Obsessive-compulsive disorder and migraine: The “serotonin” connection

Obsessive-Compulsive Disorder (OCD) is characterized by uncontrollable, intrusive and recurring thoughts (obsessions), resulting in repetitive behaviours (compulsions). Migraine is a debilitating neurovascular disorder characterized by recurrent throbbing one-sided headache. Several investigations suggest that both OCD and migraine are associated with serotonergic dysfunction.
 OCD: The Cortico-Striatal-Thalamic-Cortical loop (CSTC) is considered the most important brain circuit involved in the pathophysiology of OCD, wherein serotonin is the principal neurotransmitter involved. Serotonergic medications act on specific circuits of CSTC leading to increased synaptic serotonin levels, which in turn help in amelioration of various symptoms of OCD.               
 Migraine: The serotonergic system present in the brainstem raphe nucleus has been most commonly attributed in migraine pathophysiology. Reduced brain 5-HT synthesis and, thereby, reduced 5-HT neurotransmission in migraineurs can dilate cranial blood vessels and initiate migraine. Triptans act as 5-HT1B/1D receptor agonists and mimic the role of serotonin in binding to its receptors in trigeminal nerve endings and blood vessels, leading to cranial vasoconstriction as well as decrease in the release of peptides like Calcitonin Gene-Related Peptide (CGRP) and substance P, which ultimately stops the headache.
 There is a possible association between migraine and OCD. More research is warranted in this area to confirm this association. Considering the common role of serotonin in both these pathologies, there is a room for research on novel pharmacotherapy which can simultaneously act on the serotonergic pathways implicated in the pathology of both the disorders.