Serotonin neurotransmission is widely reported as reduced in suicide attempt and completion. Evidence suggests reduced serotonin innervation of the prefrontal cortex and homeostatic upregulation of postsynaptic 5-HT1A and perhaps 5-HT2A receptors in suicide. However, in the brainstem, we have previously found more tryptophan hydroxylase serotonin biosynthetic enzyme and more serotonin in suicide decedents suggesting serotonergic hyperfunction, but also more autoreceptor binding that could result in reduced neuronal firing. We sought evidence of a disconnect between the brainstem and prefrontal cortex examining the serotonin transporter (SERT) and 5-HT1A receptor in the dorsal and median raphe nucleus and SERT, 5-HT1A and 5-HT2A receptor binding in prefrontal cortex and in anterior cingulate cortex postmortem.
Suicide decedents (n=11) and controls (n=18) died suddenly minimizing agonal effects and had a postmortem interval ≤ 24 hour. Autoradiography was performed in right hemisphere coronal sections at a pre-genual level and in transverse sections through the brainstem.
In controls, there were correlations between DRN and MRN SERT and 5-HT2A receptor binding throughout prefrontal cortex, and between DRN and MRN 5-HT1A receptor binding and medial and ventral prefrontal cortex. In suicide decedents there were no such relationships.
The absence of correlations between brainstem source serotonergic neuron function and receptors on target neurons in prefrontal cortex in suicides suggests a disconnect that may contribute to suicide neuropathology.
Mark D Underwood* and Victoria Arango