Figure 2.

Excitatory bouton areas and spinule prevalence increase over development. A, 2D synapse profile length, as defined by the PSD, remains relatively stable from before eye-opening (p28) until the end of the critical period for plasticity in ferret visual cortex (p60). However, PSD length increases substantially from the end of the critical period until at least the cusp of maturity (>p90 ages). B, Excitatory presynaptic bouton areas are largest at a time when most boutons appear to have elongated en passant morphology (p21–p28). Bouton size decreases significantly by p46–p47 and then shows a steady increase until at least p90. C, Average spinule profile areas do not appreciable change across the postnatal ages examined. Note that spinule areas show relatively large interanimal variation attributed to the variation in spinule sizes from distinct parent neurite/glia origins. D, Excitatory SBBs are most prevalent in late adolescence (>p90) versus at the height (p46–p47) or end (p46–p47) of the critical period for plasticity in ferret V1. A trend toward increased SBB prevalence is also seen between p46–p47 and p60 ages. For A–D, statistical comparisons were performed between p21–p28 and p46–p47, p46–p47, and p60–p66, and p60–p66, and >p90 (for details, see Table 3). Gray circles = individual animal means; Purple circles = group means ± SEM; **p < 0.015, ***p < 0.001.