Head-Mounting Transmitter Surgical Implantation Protocol

Purpose: This protocol is intended for use only with OSI Head Mounting Transmitters and the OSI Telemetry System. HMT Implantation Protocol. What is the procedure for implanting an HMT? How do I attach an EIF to a mouse?

Acknowledgement: Photographs and instructions provided by Neela Krushna Codadu, PhD, and Kate Hills, PhD, Postdoctoral Research Fellows at UCL.

Contents

1. Introduction

Disclaimer: These protocols serve as a general guide. Surgical and animal welfare requirements vary across institutions. Always consult your institution’s veterinary staff to ensure compliance with local guidelines. Warning: Bare, unwrapped HMTs are vulnerable to static electricity. Do not carry bare HMTs around while wearing rubber shoes, wool sweaters, or any other static-generating item of clothing.

Materials

• Electrode Interface Fixture (EIF)
• Head-Mounting Transmitter (HMT)
• 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%)
• Sterile surgical tools (forceps, scissors, scalpel, burr drill)
• Stereotaxic apparatus
• Sterile marker
• Medical tape, clear plumber's tape, white Teflon tape
• Wooden applicators
• Cotton applicators (Q-tips)
• All necessary electrode materials

Related Protocols

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

2. Device Preparation

1. Ensure the EIF and electrodes are pre-assembled.
2. Sterilize all tools and materials prior to use.
3. Calibrate and check stereotaxic apparatus.

3. Animal Preparation and Anesthesia

1. Weigh the animal.
2. Anesthetize the animal according to protocol provided by your institutions guidelines. Perform toe-pinch method to ensure proper anesthesia depth. Administer pain medications (consult your institutional guidelines for guidance on pain medication protocols).
3. Place the animal in a stereotaxic stand, connect to anesthetic, and apply eye lubricant.
4. Disinfect the surgical site.

4. Head Incision and Exposure

1. Using forceps and scissors, lift the scalp and remove a patch of skin to expose the top of the skull. This is where you will mount the EIF and insert the electrodes.
2. Apply Vetbond to the skin edges to prevent bleeding and to secure the skin in place. Avoid getting Vetbond in the eys and on the exposed skull as you will be cleaning it shortly. See Step 4 image.

5. Skull Cleaning

1. Clean the skull surface thoroughly using a bone scrapper to remove the connective tissue.
2. 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.

6. Burr Hole Mapping and Drilling

1. Zero the stereotaxic stand at bregma..
2. Locate and mark burr hole coordinates with a sterile pen.
3. Drill burr holes carefully.
4. Test the fit of the set screws in the burr holes (if used for electrodes).

7. EIF Connector Placement

Note:The EIFs are not reusable once implanted. The HMTs, however, are reusable. End note.

1. Secure the EIF in the stereotaxic arm.
2. Align the EIF:
   • Anterior-posterior axis straight
   • Pins facing left (antenna should point backward)
3. Lower the connector such that the bottom of the connector just touches the skull.
4. Measure, mark, and trim silicone leads.
5. Remove the EIF from holder if needed to adjust leads. Strip the ends as the electrode implantation protocol describes.
6. Remount the EIF to the previous positions (i.e., touching the skull) and apply a small amount of dental cement under the connector. This is to secure the EIF in place on the skull. Precaution must be taken to avoid the flow of the detal cement into the burr holes.

8. Electrode Placement

1. Insert electrodes into burr holes-surface electrodes first, then depth electrodes. For more information on inserting our different types of electrodes, see our Electrode Implantation Protocol.
2. Control bleeding with cotton applicators.
3. If using screws, secure electrodes with Vetbond before cementing.
4. Wrap excess leads around the EIF to reduce protrusion.

9. Securing EIF Implantation

Note: Do not close the animal up by suturing the skin back together on the head, rather, we reccommend creating a head fixture out of dental cement to secure the EIF and cover the electrodes. You will not attach the HMT until the animal recovers from surgery. This means the EIF will be sitting exposed on the animals head for a few days and needs to be covered in some way to protect from debris and damage. End notes.

1. Apply dental cement to secure electrodes and connector base.
2. Cover exposed leads and skull surface-avoid covering the connector top.
3. Allow cement to fully cure and trim excess.
4. Cover the EIF top with tape/parafilm and optionally Kwik-Cast to protect it from debris and dislodging while the animal recovers and the HMT is not yet connected.

10. Surgical Recovery

• Allow several days of recovery in a qiet, clean environment.
• Monitor for pain, distress, weight loss, or infection.
• Consult your vet for protocols on antibiotic treatments.
• If the dental cement cap detaches or electrodes become exposed, consult a vet immediately-euthanasia may be required.

11. HMT Attachment

Directions

1. Discharge you body of any electric static before handling the bare HMT, if possible.
2. Prepare the HMT:
   • Confirm the HMTs connection to the telemetry system.
   • Fold the HMT in half as shown here.
   • Wrap the HMT in 2-3 layers of teflon tape, do not cover the connector.
   • Wrap the HMT in one layer of transparent tape and one layer of clear plumbers tape.
3. Briefly re-anesthetize the animal.
4. Attach the HMT to the EIF connector.
5. Secure the connection with Kwik-Cast.
6. Confirm electrical contact and alignment.
7. Monitor for scratching or attempts to dislodge the device.

12. HMT Replacement

Note: Replacement can be done with or without anesthesia. Some users prefer anesthesia to reduce stress. End note.

1. Carefully remove Kwik-Cast from the old HMT.
2. Gently disconnect it from the EIF.
3. Attach the partner HMT (identical configuration and channel) to the EIF.
4. Secure the new HMT with Kwik-Cast
5. Return the animal to housing monitor its recovery.
6. Unwrap the original HMT and remove the battery by gently pushing it out with a wooden applicator.

13. Battery Replacement

Note: Only insert the new battery into the HMT right before surgery, otherwise it can damage the HMT and drain the battery. End note.

1. Load a new battery just before use.
2. Clean the HMT before use:
   • Scrub with hot water and toothbrush
   • Soak briefly in ethanol
   • Dry with compressed air (20 psi) if available
3. Wear sterile gloves when loading the new battery.
4. Wrap the HMT with Teflon and transparent tape.

Notes and Best Practices

• Maintain sterility of all tools and materials.
• Use minimal cement beneath the connector.
• Avoid getting Vetbond on fur or unintended skin areas.
• Carefully document electrode coordinates and placements.
• Do not co-house animals with HMTs; they may remove each other's transmitters.