Aspartoacylase is an enzyme that specifically de-acetylates NAA, and which was observed almost exclusively in oligodendrocytes (Figure 5A). In contrast, NAA and NAAG were expressed primarily in neurons (Figures 5B, C). Aspartoacylase-stained cells were arranged in characteristic rows between axon bundles in the corpus callosum. Low levels of NAA can also be seen in rows of oligodendrocytes. The level of NAA-IR in adult rat oligodendrocytes is substantially lower than the level in neurons. NAAG is present in scattered axons in the corpus callosum, whereas NAA is present in most or all axons in the corpus callosum, although at only a moderate level. It remains to be determined if the NAA present in oligodendrocytes is synthesized within the glial cells themselves, or if it is made in neurons, and passed from axon to glia.
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