatment of depression, anxiety disorders, and some personality disorders. They block the reuptake of serotonin to the presynaptic cell and therefore increase the extracellular level available to the postsynaptic cell downstream. Here serotonin is represented as white beads that have been blocked from reentering the presynaptic cell by the SSRI (red), at left. Serotonin is made in the frontal lobes of the brain and controls our moods.