II. Localization of Pi class glutathione‐S‐transferase in the forebrains of neonatal and young rats: Evidence for separation of astrocytic and oligodendrocytic lineages

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Abstract
The Yp isoform (Pi class) of glutathione‐S‐transferase has recently been localized in oligodendrocytes in the brains of mature rats. To examine at what postnatal age Pi first appears in oligodendrocytes or precursor cells, antibodies against Pi were used to immunostain tissue sections from the forebrains of neonatal rats and young rats up to 17 days of age. In the brains of neonates Pi immunofluorescence was observed in ovoid cells in the subependymal layer, and in ovoid cells and cells bearing short, thick processes in the corpus callosum and cingulum. These cells did not immunostain for vimentin. During the first postnatal week Pi‐positive cells showed positive immunostaining for ganglioside GD3, which is characteristic of oligodendrocyte precursors, and process‐bearing Pi‐positive cells appeared in the cingulum and at the lateral borders of the corpus callosum in increasing numbers. During the second postnatal week the cytoplasm of Pi‐positive cells became more compact, and the processes thinner, and the Pi‐positive cells and their processes began to immunostain for 2′,3′‐cyclic nucleotide‐3′‐phosphohydrolase, which is characteristic of immature and mature oligodendrocytes and myelin sheaths. By age 17 days Pi was observed in relatively mature oligodendrocytes. The observations suggest that Pi occurs in oligodendrocyte precursors, immature oligodendrocytes, and mature oligodendrocytes in the postnatal through 17 day old rat forebrain.In the accompanying paper (Cammer and Zhang, '92)—if references are permitted in the Abstract a different glutathione‐S‐transferase isoform, Yb (Mu class), was localized in cells of the astrocyte lineage, beginning in the forebrains of neonatal rats. At each postnatal age Mu‐and Pi‐positive cells differed in size and shape as well as in their contents of “marker” antigens. These findings support the conclusion that the oligodendrocyte and astrocyte lines have separate precursors in the neonatal rat forebrain.