Abstracts

Rationale: California sea lions (Zalophus californianus-CSLs) develop epilepsy after natural exposure to domoic acid (DA) produced by Pseudo-nitzchia algae. DA is a potent ligand of kainate-type glutamate receptors, leading to strong excitation of hippocampal neurons. An approximate average of 70 CSLs suffering from epilepsy caused by exposure to DA are admitted annually into The Marine Mammal Center, a marine mammal research hospital in Sausalito, California. Chronic DA cases have > 50% mortality and have been shown to demonstrate radiographic and pathologic evidence of predominantly unilateral hippocampal sclerosis.

CSLs offer a naturally occurring large animal comparative model of mesial temporal lobe epilepsy, with potential mutual translational benefit to the animal and human. This study aims to develop a novel untethered, waterproof, surface electrode, long-term EEG monitoring system to characterize normal and abnormal CSL electrophysiology, and to aid in the diagnosis and treatment of seizures in rehabilitation settings or under human care.


Methods: A novel untethered surface-mounted EEG for CSLs was developed by modifying an existing device initially used to record sleep over multiple days in freely moving northern elephant seals. The headcap was customized for CSLs with 16 embedded Natus Gold Cup electrodes between two layers of neoprene. The system utilized the portable data logger: Neurologger3, sampling at 500 Hz, and enclosed in a robust aluminum cylinder. EEG waveforms were visualized in bipolar montage using CURRY software.


Results: Twenty-four-hour continuous EEG monitoring was performed on a 14-year-old male CSL with history of epilepsy and radiographic evidence of unilateral hippocampal sclerosis, while on maintenance anti-seizure medication. Placement of the equipment was performed under voluntary behavioral control and sedation was not required for application nor the subsequent monitoring period. Quality of EEG was technically adequate during the entirety of the recording. EEG showed active periods with EMG signal and eye movements and resting periods with distinct physiologic cerebral rhythms. There were no clear seizures or epileptiform discharges. There were no events of concern during this recording and the equipment was well tolerated by the CSL.


Conclusions: Non-invasive, non-sedated, long-term EEG monitoring is feasible in untethered CSLs. Additional recordings are necessary to further characterize normal versus abnormal CSL neurophysiology, including the capture of electrographic seizures. Data may improve the detection and treatment of seizures in CSLs. Furthermore, this work may serve as the foundation for translational research utilizing CSLs as a large animal model for temporal lobe epilepsy.


Funding: NIH NS107290, T32OD11121 and NSF ES021960