Upregulation of nerve growth factor following cortical trauma.

As part of the inflammatory response to brain injury, CSF and tissue levels of interleukin-1 beta (IL-1 beta) are elevated after trauma. This elevation in IL-1 beta initiates a cascade of events among which may be an upregulation in nerve growth factor (NGF) in brain tissue. We infused IL-1 beta into the ventricle of adult rats and found a two- to fourfold increase in NGF in the cerebral cortex, hippocampus, and cerebellum, suggesting that IL-1 beta induced in vivo may also increase NGF in the brain. To test this hypothesis we utilized two models of traumatic brain injury (TBI) in the rat and examined NGF protein and RNA in the cortex over a period of several days. Both weight drop and controlled cortical contusion models of CNS trauma demonstrated large and significant increases in NGF protein in the cortex. NGF RNA was assessed in the controlled cortical contusion model and increased approximately fivefold by 1 day post-trauma. The remarkable elevation of NGF observed following TBI suggests that its role in response to injury may be other than as a target-derived growth substance. We hypothesize that the elevation of NGF in trauma induces upregulation of enzymes which suppress free-radical formation after injury.