Two-Photon Imaging to Unravel the Pathomechanisms Associated with Epileptic Seizures: A Review

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.

The Role of the Glycocalyx in the Pathophysiology of Subarachnoid Hemorrhage-Induced Delayed Cerebral Ischemia

“…On the luminal side of the endothelium, the glycocalyx contributes to the barrier function of the BBB (Figure 1). Using two-photon microscopy, several studies have shown that the glycocalyx acts as a barrier for large molecules (Kutuzov et al, 2018;Khan et al, 2021). The glycocalyx also functions as an electrostatic barrier to plasma proteins due to its negative charge carried by core proteins like hyaluronan, thereby repelling negatively charged cells and preventing them from binding the endothelium (Iba, 2016).…”

“…However, these techniques are nevertheless limited by the frailty of the glycocalyx in ex-vivo conditions (Reitsma et al, 2007;Haeren et al, 2016). Recent advances in handheld multi-photon microscopy probes could potentially provide a novel in vivo technique to evaluate the glycocalyx (Khan et al, 2021).…”

Temporal Alterations in Cerebrovascular Glycocalyx and Cerebral Blood Flow after Exposure to a High-Intensity Blast in Rats

“…The endothelial glycocalyx is a mechanosensor that modulates vascular response to mechanical forces such as shear stress from flowing blood; transduces the force to a biochemical response to maintain vascular tone; and plays a role in preventing coagulation, characteristics that facilitate regulation of CBF. The glycocalyx, by virtue of being a physical electrostatic barrier (due to negative charges on components like HA), prevents plasma proteins and negatively charged cells from attaching to the endothelium, thus averting perturbances in blood flow [29,54,55]. There is emerging evidence that components of the glycocalyx (HS and SD-1) bind with anticoagulant molecules [19,56] that trigger multistep processes which eventually inhibit platelet aggregation and cause relaxation of smooth muscles and vasodilation [57].…”

Cerebrovascular glycocalyx damage and microcirculation impairment in patients with temporal lobe epilepsy

“…Further histological vascular density analysis of thicker slices (30–50 µm) might provide this result, preferably using 3 D visualization such as two-photon microscopy imaging. 72 …”