P

<0.001

<0.001

<0.001

<0.01

<0.001

It is of great interest to enquire whether the rate of synthesis of NAAG can be determined in the human brain? Although the turnover of NAAG has been reported similar to that of glutamate in in vitro analyses of rat brain10, the concentration of NAAG is less than 10% that of NAA. As a result, we have not observed 13C NAAG or its enrichment from 1-13C glucose in in vivo human brain studies to date.

3.3. Determination of NAA-Synthesis in Neurodegenerative and Other Brain Disorders

Because the assay as described requires that 13C aspartate be enriched to reach steady state, the forgoing results were obtained using a high-dose 1-13C glucose infusion protocol. When this dose is reduced, no steady state was achieved. Nevertheless, an estimate of NAA-synthesis can be obtained simply by comparing the relative enrichments of aspartate, the precursor with that of NAA, the product of the reaction11. Results of this assay are displayed in Figure 6 and 7. NAA2/Aspartate2 was markedly higher in all patients examined with Alzheimer's disease, but the value was not correlated with NAA/Cr (Figure 6). Results in schizophrenics (N=4) were also slightly higher than in controls. However, there was no statistical difference (Figure 7).

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