Pharmacology of SSRI Compounds
What do SSRI compounds do to a neuron? As the name implies, SSRI compounds interact with a type of neurotransmitter receptor known as the serotonin transporter and block reuptake of serotonin into the pre-synaptic neuron. Thus, the initial mechanism of action of SSRIs is to increase levels of serotonin in the synapse. More specifically, SSRI compounds decrease the rate of serotonin reuptake. The following figure illustrates the relationship between levels of serotonin (y-axis) and time (x-axis). At time 0, the pre-synaptic neuron releases serotonin into a synapse, resulting in high levels of serotonin. In the absence of an SSRI (blue line), serotonin transporters rapidly decrease levels of serotonin from the synapse. Thus, serotonin has a short period of time to interact with serotonin receptors. In the presence of an SSRI (red line), the activity (effectiveness) of serotonin transporters is greatly diminished, resulting in slower reuptake of serotonin. The bottom line is that SSRIs do not directly alter the maximum amount of released serotonin although it is true that SSRIs increase relative levels of serotonin. It should be noted that separating "release" from "re-uptake" on a time scale is an oversimplification.
Related topics:
Antidepressants
Molecular mechanisms of antidepressant action