Can mammals be cleared and stained?

[A Anchan]

On the internet, I've only seen examples of fish and some amphibians being cleared and stained.
If mammals can be cleared and stained, what is the difference in procedure?

 

[Ygggdrasil]

Yes, researchers have modified a technique called CLARITY to clear and stain whole mice. Details of the procedure can be found in the second link.
http://www.bbc.com/news/health-28582452
http://glab.caltech.edu/doc/Yang%202014%20Cell.pdf

 

[BillTre]

It depends a lot on what you are interested in doing. But probably not as well as the (presumably small sized, or thin) fish and amphibians you have seen.

People often stain cartilage and bone, which looks nice but will also stain scales on fish (if they have them). These outer layers are often removed or special treated in order to see what lies underneath them. I'm not so experienced with mammals, but I would expect that mammals with a thick fur coat would present similar issues.

In research lab, whole mounts are often combined with partial dissections (removing the parts you are not interested in in order to get a better look at the other parts.
"Plastination" is a process (popular with museums recently) that has been applied to another other things, humans. This does not clear whole humans but involves in partial dissections to reveal inner parts or in some cases removal of a part from the body (such as a lung) which could then be cleared to show the blood vessels (which could be pumped full of colored plastic).

Staining and clearing both will require chemicals to diffuse into the sample which requires the removal or breaking (in some way) of any barriers to permeabillity for the chemicals you are using. This will often be combined with long times, gentle agitation, and some preservation method depending on how the tissue is treated (such as fixed or not fixed). Fixation chemically modifies molecules found in the tissue, making them immobile. For example gluteraldehyde cross links proteins which prevents them from moving, but also making the spaces for staining molecules to pass through smaller.

Clearing involves several steps with the goal of removing small scale differences in optical density so that as a whole the object is optically homogeneous, giving a clear view. This usually involves removing lipids and water and replacing them with other chemicals. Recently there have been several advances in clearing large structures like mammalian brains to allow clear views of labelled neurons deep in the brain.