Anxiety disorders can be deconstructed into their symptoms, which is fear and worry. Extreme fears and anxiety can take the form of panic attacks or phobias; worry can take the form of ruminating negative thoughts (what if I can’t cope with the danger?), anticipatory anxiety (I might have another panic attack), or obsessions (I am contaminated with germs). The fear and anxiety symptoms are regulated by the amygdala- the fear circuit; whereas the worry symptoms are regulated by the cortico-striatal-thalamic-cortical (CSTC) circuit- the worry circuit (Shin and Liberzon, 2010; Stahl, 2008).
Serotonin is one of the neurotransmitters that may regulate the fear circuit (amygdala) and the worry circuit (CSTC circuit) of the anxiety disorders. Serotonin neurons project to the amygdala (fear circuit), which serve to inhibit the overactive amygdala of an extreme fear response. So when you have panic attacks or are experiencing a phobia, your amygdala is overactive. SSRIs (i.e. sertraline- Zoloft) and SNRIs (i.e. venlafaxine- Effexor) increase the serotonin in the serotonin neuron, which projects to the amygdala…this then inhibits the amygdala and decreases the fear response mediated by the amygdala. The result is reduced panic and phobia.
Serotonin also regulates the CSTC circuit. So when you have extreme worries and obsessions, your CSTC circuit is overactive. SSRIs and SNRIs increase the serotonin concentrations, and hence dampen the overactive CSTC circuit, leading to a decrease in worry and obsessions.
In summary, serotonin is an important neurotransmitter in anxiety disorders, as serotonin serves to inhibit overactive fear circuits (amygdala) and overactive worry circuits (CSTC circuit). SSRIs and SNRIs are effective for anxiety disorders, and may increase the serotonin concentrations at these fear circuits and worry circuits. The increase in serotonin at the amygdala and CSTC circuits from these medications dampens the overactivity of these circuits, leading to a decrease in fear and worry symptoms.