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The hippocampus (HC) is a subcortical brain region that plays essential roles in learning and memory. It is strongly associated with Alzheimer’s disease (AD), an incurable and deadly neurodegenerative disease which is progressive and requires longitudinal observation. Two-photon microscopy (2PM) is applied here to investigate hippocampal alterations in living mouse models and better understand pathological changes during neurodegeneration. The common procedure is to surgically expose the rodent cortex and have it sealed with a coverslip to allow optical access. However, in some studies, repeated tissue injections are needed to deliver exogenous contrast agents or pharmacological agents, and current injection strategies are not compatible with subcortical imaging, which limits the ability to study subcortical lesions longitudinally. To tackle this issue, we developed a technique where both imaging and injection can be conducted. Our previous development enabled 2PM imaging in the HC using a gradient-index (GRIN) lens. We engineered a customized cannula using polyimide tubing and transparent acrylic, and implanted it into mouse brain. It allows removable insertion of a GRIN lens and enables longitudinal investigation. In this study, we improved our cannula design to enable imaging and injections. The acrylic window is replaced with an optically-transparent, biocompatible, oxygen impermeable plastic, which maintains seal after needle penetration. Here we report injection and imaging results in phantoms and animals. Our design opens opportunities for comprehensive longitudinal imaging of subcortical lesions.
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