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NEUROPHARMACOLOGY
Mailman Research Center, McLean Division of Massachusetts General Hospital, Belmont, Massachusetts (F.I.T., R.J.B., N.S.K., K.Z.); and Consolidated Department of Psychiatry and Neuroscience Program, Harvard Medical School, Boston, Massachusetts (F.I.T., R.J.B., N.S.K., K.Z.)
Levels of ionotropic glutamate (Glu)
N-methyl-D-aspartate (NMDA),
-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), and kainic
acid (KA) receptors in rat forebrain regions were compared by quantitative in
vitro receptor autoradiography after continuous treatment for 28 days with the
atypical antipsychotics olanzapine, risperidone, and quetiapine, or vehicle
controls. All three treatments significantly decreased NMDA binding in
caudate-putamen (CPu; by 30, 34, and 26%, respectively) but increased AMPA
receptor levels in same region (by 22, 30, and 28%). Olanzapine and
risperidone, but not quetiapine, also reduced NMDA receptor labeling in
hippocampal CA1 (21 and 19%) and CA3 (23 and 22%) regions. KA receptors were
unaltered by any treatment in the brain regions examined. These findings
suggest that the antipsychotic effects of olanzapine and risperidone may be
mediated in part by NMDA receptors in hippocampus, and perhaps AMPA receptors
in CPu. The findings also support the hypothesis that down-regulation of NMDA
receptors by atypical antipsychotic agents in CPu contributes to their low
risk of extra-pyramidal side effects. Inability of olanzapine, risperidone,
and quetiapine to alter KA receptors suggests their minimal role in mediating
the central nervous system actions of these drugs.
Address correspondence to: Dr. Frank I. Tarazi, Mailman Research Center, McLean Hospital, Harvard Medical School, 115 Mill St., Belmont, MA 02478. E-mail: ftarazi{at}hms.harvard.edu
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