title: Central serotonin 3 receptors play an important role in the modulation of nociceptive neural activity of trigeminal subnucleus caudalis and nocifensive orofacial behavior in rats with persistent temporomandibular joint inflammation.
abstract: The role of central serotonin 3 receptors on neural activities recorded from superficial laminae of trigeminal subnucleus caudalis/upper cervical spinal cord junction region was investigated using rats with (Complete Freund's Adjuvant day 7 group) or without (non-Complete Freund's Adjuvant group) persistent temporomandibular joint inflammation evoked by Complete Freund's Adjuvant for 7 days. We identified two types of units, Deep-wide dynamic range units and Skin-wide dynamic range units from extracellular recordings. Deep-wide dynamic range units have mechanoreceptive fields in the deep craniofacial tissues including masseter muscle but do not have cutaneous mechanoreceptive fields. Deep-wide dynamic range unit discharges evoked by the formalin injection into masseter muscle were significantly enhanced in the late phase in Complete Freund's Adjuvant day 7 group. Discharges of Skin-wide dynamic range units evoked by the noxious pinch stimulation to facial skin in Complete Freund's Adjuvant day 7 group were significantly enhanced compared with those in non-Complete Freund's Adjuvant group. Topical administration of central serotonin 3 receptor antagonist, tropisetron, onto trigeminal subnucleus caudalis/upper cervical spinal cord junction region significantly reduced both formalin-evoked Deep-wide dynamic range unit and pinch-evoked Skin-wide dynamic range unit discharges in non-Complete Freund's Adjuvant and Complete Freund's Adjuvant day 7 groups significantly. The inhibitory effects of tropisetron on pinch-evoked Skin-wide dynamic range unit discharges were prolonged in Complete Freund's Adjuvant day 7 group compared with those in non-Complete Freund's Adjuvant group. The role of central serotonin 3 receptors in trigeminal subnucleus caudalis/upper cervical spinal cord junction region was also tested by orofacial formalin test in Complete Freund's Adjuvant day 7 group. Intracisternal administration of tropisetron decreased the orofacial nocifensive behavior in the late phase evoked by the injection of formalin into the masseter muscle. These results suggest that central serotonin 3 receptors in trigeminal subnucleus caudalis/upper cervical spinal cord junction region are involved in mediating pronociceptive effects in both superficial and deep craniofacial tissues nociception during persistent temporomandibular joint inflammation.
authors.affiliation: Department of Physiology, Wakayama Medical University, Kimiidera 811-1, Wakayama City 641-8509, Japan. jubedog@aol.com
authors.forename: K
authors.initials: K
authors.lastname: Okamoto
authors.forename: A
authors.initials: A
authors.lastname: Kimura
authors.forename: T
authors.initials: T
authors.lastname: Donishi
authors.forename: H
authors.initials: H
authors.lastname: Imbe
authors.forename: E
authors.initials: E
authors.lastname: Senba
authors.forename: Y
authors.initials: Y
authors.lastname: Tamai
mesh_terms: D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000287:Administration, Topical; D000704:Analysis of Variance; D000818:Animals; D001522:Behavior, Animal; D004195:Disease Models, Animal; D004305:Dose-Response Relationship, Drug; D005157:Facial Pain / Q000209:etiology*; D005557:Formaldehyde / Q000009:adverse effects; D005620:Freund's Adjuvant; D007211:Indoles / Q000494:pharmacology; D007249:Inflammation / Q000209:etiology; D008297:Male; D009619:Nociceptors / Q000503:physiopathology*; D010147:Pain Measurement / Q000187:drug effects / Q000379:methods; D010812:Physical Stimulation / Q000009:adverse effects; D051381:Rats; D017207:Rats, Sprague-Dawley; D044406:Receptors, Serotonin, 5-HT3 / Q000502:physiology*; D012702:Serotonin Antagonists / Q000494:pharmacology; D013705:Temporomandibular Joint Disorders / Q000139:chemically induced / Q000503:physiopathology*; D013997:Time Factors; D014275:Trigeminal Caudal Nucleus / Q000503:physiopathology*; D000077526:Tropisetron
chemical_list: D007211:Indoles; D044406:Receptors, Serotonin, 5-HT3; D012702:Serotonin Antagonists; D005557:Formaldehyde; D000077526:Tropisetron; D005620:Freund's Adjuvant