Intermittent Photic Stimulation in Rabbit Model: A Technique to Induce Epileptic Seizures and Simultaneously Record Multisystem Parameters

All procedures involving animal models have been reviewed by the local institutional animal care committee and the JoVE veterinary review board.

1. Photic stimulation experiment

1. Place a light source with a circular reflector 30 cm in front of the rabbit at eye level, with the flash intensity set to the maximum (16 candela). The light source is indicated by a white dot in Figure 1E.
   NOTE: A dimly lit room should be used to elicit the photosensitive response.
2.  As the rabbit's eyes are on the side of the head instead of the front of its head (as in humans), place 2 mirrors on either side of the rabbit, and 1 behind the rabbit so that the light enters the rabbit's eyes.
   NOTE: A flat mirror that is ≥ 20 cm tall, by ≥ 120 cm long creates a triangular enclosure around the rabbit to ensure that the flashing light enters the rabbit's eyes, as seen in Figure 1E.
3. Connect the light source to a controller that has an adjustable rate, intensity, and duration.
4. Record video using a camera with a red light and infrared recording capabilities.
5. Expose the rabbits to each frequency for 30 s with their eyes open and then another 30 s with a surgical mask covering their face to simulate or cause eye closure at each frequency.
   NOTE: Previous studies have shown that eye closure is the most provocative maneuver for eliciting photosensitivity to seizure. In addition, 10% of photosensitive patients only exhibit electroencephalographic signs while their eyes are closed. A seizure can be identified clinically by observing the presence of head and whole-body myoclonic jerks, clonus, or a tonic state. The EEG recording is more thoroughly analyzed for electroencephalographic correlation (e.g., spikes, poly-spikes, and rhythmic discharges) with motor manifestations for a definitive diagnosis of seizure activity. Movements in which the EEG is obscured by muscle artifact or waves of indeterminant epileptogenicity should be reviewed by an epileptologist for confirmation.
6. Increase the photic stimulator frequency from 1 Hz to 25 Hz in 2 Hz increments. Then perform the same photo-stimulation protocol, but this time decrease the frequency from 60 Hz to 25 Hz in 5 Hz increments.
   NOTE: If a rabbit has a seizure, the experiment should be stopped. Continue to monitor the rabbit for 30 min. Then return the rabbit to the housing room and monitor every 1 h for 3 h for full recovery. However, if the photic stimulation induces a photoparoxysmal response, then the remainder of ascending frequencies are skipped, and the series is started again by descending from 60 Hz until another photoparoxysmal response occurs. This will allow for the determination of the upper and lower photic stimulation thresholds. No delay is necessary as the photoparoxysmal response will cease after the photic stimulation is discontinued. If it is unclear whether a photoparoxysmal response has occurred, the frequency is repeated after a 10 s delay.
7. After the experiment is completed, remove EEG and ECG leads from the rabbit and return it to its home cage for routine care by husbandry staff.