Figure 2.

Visual experience regulates dendritic spine structure in the visual cortex. A, In vivo two-photon image of the apical tuft of a layer 5 pyramidal neuron in visual cortex of a P28 mouse. The image is a collapsed z stack showing the extent of the apical tuft dendritic arbor. Scale bar, 100 μm. B, Three-dimensional reconstruction showing the dendritic arbor from the side. Scale bar, 100 μm. C, Two-photon image of dendritic spines in vivo from dendrite shown in A (boxed area). Scale bar, 5 μm. D, Following imaging, red tracer was injected into the imaged area based on the blood vessel pattern. The animal was perfused and the imaged area identified in fixed section. The injection site is shown in red and resides in visual cortex as identified using coordinates of the mouse brain atlas. E, Time-lapse image of dendritic spines in the visual cortex of a control mouse in vivo. Images shown were taken 30 min apart. Scale bar, 2 μm. Spines are motile at these ages (notice spine 3 withdraws into the dendrite during the first hour of imaging). F, Lengths of the 4 spines at left are shown plotted over 2 h. G, The motility index for the same four spines showing the approximate range of motilities observed in control animals (filopodia are not shown in this figure—filopodia were generally more motile and were rarely observed in control animals). H, Spine motility indices for P28 mice exposed to different visual environments. Analysis included all spine classes and filopodia. There is a significant increase in spine motility in visually deprived animals (DR) compared with controls. Two days of exposure to a normal light-dark cycle does not affect motility but after 7 d of exposure to normal dark-light conditions the motility index is no longer significantly different from that in control animals. *p < 0.05 compared with control.