Fig. 5. Effect of erythropoietin on the viability of embryonic neurons. (A) Cell viability was determined for primary embryonic rat cortical neurons supplement starved for 24 hours in Locke’s solution with or without erythropoietin (5 U ml^–1) under normoxia (20% O₂) and hypoxia (2% O₂). (B) The percentage of cells undergoing apoptosis was determined by TUNEL analysis. (C-E) Real-time RT-PCR quantitation was used to determine the levels of Epor (C), erythropoietin (Epo) (D) and Bcl-x_L (E) gene expression in the cells after 24 hours of culture in Locke’s solution. Expression is normalized to ribosomal protein S16 levels as control. (F) Induction of phosphorylation of Jak2 and STAT5 in cortical neurons treated with erythropoietin cultured at 20% or 2% oxygen tension was examined. (A-C) Cultures with and without supplemental erythropoietin (5 U ml^–1) are represented by solid and open bars, respectively.