LHA/mfb Electrode Implant

The following is a simple, step-by-step set of instructions for implanting a single chronic electrode into the LHA/mfb area of the rat brain. The illustrations show the surgery being done in the skull-flat orientation. The text describes the procedure for both skull-flat and de Groot orientations. Note the difference in the ccordinates for the two methods.

1. Prior to surgery, electrodes or cannulae should be autoclaved. Instruments should be sterilized. A hot bead sterilizer is an easy and effective sterilizing alternative. Set up a clean, well illuminated operating area.
2. Weigh the rat.
3. Anaesthetize the rat with an intra-peritoneal(IP) injection of the appropriate dose of somnotol, avertin, chloral hydrate, or ketamine/xylazine.
4. Shave the head using surgical clippers.
5. Inject 0.2 ml Marcaine-E subcutaneously(SC) in the centre of the shaved area. Marcaine-E is a long-lasting local anaesthetic with added epinephrine. It will further anaesthetize the surgical site. The epinephrine will decrease the amount of bleeding.
6. Insert the rat in the stereotaxic instrument.
7. Using a cotton bud soaked with 70% Ethanol, swab the shaved area to remove any loose hair.
8. Using a scalpel, make a midline incision starting at the back of the eyes and extending posteriorly for about 2 cm. Insure that the periosteum (shiny membrane under the skin) is also incised.
9. Using a cotton bud, roll the periosteum to the edges of the incision
10. Attach retractors to the periosteum to keep skin and membrane away from the surgical area.
11. (optional step) Using a fine tipped marker, make a small mark at Bregma and Lambda. If you are using the de Groot orientation, omit the mark at Lambda.
12. Adjust angle of head to chosen orientation.
• For de Groot orientaion: Raise the incisor bar until the scale reading on the incisor bar reads 5.0 mm above zero.
• For Skull-flat orientation: Raise or lower the incisor bar until Bregma and Lambda are in the same horizontal plane. For greatest accuracy, clamp the felt tipped marker into the electrode carrier and lower the tip of the pen, using the DV drive screw, until the pen tip is just touching your mark at Lambda. Take the DV reading on the vernier scale. Repeat this process at Bregma. If the DV readings are the same the head is correctly oriented. If the readings are not the same, raise or lower the incisor bar until they are.
13. Clamp the dental drill onto the electrode carrier of the stereotaxic instrument. Using the AP, ML, and DV drive screws, position the tip of the drill directly over Bregma.
14. Take the AP and ML vernier scale readings. (Illustration of AP vernier scale reading 51.8 mm)
• For Skull-Flat: Subtract 2.8 mm fom AP reading and add 1.7 mm to ML reading.
• For de Groot: Subtract 0.4 mm from AP reading and add 1.7mm to ML reading.
15. Move the dental drill to the calculated coordinates and drill a hole through the skull. The skull is about 1 mm thick. Disconnect the drill from electrode carrier after electrode hole is drilled.
16. Using a hand drill or pin vise drill 4 smaller holes around the electrode hole. These holes should be approx 3 mm away from the edge of the electrode hole. Do not drill on a skull suture.
17. Using curve forceps and small screw driver, thread jeweller's screws into the 4 smaller holes. You don't want to thread the screws in too deep. For the Stainless steel screws from Lomat Inc., 4 turns of the screw will adequately hold the screw without putting pressure on the brain. The number of turns will depend on the pitch of the screw.
18. Attach the electrode onto the electrode carrier of the stereotaxic instrument. Using the AP, ML, and DV drive screw move the electrode until the tip is just touching Bregma. Take the AP, ML, and DV vernier scale readings at Bregma. When readings are made raise the electrode a few mm. to prevent electrode from scraping the skull during movement
• For Skull-Flat: Subtract 2.8 mm from AP reading, Add 1.7 mm to ML reading, and Subtract 8.6 mm from DV reading.
• For de Groot: Subtract 0.4 mm from AP reading, Add 1.7mm to ML reading, and Subtract 9.3 mm from DV reading.
19. Using AP and ML drive screws, move the electrode to the calculated location. At this point the electrode tip should be situated directly over the drilled electrode hole.
20. If the Dura was not broken by the dental drill, use a fine, sterile needle to cut the dura now. The Dura is tough enough to bend your electrode if it is not broken.
21. Using the DV drive screw, slowly lower the electrode to the calculated DV coordinate.
22. Swab away any blood or cerebrospinal fluid that was displaced when lowering the electrode.
23. Mix up a small amount of dental cement and apply it around the electrode and screws using a small spatula.
24. As the cement thickens, mold it around the screws and electrode to form a nice smooth cap.
25. Disengage electrode holder from electrode.
26. Close the wound with wound clips, suture, or a second layer of dental cement.
27. Remove the rat from stereotaxic instrument to warm cage until recovered from anaesthesia.
28. Clean UP !

"Suture" photo taken by Richard Cooley in 1975 at MUN Psychology Dept. After leaving Memorial R. Cooley published a pictorial guide to stereotaxic surgery: Stereotaxic Surgery in the Rat: A Photographic Series by Richard K. Cooley and C. H. Vanderwolf. (c)1990 published by the A.J.Kirby, London,CA. This guide is still available from A.J.Kirby.