John,
 I am suprised that someone as wise as you woould even have the word
"overfixation" in their vocabulary!! Let's hope none of the vet students or
surgeons see this post!

Cindy Tily, HTL
Dept of Pathobiology
AU Coll of Vet Med
Auburn Univ
----- Original Message -----
From: John C. Dennis <dennijc@vetmed.auburn.edu>
To: Stephanie Moore <smoore@brandeis.edu>
Cc: HistoNet Server <histonet@pathology.swmed.edu>
Sent: Friday, January 12, 2001 11:04 AM
Subject: Re: "Venetian Blind" Artefact


> Stephanie
>
> The freeze artifacts I've seen in mouse and rat brain are round and make
> the sections look like a mature swiss cheese.  My cryogenius sections
> brain at just the temperatures you specify without problems EXCEPT when
> we've failed to cryoprotect sufficiently.  I've rectified that problem by
> cutting the brain hemispheres into smaller pieces to run through the
> sucrose series.
>
> I solved the venetian blind problem in paraffin by reducing the processing
> time of the infiltration cycles.  I think I mean by that that venetian
> blind effect is caused by at least hardening of the tissue and in your
> case I would say overfixation may be a problem.  Squirrel brain may well
> be different enough that different temperatures would be a
> solution.  You'd hardly think so since they're really just cute rats.  But
> now I'm rambling so I'll save you further time and stop.
>
> Cheers
>
> John Carroll Dennis
> Anatomy, Physiology, and Pharmacology
> 109 Greene Hall
> Auburn University, AL  36849
>
>
> On Fri, 12 Jan 2001, Stephanie Moore wrote:
>
> > I have recently experienced what I believe to be this artefact while
slicing
> > sections of squirrel brain.  I know that this was not properly sunk and
also that
> > it was likely in too little volume of paraformaldehyde (4%) fixative.
The person
> > who gave me the specimen is not very experienced, but wanted to slice it
anyway.
> > My question is, does insufficient cryoprotection from sucrose cause
ventetian
> > blinds?  I use a cryostat set at -20C chamber temperature and -18C
object
> > temperature, and Tussue Tek OCT medium for embedding the specimen.
> >
> >
>
>