Thanks to you all for your advice. I think the damage in my tissue 
happens even before I put the sections in the LFB solution- so it is 
probably a matter of poor dehydration (I hope). I'm going to try 
fixing a brain in formalin, without perfusion, and then dehydrate in 
30% sucrose for 24h. Does this make sense?

Also, for the people who have trouble with sections floating off the 
slide: try Superfrost Plus Gold slides, they work pretty well.

Christina Benou
Research Fellow
Brigham & Women's Hospital
Boston MA