Ischaemic injury of developing white matter is thought to be the major cause of cell damage in the lesions that underlie cerebral palsy (CP). Typically, these lesions may include an infarcted core and/or an extensive region of hypomyelination. Immature (O4+/GalC-) oligodendroglia appear to be selectively damaged by ischaemia, with activation of non-NMDA type glutamate receptors central to ischaemic injury in these cells. We here examine the role that neighbouring astrocytes may have in immature oligodendroglial injury, focusing upon early astrocyte swelling and the putative release of glutamate.

Neonatal rats were humanely killed and the optic nerves were dissected. Neonatal rat optic nerve (nRON) glial cells were then AM-loaded with Fura-2 and imaged in situ for changes in [Ca²⁺]_i prior to and during perfusion with artificial CSF (aCSF) absent in oxygen and glucose (to mimic ischaemia). Post-natal day 8-12 nRONs were used since at this age the nRON is close developmentally to the human white matter that is subject to injury in CP. The nRONs were continuously perfused and maintained throughout at 37 °C. Cells of the oligodendrocyte and astrocyte lineage were differentiated by rapid-live staining using RAN-2 and platelet derived growth factor α antibodies (Wilke et al. 2002).

The onset of ischaemic conditions produced a rapid elevation in [Ca²⁺]_i and a degree of cell death in both cell types. Astrocyte death was independent of the [Ca²⁺]_i rise, and dependent upon the presence of Na⁺ and Cl^– in the aCSF. Astrocyte death was prevented by blocking the Na⁺-K⁺-Cl^– cotransporter (NKCC) with 50 mM bumetanide and therefore had characteristics consistent with cell swelling-mediated lysis. Oligodendroglial death during ischaemia was dependent upon [Ca²⁺]_i elevation and was eliminated by blocking non-NMDA glutamate receptors with 30 µM CNQX. However, both the [Ca²⁺]_i rises and cell death seen in oligodendroglia during ischaemia were blocked by bumetanide, even though NKCC expression was restricted to astrocytes (determined by immuno-histochemistry). We hypothesise that early astrocyte swelling and death is associated with glutamate release that gates non-NMDA receptors on oligodendroglia resulting in their injury.