Serotonin is a neurotransmitter present in the brain, small intestines, platelets, etc. It is said to involve in emotional control such as lifting
and suppression as well as sleep and wake, and dieting. Noradrenaline is a neurotransmitter transmitting excitement and it is distributed in sympathetic
nerve terminals and central nervous system. It is secreted in the brain due to stress such as pain and fear and is said to induce the fight or
It is considered that insufficiencies of serotonin and noradrenaline in the brain induce depressive symptoms.
Tricyclic antidepressants bind to amine transporters, thereby inhibit serotonin and noradrenaline reuptakes in the brain. Consequently, the serotonin and
noradrenaline concentrations in the synaptic gaps increase exhibiting antidepressant activity. Tricyclic antidepressants also block monoamine transporters other
than serotonin or noradrenaline.