How SSRIs and SNRIs Work For Anxiety

Hello I’m Dr. Carlo Carandang and I’m a psychiatrist. Today, I will talk about how SSRIs and SNRIs work for anxiety. SSRIs, also known as selective serotonin reuptake inhibitors, and SNRIs, also known as serotonin norepinephrine reuptake inhibitors, work for anxiety by increasing serotonin in the brain.

Specifically SSRIs and SNRIs increase serotonin by acting on the raphe nuclei, which is located in the brainstem. What happens is that these raphe nuclei provide serotonin to the rest of the brain via its projections of the serotonin neurons that go from the brainstem (where the raphe nuclei are located) to other parts of the brain.

So here’s a serotonin neuron that originates in the raphe nuclei that is located in the brainstem, and one of the places where the serotonin neuron connects to in the brain. From the raphe nuclei in the brainstem, it connects to the amygdala. So the amygdala is located deep within the temporal lobes of the brain, and the amygdala is a part of the brain which is known as the fear center of the brain.

So the fear circuits of your brain are centred on the amygdala. When you have anxiety, the amygdala and the fear circuits that are centred on the amygdala are hyperactive. So anxiety occurs because of these hyperactive fear circuits which are centered on the amygdala. So if you can imagine in a brain that is highly anxious, this amygdala is over stimulated and hyperactive. So one of the ways to decrease the hyperactivity of the amygdala and hence decrease anxiety is to release more serotonin to the amygdala. Because serotonin that’s released here from the serotonin neuron that connects to the amygdala, the serotonin that travels across the synapse to the receptor sites here, the serotonin serves to inhibit the activity of the amygdala and therefore calms down the amygdala and hence the fear circuits. Therefore, this leads to decreased anxiety.

So one of the ways to increase serotonin, as you know, is to take an SSRI or an SNRI, as the SSRI and the SNRI work similarly, in that they serve to block the reuptake of serotonin back into the neuron. So this is the serotonin reuptake pump, and SSRIs and SNRIs work by blocking this serotonin reuptake pump. But when you block the reuptake pump, which basically recycles serotonin back into the serotonin neuron, what happens is that it increases the concentration of serotonin in the synapse. Hence, there’s more binding of serotonin to the postsynaptic receptors that are connected to the amygdala, and the binding of serotonin to the serotonin receptors on the amygdala serves to inhibit the amygdala.

Thus, it serves to calm the amygdala in the fear circuits, and hence it decreases anxiety. So SSRIs and SNRIs work for anxiety by increasing the concentration of serotonin in the synapse by blocking the reuptake of serotonin via blocking this serotonin reuptake pump. Hence, increasing serotonin in the synapse leads to increased binding of serotonin to postsynaptic serotonin receptors which are attached to the amygdala. So this increase in binding of serotonin serves to inhibit the amygdala and hence to decrease anxiety.

So this is how SSRIs and SNRIs work to decrease anxiety, by increasing the concentration of serotonin in the synapse. This leads to increased binding of serotonin to postsynaptic serotonin receptors connected to the amygdala, which then decreases the hyperactivity of the amygdala and fear circuits, which then leads to decreased anxiety.

For more information and help on SSRIs, SNRIs, and anxiety, please visit the rest of AnxietyBoss.com. I’m Dr. Carlo Carandang- thank you for listening.

photo credit: National Institutes of Health (NIH) Illustration of brain regions via photopin (license)