Escitalopram enhances the association of serotonin-1A autoreceptors to heteroreceptors in anxiety disorders.

Selective serotonin reuptake inhibitors (SSRIs) represent one of the most common treatment options in major depression and anxiety disorders. By blocking the serotonin transporter, SSRIs modulate serotonergic neurotransmission as well as the function of autoreceptors and heteroreceptors. However, treatment-induced changes on a network level primarily remain unknown. Thus, we evaluated the association between serotonin-1A (5-HT1A) autoreceptors and heteroreceptors before and after SSRIs. Twenty-one patients with anxiety disorders underwent positron emission tomography using [carbonyl-11C]WAY-100635 before and after 12 weeks of escitalopram treatment; 15 of them completed the study protocol. Additionally, 36 drug-naive healthy controls were measured once. The 5-HT1A receptor binding potential (BPND) was quantified for the dorsal raphe nucleus (DRN) using a region-of-interest approach and for the entire brain by calculating parametric maps. Voxel-wise linear regression was applied between DRN autoreceptor and whole-brain heteroreceptor 5-HT1A BPND. Consistent with previous observations, healthy subjects showed widespread positive correlations of 5-HT1A BPND between autoreceptors and heteroreceptors. Comparing patients before versus after escitalopram treatment revealed enhanced associations of autoreceptor-to-heteroreceptor 5-HT1A BPND within the amygdala and hippocampus (R2=0.21-0.28 vs 0.49-0.81; p<0.05-0.001). In contrast, no significant SSRI-induced changes were found for correlations of heteroreceptor-to-heteroreceptor 5-HT1A BPND between several limbic regions. This interregional approach suggests a treatment-induced reinforcement of the association of 5-HT1A binding between autoreceptors and heteroreceptors specifically in areas involved in anxiety disorders. These findings provide complementary information about treatment effects on a network level and confirm the central role of the DRN as a prime regulatory area.