Nicholas W. Oesch, Ph.D. - US grants

Oxygen is being lost in the ocean worldwide as a result of ocean warming and the input of nutrients from land. Vision requires a large amount of oxygen, and may be less effective or require more light when oxygen is in short supply. This is especially true for active marine animals with complex eyes and visual capabilities, including active arthropods (crabs), cephalopods (squid), and fish. The California coastal waters exhibit a sharp drop in oxygen and light with increasing water depth. This project examines how visual physiology and ecology in young (larval) highly visual marine animals respond to oxygen loss, with a focus on key fisheries and aquaculture species. Experiments and observations will test the hypothesis that oxygen stress will change the light required for these organisms to see effectively, influencing the water depths where they can live and survive. The project will provide interdisciplinary experiences to students and an early career scientist and inform both the public (through outreach at the Birch Aquarium at Scripps Institution of Oceanography) and policy makers about the effects of oxygen decline in the ocean.

Negative effects of oxygen loss on vision have been described for humans and other terrestrial organisms, but never in the marine environment, despite the large changes in oxygen that can occur with depth and over time in the ocean, and the high metabolic demand of visual systems. This project will test the effects of low oxygen on vision in 3 combinations of eye design and photo-transduction mechanisms: compound eye with rhabdomeric photoreceptors (arthropods), simple eye with rhabdomeric photoreceptors (cephalopods), and simple eye with ciliary photoreceptors (fish). A series of oxygen- and light-controlled laboratory experiments will be conducted on representative taxa of each group including the tuna crab, Pleuroncodes planipes; the market squid, Doryteuthis opalescens, and the white sea bass, Atractoscion nobilis. In vivo electrophysiology and behavioral phototaxis experiments will identify new oxygen metrics for visual physiology and function, and will be compared to metabolic thresholds determined in respiration experiments. Hydrographic data collected over 3 decades by the CalCOFI program in the Southern California Bight will be evaluated with respect to visual and metabolic limits to determine the consequences of oxygen variation on the critical luminoxyscape (range of oxygen and light conditions required for visual physiology and function in target species) boundary in each species. Findings for the three vision-based functional groups may test whether oxygen-limited visual responses offer an additional explanation for the shoaling of species distributions among highly visual pelagic taxa in low oxygen, and will help to focus future research efforts and better understand the stressors contributing to habitat compression with expanding oxygen loss in the ocean.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

PROJECT SUMMARY Blindness caused by photoreceptor death, such as in Retinitis Pigmentosa and Macular Degeneration, is among the leading causes of irreversible blindness in the world today. Electrical stimulation of spared retinal circuitry by retinal prosthetic devices holds promise for restoring vision, but results so far have been modest at best. Our understanding of how electrical stimulation engages the remaining retinal circuitry to perform basic visual computation is poor. To design more effective retinal prosthetic devices, we need to better understand how prosthetic stimulation activates the diseased retinal circuitry. Two major challenges to studying how sub-retina stimulation activates retinal circuitry are: 1) the lack of techniques to measure electrical activation of bipolar cells, and 2) an incomplete understanding of how retinal degeneration changes visual processing circuits. Here we use a new approach. By recording synaptic output of bipolar cells ex vivo, we can directly readout relevant bipolar cell activity, which is the first stage in sub-retinal prosthetic stimulation. By using a new retinal prosthetic technology, the nanowire detector array, to mimic light input to bipolar cells with high temporal and spatial precision, we can determine how basic computations such as contrast are altered during degeneration. The results from this proposal will be significant and will: 1.) Determine optimal stimulation strategies to restore vision with prosthetics 2.) Uncover basic physiological mechanisms that determine how spared retina responds to electrical stimulation, and 3.) Determine how prosthetics can engage basic computational circuitry in diseased retina to extract temporal contrast information from spatio- temporal patterns of electrical stimulation. These experiments will produce needed insight on the fundamental mechanisms underlying early visual computation and guide strategies to improve the design and execution of retinal prosthetic devices. The long-term goal of this work is to improve the design of retinal prosthetics for vision restoration, ultimately improving the quality of life for a broad patient population.