Super‐resolution structural analysis of dendritic spines using three‐dimensional structured illumination microscopy in cleared mouse brain slices

Three‐dimensional (3D) super‐resolution microscopy technique structured illumination microscopy (SIM) imaging of dendritic spines along the dendrite has not been previously performed in fixed tissues, mainly due to deterioration of the stripe pattern of the excitation laser induced by light scattering and optical aberrations. To address this issue and solve these optical problems, we applied a novel clearing reagent, LUCID, to fixed brains. In SIM imaging, the penetration depth and the spatial resolution were improved in LUCID‐treated slices, and 160‐nm spatial resolution was obtained in a large portion of the imaging volume on a single apical dendrite. Furthermore, in a morphological analysis of spine heads of layer V pyramidal neurons (L5PNs) in the medial prefrontal cortex (mPFC) of chronic dexamethasone (Dex)‐treated mice, SIM imaging revealed an altered distribution of spine forms that could not be detected by high‐NA confocal imaging. Thus, super‐resolution SIM imaging represents a promising high‐throughput method for revealing spine morphologies in single dendrites.