Abstracts

Rationale: Absence seizures (AS) are the most common seizure type across generalized epilepsy syndromes, consisting of widespread EEG spike-and-wave discharges with concurrent behavioral arrest. They are the main seizure type found in childhood and juvenile absence epilepsy, syndromes which are associated with cognitive disorders. In a significant proportion of cases, these conditions also act as precursors for the development of generalized tonic-clonic seizures. These facts, together with the dearth of advances in gold-standard AS treatment over the past 50 years, demand an improved understanding of the neural mechanisms of these seizures and syndromes, including those by which AS cause varying (from seizure to seizure) degrees of behavioral arrest and apparent unconsciousness. Mechanistic investigations in experimental AS models have historically taken place under anesthesia or sedation, hence differing in arousal state from, and lacking the behavioral component of, clinical AS. Simultaneously, hemodynamic measurements in these models don't agree with clinical blood flow changes. We have addressed these issues by developing a protocol for head fixation training, together with repeated electrophysiological, behavioral and hemodynamic measurements, in Genetic Absence Epilepsy Rats from Strasbourg (GAERS).Methods: Rats were incrementally introduced to body and head restraint, using a water restriction regime both to allow rewarding for cooperation with each level of restraint and to facilitate behavioral assessment of stimulus detection and motor response during AS. Stages included manual handling, drinking from open spout, drinking with body restraint, and drinking with increasing degrees of head restraint. The method centred on positive reinforcement for satisfactory performance with minimization of aversive stimuli and sources of stress. Training time after head plate implantation was also minimized in order to facilitate high quality electrophysiological and hemodynamic measurements.Results: Rats became accustomed to >20 minute periods of body and head restraint within 1 month of training initiation, with linearly decreasing adverse events (stress grooming/defecating/urinating, biting, audible vocalizations, escape attempts) (n=6 rats). After head plate implantation, head fixation with minimal stress (drinking proceeds uninterrupted, no audible vocalizations) could be achieved within 1 week (n=2 rats), with initial fixation sessions lasting up to 8 minutes and multiple sessions per animal possible.Conclusions: The timeline of this protocol appears suitable for repeated electrophysiological, hemodynamic and behavioral measurements of AS. The rats low stress levels during fixation are also appropriate for the study of an arousal-dependent phenomenon. This will offer unprecedented access to unadulterated AS in an awake behaving model.