Neurons continuously maintain ion gradients across their cell membrane in order to facilitate electrical signaling. ATP produced by the mitochondria is required to re-establish these gradients following the electrical activity necessary for information transmission. Reactive oxygen species (ROS) are produced as an inevitable consequence of energy production in the mitochondria. ROS interact with many of the ion channels that control neuronal excitability however the degree to which ROS modulate neuronal function under normal circumstances is not clear. While a basal level of ROS is a normal feature of the intracellular milieu, prolonged elevation of ROS is part of the metabolic dysregulation that appears to be a key factor in optic neuropathies, including glaucoma. In retinal ganglion cells (RGCs) the rate of action potentials (spikes) produced by a visual scene is strongly dependent on contrast, the range of light intensities varying around the mean. The retina adapts both to mean luminance and contrast and reduces sensitivity in response to prolonged high contrast stimuli. The switch between low and high contrast dramatically increases mean spike rate and consequently metabolic demand. The primary focus of this research project is to understand how changes in ROS modulate the function of genetically identified RGCs under normal conditions particularly during the shifts in metabolic demand that occur during shifts in contrast. Experiments proposed in Aim 1 will elaborate on preliminary data showing subtype specific modulation of RGC excitability by elevating or reducing endogenous ROS levels. Experiments will test effects of elevated ROS levels on excitatory and inhibitory input as well as intrinsic excitability using injected current steps.
In Aim 2, I will used paired, injected current steps as well as Gaussian white noise current injection of either low or high variance to model states of low or high metabolic demand and determine the contribution of ROS to contrast adaptation. Finally in Aim 3, I will investigate the underlying biophysics of the interaction of ROS with voltage-gated conductances measured in nucleated patch recordings from identified RGC subtypes. Metabolism, adaptation, and resilience to degeneration are fundamental features of neural function therefore these studies will further our understanding of processes mediating visual function in the retina. This objective is consistent with the health-related goals of the National Eye Institute for the understanding of retinal circuits and the development of therapeutic approaches essential for the treatment and prevention of retinal disease.
Relative to the other cells of the body, neurons consume enormous amounts of energy, a fact made necessary by the energy intensive task of communication within large networks. A key early step in many neurodegenerative diseases, including optic neuropathies such as glaucoma, is the chronic elevation of reactive oxygen species (ROS), which are produced as an inevitable by product of cellular metabolism. By understanding the physiological ranges of metabolic demand and ROS production, I hope to understand the earliest transition states that drive ganglion cell dysfunction and to develop interventions to slow, prevent or restore vision loss.
