Ascorbate inhibits edema in brain slices

Ascorbate is an essential antioxidant in the CNS, localized predominantly i n neuronal cytosol. Slices of mammalian brain rapidly lose ascorbate, howev er, when incubated in ascorbate-free media; brain slices also take up water and swell. Here we investigated water gain in coronal slices of rat forebr ain incubated with and without ascorbate for 1-3 h at 34 degrees C. Slices progressively gained water in ascorbate-free media, with a significant 12% water increase after 3 h at 34 degrees C, compared with the water content o f slices after a 1-h recovery period at 24 degrees C, immediately following slice preparation. Inclusion of 400 mu M ascorbate in the medium led to an increase in tissue ascorbate content and prevented water gain at 34 degree s C. By contrast, water gain was not inhibited by isoascorbate or thiourea, which are antioxidants that are not accumulated in brain cells. The oxidan t H2O2 enhanced water gain, whereas a cocktail of NMDA and non-NMDA recepto r blockers inhibited edema formation to the same extent as ascorbate. These data demonstrate that brain edema, linked to glutamate-receptor activation , can result from intracellular oxidative stress and that this can be preve nted by ascorbate.