CAREER: Aberrant Rewiring of Neurons after Injury - Intracellular Interactions in Vivo

Cornell University, Ithaca NY

Investigators

Abstract

Neurons in the brain interact with other cell types. One type, microglia, are star-shaped cells that survey the connections between neurons with their arm-like branches. It is important to understand these interactions because changes in neural connections underlie learning and memory formation. The Principal Investigator hypothesizes that microglia might regulate such changes in neural connectivity. This project will investigate whether microglia are directly involved in disconnecting neurons, and whether these actions are disrupted by injury. In response to injury, microglia lose their branches, and the Principal Investigator hypothesizes that this prevents them from properly regulating neural connections. The work will use a specially-designed microscope that images cells within the living brain. To make the cells visible, the microglia will be engineered to look green under the microscope, and, using a strategy developed in this project, each neuron will be labeled with a unique color. With this approach, it will be possible to visualize how microglia interact with neurons under normal conditions and after injury. Analyzing such images is complicated and requires neurobiologists who are trained to use high-level mathematics. This project will develop software and teaching tools to make the mathematics behind image analysis understandable to scientists who were not trained as engineers. The Principal Investigator will create an inquiry-based module about these ideas called "Beyond the Image," which will introduce high school students to image analysis and digital processing. The module will be made available to teachers everywhere through websites such as the Cornell Cooperative Extension School's 4-H STEM site. Because neural branches are small and densely packed, the proposed imaging of microglial modulation of neural connections is challenging. A technical innovation will be to infect neurons using a combination of virus strains that each generate a different color of fluorescent protein. Each neuron will be labeled with its own unique color code, enabling its branches to be distinguished. An advantage of using viruses is that both the type and location of labeled cells can be varied to optimize color-coding. Rather than wait for neurons to disconnect by chance, a laser will be used to precisely cut a branch off of a neuron. Time-lapse imaging will capture the reactions of microglia and neurons to the now useless, severed branch. The prediction is that microglia will reach out with processes to engulf and remove defunct connections. However, with injury, the microglia might erroneously allow aberrant connections to linger or might inappropriately damage normal connections.