Platelet Serotonergic Markers and Tridimensional Personality Questionnaire Measures in a Clinical Sample Elliot C. Nelson, C. Robert Cloninger, Thomas R. Przybeck, and John G. Csernansky A group of patients with major depressive disorder, with and without comorbid obsessive- compulsive disorder, completed the Tridimensional Personality Questionnaire (TPQ). Harm Avoidance scores were found to be high compared to published age-matched norms and to display a significant positive correlation with Hamilton Depression Rating Scale scores. Platelet 12SI-lysergic acid diethylamide (125I-LSD) and 3H-paroxetine binding Bmax values were measured to test Cloninger's hypothesis that Harm Avoidance scores would correlate significantly with measures of serotonergic function. A significant inverse correlation was found between Harm Avoidance scores and ~2SI-LSD Bma x values. Correlations between 3H-paroxetine Bma x values and TPQ scale scores were not significant. These results suggest an alternative view of the literature relating platelet 5-hydroxytryptamine-2a receptors and mood disorders in that the temperament dimension, Harm Avoidance, may explain prior inconsistencies involving links with depression and suicidality. Key Words: Biological markers, major depressive disorder, obsessive-compulsive disorder, paroxetine binding, personality inventories, serotonin BIOL PSYCHIATRY 1996;40:271--278 Introduction Abnormalities of serotonergic neurotransmission are be- lieved to be involved in the pathophysiology of both major depressive disorder (MDD) and obsessive-compulsive disorder (OCD). Because direct measures of brain 5-hy- droxytryptamine (5-HT) function are not readily accessi- From the Department of Psychiatry, Washington University School of Medicine, St. Louis, Missouri. Address reprint requests to Elliot Nelson, MD, Department of Psychiatry, Wash- ington University School of Medicine, 4940 Children's Place, St. Louis, MO 63110. Received January 16, 1995; revised June 5, 1995. ble, peripheral 5-HT measures in platelets have been studied for more than a decade (Pletscher 1987). Platelet membranes contain 5-HT uptake sites and 5-HT2a recep- tors that are nearly identical to those in the brain (Lesch et al 1993; Cook et al 1994). A consensus is emerging from many laboratories sug- gesting that in individuals with MDD the number of 5-HT uptake sites (i.e., 3H-imipramine binding sites) is signifi- cantly reduced compared with normal controls (for a review, see Mellerup and Plenge 1988; for a metaanalysis, see Ellis and Salmond 1994); however, methodological issues that have been raised to explain inconsistencies © 1996 Society of Biological Psychiatry 0006-3223/95/$15.00 SSDI 0006-3223(95)00381-P