Elevated serotonin 1A receptor binding in borderline personality disorder co-morbid with major depressive episodes appears attributable to major depression alone.

Borderline personality disorder (BPD) is characterized by interpersonal dysfunction, emotional lability, impulsivity, and risk of self-injurious behaviors, and is frequently comorbid with mood disorders. Several BPD symptoms have been associated with altered serotonin (5-HT) system function. We sought to determine whether 5-HT 1A (5-HT1A) receptor binding measured with [11C]WAY-100635 positron emission tomography (PET) differed in individuals with mood disorders (Major Depressive Disorder or Bipolar Disorder I or II) and comorbid BPD (n = 21), compared to those with mood disorders without comorbid BPD (n = 63) and healthy volunteers (HV; n = 27). In thirteen a priori determined brain regions, the groups differed significantly in binding potential (BPF), with higher relative BPF in the mood disorders group compared to HV (F = 3.64; p = 0.03). Planned post-hoc analyses found that these differences in binding compared to HV were driven by higher binding associated with mood disorder, and not with BPD. There were no effects of impulsivity, aggression, depression severity or suicidal ideation on 5-HT1A receptor binding. The finding that higher 5-HT1A binding appears to be related primarily to the presence of a comorbid mood disorder may explain why treatments that target the 5-HT1A autoreceptor, like selective serotonin uptake inhibitors (SSRIs), are effective for mood disorders but have limited efficacy for BPD.