In the past decade, reactive oxygen species (ROS) and particularly superoxide have become important in neurophysiological research due to their effects on signaling cascades and gene transcription during programmed cell death (PCD) in many models of neurodegeneration and during cellular differentiation. Although multiple cellular sources of ROS have been described, such as leakage from the mitochondrial electron transport chain, only a few non-mitochondrial superoxide-producing enzymes have been implicated in PCD. In sympathetic neurons, free oxygen radical formation occurs within three hours after nerve growth factor (NGF) withdrawal. Further, the production of these reactive oxygen species (ROS) is necessary and appears to serve as an early signal to trigger the apoptotic pathway in neurons. NADPH oxidase is an enzyme known to produce significant ROS levels in non-neuronal cell types. We previously reported that NADPH oxidase, or an enzyme that is NADPH oxidase-like, is present in sympathetic neurons at both the mRNA and protein levels. Further, neurons from NADPH oxidase-deficient mice exhibit delayed death following NGF deprivation. The exact identity of the NADPH oxidase-like enzyme has yet to be elucidated, but we have preliminary data suggesting Nox1 and Nox4 are the catalytic subunits of the neuronal NADPH oxidase, as opposed to Nox2 (gp91-phox) the subunit that is expressed in phagocytic cells. Further, at least Nox1 is differentially regulated following NGF withdrawal from neonatal sympathetic neurons and differentiated PC12 cells. Based on these data, we hypothesize that Nox1 activity is necessary for the burst of superoxide following NGF withdrawal from differentiated PC12 cells. The work proposed here is highly novel given that the precise identity of the NADPH oxidase-like enzyme in neurons has not been established, much less its contribution(s) to neuronal apoptosis. Since oxidative stress has been implicated in neurodegenerative disease, stroke and aging, as well as differentiation, elucidating the role of NADPH oxidase, specifically Nox1 and Nox4, and the means to modulate this activity in neurons may contribute to eventual treatment modalities. Oxidative stress has been linked to many neurodegenerative conditions including Alzheimer's Disease, Parkinson's Disease, ALS and stroke. Two enzymes that are known to generate superoxide radicals will be examined in models of neuronal apoptosis and differentiation. Results from these experiments may identify enzymatic targets for treatment of neurodegenerative disease. ? ?