Biological aspects of suicidal behaviour 

To understand the biological underpinnings of multi-determined behaviours such as suicide and attempted suicide it is necessary to situate them within an explanatory model that can elaborate the causal pathways and interrelations between biological, clinical, genetic, and environmental factors that all play a role in suicidal behaviour. Where possible, such a model should be clinically explanatory, incorporate biological correlates, be testable in both clinical and biological studies, and have some utility in identifying high-risk individuals. We have proposed a stress–diathesis model of suicidal behaviour wherein exposure to a stressor precipitates a suicidal act in those with the diathesis, or propensity, for suicidal behaviour. Stressors are generally state-dependent factors such as an episode of major depression or adverse life event. The diathesis, we have hypothesized, comprises trait characteristics such as impulsive aggression, and pessimism. Uncovering the biological mechanisms relevant to the stress and the diathesis dimensions of suicidal behaviour will facilitate the identification of both enduring and proximal markers of risk, as well as potential targets for treatment. One biological correlate of the diathesis for suicidal behaviour appears to be low serotonergic activity. Abnormal serotonergic function may be the result of numerous factors including genetics, early life experience, chronic medical illness, alcoholism or substance use disorder, many of which have been correlated with increased risk for suicidal behaviour. Moreover, serotonergic dysfunction may underlie recurrent mood disorders or behavioural traits that characterize the diathesis, such as aggression and impulsivity. In terms of stress response, the noradrenergic and HPA axis have been the focus of biological studies in suicidal behaviour. This chapter gives an overview of the major neurobiological findings in suicide and attempted suicide, as well as emerging findings from studies of genes related to those systems.