What Happens at a Synapse to Increase Serotonin?

As one of the main neurotransmitter substances in the brain, serotonin plays an important role in normal brain health. However, this specific chemical also has a powerful effect on mood, with too little causing depressive mood. Seeking to exploit this phenomenon, doctors have developed medications like fluoxetine (Prozac) to treat depression by increasing the amount of serotonin in the brain.

Serotonin Production

• Serotonin is produced at various synapses throughout the brain. The chemical is used to transmit messages across nerve endings, allowing the brain to operate properly. To communicate, a transmitting neuron releases a certain amount of serotonin, which is then taken up by the receiving neuron at a prescribed rate.

Uptake Rate Problems

• Most problems with serotonin come from an inappropriate level of uptake by the receiving neuron. The longer the serotonin is in the synapse, or the space between nerve endings, the more effect it has, especially when it comes to alleviating depression. When the receiving neuron takes up the serotonin too quickly, it does not allow enough time for the chemical to take effect.

Increasing Serotonin Levels

• Scientists cannot effectively regulate the level of serotonin in the brain by changing how much is produced, so instead they change how long it is in the synapse. This is done by manipulating the rate of uptake by the receiving neuron with drugs called selective serotonin reuptake inhibitors, or SSRIs. The longer the serotonin is in the synapse, the more effective it is at doing its job, whether that's coordinating muscle movement or regulating mood cycles.

Mechanism of Action

• Though no one is exactly sure how SSRIs function, the general process is simple. As the transmitting neuron releases serotonin into the synapse, the chemicals contained within the SSRIs interact with the receiving synapses to very selectively choose which chemicals they will take up and remove from the synapse and which they will leave behind. By carefully discriminating between chemicals, SSRIs help the brain to modulate its activity effectively and return this activity to a normative level, leading to more regular moods and less depression.