Abstracts

Rationale: Post-traumatic epilepsy occurs in one in fifty patients suffering from traumatic brain injury (TBI) and is often treatment-resistant. Understanding mechanisms of post-injury epileptogenesis has long been a goal, as this represents a critical window during which effective intervention could potentially prevent seizures rather than treat the consequences of epileptic networks once developed. The EPISTOP trial in children with tuberous sclerosis complex suggests that epilepsy can be more effectively treated when targeted during a critical period before epileptic onset. However, there are currently no effective treatments that prevent or modify the development of epilepsy after TBI. Focused ultrasound (FUS) is a promising non-invasive neuromodulatory treatment that can alter molecular features associated with epileptogenesis when delivered during a critical post-injury period. In the present study, we utilized a rat kainic acid (KA) epilepsy network model to investigate the functional, tissue, and molecular-level impact of low-intensity FUS (LOFU) on epileptogenesis.

Methods: In adult male Sprague-Dawley rats, unilateral right-sided dorsal hippocampal stereotactic injection of KA was administered to induce status epilepticus, followed by Racine scoring during a 60-minute observation period. Three different doses of KA (125, 250, and 500ng) were compared with control artificial cerebrospinal fluid (aCSF) injection. Rats were LOFU-treated using a single-element FUS system with a mechanical three-axis stage for stereotactic treatments. The single-element transducer operated at a center frequency of 1.5 MHz. Treatments were delivered at 30% duty cycle, with a mechanical index of 0.75 for 10-minute sonications. Immunohistochemistry was performed for c-Fos expression co-labeled with excitatory and inhibitory neuronal markers, VGLUT and GAD1/67, respectively, to study the critical alterations in epileptic pathology in the hippocampus.

Results: Animals with KA-induced status epilepticus demonstrated a significant increase in Racine score and in EEG spikes and bursts, compared to control animals. Importantly, these effects were attenuated with LOFU treatment. Compared to aCSF-injected controls, KA injection causes diffuse and widespread activation of hippocampal glutamatergic excitatory neurons (c-fos/VGLUT co-staining). Conversely, treatment of KA-injected animals with LOFU selectively activates hippocampal GABAergic inhibitory neurons (c-fos/GAD1/67 co-staining), attenuating epileptogenic changes (Figure 1). Importantly, LOFU did not result in increased cell death (Fluoro-Jade C staining) or astrogliosis (GFAP staining).

Conclusions: LOFU modulates epileptic network development through activation of hippocampal inhibitory neurons without causing tissue damage, and thus could serve as a promising non-invasive strategy for the prevention of post-traumatic epilepsy, when delivered during a critical latent period.

Funding: This study is funded by the Department of Neurosurgery of the university of Maryland, Baltimore.