behavioral testing and mechanical stimulation assessment in distal infraorbital nerve chronic constriction injured mouse

Establishing the Mouse Model for Trigeminal Neuropathic Pain

Neuropathic pain arises from damage to the somatosensory nervous system, leading to abnormal transmission of sensory signals to the brain. Somatosensory nerve damage does not always lead to neuropathic pain, but the prevalence increases with the severity of clinical neuropathy1,2. Neuropathic pain patients experience specific symptoms such as spontaneous sensations (burning, pins and needles, electric sensations) and abnormally intense or prolonged pain to innocuous or noxious stimulation that tend to become chronic and resistant to treatment with conventional pain medication3. Significant progress in the field of neuropathic pain research stems from the discovery that loosely constricting ligatures around the sciatic nerve in rats leads to behaviors resembling human neuropathic pain conditions4. The animals display reduced thresholds to heat, cold, and mechanical stimulation, and exhibit nocifensive behaviors. Despite the inherent biological differences in pain processing between humans and rodents, animal models are a valuable tool for studying the underlying mechanisms in the development of neuropathic pain and testing newly proposed treatment strategies.
Sensory reflex-based pain testing paradigms have been extensively used in neuropathic pain models, but measuring ongoing pain or other frequently accompanied disturbances (sleeping disorder, depression, anxiety) has not received sufficient attention considering that these are common clinical symptoms affecting quality of life5,6,7,8. Face grooming behavior in rats has been documented as a measure of spontaneous neuropathic pain following chronic constriction injury (CCI) of the infraorbital nerve (IoN)9,10. In addition, rats also develop hyperresponsiveness to mild tactile stimulation of the IoN territory, which is indicative of mechanical allodynia.
Compared to mice, because of their larger size, rats are better suited for surgical injuries. However, mice offer cost and space efficiency and require smaller drug quantities. Also, the advent of transgenic technology has further boosted the use of mice11,12. Therefore, the overall goal of this procedure is to perform a surgical infraorbital nerve injury in mice, similar to that in rats, that induces changes in spontaneous and evoked behavior for the study of trigeminal neuropathic pain.

Author Spotlight: Utilizing Infraorbital Nerve Ligation in Mice for Investigating Trigeminal Neuropathic Pain and Treatment Strategies

Chronic Constriction Injury of the Distal Infraorbital Nerve (DIoN-CCI) in Mice to Study Trigeminal Neuropathic Pain

The overall goal of this procedure is to perform an infraorbital nerve injury in mice to study the development of trigeminal neuropathic pain and to test new treatment strategies. Isolated phase grooming behavior after infraorbital nerve ligation is one of the few animal models to study spontaneous neuropathic pain. But its use has long been hampered by the complexity of performing an infraorbital nerve ligation.Compared to sensory reflex based pain testing, such as from fray or withdrawal responses from heat or cold stimulation, measuring spontaneous or ongoing pain has not received sufficient attention, considering that this is an important clinical symptom affecting quality of life. The distal approach to the infraorbital nerve has the advantage of being a surgically less demanding procedure than the intraorbital approach. It is minimally invasive, and can be performed without using a stereotaxic frame.

Behavioral Testing and Mechanical Stimulation Assessment in Distal Infraorbital Nerve Chronic Constriction Injured Mouse

To begin, carry a single mouse from the housing to the test room in a covered plastic cage without bedding material. Place the cage in front of a video camera. Then place a mirror to view the mouse's face when its back is toward the camera.Record the mouse's behavior for 10 minutes. After recording, clean the observation cage before recording the next animal. Have an observer blind to the experimental conditions to analyze the recorded behavior of the mouse.Note each face grooming episode during the 10-minute recording. Make a distinction between isolated face grooming and face grooming behaviors during body grooming. Determine the number of face grooming episodes with a four-second cutoff criterion.The time between grooming actions of less than four seconds is defined as a pause within a single episode. A time greater than four seconds is defined as a full interruption of grooming actions between two episodes. Place the mouse tail in a soft silicone clamp and attach the clamp magnetically to a metal plate on the table.Place a three-walled plastic holder over the mouse so that only the head protrudes from the container. Place a weight on top of the holder to keep it in place. Use a graded series of four von Frey hairs to apply force to the mouse.Habituate the mouse to the restrainer and reaching movements for 10 minutes. When the mouse is relaxed, slowly apply the lightest von Frey hair within the infraorbital nerve territory near the center of the vibrissae until it bends. Score the mouse response to the stimulation into one of the following categories.Calculate the mean score for ipsilateral responses to the four von Frey hairs, then calculate mean scores for the contralateral sides. Distal infraorbital nerve chronic constriction injury mice exhibited a significant postoperative increase in isolated face grooming time and episodes, peaking in the first week and then gradually decreasing, remaining elevated for six weeks. Initially, distal infraorbital nerve chronic constriction injury mice showed almost complete unresponsiveness to mechanical stimulation, which, during subsequent weeks, transformed into hyperresponsiveness lasting for six weeks.A slight increase in responsiveness to contralateral mechanical stimulation was also observed.

Research

JoVE Journal

Neuroscience

Animal models remain necessary tools to study neuropathic pain. This manuscript describes the distal infraorbital nerve chronic constriction injury ...