Fig. 1: Newborn neuroblasts migrate from the V-SVZ towards the NAc in the adult mouse brain and their numbers decrease with age.

a Sagittal brain section from a P40 wild-type mouse, immunostained for DAPI. a1, a2 Magnifications of the inset marked in squared yellow dashed outlines in a and a1, respectively, and show a density gradient of DCX+ neuroblasts from the anterior–ventral V-SVZ to the dorsal NAc. b TEM images of neuroblasts (A) in close vicinity to a mature neuron (N) and a microglia cell (M) in the NAc. c The surface occupied by DCX+ neuroblasts in the NAc over the total NAc surface decreases with age from P40 to P180 (one-way ANOVA with Bonferroni’s multiple comparison post hoc test; mean ± SD; ****p < 0.0001; ***p < 0.001; **p < 0.01; *p < 0.05). d Live-imaging image reconstruction of a sagittal brain section from a P42 5HT3A-EGFP mouse. Inset: schematic of the anatomical region, green arrows illustrate the migratory routes followed by neuroblasts, the dashed red rectangle denotes the area in the picture. e Image of the V-SVZ-NAc (area indicated with the small yellow dashed square in d) after 240 min of recordings. Supplementary Movie 1 was recorded from this region. White lines illustrate the trajectory of recorded cells and dots indicate the end of the trajectory. e1 Detailed image from the area indicated with the yellow dashed rectangle in e, containing 5HT3A-expressing neuroblasts whose trajectories were tracked. f Post hoc immunochemistry performed on the same brain section used in d-e to ascertain DCX expression of 5HT3A+ migrating neuroblasts. The corresponding brain area is indicated with the big yellow dashed rectangle in d. f1 High-magnification image from the area indicated with the yellow dashed box in f, showing that 5HT3A+ migrating neuroblasts also express DCX. g Speed of 5HT3A-expressing neuroblasts migrating in the NAc (green dots) or within the V-SVZ (orange dots) (***p < 0.0001; Mann–Whitney test; median ± IQR), measured in acute brain slices. h Percentage of time that 5HT3A+ neuroblasts spent in stationary (non-moving) state when migrating in the NAc or in the V-SVZ (***p = 0.0006; Mann–Whitney test; median ± IQR). i Net speed of 5HT3A+ neuroblasts migrating in the NAc or V-SVZ, calculated as migration velocity excluding time spent in stationary state (**p = 0.0077; Mann–Whitney test; median ± IQR). g–i p-values are indicated in the figure; the total number of tracked cells was 32 in the NAc and 46 in the anterior–ventral V-SVZ (8 slices from 6 mice were used). j Relative distribution of DCX+ neuroblasts with respect to the distance from the V-SVZ in P65 wild-type mice (n = 756 cells from 4 mice). Abbreviations: 3v, third ventricle; ac, anterior commissure; Cx, cortex; lv, lateral ventricle; NAc, nucleus accumbens; RMS, rostral migratory stream; V-SVZ, subventricular zone. Scale bars in µm: 200 (a1), 100 (a2, d–f), 20 (e1, f1), 5 (b), 2 (b1). See also Supplementary Figs. 1 and 2.