Neuroscience Research: Related to the Neuropathology of Schizophrenia, Neuroendocrinology of Obesity, and Brain Map

Aripiprazole has been used effectively to treat schizophrenia in the clinic ; however, its mechanisms of action are not clear. This study examined how shortand long-term aripiprazole treatment affects dopaminergic transmission in mesolimbic and nigrostriatal pathways. For comparison, the effects of haloperidol and olanzapine treatment were also examined. Aripiprazole significantly increased D2 receptor mRNA expression and decreased tyrosine hydroxylase (TH) mRNA expression in the ventral tegmental area (VTA) after 1and 12-wk treatment, but had no effect in substantia nigra (SN) and nucleus accumbens (NAc). Aripiprazole also decreased dopamine transporter (DAT) binding density in NAc (for 1and 12wk treatment) and VTA (1-wk treatment). In contrast, haloperidol significantly increased D2 receptor binding density and decreased DAT binding density in NAc and caudate putamen (CPu) after 1and 12wk treatment, and it also decreases DAT binding in VTA after 12-wk treatment. Olanzapine had less widespread effects, namely an increase in D2 receptor mRNA in VTA after 12-wk treatment and decreased DAT binding in NAc after 1-wk treatment. These results suggest that aripiprazole has selective effects on the mesolimbic dopaminergic pathway. Selectively reducing dopamine synthesis in VTA is a possible therapeutic mechanism for the long-term efficacy of aripiprazole in controlling schizophrenia symptoms with reduced extrapyramidal side-effects. Received 2 October 2008 ; Reviewed 4 November 2008 ; Revised 16 December 2008 ; Accepted 30 December 2008 ; First published online 10 February 2009