Tumor necrosis factor-alpha alpha (TNF-alpha) and reactive oxygen species (ROS) are produced in the brain after traumatic injury and have deleterious effects. In a rat model of closed head injury (CHI), the synthetic antioxidant from the nitroxide family, Tempol, improved recovery and protected the blood-brain barrier. Similar protection was found after CHI in heat-acclimated rats, in which the endogenous antioxidants have been shown to be elevated after CHI. The present study examined the relationship between TNF-alpha and ROS after CHI, namely, whether after CHI, antioxidants that afforded cerebroprotection also attenuated brain levels of TNF-alpha. Three groups of rats were subjected to CHI: (1) control, nontreated, (2) Tempol-treated, and (3) heat-acclimated (30 days at 34 degrees C). Four hours after injury (time for peak production of TNF-alpha), the activity of TNF-alpha was measured. Although clinical recovery was facilitated in rats of the two treated groups, TNF-alpha activity was as high as in the traumatized, untreated rats. Moreover, direct injection of TNF-alpha into mouse brain induced disruption of the blood-brain barrier, indicating its acute harmful effect. This toxic effect was attenuated by before and after treatment with Tempol. Our results support the hypothesis that in vivo antioxidants neutralize TNF-alpha toxicity, probably by interfering with activation of the transcription factor NF-kappa-B.