Rationale:
Though medial-temporal lobe epilepsy is the most common type of focal epilepsy, the mechanisms underlying signal generation and propagation remain poorly understood. Previous experiments showed that epileptic activity can propagate non-synaptically across tissue cuts less than 400 mm wide via electric field (EF) coupling1. This phenomenon stems from electric fields produced by synchronous pyramidal neuron firing, which excites adjacent neuronal clusters.
To counteract these fields, the lab made an extracellular clamp that successfully eliminated epileptiform activity in a 4-Aminopyridine (4-AP) hippocampal in-vitro mouse model by maintaining the focus at zero volts. However, the clamp had limitations, such as sensitivity to electrode positioning.
Our research explores a novel solution using highly conductive (s » 5±1 Ms/m), flexible, thin (10 mm), and biocompatible carbon nanotube films (CNTFs). We show that inserting a CNTF into a tissue cut in an in-vitro hippocampal mouse model effectively blocks propagation of EF-coupled epileptiform activity by short-circuiting the EF.
Methods:
Transgenic mouse brains were cut into 400 mm thick transverse slices, and placed in an interface chamber with oxygenated and heated (to 32 °C) artificial cerebral spinal fluid with 150 mM 4-AP to preserve tissue viability and induce epileptiform activity.
Local field potentials were recorded from the CA3 and CA1 hippocampal regions via micropipette electrodes connected to amplifiers and an analog-to-digital-signal converter (20 kHz sampling, 2 kHz low-pass filter). Baseline recordings show that seizures and spikes propagate from the CA3 to the CA1 region. After a 30-minute baseline, a < 400 mm cut was made between regions followed by A 10-minute recording to confirm continued EF-coupled propagation across the cut.
A perforated CNTF was then inserted into the cut and activity was recorded for 10 minutes. The film was then removed, and a 10-minute control confirmed the return of EF coupled signal propagation. Signal amplitude and frequency were analyzed in each phase, with spontaneous spikes and seizure events assessed independently.
Results:
Insertion of CNTFs significantly reduced both the amplitude and frequency of EF-coupled epileptiform signals crossing the cut (n=4 in-vitro) from CA3 to CA1 (Fig 1).
During CNTF placement, 100% of seizure amplitude was suppressed (n=3 in-vitro) (Fig 2). Spontaneous Spike count was reduced by 99.5% (n=4 in-vitro).
Conclusions:
By short-circuiting the electric field responsible for seizure propagation, perforated CNTFs halt nearly all epileptiform propagation, offering a non-invasive, reliable, and biocompatible alternative to more complex interventions. Their flexibility, permeability, and lack of active electronics make them especially suitable for clinical translation, potentially reducing the need for tissue resection and minimizing the risk of reintervention.
References
- Subramanian, M., et al., “Controlling the local extracellular electric field can suppress the generation and propagation of seizures and spikes in the hippocampus” Brain Stim, 2025.
Funding:
- NIH T32 Trainee Grant
- NIH NINDS Grant # R01 N114120, # R01 NS121084
- NIH Brain Initiative Grant # R01 NS124592