Synaptic Remodeling of the Auditory Cortex Following Bilateral Blindness: Evidence of Cross-modal Plasticity

We aimed to evaluate structural dynamic changes of neurons in the auditory cortex after visual deprivation. We longitudinally tracked dendritic spines for 3 weeks after visual deprivation in vivo using a two-photon microscope. GFP-labeled dendritic spines in the auditory cortex were serially followed after bilateral enucleation. The turnover rate, density, and size of the spines in the dendrites were evaluated 1, 2, and 3 weeks after visual deprivation. The turnover rate of the dendritic spines in the auditory cortex increased at 1 week (20.1 +/- 7.3%) after bilateral enucleation compared to baseline (12.5 +/- 7.9%); the increase persisted for up to 3 weeks (20.9 +/- 11.0%). The spine loss rate was slightly higher than the spine gain rate. The average spine density (number of spines per 1 1m of dendrite) was significantly lower at 2 weeks (2W; 0.22 +/- 0.06 1/1m) and 3 W (0.22 +/- 0.08 1/1m) post-nucleation compared to baseline (0.026 +/- 0.09 1/1m). We evaluated the change of synaptic strength in the stable spines at each time point. The normalized spine size in the auditory cortex was significantly increased after bilateral blindness at 1 W postoperatively (1.36 +/- 0.92), 2 W postopera-tively (1.40 +/- 1.18), and 3 W postoperatively (1.36 +/- 0.88) compared to baseline. Sensory deprivation resulted in remodeling of the neural circuitry in the spared cortex, via cross-modal plasticity in the direction of partial breakdown of synapses, and enhanced strength of the remaining synapses.