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Selective serotonin reuptake inhibitors (SSRIs) are a class of drugs used to treat conditions like depression, which is often associated with low serotonin levels. Unlike agonists or antagonists that bind to receptors, SSRIs work by blocking the reuptake process. This action prevents unused serotonin from being reabsorbed by the presynaptic neuron, allowing it to remain in the synaptic cleft for a longer period. The extended presence of serotonin enhances its interaction with postsynaptic receptors, thereby strengthening its overall effect. Common examples of SSRIs include Prozac, Paxil, and Zoloft.

SSRIs and SNRIs

SSRIs appear to regulate the activation state of microglia in addition to their effects on the serotonergic system when studied in vitro. Fluoxetine (Prozac) and its metabolite, norfluoxetine, have been shown to induce apoptosis in microglia, which limits the amounts of neuroinflammation they can cause. There appear to be both direct and indirect (modulating amount of serotonin available to microglia, or changing the extracellular environment) mechanisms by which this is done. 

Effects of SSRIs on Microglia

Selective Serotonin Reuptake Inhibitors (SSRIs) work by blocking the reabsorption of the neurotransmitter serotonin into neurons. This increases the levels of serotonin in the brain. 

SSRIs include:

- Citalopram

- Escitalopram

- Fluoxetine

- Paroxetine

- Sertraline

Selective Serotonin Reuptake Inhibitors (SSRIs)

Selective Norepinephrine Reuptake Inhibitors (SNRIs) work by blocking the reabsorption of both serotonin and norepinephrine into neurons. This increases the levels of both these neurotransmitters in the brain.

Serotonin Norepinephrine Reuptake Inhibitors include:
- Venlafaxine

- Desvenlafaxine

- Duloxetine

Serotonin Norepinephrine Reuptake Inhibitors (SNRIs)

Although there is significant debate around psychiatric drug use during pregnancy, evidence from population-based studies show no increased risk for stillbirth or infant mortality as a result of SSRI usage during pregnancy and no increased risk of congenital malformations or stillbirth as a result of SNRI usage (specifically duloxetine) during pregnancy.

SSRI/SNRI Use During Pregnancy

The serotonin theory claims that depression and other mental disorders are caused from an imbalance of serotonin in the brain, leading to a widespread use of SSRIs. This theory was first proposed in the 1960's and was publicized in the 1990's. SSRIs aim to increase serotonin levels in the synaptic cleft by blocking the reuptake of serotonin. However, the theory has been questioned in recent years, as studies haven’t consistently found a clear link between low serotonin and mental illnesses like depression.

The Serotonin Theory

A new medication is developed to treat a mood disorder. Its mechanism involves preventing the presynaptic neuron from reabsorbing a specific neurotransmitter after it has been released into the synapse. This results in a higher concentration of that neurotransmitter remaining in the synaptic cleft for a longer time. Based on this description, what is the primary way this medication enhances the neurotransmitter's effect?

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