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.
The Neurovascular Unit (NVU) dynamically regulates oxygen supply to satisfy neural metabolic demand. Amyloid-β (Aβ) accumulation and hyperphosphorylated Tau in Alzheimer’s disease (AD) disrupt the NVU. Empirical evidence strongly indicates that physical activity (PA) reduces the rate of cognitive impairment, but the physiological mechanism(s) PA’s neuroprotective benefits remain unclear. We propose PA improves the brain parenchymal oxygenation and reduces metabolic deficits. Using the novel oxygen sensitizer, Oxyphor 2P, and 2-photon phosphorescence lifetime imaging (2P-PLIM), our results indicate that the PA shows the potential to curtail AD progression by increasing microvascular oxygenation and preserving NVU function.
Dementia afflicts more than 55 million patients worldwide, and Alzheimer’s disease (AD) accounts for around 60% to 80% of total cases1. During the onset of AD, the hippocampus (HC) is among the first-affected brain regions to experience pathological changes. Therefore, identifying changes to HC in AD subjects will be extremely helpful in providing early-stage diagnosis and interventions. We are developing in vivo techniques to investigate microscopic alterations to hippocampal structure and function in animal models of AD. Imaging will be performed using removable GRIN (gradient-index) lenses to chronically access subcortical brain structures with two-photon microscopy. Here, we report the development and characterization of a customized cannula (1 mm diameter, 6 – 7 mm length) to repeatedly insert a GRIN lens for two-photon imaging. The cannula allows for easy removal of the lens after imaging sessions and enables detailed investigations of hippocampal changes during AD progression in mouse models. The cannula is made of polyimide tubing and tipped with transparent acrylic coverslip. We compare acrylic coverslips and existing glass coverslips in terms of physical and optical properties. Acrylic coverslips display comparable imaging quality and therefore serves as a reliable alternative to glass coverslips which is more economical, reproducible, and mechanically stable. We also present preliminary hippocampal images collected in vivo with our custom cannula. These results will guide more extensive efforts to measure hippocampal metabolic and hemodynamic alterations in awake animal models of AD.
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