This article details a procedure for implanting tungsten microwire electrodes in the brain of an anesthetized rat to record electrophysiological activity. The method involves precise drilling and electrode placement to ensure accurate data collection from multiple brain regions.
Begin with an anesthetized rat secured in a stereotactic frame with its skull exposed.
Use reference points on the skull to calibrate and mark the desired coordinates.
Drill holes at the marked locations.
Remove debris and cut open the brain's outer layer.
Frequently flush the holes with saline to prevent drying.
Drill additional holes and anchor screws to support the electrodes.
Install the reference electrodes and electrophysiological recording electrodes. Secure them by applying acrylic resin.
Arrange tungsten microwire electrodes on a frame according to the multi-target locations in the brain.
Multiple electrodes allow simultaneous recording of brain activities from multiple target sites.
Using the reference point on the skull, position the tungsten microwire electrodes.
Gently insert them into the brain.
Configure the recording software to detect brain activity.
Lower the electrodes to the target depth and begin data recording.
Under the microscope, use a standard stereotaxic rat alignment tool to calibrate the designated tip to the bregma and adjust the incisor bar until the designated points for the bregma and lambda on the tool touch the skull at the same time. Using a stereotaxic holder with cannula, calibrate it to the bregma and then calculate the position of all drill holes on the skull.
Then, mark the positions of the holes to be drilled either by carefully scratching the skull or by using a surgical color marker. Then, using a micro-drill, carefully drill all the holes with a diameter of about 1 millimeter. For the STN and SNr, drill a common hole approximately 2 millimeters by 3 millimeters.
Take one fine cannula, and bend the tip to form two hooks. Then, use the hooks to remove any debris from the drill holes and carefully cut and remove the dura mater in the common STN/SNr hole. After that, flush the drill holes with physiological saline.
Apply a drop of physiological saline every 15 minutes to the drill holes to prevent the brain and dura from drying out. Then take a micro-drill and matching stainless steel micro screw. Drill a hole, and screw in a micro-screw between the drill holes of the reference epidural electrodes above the cerebellum.
Next, guide the electrode tips with fine tweezers and slide them directly below the skull bone into the drill holes. Fix all epidural electrodes with two-component dental acrylic. Make sure not to cover the bregma point nor affect the common STN/SNr hole.
Then, insert the prepared holder with the tungsten microwire electrodes into the stereotaxic frame. Calibrate the most ventral electrode to the bregma, which is intended to target the STN. Adjust to the calculated position above the common STN/SNr hole, and lower the electrodes down to the brain.
Make sure that the tungsten microwire electrodes go inside the brain smoothly. In this procedure, set up the recording software such as bandpass filter, and amplify the raw data signal. Then, use an online LFP and spike filter with appropriate settings.
For all filters, use a Butterworth-type filter. Set up a spike threshold for online spike sorting. Most recording software allows for the setting up of a spike threshold, which is an amplitude value above the threshold that a signal is marked as a spike by the software. Next, slowly lower the tungsten microwire electrodes to 1 millimeter above the STN and wait for the signal to stabilize if necessary.
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