All 13C changes except neuronal DNA, since DNA is synthesized only when
the cell divides, and cerebellar neurons divide only early in life.  The
paper below contains data on overall 13C/12C for tissue also.

Tom Brenna

***
Slatkin DN, Friedman L, Irsa AP, Micca PL.
The stability of DNA in human cerebellar neurons.  Science. 1985 May
24;228(4702):1002-4.
Human tissues have carbon-isotope ratios (13C/12C) that reflect dietary
ratios.  This observation has been used to determine the extent of
metabolic turnover of DNA in cells of the adult human cerebellum (90
percent of which are neuronal). If adult human neuronal DNA were
metabolically stable, its 13C/12C would reflect that in the maternal diet
during fetal development as nearly all neurons are formed during
maturation of the fetal brain and do not undergo cell division thereafter.
The 13C/12C ratios in the food chains and body tissues of Europeans differ
from corresponding American ratios by about 50 parts per million on the
average. Therefore, turnover was studied by comparing 13C/12C ratios in
cerebellar DNA of American-born Americans, European-born Americans, and
European-born Europeans. The 13C/12C ratios in cerebellar DNA from
European-born Americans were closer to 13C/12C ratios in cerebellar DNA
from European-born
Europeans than from American-born Americans, indicating that there was
little or no turnover of neuronal DNA.
***

> Dear Folks,
>
> I received this message from a colleague who is teaching students
> about the influence of corn. Do any of you alert readers have a
> reference at your fingertips that you could recommend for Charlie?
>
> "Next Tuesday Washington College is hosting a viewing of the movie "King
> Corn," which is a critique of the use of corn products in our country
> (see
> description below).
>
> One of the most fascinating things I heard about this issue was in one
> of
> your talks: The stable isotope evidence that Europeans coming to the US
> experience a shift in their carbon isotope ratios in response to the
> corn-heavy diet.  Does that data appear in publication anywhere? I would
> love to bring that up at the viewing of this movie during the discussion
> period."
>
> Marilyn Fogel
>
>
> Dr. Marilyn L. Fogel
> Geophysical Laboratory
> Carnegie Institution of Washington
> 5251 Broad Branch Rd., NW
> Washington, DC 20015
> Phone (202) 478-8981
> Main office (202) 478-8900
> FAX (202) 478-8901
> Website: http://fogel.gl.ciw.edu/
>
>