On Mon, 9 Jul 2001 rita.russell@syngenta.com wrote:

> I am currently experiencing problems with sections of rat brain following
> perfusion fixation with Modified Karnovsky's fixative. They are proving very
> difficult to flatten. I think the main cause is inadequate paraffin wax
> impregnation following an overnight schedule.

Glutaraldehyde fixation makes sectioning in paraffin
difficult. The usual explanation is that the abundant
cross-links among protein molecules impede penetration
of the wax molecules. Longer times in melted wax
might help. If it doesn't, you could cut frozen or
cryostat sections instead, or fix in a mixture that
doesn't contain glutaraldehyde. There are very few
circumstances in which glutaraldehyde fixation is
necessary for subsequent light microscopy.
----------------------------------------
John A. Kiernan
Department of Anatomy & Cell Biology
The University of Western Ontario
London,  Canada   N6A 5C1
   kiernan@uwo.ca
   http://publish.uwo.ca/~jkiernan