My brains won't sink in 30% sucrose!

[disco volante]

Hi all,

I am cutting frozen sections of mouse brains.  These brains were perfused first with 4%pfa, then post-fixed overnight in the same solution at 4C.  I then put them in 30% sucrose in 0.1M PB (ph 7.4) at 4C.  About half of my brains won't sink, even 5 days later.  Curiously, half of them in the same solution do sink.

All the brains were collected and processed in an identical manner, and the sucrose solution was also the same between the brains that did and did not sink.

What's up with this?  Do I dare trying to slice them?

Thanks!

[richard03]

you need to put them in 15% sucrose first. Then transfer to 30% sucrose after the brain sink to bottom.

[MDeng]

Don't worry. It happens to me occasionally. I think it is caused by some bubbles hid in the brain. Just go ahead to section it.

[disco volante]

Strange stuff.  Anyhow what I ended up doing was dilution the solution in each vial until the brain just sank (took very little buffer to reach this point), then changed it back to 30% sucrose again the next morning.  Then they all sank comfortably.  I guess some brains like to start with lower concentration sucrose first.  Thanks for your help everyone!