Serotonergic responsivity in obsessive-compulsive disorder. Effects of chronic clomipramine treatment.

Clomipramine is a potent serotonin reuptake blocker that decreases the symptoms of obsessive-compulsive disorder (OCD). To investigate whether clomipramine treatment in OCD affects brain serotonergic responsiveness, metachlorophenylpiperazine (mCPP), a selective serotonin agonist, and placebo were given under double-blind conditions to nine patients with OCD before and after treatment with clomipramine. Unlike our previous observations of a marked transient increase in obsessional symptoms and anxiety following 0.5 mg/kg of mCPP, readministration of mCPP after four months of treatment with clomipramine did not significantly increase obsessional symptoms and anxiety. Similarly, the hyperthermic effect of mCPP observed before treatment was eliminated after treatment with clomipramine. These findings are consistent with the development of adaptive subsensitivity to the serotonergic agonist mCPP during clomipramine treatment. A similar alteration in the response to endogenous serotonin may mediate clomipramine's antiobsessional effects.