Neurotransmitters

Illustration showing the action of neurotransmitters in the synaptic cleft before (left) and after the addition of a selective reuptake inhibitor class of drug (right) such as an SSRI or anNRI. Vesicles containing the neurotransmitter (green) move towrds the pre- synaptic membrance where they fuse with the cell membrane, releasing their contents into the synaptic cleft. The neurotransmmitter molecules act on the post-synaptic cell by binding to specific receptors on the cell surface (purple). They can also be taken back up by the presynaptic cell via other receptors (orange) for re-use. When the drug (red) is present, the reuptake receptors (orange) are selectively blocked and the neurotransmitters (green) such as serotonin or noradrenaline cannnot be taken back up into the pre- synaptic cell. This allows more neurotransmitter molecules to remain in the synaptic cleft and increases the likelihood of them binding to receptors (purple) on the post-synaptic cell, thereby strengthening their effect.