Figure 7.

Light exposure induces a rapid, transient outgrowth of dendritic protrusions. A, Top, A dendritic arbor imaged over 2 d in a dark-reared animal exposed to light after the first imaging session. Bottom, A higher magnification of a dendrite bearing dendritic spines. Notice the outgrowth of a filopodium (arrowhead) and spine (arrow). The filopodium withdraws after 2 d of light exposure but the spine is maintained. Scale bar, 30 μm (top); 5 μm (bottom). B, The formation of dendritic protrusions is enhanced after 2 h of light exposure in dark-reared animals relative to animals maintained in the dark and relative to normal light-reared controls (*p < 0.05), while the rate of elimination is not altered. C, The percentage of new protrusions formed between the end of the dark rearing period and after 2 d of light exposure is not different from that over a 2 d period in light-reared animals. However, the elimination of spines is significantly enhanced suggesting a pruning of preexisting synapses.