Role of serotonin in obsessive-compulsive disorder.

BACKGROUND: Serotonin may play a role in the pathophysiology of obsessive-compulsive disorder (OCD) because of the anti-obsessional effect of selective serotonin reuptake inhibitors (SSRIs). METHOD: The literature is reviewed on knowledge of the role of serotonergic neurons in brain function, studies on monoamine metabolites in cerebrospinal fluid (CSF), various stress neuropeptides, neuroendocrine and behavioural challenge after administration of direct and indirect serotomimetic compounds, and neuroanatomical data on brain circuits organising behaviour. RESULTS: In most of the OCD cases analysed, CSF 5-hydroxyindoleacetic acid and homovanillic acid concentrations do not significantly differ from age-corrected controls. However, a relationship appears to exist between pre-treatment levels of these metabolites and clinical response to drugs acting on the serotonin transporter. Abnormalities in CSF arginine vasopressin, corticotropin-releasing hormone, oxytocin and somatostatin levels have been reported in OCD. Long-term treatment with high-doses of clomipramine, fluvoxamine, and fluoxetine tend to correct these neuropeptide abnormalities. CONCLUSIONS: We hypothesise that continuous treatment with SSRIs alters serotonin turnover and neuropeptide expression patterns in OCD-entertaining functional forebrain/midbrain circuits.