Authors :
Presenting Author: Eduardo Bravo, PhD – University of Iowa
Benjamin Kreitlow, MS – Univeristy of Iowa
Claire Enyart, BS – University of Iowa
Gordon Buchanan, MD, PhD – University of Iowa
Brian Dlouhy, MD. – University of Iowa
George Richeron, MD, PhD – University of Iowa
Rationale:
Fatal apnea is a common cause of death from SUDEP. The mechanisms involved in seizure-induced apnea remain unknown. The amygdala is an important part of the pathway for seizures to propagate to the brainstem where they inhibit the respiratory network. Breathing is dependent on two main sources of tonic drive. Chemoreceptor drive comes from central chemoreceptors and is proportional to the level of systemic CO2. Wakefulness drive comes from the forebrain and increases with the level of arousal. We have shown that seizures impair chemoreceptor drive for breathing in multiple mouse models and in humans. For fatal apnea to occur it would be necessary to also lose wakefulness drive. We hypothesized that seizures spreading into the amygdala are more likely to lead to loss of spontaneous breathing during sleep or light anesthesia.Methods:
In the first cohort of mice (n=4), the rostral central nucleus of the amygdala (rCeA) was stimulated under light isoflurane (1%) anesthesia by injecting current (500 mA, 50 Hz) with monopolar electrodes guided by a stereotaxic manipulator. Breathing was simultaneously measured with head-out plethysmography. The locations of the electrodes were verified post hoc by electrolytic lesions and histology. A 3D map of rCeA sites that modulated breathing was created.
In a second cohort (n=12), the location within the rCeA where maximal inhibition of breathing was induced was determined under isoflurane anesthesia, and the electrode was mounted permanently with dental cement. The mice were allowed to 5 days. Unanesthetized mice were stimulated in different sleep/wake stages as determined by EEG while breathing was analyzed with whole-body plethysmography.
Results:
Amygdala stimulation induced prolonged central apnea in lightly anesthetized mice in a small region of the rCeA, similar to what has been identified as the AIR site in human epilepsy patients (Harmata et al 2023).
In unanesthetized, unrestrained mice, rCeA stimulation during wakefulness only induced apnea in 2.94% of trials. In contrast, rCeA stimulation during sleep induced apnea in 42.86% of trials, and was fatal in 5%.
Conclusions:
Our results confirm that the amygdala plays a key role in modulating breathing. Stimulation of the rCeA can induce prolonged central apnea in mice that are lightly anesthetized or during sleep, but not during wakefulness. These results can explain the higher incidence of SUDEP during sleep and after generalized convulsive seizures, when there is loss of both wakefulness drive and chemoreceptor drive to breathe. Propagation of seizures into the amygdala when wakefulness drive to breathe is absent can increase the risk of fatal central apneas.Funding: NIH/NINDS U01-NS0904143 SUDEP Research Alliance
RO1NS123155 (GBR)