DR. LIEBERMAN: I would like to suggest that you be careful about the specificity of any -- One of the things that is clear from a number of studies is that, as soon as you destroy the axon and glial cells, that metabolically they may be quite different, and where they may have expressed NAA or any other number of substances, they will not do that following transection.
One of the things that would be very interesting for you to test to see that is look at just oxygen consumption of the optic nerve just after transection, and then look at it after a period of time to see if there is a significant change; because the change would be in the metabolic capacity of the glial cells.
DR. TRAPP: I see. So the question was that it is possible that the transection itself is going to change the expression of NAA. Certainly, I think that must happen.
So we know NAA is transferred to the oligodendrocytes to be degraded. Certainly, if you transect the axon, that probably can't happen. But, you know, whether these cells are making NAA -- the oligodendrocytes -- certainly, I don't think it is at significant levels.
I didn't show it here, but we do immunostaining for NAA and really cannot detect any NAA or very little NAA within the oligodendrocytes. But certainly, I don't think it is something that one could prove conclusively, because we know NAA gets transferred to the myelin-oligodendrocyte unit. So there's got to be some there.
I think, for the purposes of this, though, in looking at spectroscopy, I still think that the glia cells are probably contributing in the adult brain very little NAA to the total amount that is there. So I don't think they are going to significantly change the values that the spectroscopists are obtaining within the tissue.
DR. ROSS: Thank you. It is very challenging data, and it really asks the question: Can we measure NAA in the spinal cord? Peter Barker with his phased ray coils or you in Cleveland actually do that.
DR. TRAPP: Yes. I am not the one to answer that question. So Peter or Doug probably -- we certainly would like to.
DR. BARKER: There are two or three papers now on spectroscopy in the spinal cord. It is definitely possible, at least in the cervical spine.
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