Authors :
Presenting Author: Shixin Liu, BS – Yale School of Medicine
patrick Paszkowski, Undergraduate – Yale University; Lim-Anna Sieu, PhD – Yale School of Medicine; Jiayang Liu, PhD – Yale School of Medicine; Marcus Valcarce-Aspegren, MD – Yale School of Medicine; Waleed Khan, MD – Yale School of Medicine; Sarah Mcgill, PhD – Yale School of Medicine; Dana Lee, Undergraduate – Yale University; Alvaro Duque, MD – Yale School of Medicine; Hal Blumenfeld, MD, PhD – Yale School of Medicine
Rationale:
Human temporal lobe epilepsy (TLE) is a debilitating disorder characterized by epileptic discharges originating from the limbic system and concurrent alterations of consciousness, often leading to patients’ impaired quality of life, impaired cognitive functions, increased risk of accidents, and social stigma and discrimination. Understanding ictal unconsciousness's neurobiological and neurophysiological basis is crucial for developing effective interventions. While prevailing views hold that TLE impairs consciousness through seizure spread to the bilateral temporal lobes, we propose a network inhibition hypothesis: impaired consciousness occurs in TLE due to decreased subcortical arousal, leading the neocortex to enter a state of slow-wave activity similar to deep sleep or encephalopathy. To test this hypothesis, we employed a novel awake, behaving mouse model for in vivo electrophysiological recordings, allowing assessment of changes in pupillary diameter and mouse behavior to evaluate the loss of consciousness during TLE seizures.
Methods:
In this study, mice were head-fixed on running wheels, and local field potentials were recorded using chronically implanted bipolar electrodes in the right lateral orbitofrontal cortex and bilateral hippocampi. Focal limbic seizures were induced by applying current pulses (2s, 60 Hz) to the hippocampus. Juxtacellular single unit activity (SUA) recordings were performed using glass capillaries filled with 4% Neurobiotin in the nucleus basalis of Meynert (NBM) and brainstem pedunculopontine tegmental nucleus (PPT). Simultaneously, running wheel behavior and pupillary diameter changes were monitored. Post-recording, a double immunofluorescence procedure confirmed the cholinergic nature of the Neurobiotin-injected neuron (stained with Cy3-conjugated streptavidin) using an anti-choline acetyltransferase antibody.
Results:
We found that focal limbic seizures suppressed running wheel behavior, while orbitofrontal cortex local field potentials exhibited synchronized slow-wave activity resembling coma or deep sleep. Pupillometry showed pupil dilation at the seizure onset and pupil fluctuations during slow waves. SUA in neurons during focal limbic seizures exhibited diverse firing pattern changes in NBM (n=37) and PPT (n=61), with some neurons displaying reduced firing, others exhibiting increased firing, and some showing no change. Notably, cholinergic neurons demonstrated decreased firing during focal limbic seizures, particularly in the PPT (n=8).
Conclusions:
This project demonstrates the feasibility and reproducibility of stable SUA recordings from deep subcortical neurons during seizures in awake, behaving mice. Inhibition of cholinergic neurons within key subcortical arousal regions, such as NBM and PPT, may have a crucial role in modulating consciousness during focal temporal lobe epilepsy seizures. These findings also suggest that therapeutic neurostimulation of subcortical arousal systems may be a reasonable future treatment option, with the goal of improving consciousness in medically and surgically refractory focal impaired awareness seizures.
Funding: NIH R01 NS066974