title: Assessment of chronic trigeminal neuropathic pain by the orofacial operant test in rats.
abstract: Classical behavioral tests in animal models of trigeminal neuropathic pain measure reflexive responses that are not necessarily measures of pain. To overcome the problem, we created a chronic constrictive nerve injury (CCI) rat model of pain by ligation of the infraorbital nerve (ION), and applied the orofacial operant test to assess behavioral responses to mechanical and cold stimulation in these rats. Animals were trained to voluntarily contact their facial region to a mechanical or a cold stimulation module in order to access sweetened milk as a positive reward. ION-CCI rats displayed aversive behaviors to innocuous mechanical stimuli, as indicated by a significant decrease in both contact time and the numbers of long contact events in comparison with sham group. For cold stimulation, ION-CCI rats displayed aversive behaviors to both innocuous (17 °C) and noxious cold temperatures (12 °C and 5 °C), as indicated by a significant decrease in both contact time and the numbers of long contact events at the cooling temperatures. The decreases of the contact time and numbers in ION-CCI rats were partially abolished by morphine. Our orofacial operant test demonstrates mechanical allodynia, cold allodynia, and hyperalgesia in rats with chronic trigeminal nerve injury. The neuropathic pain in ION-CCI rats was partially alleviated by morphine. Thus, orofacial operant test provides a desirable behavioral assessment method for preclinical studies of chronic trigeminal neuropathic pain.
authors: Department of Anesthesiology and the Graduate Program in Neuroscience, The University of Cincinnati College of Medicine, PO Box 670531, 231 Albert Sabin Way, Cincinnati, OH 45267-0531, USA.
authors: Myeounghoon
authors: M
authors: Cha
authors: Kevin J
authors: KJ
authors: Kohan
authors: Xiaozhuo
authors: X
authors: Zuo
authors: Jennifer X
authors: JX
authors: Ling
authors: Jianguo G
authors: JG
authors: Gu
mesh_terms: D000701:Analgesics, Opioid / Q000627:therapeutic use; D000818:Animals; D001522:Behavior, Animal / Q000502:physiology*; D059350:Chronic Pain / Q000188:drug therapy / Q000503:physiopathology*; D003080:Cold Temperature; D004195:Disease Models, Animal; D005157:Facial Pain / Q000188:drug therapy / Q000503:physiopathology*; D006930:Hyperalgesia / Q000503:physiopathology; D008297:Male; D009020:Morphine / Q000627:therapeutic use; D009437:Neuralgia / Q000188:drug therapy / Q000503:physiopathology; D010147:Pain Measurement; D017288:Pain Threshold / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D012201:Reward; D020433:Trigeminal Nerve Diseases / Q000188:drug therapy / Q000503:physiopathology*
chemical_list: D000701:Analgesics, Opioid; D009020:Morphine