title: Changes in synaptic transmission of substantia gelatinosa neurons after spinal cord hemisection revealed by analysis using in vivo patch-clamp recording.
abstract: After spinal cord injury, central neuropathic pain develops in the majority of spinal cord injury patients. Spinal hemisection in rats, which has been developed as an animal model of spinal cord injury in humans, results in hyperexcitation of spinal dorsal horn neurons soon after the hemisection and thereafter. The hyperexcitation is likely caused by permanent elimination of the descending pain systems. We examined the change in synaptic transmission of substantia gelatinosa neurons following acute spinal hemisection by using an in vivo whole-cell patch-clamp technique.
  
  
  
  An increased spontaneous action potential firings of substantia gelatinosa neurons was detected in hemisected rats compared with that in control animals. The frequencies and amplitudes of spontaneous excitatory postsynaptic currents and of evoked excitatory postsynaptic currentss in response to non-noxious and noxious stimuli were not different between hemisected and control animals. On the contrary, the amplitude and frequency of spontaneous inhibitory postsynaptic currents of substantia gelatinosa neurons in hemisected animals were significantly smaller and lower, respectively, than those in control animals (P < 0.01). Large amplitude and high-frequency spontaneous inhibitory postsynaptic currents, which could not be elicited by mechanical stimuli, were seen in 44% of substantia gelatinosa neurons in control animals but only in 17% of substantia gelatinosa neurons in hemisected animals. In control animals, such large amplitude spontaneous inhibitory postsynaptic currents were suppressed by spinal application of tetrodotoxin (1 µM). Cervical application of lidocaine (2%, 10 µl) also inhibited such large amplitude of inhibitory postsynaptic currents. The proportion of multi-receptive substantia gelatinosa neurons, which exhibit action potential firing in response to non-noxious and noxious stimuli, was much larger in hemisected animals than in control animals.
  
  
  
  These suggest that substantia gelatinosa neurons receive tonic inhibition by spinal inhibitory interneurons which generate persistent action potentials. Spinal hemisection results in hyperexcitation of substantia gelatinosa neurons at least in part by eliminating the tonic descending control of spinal inhibitory interneurons from supraspinal levels.
authors: Department of Anesthesiology, Sapporo Medical University School of Medicine, Sapporo, Japan.
authors: Yuji
authors: Y
authors: Kozuka
authors: Department of Anesthesiology, Sapporo Medical University School of Medicine, Sapporo, Japan Department of Anesthesiology and Resuscitology, Shinshu University School of Medicine, Matsumoto, Japan kawamata@shinshu-u.ac.jp.
authors: Mikito
authors: M
authors: Kawamata
authors: Department of Information Physiology, National Institute for Physiological Sciences, Okazaki, Japan.
authors: Hidemasa
authors: H
authors: Furue
authors: Department of Anesthesiology and Resuscitology, Shinshu University School of Medicine, Matsumoto, Japan.
authors: Takashi
authors: T
authors: Ishida
authors: Department of Anesthesiology and Resuscitology, Shinshu University School of Medicine, Matsumoto, Japan.
authors: Satoshi
authors: S
authors: Tanaka
authors: Department of Anesthesiology, Sapporo Medical University School of Medicine, Sapporo, Japan.
authors: Akiyoshi
authors: A
authors: Namiki
authors: Department of Anesthesiology, Sapporo Medical University School of Medicine, Sapporo, Japan.
authors: Michiaki
authors: M
authors: Yamakage
mesh_terms: D018686:Anesthetics, Intravenous / Q000494:pharmacology; D000818:Animals; D001640:Bicuculline / Q000494:pharmacology; D004195:Disease Models, Animal; D004558:Electric Stimulation; D007839:Functional Laterality; D006930:Hyperalgesia / Q000209:etiology / Q000503:physiopathology; D008297:Male; D009474:Neurons / Q000145:classification / Q000187:drug effects / Q000502:physiology*; D018377:Neurotransmitter Agents / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D010812:Physical Stimulation; D051381:Rats; D017207:Rats, Sprague-Dawley; D013119:Spinal Cord Injuries / Q000150:complications / Q000473:pathology*; D013331:Strychnine / Q000494:pharmacology; D013376:Substantia Gelatinosa / Q000473:pathology*; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology*; D013779:Tetrodotoxin / Q000494:pharmacology; D014520:Urethane / Q000494:pharmacology
chemical_list: D018686:Anesthetics, Intravenous; D018377:Neurotransmitter Agents; D014520:Urethane; D013779:Tetrodotoxin; D013331:Strychnine; D001640:Bicuculline
keywords: Substantia gelatinosa; excitatory postsynaptic currents; hemisection; inhibitory postsynaptic currents; in vivo; patch-clamp; spinal cord injury