Serotonin is a neurotransmitter in the brain that gives us feelings of pleasure and well-being. When serotonin is released from cells in the brain (neurons), it sends out signals to be happy and content.
The serotonin transporter moves serotonin from the synaptic cleft into the presynaptic neuron, allowing serotonin recycling in a sodium-dependent manner. It is also important for maintaining functional neural circuits that connect the amygdala and the cingulate regions of the brain.
People with the “grouchy” gene produce lower levels of the serotonin transporter, and have smaller amygdala and cingulate regions – two brain regions involved in emotional responses.
These changes result in an increased likelihood of anxiety and depression in people with one or more copies of the “grouchy” gene. It may also reduce the response to commonly used selective serotonin reuptake inhibitors (SSRI antidepressants).