NAAG and NAA immunoreactivities (NAAG-IR and NAA-IR) have been found to be distinct in many areas of the CNS in the species studied to date. The rat has been the most thoroughly studied species in terms of the extent of the coverage of NAA and NAAG localization in various CNS regions. As compared with other species studied, the rat has relatively high levels of NAA (approximately 8mM) and relatively moderate levels of NAAG (approximately 0.75mM).2 We consider the rat to be a good representative species for the description of the distributions of NAA and NAAG in the CNS, despite having lower levels than carnivores and primates. In the rat, the staining patterns for NAAG and NAA were very distinct in forebrain and cerebellar cortex, but were more similar in areas of the brainstem and spinal cord, as will be shown below. The greatest disparities in localization are observed in the cerebral and cerebellar cortices of the rat, where NAA is present in most neurons, but NAAG is only present in subpopulations of neurons. For a thorough examination of the disparities between NAAG and NAA expression, see Moffett and Namboodiri.11

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