“…Specifically, the findings that serotonin reuptake inhibitors are effective in alleviating obsessions and compulsions in patients have directed much attention to the involvement of the serotonergic system in OCD (for review see Sasson and Zohar, 1996;Stein, 2000), with more recent studies implicating specific serotonin receptors (most notably 5-HT1a, 5-HT2a, and 5-HT2c) in the pathophysiology of OCD and in the response to treatment (for review see El Mansari and Blier, 2006;Goddard et al, 2008;Van Oekelen et al, 2003). Abnormalities of the dopaminergic system have been implicated in OCD on the basis of several lines of clinical and preclinical evidence (for review see Denys et al, 2004), including changes in OC symptoms following the administration of amphetamine and cocaine to OCD patients (Insel et al, 1983;Leonard and Rapoport, 1987;McDougle et al, 1989), and the surplus therapeutic benefits obtained with co-administration of SSRIs and dopaminergic blockers (McDougle et al, 1994;Sasson and Zohar, 1996;Saxena et al, 1996). Involvement of the striatum (mainly the caudate nucleus) in OCD has been derived mainly from functional imaging studies revealing higher metabolic activity in this region in OCD patients compared to healthy controls, and metabolic normalization following a successful behavioral or SSRI treatment (Baxter et al, 1992;Saxena et al, 1999).…”