electroencephalography recording in a rat model of focal epilepsy

Electroencephalography Recording in a Rat Model of Focal Epilepsy

To begin this procedure, mix EEG electrode paste with 0.9% NaCl solution. Add a drop of methylene blue to help to visualize the electrode paste inside the electrodes and on the skin. Next, place the mixed paste in a syringe, and make sure that there are no air bubbles in it. Then, fill all 32 electrodes with the paste from the bottom without introducing any air bubbles.
As part of the preparation procedure for the rat, trim the rat&#39;s head. Afterward, reduce the isoflurane to 2%. Then, place the rat on the heating pad in the stereotaxic apparatus. Fix the ear canals with the ear bars and secure the nose cone for the supply of anesthetic. Next, apply ophthalmic ointment to the eyes of the animal.
Subsequently, shave its head, and rub the skin with 90% isopropyl alcohol to stimulate the blood vessels and remove the grease. Then, place a saline swab on the scalp and cover it completely to keep good skin conductance, until the EEG mini-cap is ready to be placed. Connect the respiration, temperature, and three-lead electrocardiogram probes to the rat&#39;s body to continuously monitor its physiology during the recording procedure.
In this procedure, remove the saline swab on the rat&#39;s scalp, and place the prepared EEG mini-cap on its skin. Fix the mini-cap with rubber bands. Apply a layer of high-conductance electrode paste on both the ground and reference electrodes. Subsequently, place them on the respective ears. Then, connect the EEG mini-cap to the amplifier. Look at a preview of the EEG traces and check the performance of all electrodes.
Then, administer Dexdomitor at 0.25 milligrams per kilogram to the rat intraperitoneally, and immediately reduce the isoflurane rate to 0%. If the respiration rate is not within 30 to 60 BPM range, increase the isoflurane rate gently at the maximum of 1%. Now, begin EEG recording and verify the existence of paroxysmal activity in the EEG traces. After the recording, mark the positions of the three jutting circles of the EEG mini-cap on top of the skin by inserting a color pen inside them before the EEG mini-cap is removed. Take a picture of the rat head with the landmarks.

