  Extensive mapping of neuronal connections in the central nervous system
requires high-throughput um-scale imaging of large volumes. In recent years,
different approaches have been developed to overcome the limitations due to
tissue light scattering. These methods are generally developed to improve the
performance of a specific imaging modality, thus limiting comprehensive
neuroanatomical exploration by multimodal optical techniques. Here, we
introduce a versatile brain clearing agent (2,2'-thiodiethanol; TDE) suitable
for various applications and imaging techniques. TDE is cost-efficient,
water-soluble and low-viscous and, more importantly, it preserves fluorescence,
is compatible with immunostaining and does not cause deformations at
sub-cellular level. We demonstrate the effectiveness of this method in
different applications: in fixed samples by imaging a whole mouse hippocampus
with serial two-photon tomography; in combination with CLARITY by
reconstructing an entire mouse brain with light sheet microscopy and in
translational research by imaging immunostained human dysplastic brain tissue.
