SERT and DAT availabilities under citalopram treatment in obsessive–compulsive disorder (OCD) Oliver Pogarell a, T , Gabriele Poepperl b , Christoph Mulert a , Christine Hamann b , Nikolai Sadowsky a , Michael Riedel a , Hans-Juergen Moeller a , Ulrich Hegerl a , Klaus Tatsch b a Department of Psychiatry, Section of Clinical Neurophysiology, Ludwig-Maximilians-University of Munich, Nussbaumstr. 7, D-80336 Munich, Germany b Department of Nuclear Medicine, Ludwig-Maximilians-University, Munich, Germany Received 20 July 2004; received in revised form 27 January 2005; accepted 27 January 2005 Abstract Serotonin and dopamine transporter (SERT, DAT) availabilities have prospectively been investigated using [ 123 I]h-CIT and single photon emission computed tomography in subjects with obsessive–compulsive disorder under treatment with the selective serotonin reuptake inhibitor citalopram. SERT availability decreased by a mean 36.5%, whereas DAT availability increased by about 40%. The data point at a citalopram induced modulation of both serotonergic and dopaminergic activity and support the notion of functional interactions of monoaminergic systems in the human brain. D 2005 Elsevier B.V. and ECNP. All rights reserved. Keywords: Serotonin and dopamine transporters; Single photon emission computed tomography; h-CIT; Serotonin reuptake inhibitor; Obsessive–compulsive disorder 1. Introduction Selective serotonin reuptake inhibitors (SSRI) are char- acterised by a lower incidence of adverse effects as compared to classical tricyclic antidepressants and are now widely used in the pharmacotherapy of depression and other psychiatric disorders with an assumed serotonergic dys- function (Schatzberg, 2000). The main mechanism of action of these compounds is suggested to be mediated via inhibition of serotonin transporters (Hyttel, 1994; Schloss and Williams, 1998), which are present in highest densities in midbrain and pontine regions (Staley et al., 1994). SSRI have also been reported to influence the central dopaminer- gic system (Smith et al., 2000), and a recent study showed even an increase in dopamine transporter availability in healthy subjects under medication with SSRI (Kugaya et al., 2003). Single photon emission computed tomography (SPECT) and the iodine-labelled radioligand [ 123 I] h-CIT (2 h- carbomethoxy-3 h-(4-iodophenyl)tropane) can be used to visualise both central serotonin and dopamine transporters (SERT, DAT) in the human brain (Bru ¨cke et al., 1993; Pirker et al., 2000). Striatal h-CIT uptake mainly reflects binding to DAT, whereas in other regions comprising hypothalamus, thalamus, midbrain and pons, h-CIT uptake has been predominantly associated with SERT availability (Laruelle et al., 1993; Staley et al., 1994; Pirker et al., 1995). Aim of the present study was to investigate SERT and DAT availability by using h-CIT and SPECT in patients with obsessive–compulsive disorder (OCD) before and under treatment with the SSRI citalopram. OCD is a neuropsychiatric disorder with increasing evidence of an abnormality of serotonergic neurotrans- mission (Baumgarten and Grozdanovic, 1998; Pogarell et al., 2003). 0924-977X/$ - see front matter D 2005 Elsevier B.V. and ECNP. All rights reserved. doi:10.1016/j.euroneuro.2005.01.003 T Corresponding author. Tel.: +49 89 5160 3409; fax: +49 89 5160 5542. E-mail address: oliver.pogarell@med.uni-muenchen.de (O. Pogarell). European Neuropsychopharmacology 15 (2005) 521 – 524 www.elsevier.com/locate/euroneuro