We further find that viral-mediated replacement of VMAT2 in astrocytes and/or systemic treatment with L-3,4-dihydroxyphenylalanine (L-DOPA) prevent the onset of cognitive phenotypes, thus providing a causal link between absence of VMAT2 in astrocytes, decreased levels of DA and onset of cognitive deficits. The gene discussed is SLC18A2; the disease is Cognitive impairment.