Figure 6.

Light exposure induces rapid structural reorganization mediated by NMDA receptors. A, Time-lapse image of dendritic spines in the visual cortex of a dark-reared mouse in vivo following light exposure for 2 h at P28. Images shown were taken 20 min apart. Scale bar, 2 μm. Dendritic protrusions are highly motile in this group of animals (DR/2hL). B, Lengths of the 4 protrusions labeled in A are shown in the left panel plotted over 2 h. Notice the large changes observed in length over this timescale. The right panel shows the motility index for the same four protrusions. Protrusion 1 was classified as a filopodium due to its length. Not all spines are highly motile. Spine 3 exhibits length changes and a motility index typical of spines in control mice at this age. C, Brief light exposure rapidly increases spine motility in dark-reared animals (*p < 0.05). This effect is prevented when CPP is administered systemically before light exposure. D, High-magnification two-photon images of representative dendrites in the visual cortex of animals exposed to light for 2 h following dark rearing. Notice the increased numbers of thin spines and filopodia in dark-reared animals briefly exposed to light. Animals pretreated with CPP before light exposure have fewer thin spines and filopodia than untreated animals, but similar in proportion to dark-reared animals. Scale bar, 5 μm. E, Brief light exposure increases the proportion of thin protrusions (thin spines and filopodia) and decreases the proportion of mushroom and stubby spines compared with DR animals (*p < 0.05). The reorganization of dendritic spine morphology is prevented by administration of CPP before light exposure.