Tumor necrosis factor alpha (TNFalpha) is a pleiotropic cytokine with several CNS physiological and pathophysiological actions including sleep, memory, thermal and appetite regulation. Short interfering RNAs (siRNA) targeting TNFalpha were incubated with cortical cell cultures and microinjected into the primary somatosensory cortex (SSctx) of rats. The TNFalpha siRNA treatment specifically reduced TNFalpha mRNA by 45% in vitro without affecting interleukin-6 or gluR1-4 mRNA levels. In vivo the TNFalpha siRNAalpha reduced TNFalpha mRNA, interleukin-6 mRNA and gluR1 mRNA levels compared to treatment with a scrambled control siRNA. After in vivo microinjection, the density of TNFalpha-immunoreactive cells in layer V of the SSctx was also reduced. Electroencephalogram (EEG) delta wave power was decreased on days 2 and 3 on the side of the brain that received the TNFalpha siRNA microinjection relative to the side receiving the control siRNA. These findings support the hypothesis that TNFalpha siRNA attenuates TNFalpha mRNA and TNFalpha protein in the rat cortex and that those reductions reduce cortical EEG delta power. Results also are consistent with the notion that TNFalpha is involved in CNS physiology including sleep regulation.