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Rationale Amisulpride is approved for clinical use in treating schizophrenia in a number of European countries and also for treating dysthymia, a mild form of depression, in Italy. Amisulpride has also been demonstrated to be an antidepressant for patients with major depression in many clinical trials. In part because of the selective D2/D3 receptor antagonist properties of amisulpride, it has long been widely assumed that dopaminergic modulation is the proximal event responsible for mediating its antidepressant and antipsychotic properties. Objectives The purpose of these studies was to determine if amisulpride’s antidepressant actions are mediated by off-target interactions with other receptors. Materials and Methods We performed experiments that: (1) examined the pharmacological profile of amisulpride at a large number of CNS molecular targets and (2) after finding high potency antagonist affinity for human 5-HT7a serotonin receptors, characterized the actions of amisulpride as an antidepressant in wild-type and 5-HT7 receptor knock-out mice. Results We discovered that amisulpride was a potent competitive antagonist at 5-HT7a receptors and that interactions with no other molecular target investigated here could explain its antidepressant actions in vivo. Significantly, and in contrast to their wildtype littermates, 5-HT7 receptor knockout mice did not respond to amisulpride in a widely used rodent model of depression, the tail suspension test. Conclusions These results indicate that 5-HT7a receptor antagonism, and not D2/D3 receptor antagonism, likely underlies the antidepressant actions of amisulpride.

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Rationale The 5-HT7 receptor is a more recently discovered G-protein-coupled receptor for serotonin. The functions and possible clinical relevance of this receptor are not yet fully understood. Objective The present paper reviews to what extent the use of animal models of human psychiatric and neurological disorders have implicated the 5-HT7 receptor in such disorders. The studies have used a combination of pharmacological and genetic tools targeting the receptor to evaluate effects on behavior. Results Models of anxiety and schizophrenia have yielded mixed results with no clear role for the 5-HT7 receptor described in these disorders. Some data are available for epilepsy, migraine, and pain but it is still very early to draw any definitive conclusions. There is a considerable amount of evidence supporting a role for the 5-HT7 receptor in depression. Both blockade and inactivation of the receptor have resulted in an antidepressant-like profile in models of depression. Supporting evidence has also been obtained in sleep studies. Especially interesting are the augmented effects achieved by combining antidepressants and 5-HT7 receptor antagonists. The antidepressant effect of amisulpride has been shown to most likely be mediated by the 5-HT7 receptor. Conclusions The use of pharmacological and genetic tools in preclinical animal models strongly supports a role for the 5-HT7 receptor in depression. Indirect evidence exists showing that 5-HT7 receptor antagonism is clinically useful in the treatment of depression. Available data also indicate a possible involvement of the 5-HT7 receptor in anxiety, epilepsy, pain, and schizophrenia.