Fig. 6. Effect of erythropoietin pretreatment on viability of embryonic neurons. (A) Primary embryonic rat cortical neurons were treated with (closed bars) and without (open bars) erythropoietin (5 U ml^–1) on day 4 of culture and cell viability determined on day 8. (B,C) On day 8, cells were cultured in Locke’s solution without supplemental erythropoietin under normoxia (20% O₂) (B) and hypoxia (2% O₂) (C). After 24 hours, undamaged neurons were counted in premarked microscopic fields. At least six fields were observed for each well, at least three wells were studied in three separate experiments. A total of 300-900 neurons in each condition were counted.