Fig. 8. HIF-1 accumulates in vivo in response to both hypoxic hypoxia and cobalt chloride, administered intraperitoneally, in the 6 month rat brain cortex. At 24 months, however, there is greatly diminished accumulation of HIF-1 under hypoxic conditions, but the response to cobalt chloride is still robust. ß-actin was used as a loading control (Chavez and LaManna, 2003).