SLC18A2 and bipolar disorder: VMAT2 is fundamentally required for neurotransmitter recycling and release (Wang et al., 1997; Takahashi et al., 1997; Fon et al., 1997) and changes in VMAT1 and VMAT2 activities either through small-molecule agents or mutations are thought to contribute to many human neuropsychiatric disorders including infantile-onset Parkinson’s, schizophrenia, alcoholism, autism, and bipolar depression (Lohoff et al., 2006; Vaht et al., 2016; Fehr et al., 2013; Bohnen et al., 2006; Han et al., 2020; Simons et al., 2013; Lohoff et al., 2008).