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All procedures involving animal models have been reviewed by the local institutional animal care committee and the JoVE veterinary review board.
1. Electroencephalogram (EEG) Recordings
<ol>
	<li>Preparation of the EEG mini-cap
	<ol>
		<li>Immerse the electrode tips of the EEG mini-cap for at least 12 hrs in distilled water with 0.2% chloride. Rinse the EEG mini-cap gently in distilled water. Dry the cap and the electrodes in the air.</li>
		<li>Mix EEG electrode paste with 0.9% NaCl solution in the volume proportion of 2:1. Add a drop of methylene blue, which will help to visualize the electrode paste inside the electrodes and on the skin. Take the mixed paste in a syringe. Make sure there are no air bubbles in the syringe. Inject the gel into each of the 32 electrodes, filling them without introducing any air bubbles. It is recommended to inject from the bottom rather than the top. This provides better access to each electrode and reduces the possibility of the gel spilling over.</li>
		<li>Turn on the EEG and physiological recording system and open the corresponding recording software on the computer in use.</li>
	</ol>
	</li>
	<li>Animal preparation and anesthesia 
	NOTE: Chronic epilepsy was created using a protocol for focal cortical dysplasia (FCD)&#160;in Wistar rats. The EEG recordings were conducted in adult Wistar rats (8 weeks old, 300 - 400 g).
	<ol>
		<li>Record the rat&#39;s weight in an experiment sheet. Use this information to calculate the sedative dose (dexdomitor 0.25 mg/kg). Induce anesthesia in the rat with 5% isoflurane and 100% oxygen (1 L/min at 14.7 psi).</li>
		<li>After trimming the rat&#39;s head, reduce isoflurane to 2% and maintain it during the entire setting of the EEG mini-cap. Check rat reflexes are absent (toe-pinch).&#160;Place the rat on a heating pad in the stereotaxic apparatus by fixing the ear canals using ear bars. Make sure the anesthesia nose cone is secure.</li>
		<li>Apply lubricant ophthalmic ointment to each eye.</li>
		<li>Shave the extra hair on the rat&#39;s head and ears using a razor. Avoid any bleeding during shaving. 
		NOTE: Any hair left on the skin will produce noise in the EEG recordings. Rub the rat&#39;s skin with 90% isopropyl alcohol to stimulate the blood vessels and degrease the skin.</li>
		<li>Place a saline swab on the scalp and cover it completely to keep good skin conductance until the EEG mini-cap is ready to be placed.</li>
		<li>Connect temperature, respiration, and three lead electrocardiogram probes. Note that the temperature is measured by a rectal probe. Continuously monitor the physiology of the rat during the recording procedures. Ensure that the normal temperature is 37 &#176;C, respiration range is 30 - 60 breaths per minute, and heart rate is around 350 - 450 beats per minute.</li>
	</ol>
	</li>
	<li>Recording procedures
	<ol>
		<li>Remove the saline swab from the rat&#39;s scalp and place the prepared EEG mini-cap on its skin. Fix the mini-cap with rubber bands. Place one rubber band on the front side of the scalp, usually in front of the eyes, and another band at the back of the scalp between the ears and neck. Use a plastic protector under the neck to facilitate normal respiration.</li>
		<li>Put a layer of high-conductance electrode paste on both the ground and reference electrodes. Place them on the respective ear. 
		NOTE: The reference electrode can be possibly placed in other locations.</li>
		<li>Connect the EEG mini-cap to the amplifiers and observe a preview of the workbench for electrode impedance. Check the performance of all electrodes. For a high-quality recording, ensure that the impedance value is in the range of 5 - 30 k&#937;. If there are any noisy electrodes, provide better contact with the scalp by either moving them inside the scaffold toward the scalp or gently injecting more gel from the top of the electrode.</li>
		<li>Administer dexdomitor (0.25 mg/kg) intraperitoneally and immediately reduce the isoflurane rate to 0%. If the respiration rate is not within 30 - 60 breaths per minute range, start increasing the isoflurane rate gently. Do not exceed the value of 1% isoflurane. Monitor this step carefully because the mixture of isoflurane and dexdomitor could prompt the animals to a critical condition. 
		NOTE: In the preclinical model of focal epilepsy, isoflurane affects interictal epileptiform discharges (IEDs), whereas dexdomitor does not. Subjects under isoflurane have weaker epileptogenic properties,&#160;i.e.,&#160;relatively fewer IEDs can be detected compared to other conditions. The dexdomitor dose is effective for about 2 hrs. Thus, to save the time for its effect, the preparation was carried out under isoflurane.</li>
		<li>Conduct EEG recordings. After the recording, mark the positions of the three jutting circles of the EEG mini-cap on top of the skin by inserting a color pen inside them before the EEG mini-cap is removed. Use them as landmarks for MRI co-registration. Take a picture of the rat head with the landmarks. Place the rat back inside the cage and monitor it until complete recovery from dexdomitor&#39;s effect. 
		NOTE: In this experiment, red color (opponent color to green) was used to distinguish from the electrode positions (green). However, it is recommended to use other colors (purple/green) if small bleeding spots are observed in the skin.</li>
	</ol>
	</li>
</ol>

Source: Bae, J. et al., <a href="https://app.jove.com/v/52700">Brain Source Imaging in Preclinical Rat Models of Focal Epilepsy using High-Resolution EEG Recordings.</a>&#160;J. Vis. Exp. (2015)
This video demonstrates a method for high-resolution EEG recording in a rat model of focal epilepsy. It outlines the steps involved in preparing the rat, connecting a multichannel EEG mini-cap to the rat&#39;s scalp, and recording the EEG to identify seizure-related events characteristic of the epilepsy model.

All procedures involving animal models have been reviewed by the local institutional animal care committee and the JoVE veterinary review board.
1. ...

Take an anesthetized rat with focal epilepsy, characterized by abnormal brain electrical activity.
Secure the rat in a stereotaxic apparatus and administer anesthesia through a nose cone.&#160;
Completely remove the head fur to prevent signal interference during electroencephalogram, or EEG recording.
Clean the skin with alcohol and place saline swabs to enhance electrical conductance.
Apply EEG paste to each electrode of a multichannel EEG mini-cap to ensure optimal conductivity between the electrodes and the skin.
Fix the mini-cap on the scalp.
Position the ground and reference electrodes on the ears.
Connect the mini-cap to the amplifier. Visualize the EEG signals to identify loosely connected electrodes and improve their connectivity.
Administer a sedative and stop the anesthetic flow to minimize its interference with brain activity.
Record the EEG and identify the abnormal electrical activity events.
Mark the mini-cap&#39;s position on the skin for spatial correlation during subsequent brain imaging.

25 Views. Electroencephalography Recording in a Rat Model of Focal Epilepsy

Electroencephalography Recording in a Rat Model of Focal Epilepsy

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