Figure 4.

Increased inhibitory drive causes functional and structural reorganization in dark-reared visual cortex. A, Time course of the experiment: all animals were imaged at P28. Five groups of animals were used: DR animals were maintained and anesthetized before imaging in complete darkness; DR/7 dl animals were dark-reared until P21 and then exposed to light; DR/7dDIA animals were maintained in the darkness but injected with a daily dose of diazepam starting at P21; control animals were reared in a normal 12 h light/12 h dark environment. B, Representative images of the cortical intrinsic signal in response to light in individual mice from the different groups imaged. Red hues indicate strong activation, according to the dR/R scale at right. Mice treated with diazepam (DR/7dDIA) show strong visually driven responses similar to control mice and dark-reared mice exposed to light for 7 d (DR/7 dl). Scale bar, 0.5 mm. C, Representative retinotopic maps of elevation in individual mice, as per key at right. Diazepam treatment results in an increase in the level of organization of the visual map similar to light exposure. Scale bar, 0.5 mm. D, Quantification of the visually evoked optical signal across animals with different visual experience. The strength of the signal (normalized change in reflectance, dR/R) is low in dark-reared animals and increases in animals exposed to light for 7 d as well as in animals treated in the dark with diazepam (n = 3 animals). Only animals in the DR group had ΔR/R values that were significantly different from control animals (*p < 0.05). E, Image showing a dendritic branch in an animal treated with diazepam (DR/7dDIA). Scale bar, 5 μm. F, Diazepam treatment reduced the motility of spines in dark-reared animals (n = 7 animals) to control levels. G, Spine morphology was not affected by diazepam treatment and these animals had increased numbers of thin spines and filopodia when compared with control animals (*p < 0.05).