Fig. 3: Synj1+/− neurons exhibit decreased surface DAT expression and function.

a Top, representative images of MB culture live stained with a fluorescent cocaine analog JHC1-64, which was blocked in the presence of 10 μM cocaine. Bottom, representative images of JHC staining in Synj1+/+ and Synj1+/− cultures. b Normalized fluorescence of JHC1-64 at the axons (by line selection) and the soma (by area selection). ****p < 0.0001. Mann–Whitney test. Data from 2 to 3 batches of cultures. c Representative DAT-pHluorin trace to sequential perfusion of a membrane-impermeable MES acid solution and a pH 7.4 NH₄Cl solution. Insets, illustration of DAT-pHluorin fluorescence change during the perfusion of the two distinct pH solutions. d and e Box plots summarizing the surface fraction (d) and vesicular pH (e) of DAT-pHluorin in the neuronal axons and soma calculated using the Henderson–Hasselbalch equation. *p < 0.05, **p < 0.01, Student’s t-test. f and g Amphetamine-induced locomotor activity was analyzed in a young cohort (3–6 months, f) and an old cohort (12–18 months, g) littermate mice using the open-field assay. Male and female mice were plotted separately due to sex-segregated responses to amphetamine in the Synj1+/− mice. Two-way ANOVA, p < 0.0001 for a time in all groups. *p = 0.025 for genotype in the young male cohort (f, left). p = 0.14 for the genotype in the young female cohort (f, right). ****p < 0.0001 for genotype in the old male cohort (g, left), p = 0.58 for genotype in the old female cohort. Arrow indicates the time of amphetamine 5 mg/kg i.p. injection. Asterisk on trace were *p < 0.05, **p < 0.01 from Tukey’s multiple comparison test.