Carbon 14 is a high-energy beta emitter, so you cannot expect high
 resolution autoradiographs (for which you need low energy beta
 particles as from tritium or internal conversion electrons as
 from Iodine 125). If the isotope is in a drug, you need to know
 that it will be immobilized by whatever fixative you use. If the
 drug is not made insoluble or irreversibly bound to the tissue,
 autoradiography will be a meaningless exercise because all the
 radioactive material will be lost long before you cut any sections.

 If there is uncertainty, you could place pieces of freshly killed
 mouse on X-ray film in darkness for a day or two, and then develop.
 Do controls with mice that had the non-radioactive drug to
 exclude chemographic artifact. This will show if the compound
 becomes concentrated in any particular organs, and could provide
 the baseline for a study to show if the drug can be retained
 in fixed and processed material, cryostat sections etc.

 As for safety, you should consult your radiation protection
 officer, from whom you should already have received authorization
 and advice. Amounts of some isotopes less than a millicurie are not
 recognized as above background, but there could be a hazard if the
 compound containing the radioactive element is concentrated in
 some particular organ. 

 John A. Kiernan,
 Department of Anatomy & Cell Biology,
 The University of Western Ontario,
 LONDON,  Canada  N6A 5C1
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On Mon, 7 Aug 2000 GSennello@nexstar.com wrote:

> I have been asked to do auto-radiography on 14 C labeled rat tissue.  The
> animals are receiving a single oral dose of
>  250 uCi/kg labeled drug that will probably not be absorbed well (we are
> thinking it will end up it the gut).  I will be looking at kidney, liver
> and bone.  My questions are:  (1) will the processor,  the solutions and
> the waste sections  be hot at this level?  In the past someone here dosed
> at 1/5 this level and it was not detectable.  (2) should I try film vs.
> emulsion, in the past nothing was seen with emulsion after  30 and 60 day
> exposures.
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