Thank you all for your great advice!  Here is the basic gist of what I
got:

1) Temp. too cold causing tissue to be too hard, solution increase T  by
increments of 2-3 degreesC (Karen Larison) -  I will try this, though
rat brains slice wonderfully at this temp - perhaps squirrels are more
different than originally seems.  Actually I was quite surprised by the
size of the brain and the large temporal "lobe" area in the squirrel!

2) Overfixation causing tissue to be too hard

3) Loose knife or specimen (I had checked all of these - often a cause
of chatter)

4) Poor cryoprotection (I have seen "swiss cheese" slices of brain due
to this - different artefact, but thanks John Dennis for the advice and
I agree we should cut brain up before running through series of
sucrose.  Squirrel is much bigger than the rat and mouse brains I am
used to)


I am brand new to this list and want to tell you I feel very welcomed!
I have a feeling that in the near future I will have some more questions
for ya'll.