This article details a surgical procedure for implanting electrodes in the brains of anesthetized rats to record electrical signals. The methodology includes precise drilling and electrode placement to ensure accurate data collection from multiple brain regions.
Secure an anesthetized rat in a stereotaxic frame. Shave and disinfect the scalp, then make an incision to expose the skull.
Drill holes above the olfactory bulb to implant recording electrodes. Drill above the frontal cortex to implant reference electrodes that acquire baseline brain activity signals.
Insert anchor screws around the hippocampus and create a large hole above the region.
Position an integrative micro-drive array with its cannula containing recording electrodes above the hole.
Use a gel-forming solution to secure the array. Apply dental cement that adheres to the anchor screws and provides mechanical stability.
Connect the array to the implanted electrodes for simultaneous recording from multiple brain regions. Insulate the connections to enhance signal quality.
Allow the rat to recover, then advance the array electrodes to contact the brain and let the signals stabilize.
The rat with the implanted electrodes is ready to record electrical signals from the brain.
Secure the rat to a stereotaxic device, then, shave and clean the skull, and start the array implantation with a 3-centimeter incision along the midline from the point between the eyes to the neck. Using a high-speed drill, make a pair of circular craniotomies between 0.7 and 1.0 millimeters in diameter above the olfactory bulb, which is 11.0 millimeters anterior and one millimeter bilateral to bregma.
Then, implant the two BR electrodes just deep enough for the tips of the screws to make contact with the brain, which is about 2 millimeters deep. Use between six and eight full turns of the screw.
Next, make another pair of craniotomies above the frontal cortex, 2.7 millimeters anterior and 2.7 millimeters bilateral to bregma. Into these holes, secure the two ground reference electrodes so they also just contact the brain, about 1.6 millimeters deep. This takes four to five full turns of the screw.
Now, plan a large circular craniotomy with a diameter of about 2.0 millimeters above the hippocampus, 3.8 millimeters posterior, and 2.5 millimeters bilateral to bregma. Then, make six to eight 1.0-millimeter holes in the area that will surround the craniotomy.
Into each of these holes, implant the anchor screws. Then, make the planned craniotomy between the screws. Above the large hole, position the integrative microdrive array such that the cannula tip is just above the large craniotomy.
Fill the gap space between the cannula tip and the brain surface with about 100 microliters of two-part epoxy. Over the next five minutes, allow the mixture to change into a transparent gel. Next, cover the cannula, BR electrodes, ground reference electrodes, and anchor screws with dental cement.
Apply about five millimeters of cement without covering the open ends of BR or ground reference electrodes. Now, solder all the open ends of the electrodes to where they connect to the board. Then, cover the bottom part of the integrative microdrive array and all electrode wires with dental cement.
It is important to completely cover the electrode wires so that the rat cannot scratch them out after the implantation. Now allow the rat to recover. After regaining sufficient consciousness to maintain sternal recumbency, house it solo without any cage mates, and give it free access to food and water.
After the surgery, gradually advance the tetrodes by advancing the screws daily. Once the tetrodes are adjacent to the target brain areas, let them settle for several days during which signals will stabilize.
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