Developmental Up-Regulation of Vesicular Glutamate Transporter-1 Promotes Neocortical Presynaptic Terminal Development
Figure 2
Expression of VGLUT1 increases while VGLUT2 decreases at individual presynaptic puncta during postnatal synapse development.
(A) Synapse density increased dramatically between 5 and 12 DIV (normalized to 5DIV). (B) Left, As synapses developed, the percentage of presynaptic puncta that express VGLUT1 increased, as indicated by the full bars. The percentage of puncta that express VGLUT1 but not VGLUT2 also increased (white portion of the bars), while the percentage of puncta that expressed both VGLUT1 and VGLUT2 did not change (grey portion of the bars). Right, During the same time period, the percentage of presynaptic puncta that express VGLUT2 did not increase (full bars), and the percentage of puncta that express VGLUT2 but not VGLUT1 was slightly, but not significantly, reduced (white portion of the bars). (C) Scatter plots of VGLUT1 versus VGLUT2 at 5 (left) and 12 (right) DIV. At all ages, puncta were observed that expressed only VGLUT1 (not shown), only VGLUT2 (not shown) or both VGLUT1 and VGLUT2 (circles). (D) The ratio of VGLUT1 to VGLUT2 at individual puncta increased during synapse development. Only puncta that expressed VGLUT1 and VGLUT2 were included in this analysis. (E–F) The mean intensity of VGLUT1 increased (E) while VGLUT2 decreased (F) at presynaptic puncta during early postnatal development. The increase in VGLUT1 was observed when all presynaptic puncta (E, left) or only VGLUT-1-positive puncta were analyzed (E, right). Similarly, the modest decrease in VGLUT2 was present regardless of whether all puncta (F, left), only VGLUT2-positive puncta (F, middle) or only VGLUT1- and VGLUT2-positive puncta (E, right) were analyzed. In (C–F), data were normalized to the mean value at 5 DIV and are presented as the mean +/− standard error. *, p<0.0001. **, p<0.01. ***, p<0.001. At 5DIV, n = 1176 total synaptophysin-positive puncta from 10 images in 3 experiments. At 12 DIV, n = 3649 total puncta from 15 images in 3 experiments.