In a series of different studies with the same mice (with increasing number of backcrosses over the years), Marazziti et al. (2004) have found GPR37 KO mice to have significantly decreased striatal DA and elevated dopamine transporter (DAT) activity due to increased presynaptic plasma membrane expression in the striatum (Marazziti et al., 2007; the same mice have also been shown to display increased anxiety, discussed below in Section “Major Depressive Disorder, Bipolar Disorder, and Non-Motor Attributes of Parkinsonism”; Mandillo et al., 2013). This evidence concerns the gene GPR37 and bipolar disorder.