In total there are 15 known serotonin receptors, and all of them can also be found outside the central nervous system. There are 5 main serotonin receptors 5-HT1A, 5-HT1B, 5-HT4, 5-HT6, 5-HT7 located in the brain.
For these to happen, brain regions like cortical, limbic, midbrain, and hindbrain regions express multiple serotonin receptors. Serotonin or 5-hydroxytryptamine (5-HT) modulates a wide range of human behavioral processes which include mood, perception, memory, anger, aggression, fear, stress response, appetite, addiction, and sexuality. This activity potentiates the effect of serotonin in the central nervous system. As SSRIs bind to SERT they inhibit the re-uptake of serotonin and thus increase the amount of serotonin in the synaptic cleft. SERT works by re-uptaking serotonin from the synaptic cleft back to the presynaptic neuron. SSRI's mechanism of action is exerted by binding to the sodium-dependant serotonin transporter protein (SERT), also known as 5-HTT, which is located in the presynaptic neuron. Escitalopram (and SSRIs) are also known for their off-label use for the treatment of social anxiety disorder, obsessive-compulsive disorder, panic disorder, posttraumatic stress disorder, premenstrual dysphoric disorder, and vasomotor symptoms of menopause. SSRIs are widely known for their use in the treatment of depression, anxiety, and other related disorders.