Subcutaneous Transmitter Surgery Protocol for Recording EEG

Contents

1. Introduction

This protocol provides a detailed guide on the placement of electrodes and the surgical implantation of transmitters. It includes supply preparation, surgical procedures, and two methods of transmitter insertion.

Materials Required

• OSI Subucatenouse Transmitter and Electrodes (if applicable)
• All necessary electrode materials
• Sterile surgical tools (forceps, scissors, scalpel, burr drill, marker)
• Stereotaxic apparatus
• Anesthetic setup (e.g., 3-4% isoflurane, ketamine, eye lubricant, antibiotics)
• Dental cement
• Vetbond biocompatible cyanoacrylate adhesive
• Hydrogen peroxide (6% v/v diluted)
• Kwik-Cast biocompatible silicone sealant
• Ethanol (70% or 100%)
• Cotton applicators (Q-tips)

Related Protocols and Guides

• X-Electrode Crimp Contact Tutorial (Video)
• J-Electrode Implantation (Visual Guide)
• Silicone Removal from Leads
• SCT Implantation, Rob Wykes
• Cleaning and Storage
• Telemetry System Set-Up

2. Device Preparation

1. Sterilize all devices in 70% ethanol for at least 10 minutes prior to implantation. Do not surpass 1 hour in ethanol to avoid dissolution of silicone.
2. Prepare the subcutaneous transmitter (SCT):
   • Confirm device channel number and proper functionality before sterilization.
   • If inserting device through the Head Incision Method:
     1. Make a general estimate as to how long your leads should be. You can measure one of your mice from the middl of its bak to the top of its head, and add length for wiggle room. If your leads are too long it could irritate the animal, if they're too short, they tension could disrupt the electrodes or result in the transitter being pulled forward too far.
     2. Connect depth electrodes or stimulators before sterilization.
   • If inserting through the Back Incision Method:
     1. Sterilize components separately; you will connect electrodes post-transmitter implantation.

3. Animal Preparation and Anesthetization

1. Weigh the animal.
2. Select an appropriate animal weight based on the transmitter model. Transmitter weight dictates the minimum allowable animal weight. For example, the A3049J2S (a 0.2-80Hz, two-channel transmitter intented for sleep studies) weighs 2.7g. Animals must weigh at least 20g at the time of implantation for this model.
3. Induce anesthesia per institutional guidelines (e.g., 3-4% isoflurane). Use the toe-pinch method to verify proper anesthetization. Administer analgesics as needed, following institutional protocols.
4. Apply eye lubricant throughout the procedure.
5. Shave and disinfect the scalp and back area (if implanting the transmitter via the Back Incision Method).
6. Place the animal on a heating pad or temperature-controlled surgical platform.
7. Secure the animal in a stereotaxic frame if EEG depth electrodes are to be implanted.

4. Head Incision and Sterilization

1. Using forceps and scissors, lift the scalp and remove a vertical oval section of skin to expose the top of the skull. Avoid the eyes.
2. Clean the skull surface thoroughly using a bone scrapper to remove the connective tissue.
3. Optional: apply diluted hydrogen peroxide (6% v/v) to the skull and immediately dry it. This highlights any remaining connective tissue on the surface of the skull that can be removed using a bone scrapper.

5. Transmitter Insertion

Head Incision Method

Note: This method involves inserting the transmitter through the head incision and tunneling it down to the back. Therefore, this method is only recommended for our A3048-family SCTs, or the slim versions of the A3049-family SCTs, all of which have side-mounted batteries.

How do I insert a Subcutaneous Transmitter into an animal? Where do I place a Subcutaneous Transmitter?
1. Lift the skin at the back of the head incision.
2. Next, you are going to create a tunnel for the leads to pass through that allows the transmitter to sit in the back of the animal. To prevent irritation in the animals neck, we advise making the tunnel along the back of the animal, up until the neck, and then bringing the tunnel around the side of the neck (rather than directly over the spine) and through the head incision at a bit of an angle.
3. Use forceps to create a tunnel under the skin and above the muscle from the head incision to where the transmitter will lay, about half way around the back, in the mid-dorsal region. To create the tunnel you will clear away connective tissue that connects the muscle and the skin. The tunnel should be about as wide as the transmitter you are inserting.
4. Gently insert the transmitter, guiding it down the spine to about half way down the back.
5. Ensure the transmitter stays centered over the spine to avoid displacement.

