Phenotypic changes in NG2+ cells after spinal cord injury.

Following contusive spinal cord injury (SCI), 50% of oligodendrocytes in the residual white matter are lost within 24 h. NG2-expressing cell proliferation is maximal 3 days after SCI, and may be the source of mature oligodendrocytes and astrocytes that chronically replace those that were lost. We studied NG2(+) cells dissociated from the 3-day injured spinal cord for comparison with those from uninjured adult and early postnatal cords. After 24 h in serum-containing medium, we performed patch clamp analysis and immunocytochemistry for NG2 in combination with nestin (progenitors), and A2B5, O4, and O1 (oligodendrocyte lineage markers). We observed an NG2(+)/A2B5-/O4-/O1- population in both adult preparations. More than double the normal number of NG2(+) cells was isolated from the injured cord, but OX42(+) microglia/macrophages were the predominant cell type after injury. Most cells isolated at P7 were NG2-/A2B5(+), whereas those from the normal adult were NG2(+)/A2B5-. NG2(+) cells after SCI displayed altered voltage-gated potassium current profiles compared to normal adult and P7 animals. Additionally, less than 25% of adult cells (normal and injured) responded to GABA and glutamate, compared to 100% of P7 cells. Our results indicate that the adult NG2(+) cell pool is antigenically and physiologically different than the early postnatal pool, and that contusive injury induces changes in adult NG2(+) cells.