Development of a Low Profile, Endoscopic Implant for Long Term Brain Imaging

The increased public awareness of concussion and traumatic brain injury has motivated continued research into the brain, its functions, and especially its response to injury, with a focus on improving the brain’s repair capabilities. However, due to the critical nature of the tissue, it is currently difficult for researchers to acquire high resolution images below the cortex without sacrificing a lab animal. Sacrificing an animal greatly reduces the amount of data that can be obtained from it, making longitudinal studies unappealing or unfeasible because a large number of animals is needed to obtain useful data over multiple time points. Additionally, inter-animal variance can further obfuscate results. The gradient index (GRIN) lens is a form of micro-endoscope that can penetrate the cortex to obtain high resolution, in vivo images when used with a multiphoton microscope system. The lens is implanted through the skull and into the brain, providing a column of material that refracts and refocuses the laser beam, unlike the natural tissue, which scatters light. This dissertation describes the development of a low profile GRIN lens implant system suitable for longitudinal imaging, as well as the co-development of a restraint system to accommodate the new implant on a microscope stage. The imaging protocol is detailed, and images acquired over three months are shown. The developed device drastically reduced the size of implant both above the skull and within the brain tissue compared to previously reported GRIN lenses, while still obtaining the expected high resolution images. This research also found that labelled axons in transgenic mice appear in unique, recognizable patterns which remain consistent over months of imaging, meaning future studies may use the axons themselves as landmarks. An experimental design for analyzing traumatic brain injury is also developed, which could incorporate a future implant