Back Incision Method

How do I insert a Subcutaneous Transmitter into an animal? Where do I place a Subcutaneous Transmitter?
1. Use tweezers to pinch and cut skin of mid-dorsal region, half way down the back. Incision must be large enough for the transmitter to fit through.
2. Make a pocket for the transmitter to sit in:
   1. Clear connective tissue between skin and muscle where transmitter should lay. There are different schools of thought on where the transmitter should lay. We want to avoid the transmitter directly settling on the spine and also do not want it to fall to the front of the animal, as it will be able to claw it out. Be cautious of making too large of a pocket inbetween the skin and the muscle to prevent the transmitter from moving too much after placement.
3. Next, you are going to create a tunnel for the leads to pass through that allows the transmitter to sit in the back of the animal. To prevent irritation in the animals neck, we advise making the tunnel along the back of the animal, up until the neck, and then bringing the tunnel around the side of the neck (rather than directly over the spine) and through the head incision at a bit of an angle.
4. Place transmitter in the pocket you created under the skin in the back.
5. Feed electrode leads up the back tunnel and pull through the head incision with tweezers.
6. Make sure leads are out of the way when drilling in next steps

6. Burr Hole Mapping and Drilling

1. Glue the skin of the scalp in place Vetbond to prevent bleeding and keep skin retracted for surgery.
2. Zero the stereotaxic stand using bregma.
3. Using your stereotaxic apparatus, locate the desired burr hole coordinates, and mark them on the skull with a sterilized pen.
4. Carefully drill burr holes at marked positions. Stop until there is a thin layer of bone covering the dura. Use a sterile syringe needle or tweezers to pock through to the dura.
5. If using set screws to anchor electrodes, confirm their fit in the burr holes.
6. Dab excess fluid with sterile cotton.

7. Electrode Placement

1. If you used Transmitter Insertion - Back Incision (option 2), you will connect and prepare your electrodes now, before inserting them into the brain. See our Electrode Surgery Notes for detailed descriptions of connection and insertion methods for our different electrodes
2. Insert electrodes into burr holes carefully according to the experimental plan.
3. If bleeding occurs, dab with a cotton bud/Q-tip.
4. Dry the exposed skull
5. Optionally apply Vetbond around burrholes (avoid brain contact).
6. Pull excess leads back into the tunnel. As little wire should be exposed through the scalp incision as possible. Make sure to leave slack in the leads under the skin. If the leads are pulled too tight between the trasnmitter and the electrodes, they can irritate the animal or cause dislodging of device parts.
7. Secure the leads in place where they exit the head incision with a bit of Vetbond.

8. Closing and Cementing

• There are two methods for closing the open head incision
1. Suturing the head incision closed: This method is less common amongst our customers, as closing the incision over the electrodes and leads creates tension in the skin. THis can result in irritation and a subsequent opening of the head wound
2. Dental cement head fixture: this method, described below, involves creating a head fixture on the head of the animal with dental cement.
• Secure burr holes in place with a bit of dental cement; allow curing.
• Clip protruding electrode posts at designed breakpoints.
• Cover over all exposed areas, metal, and leads with more cement, avoiding too much contact with the the animals fur and skin. The top of the dental cement may remain a bit tacky due to oxidation, it is fine to cover it with more dental cement anyway.
• Allow cement to fully cure and trim excess.
• Seal cement–skin interface with small amount of Vetbond.

9. Post-Surgical Care

• Allow several days of recovery in a clean, quiet environment.
• Monitor daily for:
  • Pain
  • Distress
  • Weight loss
  • Infection
• Consult your vet for protocols on antibiotic treatments.
• If the dental cement cap on the head becomes displaced, or if electrodes wired are exposed at all, please consult your vet as the animal will likely need to be culled.

Notes and Best Practices

• Document electrode placements and orientations meticulously.
• Ensure tunnels are just wide enough to prevent device migration.
• Label each SCT with animal ID and date of implantation.
• Some of our customers report the transmitter "fusing" to the skin of the animals back. If you notice the animal is not grooming where the transmitter is and the skin seems thin or stiff, move the transmitter around a bit with your fingers to detach it from the skin and then apply sudocream. While rare, we are unsure why this occurs. Additionally, customers have reported this issue does not occur with our thinner, side-mounted battery SCT.
• You can cohouse animals witht Subcutaneous Transmitter implants, but we advise letting the animals heal on their own for a few days before co-housing them