Altered Cortical GABA in Female Veterans with Suicidal Behavior: Sex Differences and Clinical Correlates.

Background: Suicide is a public health concern in the civilian and veteran populations. Stressful life events are precipitating factors for suicide. The neurochemical underpinnings of the association between stress/trauma and suicide risk are unclear, especially in regards to sex differences. We hypothesized that gamma-amino butyric acid (GABA), the major inhibitory neurotransmitter may be a neurochemical candidate that is critical in the association between stress and suicide risk in veterans.

Methods: Proton magnetic resonance spectroscopy (1 H MRS) at 3.0 Tesla was used to measure in vivo neurochemistry in the anterior cingulate cortex (ACC; predominantly the dorsal ACC) of 81 veterans (16 females), including 57 (11 females) who endorsed past suicidal ideation (SI) and/or suicide attempt (SA) and 24 (5 females) with no history of SI and/or SA. Suicidal behavior (SB) was defined as the presence of SI and/or SA.

Results: We observed no significant differences in GABA/ Creatine+phosphocreatine (Cr+PCr) between veterans with SB (SB+) and without SB (SB-). However, the female SB+ group showed significantly reduced GABA/Cr+PCr vs. the female SB- group. We observed a trend-level significant negative correlation between GABA/Cr+PCr and the defensive avoidance (DA) subscale on the Trauma Symptom Inventory (TSI) in the SB+ group. In contrast, the SB- group exhibited a positive relationship between the two variables. Furthermore, we found significant negative correlations between GABA/Cr+PCr and Hamilton Rating Scale for Depression (HAM-D) scores as well as between GABA/Cr+PCr and several subscales of the TSI in female veterans.

Conclusions: This study suggests that reduced GABA/Cr+ PCr ratio in the ACC, which may be related to altered inhibitory capacity, may underlie suicide risk in female veterans. Further, the negative association between GABA/Cr+PCr and stress symptomatology and depression scores suggests that MRS studies may shed light on intermediate phenotypes of SB.