Assessment of Nerve Injury-induced Mechanical Hypersensitivity in Rats using an Orofacial Operant Pain Assay

Area of Science:

• Neuroscience
• Pain Research
• Animal Models

Background:

• Traditional pain assays often overlook the cognitive and motivational aspects of pain.
• Operant pain assays offer a more clinically relevant approach by incorporating these factors.
• Assessing mechanical hypersensitivity is crucial for understanding neuropathic pain.

Purpose of the Study:

• To present a protocol for assessing mechanical hypersensitivity using an orofacial operant pain system.
• To evaluate the efficacy of the orofacial pain assessment device (OPAD) in rats following chronic constriction injury of the infraorbital nerves (CCI-ION).
• To demonstrate the utility of operant-based assays in preclinical pain research.

Main Methods:

• Rats were trained on the OPAD to associate facial contact with a reward (milk).
• Mechanical hypersensitivity was induced via chronic constriction injury of the infraorbital nerves (CCI-ION) or sham surgery.
• The operant system recorded licks, facial contacts, and latency to measure pain sensitivity.

Main Results:

• CCI-ION rats showed a significant decrease in licks and the lick-to-facial contact ratio.
• A significant increase in the latency to the first lick was observed in CCI-ION rats.
• These behavioral changes indicate mechanical hypersensitivity following CCI-ION.

Conclusions:

• The orofacial operant pain system provides a robust method for quantifying mechanical hypersensitivity in rats.
• Operant-based pain assays are valuable tools for preclinical research into neuropathic pain.
• This protocol advances the assessment of pain's cognitive and motivational components in animal models.