Recently, a bio-electrochemical technique known as CLARITY was reported for three-dimensional phenotype mapping within transparent tissues, allowing clearer whole-body and organ visualization with CB-perfusion (CUBIC) and leading to the development of whole-body clearing and transparency of intact tissues with the PACT (passive clarity technique) and PARS (perfusion-assisted agent release in situ) methodologies. We evaluated the structure–function relationships in circuits of the whole central nervous system (CNS) and various internal organs using improved methods with optimized passive clarity. Thus, in the present study, we aimed to improve the original PACT procedure and passive clearing protocols for different intact rodent tissues. We determined the optimal conditions for the passive clarity method that allowed the production of a transparent whole CNS by clearing the brain and spinal cord, as well as various organs. We also improved the tissue transparency using mPACT (modified PACT), a method for direct passive clearing, and whole perfusion-based PARS-mPACT, a method for fusion clearing, and we identified the appropriate experimental conditions. These optimized methods can be used for easy and economical high-resolution mapping and phenotyping of normal and pathological elements within intact tissues. A new method allows faster visualization of the three-dimensional structure of whole organs and tissues. For imaging of internal structure, animal tissue can be “cleared,” or made transparent, by replacing the lipids in the tissue with hydrogels. Passive clarity technique (PACT), a common method that involves soaking tissue in clearing solution is simple and effective, but slow. Yong Eun Cho at, Yonsei University, Seoul, Korea and coworkers have developed a faster method, called modified PACT (mPACT), which reduces clearing time. Using mPACT, researchers cleared the complete brain and spinal cord of a mouse in 14 days instead of 23. They also successfully applied the method to various mouse organs and entire mouse embryos, as well as rats and guinea pigs. mPACT will facilitate high-resolution imaging of tissues in health and disease.
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Woo et al. (2016) studied this question.