Abstract
Despite extensive research, the exact pathomechanisms associated with epileptic seizure formation and propagation have not been elucidated completely. Two-photon imaging (2PI) is a fluorescence-based microscopy technique that, over the years, has been used to evaluate pathomechanisms associated with epileptic seizures and epilepsy. Here, we review previous applications of 2PI in epilepsy. A systematic search was performed in multiple literature databases. We identified 38 publications that applied 2PI in epilepsy research. These studies described models of epileptic seizure propagation; anatomical changes and functional alterations of microglia, astrocytes, and neurites; and neurometabolic effects that accompany seizures. Moreover, various neurovascular alterations that accompany seizure onset and ictal events, such as blood vessel responses, have been visualized using 2PI. Lastly, imaging and quantitative analysis of oxidative stress and the aggregation of lipofuscin in the neurovasculature have been accomplished with 2PI. Cumulatively, these papers and their reported findings demonstrate that 2PI is an especially well-suited imaging technique in the domain of epilepsy research, and these studies have significantly improved our understanding of the disorder. The application of 2PI provides ample possibilities for future research, most interestingly on human brains, while also stretching beyond the field of epilepsy.
Highlights
Two-photon imaging (2PI) is a fluorescence-based laser scanning microscopy technique commonly used in studies across various fields of research, including neurobiology, embryology, and tissue engineering [1,2]
The following Boolean search was last conducted on 9 December 2020: ((epilepsy OR seizure OR epileptic) AND ((“fluorescence lifetime imaging”) OR)
For experimental seizure-induction, different pharmacological agents were used across the studies, including kainic acid (KA), 4-aminopyridine, pilocarpine, and bicuculline methiodide
Summary
Two-photon imaging (2PI) is a fluorescence-based laser scanning microscopy technique commonly used in studies across various fields of research, including neurobiology, embryology, and tissue engineering [1,2] In principle, it involves two infrared photons simultaneously exciting a single fluorophore in a sample, thereby causing it to emit light in a specific wavelength region, called fluorescence emission spectrum. Compared to confocal single-photon microscopy, the main advantages of 2PI include reduced damage of tissues, allowing intravital studies, greater penetration depth of up to 2 mm in the brain, and ex vivo deep tissue imaging It maintains the typical characteristics of confocal microscopy, such as optical slicing capabilities with the option to perform 3-dimensional (3D) structural visualization and quantification, and its high subcellular resolution of around 400 nanometers [3,4,5]. While many clinical techniques, such as ultrasound, CT, PET, and MRI, can penetrate much deeper in tissues, their resolution is up to a factor 1000 worse and cannot image at a subcellular level
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