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The role of cell body density in ruminant retina mechanics assessed by atomic force and Brillouin microscopy

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Weber, I 
Yun, S-H 
Scarcelli, G 


Cells in the central nervous system (CNS) respond to the stiffness of their environment. CNS tissue is mechanically highly heterogeneous, thus providing motile cells with region-specific mechanical signals. While CNS mechanics has been measured with a variety of techniques, reported values of tissue stiffness vary greatly, and the morphological structures underlying spatial changes in tissue stiffness remain poorly understood. We here exploited two complementary techniques, contact-based atomic force microscopy and contact-free Brillouin microscopy, to determine the mechanical properties of ruminant retinae, which are built up by different tissue layers. As in all vertebrate retinae, layers of high cell body densities ('nuclear layers') alternate with layers of low cell body densities ('plexiform layers'). Different tissue layers varied significantly in their mechanical properties, with the photoreceptor layer being the stiffest region of the retina, and the inner plexiform layer belonging to the softest regions. As both techniques yielded similar results, our measurements allowed us to calibrate the Brillouin microscopy measurements and convert the Brillouin shift into a quantitative assessment of elastic tissue stiffness with optical resolution. Similar as in the mouse spinal cord and the developing Xenopus brain, we found a strong correlation between nuclear densities and tissue stiffness. Hence, the cellular composition of retinae appears to strongly contribute to local tissue stiffness, and Brillouin microscopy shows a great potential for the application in vivo to measure the mechanical properties of transparent tissues.



Animals, Biomechanical Phenomena, Elastic Modulus, Microscopy, Atomic Force, Reproducibility of Results, Retina, Sheep, Domestic

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Physical Biology

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Medical Research Council (G1100312)
Human Frontier Science Program (HFSP) (RGY0074/2013)
National Institute of Child Health and Human Development (R21HD080585)
IPW is a recipient of an EMBO Long-Term Fellowship (ALTF 1263-2015; European Commission FP7 (Marie Curie Actions, LTFCOFUND2013, GA-2013-609409)). This work was further supported by the National Science Foundation (CMMI-1562863 to SHY and CMMI-1537027 to GS), the Human Frontier Science Program Young Investigator Grant RGY0074/2013 (GS and KF), the UK Medical Research Council Career Development Award G1100312/1 (KF), and the National Institutes of Health (R01EY025454 to SHY, K25EB015885 and R33CA204582 to GS, R21HD080585 to KF).