EMG Array Implantation in Rodents

 

PRE-SURGICAL DEVICE CHECK

  1. BEFORE starting your surgery, check the impedance of the array that you will be implanting in order to ensure that it is working.

  2. Set up a small weigh boat of saline and place a ground electrode in the saline (using an Intan board, insert a wire into a GND pin and then submerge the wire in saline)

  3. Plugin an array to a headstage and open the Intan recording software on a computer

  4. Go to the “Impedance” tab in the Intan software and make sure that the impedance measurement frequency is set to 1000 Hz.

  5. Click “Measure impedance”

  6. Click “Save Impedance to CSV” and save the impedance values with your data for future checking

  7. Impedance values will be shown under the x-axis of each channel

  8. Check that the impedance values are in the kOhm range. New arrays should be around 5-10 kOhm and may increase to 100-500 kOhm over use/time.

  9. If too many channels are reading more than 1 MOhm, then it is likely that there may be a defect in the array.

  10. If the array is defective, please let us know so we can identify what may have caused the issue.

 

GENERAL SURGICAL PROCEDURE

Prepare Animal for Procedure

  1. Induce anesthesia using isoflurane

  2. While keeping nose in nose cone, shave surgical areas

  3. Place animal on nose bar with nose cone

  4. Apply eye cream after fixing head with head bars

  5. Place drape over surgical area

NOTE: It may be undesirable to inject analgesia before surgery as this may subdue reflex responses used to check EMG activity during procedure. Skipping analgesia MUST be approved by your IACUC.

 

Prep Skull and Place Ground Pin

  1. Apply alternating povidone-iodine and alcohol swab to surface of head

  2. Cut away skin from head to expose skull

    1. Lift tissue with forceps and cut with scissors

  3. Use peroxide (3%) to wipe/wash remaining tissue from skull

    1. Rinse with saline

    2. Peroxide also helps to dry surface of skull so dental cement will bond

    3. Ensure skull is VERY DRY before applying cement by using cotton swab

    4. Prepare the skull for stronger adhesion by scratching the surface with a scalpel to increase roughness

  4. Use a dental drill to bore a small hole in the rostral skull to secure the ground pin

    1. The hole should penetrate the skull but not damage the brain/dura

    2. The hole should be just large enough for the ground pin to fit and be secured; a bone screw (with attached pin) may also be used as a ground

    3. If skull bleeds use cotton swab with saline

  5. Secure the ground pin with a stereotax arm and move into place

    1. Ground pin should be situated so that it makes gentle contact with the dura under the skull but does not damage the brain

  6. Use syringe needle to apply super glue to pin and skull

    1. Use accelerant “Zip Kicker Accelerator” to set glue quickly in place

Prepare Forelimb for Array

NOTE: Animal may be taken out of stereotax for EMG implantation.

  1. Tape ipsilateral ear out of the way

  2. Tape paw in an extended position

  3. Start incision along forelimb from dorso-proximal leg and cut dorsally along limb to expose areas for access; keep in mind that the incision should be as small as possible

  4. Use blunt forceps to tunnel under skin from the limb to the head/neck of the animal

  5. Direct array branch(es) subcutaneously through tunnel

    1. Place Omnetics connector in the stereotax arm to hold array in position relative to head

    2. Insert forceps subcutaneously from the limb to the medial neck and then gently open and rest on the surgical stage to keep subcutaneous tunnel open for array placement

    3. Use stereotax to reorient Omnetics connector during tunneling

    4. Use forceps to guide branch(es) through tunnel; pull from head to limb

    5. Once branch(es) are placed Omnetics connector can be removed from stereotax arm or can be left during suturing

    6. It is easier to thread the array subcutaneously with more space opened with the forceps

Suture Array ONTO Muscle (recommended: 10/0 Nylon ophthalmic)

  1. Use retractors to hold back skin around surgical area

  2. Thread suture “backwards” by taking the bare thread (end opposite the needle) and threading it through a suture hole of the array; pull the suture through until the needle is in an appropriate position to secure the array to the muscle

  3. For superficial arrays, use at least two sutures on the array pad placed on opposite sides so as to keep the array pad flat; use a third suture along the branch of the array close to the array pad to keep the branch in place

NOTE: “Reverse threading” suture through array without needle reduces the chance of damaging the array

Suture Array INTO Muscle (Method 1)

  1. Use retractors to hold back skin around surgical area

  2. Tie a suture onto the distal-most suture hole so that the suture with needle can be threaded through the muscle and used to pull the array through; it is easiest to thread the suture from the bare-threaded end and then pulling it through to an appropriate length

  3. Starting with the distal-most suture hole will allow you to make additional attempts if the array breaks (holes rip) while trying to pull it through

  4. Once the array has been threaded intramuscularly the suture can be cut or removed from the end of the array

  5. Thread a suture from the bare-threaded end until it is an appropriate length on the needle side and use the needle to secure the array to the muscle

  6. For intramuscular arrays: two sutures may be desirable – one on each side of the array to hold it flat; no suture was used on the proximal side of the intramuscular implantation

Suture array INTO muscle (Method 2)

  1. Prepare a needle and guide wire by taking the cutting a 27G needle and inserting a metal wire (seven stranded stainless steel, AM Systems #793200; ø139 µm). Crimp the needle where the wire is inserted to secure them together.

  2. Thread the wire through a distal suture hole in the array and tie a knot to secure them together.

  3. Insert the needle into muscle and draw through so that metal wire is threaded.

  4. Continue pulling needle and wire until the knot and array are pulled through the muscle.

  5. Stop pulling the needle/wire once the knot comes out of the muscle so as to avoid having to pull the array back and causing more tissue damage.

  6. You can cut the wire so as to leave the knot in place. Tighten the knot and this can be used to keep the array in place.

  7. You can also remove the wire altogether by untying the knot. Then, you can use a suture to secure the array into place.

Suture Skin Closed Around Array

  1. Avoid suturing where animal can chew through sutures.

  2. Use separate knots along the length of the incision.

NOTE: A stereotax attachment with a clip/clamp may be used on an adjustable base to hold the animal’s tail and reposition its forelimb for easier access to muscles can make procedure easier

NOTE: For threaded arrays, tunnel them subcutaneously one at a time to avoid tangling

Secure Omnetics Connector and Head Post/Bar

  1. Use stereotax to position Omnetics connector so as to avoid damaging ground pin

  2. Place head post/bar under or near Omnetics connector

  3. Mix dental cement

  4. Apply dental cement generously around head post/bar and Omnetics connector so as to allow it to seep into and around the edge of the skin/skull thus creating a seal

  5. Once surgery is complete, inject analgesic for post-operative care

  6. We encourage you to measure the impedance of the device after it has been implanted to see whether the array has been damaged. See the first page of this protocol for impedance measurement instructions (start at Step 3).

NOTE: We encourage you to measure the impedance at the BEGINNING and END of each day of data collection so that we can also track the quality of the implantation.

NOTE: Elizabethan collars can be placed around animal’s neck to prevent chewing at the stitches during the first few postoperative days. It is best to accustom animals to wearing the collars for a few days BEFORE surgery as they need to learn how to eat food while wearing the collars. Putting on the collar for the first time after surgery may lead to undesirable weight loss and stress.