title: Striatal vs extrastriatal dopamine D2 receptors in antipsychotic response--a double-blind PET study in schizophrenia.
abstract: Blockade of dopamine D2 receptors remains a common feature of all antipsychotics. It has been hypothesized that the extrastriatal (cortical, thalamic) dopamine D2 receptors may be more critical to antipsychotic response than the striatal dopamine D2 receptors. This is the first double-blind controlled study to examine the relationship between striatal and extrastriatal D2 occupancy and clinical effects. Fourteen patients with recent onset psychosis were assigned to low or high doses of risperidone (1 mg vs 4 mg/day) or olanzapine (2.5 mg vs 15 mg/day) in order to achieve a broad range of D2 occupancy levels across subjects. Clinical response, side effects, striatal ([11C]-raclopride-positron emission tomography (PET)), and extrastriatal ([11C]-FLB 457-PET) D2 receptors were evaluated after treatment. The measured D2 occupancies ranged from 50 to 92% in striatal and 4 to 95% in the different extrastriatal (frontal, temporal, thalamic) regions. Striatal and extrastriatal occupancies were correlated with dose, drug plasma levels, and with each other. Striatal D2 occupancy predicted response in positive psychotic symptoms (r=0.62, p=0.01), but not for negative symptoms (r=0.2, p=0.5). Extrastriatal D2 occupancy did not predict response in positive or negative symptoms. The two subjects who experienced motor side effects had the highest striatal occupancies in the cohort. Striatal D2 blockade predicted antipsychotic response better than frontal, temporal, and thalamic occupancy. These results, when combined with the preclinical data implicating the mesolimbic striatum in antipsychotic response, suggest that dopamine D2 blockade within specific regions of the striatum may be most critical for ameliorating psychosis in schizophrenia.
authors.affiliation: Schizophrenia Program, Centre for Addiction and Mental Health, Toronto, ON, Canada.
authors.forename: Ofer
authors.initials: O
authors.lastname: Agid
authors.forename: David
authors.initials: D
authors.lastname: Mamo
authors.forename: Nathalie
authors.initials: N
authors.lastname: Ginovart
authors.forename: Irina
authors.initials: I
authors.lastname: Vitcu
authors.forename: Alan A
authors.initials: AA
authors.lastname: Wilson
authors.forename: Robert B
authors.initials: RB
authors.lastname: Zipursky
authors.forename: Shitij
authors.initials: S
authors.lastname: Kapur
mesh_terms: D000293:Adolescent; D000328:Adult; D014150:Antipsychotic Agents / Q000494:pharmacology / Q000627:therapeutic use*; D001590:Benztropine / Q000627:therapeutic use; D018492:Dopamine Antagonists; D004311:Double-Blind Method; D004409:Dyskinesia, Drug-Induced / Q000188:drug therapy / Q000503:physiopathology; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D018727:Muscarinic Antagonists / Q000627:therapeutic use; D017072:Neostriatum / Q000000981:diagnostic imaging* / Q000378:metabolism*; D049268:Positron-Emission Tomography; D011388:Prolactin / Q000097:blood; D011446:Prospective Studies; D011569:Psychiatric Status Rating Scales; D011595:Psychomotor Agitation / Q000188:drug therapy / Q000503:physiopathology; D011759:Pyrrolidines / Q000378:metabolism; D020891:Raclopride; D017448:Receptors, Dopamine D2 / Q000187:drug effects* / Q000378:metabolism; D012457:Salicylamides / Q000378:metabolism; D012559:Schizophrenia / Q000000981:diagnostic imaging* / Q000188:drug therapy*; D012565:Schizophrenic Psychology
chemical_list: D014150:Antipsychotic Agents; D018492:Dopamine Antagonists; D018727:Muscarinic Antagonists; D011759:Pyrrolidines; D017448:Receptors, Dopamine D2; D012457:Salicylamides; C065065:FLB 457; D001590:Benztropine; D020891:Raclopride; D011388:Prolactin