Suicidal behaviour is linked to decreased activity of which of the following brain chemical pathways?

Suicidal behaviour is linked to decreased activity of brain 5-HT (serotonin) pathways. Markers of 5-HT functions like 5-HIAA (5-hydraxyindoleacetic acid), a metabolite of serotonin is low in the CSF of suicide victims. The density of serotonin transpoer sites in the brain is also low in suicide prone individuals. It is linked to aggression, violence and impulsivity. There are the factors which could make suicide likely to be successfully completed.Ref: Shoer Oxford Textbook of Psychiatry : By Philip Cowen, Paul Harrison, Tom Burns, Edition 6, Page 424