Medicine
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The Pilocarpine Model of Temporal Lobe Epilepsy and EEG Monitoring Using Radiotelemetry System in Mice
Chapters
Summary February 27th, 2018
This manuscript describes a method of inducing status epilepticus by systemic pilocarpine injection and of monitoring spontaneous recurrent seizures in live animals using a wireless telemetry video and electroencephalogram system. This protocol can be utilized for studying the pathophysiologic mechanisms of chronic epilepsy, epileptogenesis, and acute seizures.
Transcript
The overall goal of this procedure is to induce status epilepticus using pilocarpine and to monitor spontaneous recurrent seizures using a radiotelemetry system in mice. This protocol can be utilized for studying the pathophysiology mechanisms of acute seizures, epileptogenesis, and chronic epilepsy. The main advantage of this technique is to provide a mouse model of chronic epilepsy showing spontaneous recurrent seizures with high survivor rate after acute seizures.
Demonstrating the procedure will be Dr.Ji-Eun Kim, a postdoc in my laboratory. Begin by weighing each eight-week-old, male mouse. Make two milligrams per kilogram of scopolamine and terbutaline, as well as 280 milligrams per kilogram of pilocarpine solution.
Then, inject the solution intraperitoneally into each mouse, and return the mice to their cages. 30 minutes after the scopolamine and terbutaline administration, inject pilocarpine solution into each mouse. Immediately after pilocarpine injection, place the mice in an incubator with 28 to 30 degrees Celsius for observation.
Next, monitor the behavior of the mice until status epilepticus, or SE, is induced. If limbic motor seizures that correspond to stage three or higher according to Racine's scale are detected, record the time and monitor the mice. Once continuous motor seizures last more than two minutes, place the mouse in a new cage at room temperature and keep monitoring for three hours to determine whether their convulsive seizures continue and SE is induced.
Then, terminate behavioral acute seizures at three hours after SE onset by injecting 10 milligrams per kilogram of diazepam solution. After diazepam injection, administer one milliliter of 5%dextrose per individual mouse to help with recovery. At day one after SE induction, weigh the mice and keep them in the incubator for one extra day.
At day two after SE induction, weigh the mice and return them to their home cage. Provide moist food to facilitate recovery. Finally, measure daily body weight of the animals until seven days post-pilocarpine.
And if the body weight has not increased, inject the mice with 5%dextrose. Prepare 12-week-old mice, four weeks after SE induction, to perform telemetry implantation for EEG monitoring. Place the mouse in a stereotaxic frame with ear bars and a bite plate, and apply vet ointment on both eyes to avoid blindness.
Then, to maintain sterile conditions during the surgery, shave surgical sites using a razor blade, and be careful to prevent fur contamination of the surgical field. After shaving, disinfect the skin with 70%ethanol and iodine solution. Next, wipe the skin with PBS-soaked cotton swabs, followed by 70%ethanol and iodine solution.
Make a longitudinal incision in the middle of the head with scissors to expose the lambda, the bregma, and the target location. Then, position the drill bit at bregma, and note the X, Y coordinates for this point to calculate the coordinates for the screws. Next, slowly lower the drill bit to make a burr hole, being careful to avoid inserting the drill bit too far at the point where the skull becomes thinner.
Insert the body of the single-channel wireless EEG transmitter behind the nape of the neck subcutaneously, and place flexible leads near the skull. Next, place a stainless-steel screw into each burr hole with tweezers, and tighten it using a screwdriver by clockwise rotation. Ensure the screw is not inserted too far deep to prevent damage to the dura or the brain tissues.
Strip the insulation coat two millimeters from the tip of the leads, and stretch the wire long enough to round the screw shaft for a good connection between the wire and the screw. Connect the reference lead to the front screw and the recording lead to the screw in the parietal cortex. Then, apply dental cement to secure the entire assembly in place without exposing the metal parts.
Finally, after the dental cement has dried, suture the skin and apply topical mupirocin ointment. Place the mouse in a 30 degree Celsius incubator alone until it recovers from the surgery. Then, return the mouse to the home cage.
Begin by placing a mouse in an individual cage and placing the cage on top of the wireless receiver plates where the Faraday cage is installed, to avoid interruption of electrical signals from any sources including a computer, AC lines, and adjacent receivers. Then, record the electrical activity using the wireless video-EEG telemetry system. Determine seizure frequency by dividing the total number of SRS cases detected during the two weeks by the total number of recording days for each individual animal.
Then, to analyze seizure duration, measure the time from the onset to the end of the epileptiform spiking activities. After completion of the video-EEG recording and the fixation of the brain, retrieve the transmitter from the mouse for reuse after cleansing. To do this, remove the dental cement around the leads using forceps.
Then, soak the tip of the leads with dental cement in 100%acetone until the dental cement is dissolved. Next, remove tissue contaminants around the transmitter by rinsing it with distilled water. Finally, rinse the transmitter with 70%ethanol for three hours and air dry it for storage.
At seven days after SE, pyknotic cells were detected in the hilar regions of the dentate gyrus and the pyramidal cell layer of the CA3 subfield of the hippocampus. At six weeks after SE, a marked reduction was observed in the number of hilar cells. In addition, neuronal loss was observed in the CA1 and CA3 regions.
Additionally, compared to the sham group showing physiologic electrical activity, the SE group occasionally showed epileptiform discharges accompanied with convulsive behaviors. Excessively deep placement of the epidural screws during implantation surgery can induce cortical injuries, which can result in spontaneous seizures even in sham-manipulated animals. Once mastered, induction of status epilepticus and screw implantation can be done in an hour if it is performed properly.
While attempting this procedure, it is important to remember the behavioral manifestation after pilocarpine injection and not to damage brain tissues during implantation surgery. Following this procedure, other methods, like behavior test for memory and motor problems in chronic epilepsy, can be performed in order to answer additional questions, like epilepsy-associated circuitry issues. After watching this video, you should have a good understanding of how to induce status epilepticus and monitor chronic seizures in mice.
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