Biological Factors Associated with Suicide Studies have linked suicidal behavior to decreased activity of brain 5- HT pathways. Markers of 5- HT function, such as cerebrospinal fluid (CSF) 5- HIAA and the density of 5- HT transporter sites, are lowered in suicide victims. Abnormalities in brain 5- hydroxytryptamine (5-HT) neurotransmission have been reported in patients with impulsive and aggressive behavior, and low levels of the 5- HT metabolite 5- hydroxy indole acetic acid (5- HIAA) have been found in the cerebrospinal fluid of subjects who have committed acts of unpremeditated violence.  References Harrison PJ, Cowen P, Burns T, Fazel M. Shorter Oxford Textbook of Psychiatry. Oxford: Oxford University Press; 2018., 7th edition, Chapter 21, page no 613).  Linnoila VM, Virkkunen M. Aggression, suicidality, and serotonin. The Journal of clinical psychiatry. 1992 Oct).

Neurobiology of Panic Disorder "There is most evidence for changes in Gamma-aminobutyric acid , with lowered cortical Gamma-aminobutyric acid type  levels measured by magnetic resonance spectroscopy, and diminished benzodiazepine -receptor binding in the parietotemporal regions in unmedicated patients with panic disorder (Hasler et al., 2008)." This happens in panic disorder. Gamma-aminobutyric acid is the major  inhibitory  neurotransmitter in the brain. Benzodiazepine also binds to Gamma-aminobutyric acid type A receptors and increases its firing rate, thus resulting in hyperpolarisation of the cell because of increased chloride influx. So, specific regions in the brain are hyperexcitable in patients with panic disorder. Summary of Hasler et al.  Context Studies have implicated the benzodiazepine receptor system in the pathophysiologic mechanism of panic disorder  by indirect evidence from pharmacological challenge studies and by direct evidence from single-photon emission