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Choice of cranial window type for in vivo imaging affects dendritic spine turnover in the cortex
http://www.nature.com/natureneuroscience
Nature Publishing Group
200 7
Hua-Tai Xu1, Feng Pan1, Guang Yang1 & Wen-Biao Gan
Determining the degree of synapse formation and elimination is essential for understanding the structural basis of brain plasticity and pathology. We show that in vivo imaging of dendritic spine dynamics through an open-skull glass window, but not a thinned-skull window, is associated with high spine turnover and substantial glial activation during the rst month after surgery. These ndings help to explain existing discrepancies in the degree of dendritic spine plasticity observed in the mature cortex.
Recent studies using two-photon microscopy have shown markedly different turnover rates for dendritic spines in normal and sensory-deprived mouse cortex16. In the supercial layer of several cortical regions in adult mice, dendritic spines imaged through a thinned-skull window are remarkably stable with 12% turnover over 3 d, B5% over 1 month and B2026% over 19 months1,5,6. In contrast, in the same cortical regions, when the skull is removed and replaced with a glass window (open-skull), 420% of adult dendritic spines turn over in 14 d and 3050% turn over in 14 weeks24. These results lead to contradictory views on the structural plasticity of synapses in the mature brain and have different implications for information storage and maintenance in neuronal circuits7,8.
To determine the possible factors contributing to the differences in spine turnover seen in previous reports, we measured dendritic spine dynamics through either open-skull or thinned-skull windows in the barrel cortex of adult transgenic mice expressing yellow uorescent protein (YFP) in layer V pyramidal neurons. The surgical procedures, two-photon imaging and data quantication were done as previously described16 (Supplementary Methods online). Prior studies with open-skull windows usually started imaging B12 weeks after surgery, presumably because of the increased opacity of the preparation soon after craniotomy24. We found that 12 weeks (12.3 0.8 d) after craniotomy, open-skull preparations in B30% (19/59) of the mice became transparent, and allowed imaging of spines with a signal-to-noise ratio that was comparable to that of thinned-skull preparations. When these mice (4.1 0.9 months of age) were imaged over the subsequent days to weeks, we found that spine turnover in the barrel cortex...