Use of DISCO optical tissue clearing technologies for studying glymphatic function and CSF efflux in a mouse model

What transparent brains teach us about how our brain cleans itself? The brain has a high rate of metabolic activity but paradoxically it lacks lymphatic vessels. Instead, clearance of waste products is taken care of by the glial-lymphatic (glymphatic) system. The Glymphatic system works by circulating cerebrospinal fluid through and out of the brain. We have developed a new way to study the glymphatic system and CSF circulation by using mice that are processed in a way that makes them transparent. This way, the sample can be images using a microscope without sectioning the sample. This way we can collect more data from the sample. The glymphatic system circulates cerebrospinal fluid through the brain to clean the brain from metabolic waste. The system works primarily during sleep. Since the discovery of the glymphatic system in 2012 many scientists have been interested on how the cerebrospinal fluid circulates and how it can clean metabolic waste. Since accumulation of waste in the brain is connected to neurodegenerative pathologies, such as Alzheimer’s disease, it is important to understand the physiology of cerebrospinal fluid circulation. If we find a way to increase the function of the glymphatic system, we can increase waste removal from the brain. This might work as a treatment for Alzheimer’s disease or other neurodegenerative diseases. How do we make tissues transparent? When light hits a surface, it is refracted at an angle. Different tissues refract light at different angles; this property is referred to as the refractive index. By matching the refractive indices throughout the sample, we can make it appear transparent. The matching of refractive indices is done by dissolving fats and dehydrating the sample, so only proteins and cell membranes remain. Then water is replaced with an organic solvent that has the same refractive index as the sample. To study the glymphatic system using the transparent samples we have to inject a fluorescent tracer into the cerebrospinal fluid. We can see where this tracer has been distributed when we take images of the sample with a fluorescent microscope. Based on the distribution pattern we can assess how well the brain can clean itself under different conditions. For this study, we look at the effects of different anaesthetics on CSF flow. Some anaesthetics mimic natural sleep make the brain clean itself from metabolic waste more efficiently. Master’s Degree Project in Molecular Biology 45 credits 2019 Department of Biology, Lund University Advisor: Dr. Iben Lundgaard Glia-Immune interactions, Experimental medical sciences, Lund University (Less)