Altered serotonin 1B receptor binding after escitalopram for depression is correlated with treatment effect.

BACKGROUND: Major depressive disorder (MDD) is commonly treated with selective serotonin reuptake inhibitors (SSRIs). SSRIs inhibit the serotonin transporter (5-HTT) but the downstream antidepressant mechanism of action of these drugs is poorly understood. The serotonin 1B (5-HT1B) receptor is functionally linked to 5-HTT and 5-HT1B receptor binding and 5-HT1B receptor mRNA is reduced in the raphe nuclei after SSRI-administration in primates and rodents respectively. The effect of SSRI treatment on 5-HT1B receptor binding in MDD subjects has not been examined previously. This positron emission tomography (PET) study aimed to quantify brain 5-HT1B receptor binding changes in vivo after SSRI treatment for MDD in relation to treatment effect.

METHODS: Eight unmedicated patients with moderate to severe MDD underwent PET with the 5-HT1B receptor radioligand [11C]AZ10419369 before and after 3-4 weeks of treatment with the SSRI escitalopram 10mg daily. Depression severity was assessed at time of PET and after 6-7 weeks of treatment with the Montgomery-Åsberg Depression Rating Scale (MADRS).

RESULTS: We observed a significant reduction in [11C]AZ10419369 binding in a dorsal brainstem (DBS) region containing the median and dorsal raphe nuclei after escitalopram treatment (p = 0.036). Change in DBS [11C]AZ10419369 binding correlated with MADRS reduction after three (r = 0.78, p = 0.021) and seven (r = 0.94, p < 0.001) weeks' treatment.

CONCLUSIONS: Our findings align with the previously reported reduction of 5-HT1B receptor binding in the raphe nuclei after SSRI administration and support future studies testing change in DBS 5-HT1B receptor binding as an SSRI treatment response marker.