Inducing Orofacial Neuropathic Pain in a Rat Model via Infraorbital Nerve Ligations

Abstract

Source: Donertas-Ayaz, B. et al., Assessment of Nerve Injury-Induced Mechanical Hypersensitivity in Rats Using an Orofacial Operant Pain Assay. J. Vis. Exp. (2022)

This video demonstrates the induction of orofacial neuropathic pain in a rat model by ligating the infraorbital nerve. This results in nerve damage and inflammation, causing abnormal pain signaling and mimicking chronic pain conditions, which can be used to study the orofacial pain assay.

Protocol

All procedures involving animal models have been reviewed by the local institutional animal care committee and the JoVE veterinary review board.

1. Induction of orofacial neuropathic pain and evaluation of mechanical hypersensitivity

NOTE: Following baseline measurements, rats underwent chronic constriction injury of the infraorbital nerves (CCI-ION) surgery, which involved bilateral ligation of the infraorbital nerves (ION), as previously described. Control rats had sham surgery. No pre- or post-operative analgesia was used in the procedure as it can change the time course of the neuropathy. CAUTION: Waste isoflurane must be scavenged through charcoal canisters. Scalpel blades and needles must be disposed of in biohazard waste.

1. Anesthetize the rat in the induction chamber with a mixture of O₂ (1 L/min) and 4% isoflurane and maintain the anesthetic state with a specialized nose cone for the duration of the surgery.
2. Place the anesthetized rat on a surgical workbench and restrain it. Maintain the body temperature at 37 °C using a heating pad. Apply ophthalmic ointment to the eyes to prevent them from drying out. Check the anesthetic depth by pinching the toe and start the procedure when the toe withdrawal reflex is no longer observed.
3. Perform the surgical procedure under a stereo microscope. Open the mouth using retractors and retract the lip using a small clip.
4. Make a small incision between the dorsal gum and lip using a scalpel blade (#15). Gently cut away soft tissue using the tip of the scalpel blade to reveal a branch of the ION.
5. Place two chromic gut (#5-0) ligatures around the ION using a blunt, bent syringe needle.
6. Close the wound using tissue adhesive.

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Chromic gut suture size 5-0	Ethicon	687-G
Isoflurane	Patterson Veterinary	07-893-8440	Pivetal
Ophthalmic ointment	Dechra		Puralube Vet Ointment, petrolatum ophthalmic ointment
Scalpel blade #15	FST	10015-00
Small animal anesthesia system	VetFlo	VetFlo-1205S
Sprague-Dawley rats, female	Charles River Laboratories, USA
Stereo boom microscope	Omano	OM2300S-GX4
Tissue adhesive	3M Vetbond	1469SB
Water circulating heating pad and pump	Gaymar	Model TP-500