Fig. 2. HIF-1 localization in brain under physiological and pathophysiological conditions. (A) Heterogeneity of nuclear HIF-1 localization in neurons of the mouse cortex under physiological conditions is probably related to the heterogeneous distribution of tissue P_O2. In addition, HIF- expression may be influenced by other factors discussed, such as PHD activity or growth factor signaling. (B) In contrast, human brain tumors show distinct nuclear HIF-1 localization in pallisading cells close to the necrotic core (N) of glioblastoma multiforme.