Serotonin cell receptor. Animation of a molecule of the neurotransmitter serotonin binding to a receptor on a cell membrane, triggering biochemical events inside the cell. This animation is part of a sequence showing the effects of serotonin in the brain and nervous system. Serotonin is an important neurotransmitter in the brain. A lack of it has been shown to cause depression. It is this property which has led to the development of the SSRI (selective serotonin reuptake inhibitor) antidepressants.