Neuropeptide Y plasma levels and suicidal behavior in combat veterans

Interplay of combat deployment harassment, testosterone concentrations and post-deployment suicide risk in male veterans

OBJECTIVE

Many combat veterans exhibit suicidal ideation and behaviour, but the relationships among experiences occurring during combat deployment and suicidality are still not fully understood. In this study, we tested the hypothesis that harassment during a combat deployment is associated with post-deployment suicidality and testosterone function.

METHODS

Male combat veterans who made post-deployment suicide attempts and demographically matched veterans without a history of suicide attempts were enrolled in the study. Demographic and clinical parameters of study participants were assessed and recorded. Study participants were interviewed by a trained clinician using the Mini-International Neuropsychiatric Interview (MINI), the Deployment Risk and Resilience Inventory (DRRI) – Relationships within unit scale, the Scale for Suicidal Ideation (SSI), and the Brown–Goodwin Aggression Scale. Free testosterone levels were assessed in morning blood samples.

RESULTS

DRRI harassment scores were higher and free testosterone levels were lower among suicide attempters in comparison with non-attempters. In the whole sample, DRRI harassment scores positively correlated with SSI scores and negatively correlated with free testosterone levels. Free testosterone levels negatively correlated with SSI scores. Aggression scale scores positively correlated with DRRI harassment scores among non-attempters but not among attempters.

CONCLUSION

Our observations that harassment scores are associated with suicidality and testosterone levels, and suicidality is associated with testosterone levels may indicate that there is a link between deployment harassment, testosterone function and suicidality.

Differences between adult and adolescent male mice in approach/avoidance and expression of hippocampal NPY in response to acute footshock

Anxiety disorders are the most common neuropsychiatric disorders diagnosed in adolescence and adulthood. Stress can lead to an increase in anxiety-related behaviors, although the consequences of stress in rodents are typically investigated only in adults. The levels of Neuropeptide Y (NPY), a mediator of stress resilience, are reduced in adult patients with Post-Traumatic Stress Disorder. For rodents, footshock is a physical stressor that increases anxiety-like behavior and reduces NPY in adults, however, the effects in adolescents are unknown. Here we used a 30-min unpredictable footshock protocol to investigate the differences in behavior and stress-relevant molecules between adolescent (6 weeks) and adult (3 months) male C57Bl6/J mice. The protocol resulted in fear expression in both ages as observed by enhanced freezing during footshock and elevation in plasma corticosterone and NPY shortly after exposure. However, effects on approach/avoidance behavior were different between the two ages. One week after footshock exposure, adult mice showed reduced open arm time and entries on elevated plus maze (EPM), whereas adolescent mice showed no effect. Footshock mice in both age groups displayed reduced activity levels in EPM and open field. The hypolocomotion did not relate to motor deficits, as there were no differences between footshock and control groups using rotarod. Surprisingly, we found that the adolescent mice had elevated NPY peptide expression in hippocampus, whereas adults had reduced expression one week after footshock exposure. Together, these results demonstrate that stress differentially affects both behavior and the important stress resilience factor NPY in adolescents compared to adults.