Confounding effect of EEG implantation surgery: Inadequacy of surgical control in a two hit model of temporal lobe epilepsy

Abstract

In rodent models of epilepsy, EEG implantation surgery is an essential modality to evaluate electrographic seizures. The inflammatory consequences of EEG electrode-implantation and their resultant effects on seizure susceptibility are unclear. We evaluated electrode-implantation in a two-hit model of epileptogenesis in C57BL/6 mice that included brief, recurrent febrile seizures (FS) at P14 and kainic acid induced seizures (KA-SZ) at P28. During KA-SZ, latencies to first electrographic and behavioral seizures, seizure severity, and KA dose sensitivity were measured. Mice that received subdural screw electrode implants at P25 for EEG monitoring at P28 had significantly shorter latencies to seizures than sham mice, regardless of early life seizure experience. Electrode-implanted mice were sensitive to low dose KA as shown by high mortality rate at KA doses above 10 mg/kg. We then directly compared electrode-implantation and KA-SZ in seizure naive CX3CR1GFP/+ transgenic C57BL/6 mice, wherein microglia express green fluorescent protein (GFP), to determine if microglia activation related to surgery was associated with the increased seizure susceptibility in electrode-implanted mice from the two-hit model. Hippocampal microglia activation, as demonstrated by percent area GFP signal and GFP positive cell counts, prior to seizures was indistinguishable between electrode-implanted mice and controls, but was significantly greater in electrode-implanted mice following seizures. Electrode-implantation had a confounding priming effect on the inflammatory response to subsequent seizures.

Factors influencing the acute pentylenetetrazole‐induced seizure paradigm and a literature review

“…One study employing a kainic acid seizure paradigm found that EEG implantation increased seizure endpoints (specifically mortality) regardless of experimental groups. 28 This paper has two key differences from our study, however: (1) they use juvenile mice, and (2) their postoperative recovery period is much shorter (3 days). They suggest that increased seizure susceptibility is due to inflammation, which may or may not resolve at a later time point.…”

“… 27 EEG implantation increased seizures in the acute setting in a kainic acid seizure paradigm. 28 Furthermore, it is unclear if prior studies considered these factors in their preclinical research.…”

Meningeal Lymphangiogenesis and Enhanced Glymphatic Activity in Mice with Chronically Implanted EEG Electrodes

“…One study reported that EEG electrode implantation increased seizure susceptibility in mice. Furthermore, EEG implanted mice exhibited significantly more microglial activation after experiencing seizures than did their sham-operated controls (Balzekas et al, 2016). We suggest that immunohistochemical analysis of the brain should always be conducted after such experiments to exclude animals exhibiting significant inflammation or tissue damage of the brain or dura.…”

Home-cage monitoring ascertains signatures of ictal and interictal behavior in mouse models of generalized seizures

“…Combining long term home-cage monitoring with synchronized high-quality wireless EEG remains an important ongoing objective but may reveal observer effects across both ictal and interictal measures: the mere placement of EEG electrodes in mice (tethered or wireless) may impair mobility, sleep and neurovegetative function through pain or direct physical hindrance. Further, EEG implantation surgery may itself increase seizure threshold through pain, impaired sleep and postoperative inflammation [68], as well as through unintended cortical microlesions that may occur when electrodes are inadvertently advanced to subdural depths [69].…”