title: Synaptic ultrastructure changes in trigeminocervical complex posttrigeminal nerve injury.
abstract: Trigeminal nerves collecting sensory information from the orofacial area synapse on second-order neurons in the dorsal horn of subnucleus caudalis and cervical C1/C2 spinal cord (Vc/C2, or trigeminocervical complex), which is critical for sensory information processing. Injury to the trigeminal nerves may cause maladaptive changes in synaptic connectivity that plays an important role in chronic pain development. Here we examined whether injury to the infraorbital nerve, a branch of the trigeminal nerves, led to synaptic ultrastructural changes when the injured animals have developed neuropathic pain states. Transmission electron microscopy was used to examine synaptic profiles in Vc/C2 at 3 weeks postinjury, corresponding to the time of peak behavioral hypersensitivity following chronic constriction injury to the infraorbital nerve (CCI-ION). Using established criteria, synaptic profiles were classified as associated with excitatory (R-), inhibitory (F-), and primary afferent (C-) terminals. Each type was counted within the superficial dorsal horn of the Vc/C2 and the means from each rat were compared between sham and injured animals; synaptic contact length was also measured. The overall analysis indicates that rats with orofacial pain states had increased numbers and decreased mean synaptic length of R-profiles within the Vc/C2 superficial dorsal horn (lamina I) 3 weeks post-CCI-ION. Increases in the number of excitatory synapses in the superficial dorsal horn of Vc/C2 could lead to enhanced activation of nociceptive pathways, contributing to the development of orofacial pain states.
authors.affiliation: Department of Pharmacology, University of California Irvine, School of Medicine, Irvine, California, 92697.
authors.forename: John
authors.initials: J
authors.lastname: Park
authors.affiliation: Department of Anesthesiology & Perioperative Care, University of California Irvine, School of Medicine, Irvine, California, 92697.
authors.forename: Van Nancy
authors.initials: VN
authors.lastname: Trinh
authors.affiliation: Reeve-Irvine Research Center, University of California Irvine, School of Medicine, Irvine, California, 92697.
authors.forename: Ilse
authors.initials: I
authors.lastname: Sears-Kraxberger
authors.affiliation: Department of Anesthesiology & Perioperative Care, University of California Irvine, School of Medicine, Irvine, California, 92697.
authors.forename: Kang-Wu
authors.initials: KW
authors.lastname: Li
authors.affiliation: Reeve-Irvine Research Center, University of California Irvine, School of Medicine, Irvine, California, 92697.
authors.forename: Oswald
authors.initials: O
authors.lastname: Steward
authors.affiliation: Department of Pharmacology, University of California Irvine, School of Medicine, Irvine, California, 92697.|Department of Anesthesiology & Perioperative Care, University of California Irvine, School of Medicine, Irvine, California, 92697.|Reeve-Irvine Research Center, University of California Irvine, School of Medicine, Irvine, California, 92697.
authors.forename: Z David
authors.initials: ZD
authors.lastname: Luo
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D004195:Disease Models, Animal; D005157:Facial Pain / Q000209:etiology* / Q000473:pathology; D007839:Functional Laterality; D008297:Male; D008854:Microscopy, Electron; D010147:Pain Measurement; D051381:Rats; D017207:Rats, Sprague-Dawley; D013569:Synapses / Q000473:pathology* / Q000648:ultrastructure*; D013997:Time Factors; D014275:Trigeminal Caudal Nucleus / Q000166:cytology*; D061221:Trigeminal Nerve Injuries / Q000150:complications* / Q000473:pathology
keywords: RRID:RGD_70508; RRID:nif-0000-30467; RRID:rid_000081; orofacial neuropathic pain; synaptic ultrastructure; trigeminal nerve injury