title: Effects of TNF-alpha injected intracisternally on the nociceptive jaw-opening reflex and orofacial formalin test in freely moving rats.
abstract: The present study was performed to investigate the effects of central cytokines on the modulation of nociception in the orofacial area. A nociceptive jaw-opening reflex (JOR) and an orofacial formalin test were monitored after intracisternal administration of tumor necrosis factor (TNF)-alpha in freely moving rats. Experiments were carried out on 83 male rats weighing 300-350 g and surgical procedures were performed under pentobarbital sodium. After intracisternal injection of Tnf-alpha, digastric electromyogram (dEMG) and noxious behavioral responses were monitored. In the nociceptive JOR, dEMG was not significantly changed after intracisternal injection of 200 pg and 2 ng Tnf-alpha. However, 20 ng Tnf-alpha suppressed dEMG to 72+/-6% of the control values. The orofacial formalin responses showed two distinct phases separated by a time of relative inactivity with an early short-lasting response (0-9 min, first phase) and a continuous prolonged response (10-45 min, second phase). In the inflammatory orofacial formalin test, intracisternal injection of 20 pg Tnf-alpha did not change the number of noxious behavioral responses produced by formalin injection. However, 200 pg Tnf-alpha injected intracisternally significantly increased the number of noxious behavioral responses produced by formalin injection in both the early and late phases, and 2 ng Tnf-alpha increased formalin induced noxious behavioral responses in only the late phase. A higher dose of 20 ng Tnf-alpha did not change the number of noxious behavioral responses produced by formalin injection. The hyperalgesic action of Tnf-alpha injected intracisternally was blocked by pretreatment with the interleukin-1 (IL-1) receptor antagonist. These results suggest that central Tnf-alpha modulates the transmission of nociceptive information in the orofacial area. However, the hypo/hyperalgesic response of central Tnf-alpha seems to depend on the orofacial pain model or in a dose-related manner. The hyperalgesic response of central Tnf-alpha seems to be mediated by the IL-1 receptor.
authors.affiliation: Department of Oral Physiology, School of Dentistry, Kyungpook National University, 101 Dong-In 2-ga, Chung-gu, Daegu (700-422), South Korea. dkahn@knu.ac.kr
authors.forename: Hyo Sun
authors.initials: HS
authors.lastname: Choi
authors.forename: Jin Sook
authors.initials: JS
authors.lastname: Ju
authors.forename: Ho Jeong
authors.initials: HJ
authors.lastname: Lee
authors.forename: Chang Young
authors.initials: CY
authors.lastname: Jung
authors.forename: Byung Chul
authors.initials: BC
authors.lastname: Kim
authors.forename: Jae Sik
authors.initials: JS
authors.lastname: Park
authors.forename: Dong Kuk
authors.initials: DK
authors.lastname: Ahn
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000008:administration & dosage / Q000494:pharmacology*; D002946:Cisterna Magna; D004195:Disease Models, Animal; D005404:Fixatives; D005557:Formaldehyde; D007568:Jaw / Q000502:physiology; D008297:Male; D010146:Pain / Q000188:drug therapy* / Q000503:physiopathology; D010147:Pain Measurement; D051381:Rats; D017207:Rats, Sprague-Dawley; D012021:Reflex, Abnormal / Q000187:drug effects; D014409:Tumor Necrosis Factor-alpha / Q000008:administration & dosage / Q000494:pharmacology*
chemical_list: D000970:Antineoplastic Agents; D005404:Fixatives; D014409:Tumor Necrosis Factor-alpha; D005557:Formaldehyde