Ross,
Looking at your protocol I had to wonder, do you flush the circulatory
system first with normal saline? Your fixation looks similar to mine
except for that. By the way, I -regularly- perfuse P0 (day of birth)
rats intracardially using gravity perfusion. These always turn out
quite well for my in-situ hybridzations.
Terry A Austin
Dept of Biological Sciences
University of North Texas
Denton, TX
taaustin at vaxb.acs.unt.edu