extent of these reductions differed by brain region and neurotransmitter across the three reports. Indeed, Takahashi et al. (1997) found elevated levels of both dopamine and DOPAC in the striatum, although this was in the context of a variety of other changes, including reduced DAT levels and elevated expression of tyrosine hydroxylase. Wang et al., (1997) found reduced striatal dopamine levels, but in the context of increased DOPAC levels. Both serotonin and 5-HIAA were reduced in the frontal cortex in the Takahashi et al., (1997) study. Overall these initial studies indicate that even heterozygous deletion of the VMAT2 gene produces profound changes in monoaminergic function that differentially impacts the three main monoamine systems in a regionally dependent manner, but are generally indicative of reduced availability of the monoamines for exocytotic release.
