Throughout early postnatal development, cortico-cortical synapses are observed with VGLUT1, VGLUT2 or both VGLUT1 and VGLUT2.

<p>(<b>A, B and C</b>) Images of 5, 9 and 12 DIV neurons immunolabeled for synaptophysin (<i>blue</i>), VGLUT1 (<i>green</i>) and VGLUT2 (<i>red</i>). Scale bars, 10 µm. (<b>D, E and F</b>) Higher magnification images. The images of the top row in (D–F) are from the regions indicated by the dashed boxes in A-C. Scale bars, 5 µm. <i>Arrows</i> indicate the positions of presynaptic puncta in each image. Below each image, an intensity profile is shown, depicting the intensity of synaptophysin (<i>blue</i>), VGLUT1 (<i>green</i>), and VGLUT2 (<i>red</i>) along the axon in the image. The peaks that correspond to the presynaptic puncta, indicated by the <i>arrows</i> in the images, are highlighted with <i>gray bars</i>. <i>Blue, green and red dots</i> above each peak indicate whether synaptophysin (<i>blue</i>), VGLUT1 (<i>green</i>) or VGLUT2 (<i>red</i>) are found at each terminal, as indicated by the key.