Comparative NAA and NAAG Expression in Neocortex

The comparative distributions of NAA-IR and NAAG-IR in rat neocortex are shown in Figure 1. Both immunoreactivities appeared punctate, which may represent localization in intracellular organelles or vesicles. NAAG-IR was also observed in putative extracellular NAAG-positive synaptic contacts (see insert, Figure 6C). NAA-IR was not observed in synaptic-like extracellular puncta, and was more diffuse in the cytoplasm of neurons. However, NAA-IR was often observed in large, organelle-sized intracellular inclusions in certain types of neurons, including cortical pyramidal cells and principle neurons of the hippocampus (Figure 1F inserts). These could possibly be DMSO-based artifacts associated with the fusion of internal membrane structures or organelles that contained high concentrations of NAA (e.g., neuronal mitochondria).

NAAG-IR was most prevalent in apparent interneurons in all cortical layers, and in the rat, was not observed significantly in pyramidal cells (Figure 1A, C, E). This is in contrast with carnivores and primates, where both interneurons and pyramidal cells were strongly immunoreactive for NAAG (see Figures 6 and 7 below). NAAG staining was present in the proximal dendrites of immunoreactive cells in the rat, but was not seen in distal dendrites. This also contrasts with carnivores and primates, where cortical pyramidal cells were immunoreactive for NAAG throughout their dendritic arborizations. NAA-IR was present in most or all neurons in all layers of neocortex, and was also observed in the apical and basal dendrites of pyramidal neurons (Figures 1B, D, F).

Figure 1. NAA and NAAG immunoreactivity in rat neocortex. NAAG-IR is relatively limited in rat neocortex, being present mostly in small interneurons (A), but NAA-IR is observed in most or all neurons, with high levels in cortical pyramidal cells (B). NAAG-IR is present in cell bodies, proximal dendrites, and probable synaptic contacts in the neuropil (C, E), whereas NAA-IR is present in cell bodies and throughout the dendritic arborizations of neurons (D). In cortical areas, many pyramidal neurons contained large NAA-IR inclusions, often located at the base of the apical dendrite (F). These ranged in shape from round to complex (inserts in F), and could represent DMSO-fused organelles, such as mitochondria, that contained high concentrations of NAA. Bar = 100^m A, B; 30^m C, D and 20^m E, F.

Figure 1. NAA and NAAG immunoreactivity in rat neocortex. NAAG-IR is relatively limited in rat neocortex, being present mostly in small interneurons (A), but NAA-IR is observed in most or all neurons, with high levels in cortical pyramidal cells (B). NAAG-IR is present in cell bodies, proximal dendrites, and probable synaptic contacts in the neuropil (C, E), whereas NAA-IR is present in cell bodies and throughout the dendritic arborizations of neurons (D). In cortical areas, many pyramidal neurons contained large NAA-IR inclusions, often located at the base of the apical dendrite (F). These ranged in shape from round to complex (inserts in F), and could represent DMSO-fused organelles, such as mitochondria, that contained high concentrations of NAA. Bar = 100^m A, B; 30^m C, D and 20^m E, F.

Figure 2. NAA-IR and NAAG-IR in rat hippocampus. NAA is present in most neurons in the rat hippocampus (A). Large intracellular NAA-stained elements were observed in many hippocampal pyramidal cells (arrowheads C). NAAG distribution is relatively restricted in the rat hippocampus, being expressed in scattered neurons in the pyramidal layer in all subdivisions (B), and in cells of the polymorph layer. Many unstained pyramidal cell dendritic shafts were covered with NAAG-stained puncta that appeared to be NAAG-containing synaptic contacts (arrowheads in D). Bar = 100^m A, B and 20^m C, D.

Figure 2. NAA-IR and NAAG-IR in rat hippocampus. NAA is present in most neurons in the rat hippocampus (A). Large intracellular NAA-stained elements were observed in many hippocampal pyramidal cells (arrowheads C). NAAG distribution is relatively restricted in the rat hippocampus, being expressed in scattered neurons in the pyramidal layer in all subdivisions (B), and in cells of the polymorph layer. Many unstained pyramidal cell dendritic shafts were covered with NAAG-stained puncta that appeared to be NAAG-containing synaptic contacts (arrowheads in D). Bar = 100^m A, B and 20^m C, D.

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