The human gene SLC6A4 encodes the sodium-dependent serotonin transporter 5HTT which mediates the re-uptake of serotonin from the synaptic cleft thus terminating the action of serotonin (Canli T and Lesch KP, 2007). The serotonin taken up in the cytosol from the synaptic cleft may be recycled into synaptic vesicles or metabolized.