Joanne,
would you let us know what the circumstances of application are and the tissue?
When labels are added to mark specific periods in time re hard tissue growth,
there are several factors that are important. As long as the label is available,
it will continue to be incorporated. As these labels are added to the general
circulation, and some are slowly metabolized, they are still available to be
bound and therefore in these circumstances one cannot expect to see a super
sharp line. If there is a lot of resorption, as often happens with bone, then
the label that was deposited at one time period will be released even though in
smaller quantities and be reincorporated. This is generally not a problem with
cementum, dentin and enamel.
Another factor is the microscopy. Even with an 8 micron section, if you are
using transmitted light there will be some diffraction artifact. It is best to
use epi illumination so that the upper 2-3 microns of the section only are being
examined.
If you have used a low concentration of label then the weaker signal may be
partially obscured by the auto fluorescence and/or background fluorescence of
the tissue.
Finally the angle of viewing of lines may be distorted because you are often not
examining a straight edge but an inclined plane (unless you have a really thin
section.)
Barry

Joanne Schoonmaker wrote:

> We would be very grateful if those of you who in vivo label bone would share
> your experiences with us.  We are currently looking at both ground and thin
> (5-8u) sections of oxytetracycline labeled bone.  The crisp lines we were
> hoping for and see in all the published articles are rarely there.  Is this
> a microscopy or preparation related issue?
>
> Thanks,
> Joanne Schoonmaker
> Research Technician