Optical imaging of human epileptogenic tissues in vitro

Pharmacological evaluation of E2730, a novel selective uncompetitive GAT1 inhibitor, on epileptiform activities in resected brain tissues from human focal cortical dysplasia ex vivo

Focal cortical dysplasia (FCD) is an important etiology of focal epilepsy in children and adults. However, only a few preclinical models sufficiently reproduce the characteristic histopathologic features of FCD. To improve the success rate of clinical trials for antiseizure medications (ASMs) in patients with FCD, more human-relevant preclinical models are needed, and epileptic foci resected from patients are a powerful tool for this purpose. Here, we conducted ex vivo studies using epileptic foci resected from patients with FCD type II to evaluate the pharmacologic effects of the ASM candidate E2730, a selective uncompetitive inhibitor of γ-aminobutyric acid transporter 1. We used the same ex vivo assay system to assess carbamazepine (CBZ), an ASM often prescribed for focal epilepsy, as a reference. At the higher dose tested (200 µM), both E2730 and CBZ suppressed spontaneous epileptiform activities almost completely. At the lower dose (100 µM), CBZ reduced the area of brain tissue showing epileptiform activity, whereas E2730 significantly decreased the number of epileptiforms. These findings suggest that E2730-both as a single agent and in combination with CBZ-merits evaluation in clinical trials involving patients with FCD.

Visualization of cortical activation in human brain by flavoprotein fluorescence imaging

OBJECTIVE

To develop an innovative brain mapping and neuromonitoring method during neurosurgery, the authors set out to establish intraoperative flavoprotein fluorescence imaging (iFFI) to directly visualize cortical activations in human brain. The significance of iFFI was analyzed by comparison with intraoperative perfusion-dependent imaging (iPDI), which is considered the conventional optical imaging, and by performing animal experiments.

METHODS

Seven patients with intracerebral tumors were examined by iFFI and iPDI following craniotomy, using a single operative microscope equipped with a laser light source for iFFI and xenon lamp for iPDI. Images were captured by the same charge-coupled device camera. Responses to bipolar stimulation at selected points on the cortical surface were analyzed off-line, and relative signal changes were visualized by overlaying pseudocolor intensity maps onto cortical photographs. Signal changes exceeding 3 SDs from baseline were defined as significant. The authors also performed FFI and PDI on 10 mice using similar settings, and then compared signal patterns to intraoperative studies.

RESULTS

Signals acquired by iFFI exhibited biphasic spatiotemporal changes consisting of an early positive signal peak (F1) and a delayed negative signal peak (F2). In contrast, iPDI signals exhibited only 1 negative peak (P1) that was significantly delayed compared to F1 (p < 0.02) and roughly in phase with F2. Compared to F2 and P1, F1 was of significantly lower amplitude (p < 0.02) and located closer to the bipolar stimulus center (p < 0.03), whereas F2 and P1 were more widespread, irregular, and partially overlapping. In mice, the spatiotemporal characteristics of FFI and PDI resembled those of iFFI and iPDI, but the early positive signal was more robust than F1.

CONCLUSIONS

This is the first report in humans of successful intraoperative visualization of cortical activations by using iFFI, which showed rapid evoked cortical activity prior to perfusion-dependent signal changes. Further technical improvements can lead to establishment of iFFI as a real-time intraoperative tool.

Reactive astrocytes contribute to epileptogenesis in patients with cavernous angioma

OBJECTIVE

Patients with cavernous angioma (CA) often suffer from severe epilepsy, and surgical resection is often performed to attenuate these epileptic seizures. Several studies have suggested that surgical removal of the surrounding hemosiderin-pigmented tissues adjacent to CA achieves better seizure control than restricted lesionectomy. Pathological examination of the resected foci reveals not only hemosiderin pigmentation but also various degrees of inflammatory change, such as hemosiderin-laden macrophages, gliosis and fibrosis. However, there is some controversy regarding the epileptogenic potential of these regions due to the uncertain nature of the mechanisms contributing to these histopathological changes.

METHODS

To investigate the correlations between neuron hyperexcitability and evident pathological changes, we performed ex vivo flavoprotein fluorescence imaging using surgically resected epileptogenic foci surrounding CA. The mirror surfaces of the tissues used for the physiological experiment were also subjected to morphological examination.

RESULTS

Hemosiderin-laden macrophages and many gemistocytic astrocytes were observed in the area adjacent to CA, where horizontal spreading excitations were detected significantly more frequently. Outside these areas, we found fine granular iron deposits and only a few fibrillary astrocytes, and weakly propagating excitations were detected. Furthermore, areas of enhanced activation were more clearly correlated with the glial proliferation index than with iron deposition.

CONCLUSION

These results suggest that the epileptogenesis in patients with CA may be based on a biological process, such as alteration of glial function, rather than direct chemical reactions involving iron deposition.

Pathophysiological Characteristics Associated With Epileptogenesis in Human Hippocampal Sclerosis

Mesial temporal lobe epilepsy (MTLE) is the most frequent focal epileptic syndrome in adults, and the majority of seizures originate primarily from the hippocampus. The resected hippocampal tissue often shows severe neuronal loss, a condition referred to as hippocampal sclerosis (HS). In order to understand hippocampal epileptogenesis in MTLE, it seems important to clarify any discrepancies between the clinical and pathological features of affected patients. Here we investigated epileptiform activities ex vivo using living hippocampal tissue taken from patients with MTLE. Flavoprotein fluorescence imaging and local field potential recordings revealed that epileptiform activities developed from the subiculum. Moreover, physiological and morphological experiments revealed possible impairment of K⁺ clearance in the subiculum affected by HS. Stimulation of mossy fibers induced recurrent trans-synaptic activity in the granule cell layer of the dentate gyrus, suggesting that mossy fiber sprouting in HS also contributes to the epileptogenic mechanism. These results indicate that pathophysiological alterations involving the subiculum and dentate gyrus could be responsible for epileptogenesis in patients with MTLE.