Karen,
It is true that tetracycline and other fluorchromes bind to various groups
during  hard tissue formation,  some of them to the calcium ions. This is
useful in determining the amount of growth between the times of
application of the fluorchromes, however there are some drawbacks.  First
the label is only available for a limited time and is then metabolized.
Second is that the introduction of the label may interfere with the
animal's metabolism so that it may also influence the rate of hard tissue
formation.
Incremental lines are seen in a variety of structures including dentin and
enamel and reflect small changes in the composition of the material being
laid down during a particular time period. In most cases this reflects
availability of components during that time period.
Barry

Karen Larison wrote:

> Sharon,
>
> It's my understanding that the tetracycline and other fluorochromes
> used in this application (xylenol orange, calcein, etc) bind to the
> calcium in bone.  Therefore, if you decalcify, you are eliminating
> the signal, regardless of what technique you subsequently use.  Can
> you section this stuff without decalcifying?  If you can, my bets are
> that the rings will be there.
>
> -Karen
>
> >Date: Tue, 30 May 2000 10:38:35 +0000
> >From: "Marshall, Sharon," <marshall@anat.uct.ac.za>
> >Subject: ageing rings in sharks
> >To: histonet@pathology.swmed.edu
> >
> >Hi histonetters,
> >I have a student in my lab. who wants to view ageing rings in cat
> >shark vertebrae.  This has been done before (previous papers) using
> >resin sections and tetracycline fluorescence.  These sections are a
> >couple of mm thick and viewed under ultra violet light. She seems to
> >think it might be possible to process to wax, cut 7 micron thick
> >sections and still see these rings.  We tried some samples she had
> >which are 10 years old and have been in 70% alcohol all that time.(no
> >tetracycline present in sharks in these samples)
> >We decalcified in 5% formic acid, processed to wax and then stained 7
> >micron sections with H&E, Tol. Blue. No rings.  I think these rings
> >are only possible to view using thicker sections i.e.mm thick or the
> >specimens are to old.   I know that to see tetracycline flourescence
> >one needs to alcohol fix and resin embed hence the processing in the
> >previous papers.
> >Finally, we are going to try fresh samples but I am wondering if we
> >are not wasting our time.  I need to convince her that resin and
> >thicker sections cut with a diamond saw is the
> >way to go even if no tetracycline is present in the samples.
> >Any opinions,help would be great.
> >Thanks
> >Sharon Marshall
> >Anatomy & Cell Biology
> >University of Cape Town
> >South Africa
> >E-mail: marshall@anat.uct.ac.za