Along with binding to the dendritic recepters, serotonin molecules also bind to "reuptake transporters" on the axon's membrane. These transporters take the molecule and transport it back into the axon terminal. They are sometimes called "pumps" and can be thought of as a revolving door. The serotonin enters one side, and the door spins around pushing it out the other side. We have shown here four reuptake pumps in various stages of transporting serotonin. Imagine them spinning and transporting serotonin from the synapse back into the axon.

Reuptake transporters reduce the amount of serotonin in the synapse. Keep in mind that these are one-way doors. Serotonin doesn't go through them the other direction. It can only be released into the synapse from the vesicles. As the reuptake pumps are pulling the serotonin back into the axon, some of this serotonin makes its way back into the vesicles, where the MDMA may cause it to be released again. However, some of it gets broken down by Monoamine Oxidase. We show this in the next slide.