• Journal of Acupuncture Research
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• v.20 no.3
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• pp.15-23
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• 2003

Objective : The role of high frequency 120 Hz electroacupuncture(EA) in carrageenan-induced pain was studied by examining the alnalgesic effects, and prostaglandin $E_2(PGE_2)$ levels measurement and spinal N-methyl-D-aspartate(NMDA) receptor expression. Inflammation was induced by an intraplantar injection of 1% carrageenan into the right hind paw. Method : Bilateral EA stimulation with 120 Hz were delivered at those acupoints corresponding to Zusanli and Sanyinjiao in man via the needles for a total of 30 min duration in carrageenan-injected rats. Results : EA stimulation showed significant analgesic effects as measured by analgesy-meter at all time points tested compared with controls. Three hours after carrageenan injection, PGE2 levels were measured by commercial kit. EA significantly inhibited PGE2 production in the right paw. The number of NR1 and NR2A, NMDA receptor, immunoreactive neurons was significantly increased in the superficial dorsal horn(laminae I-II) and nucleus proprius(laminae III-IV) of ipsilateral spinal cord at L4-5. But the number of carrageenan-induced NR1 and NR2A immunoreactive neuron, especially NR1 immunoreaction in the superficial dorsal horn, was reduced by 120 Hz EA stimulation. Conclusions : These results indicate that NMDA receptors may mediate transmission of nociceptive information originating in tissue inflammation of hind paw and high frequency 120 Hz EA stimulation have an alleviating action against local inflammatory pain.

• The Korean Journal of Physiology and Pharmacology
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• v.9 no.3
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• pp.143-147
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• 2005

Following peripheral nerve injury, excessive nociceptive inputs result in diverse physiological alterations in the spinal cord substantia gelatinosa (SG), lamina II of the dorsal horn. Here, I report the alterations of excitatory or inhibitory transmission in the SG of a rat model for neuropathic pain ('spared nerve injury'). Results from whole-cell recordings of SG neurons show that the number of distinct primary afferent fibers, identified by graded intensity of stimulation, is increased at 2 weeks after spared nerve injury. In addition, short-term depression, recognized by paired-pulse ratio of excitatory postsynaptic currents, is significantly increased, indicating the increase of glutamate release probability at primary afferent terminals. The peripheral nerve injury also increases the amplitude, but not the frequency, of spontaneous inhibitory postsynaptic currents. These data support the hypothesis that peripheral nerve injury modifies spinal pain conduction and modulation systems to develop neuropathic pain.

• The Korean Journal of Physiology and Pharmacology
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• v.3 no.4
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• pp.365-373
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• 1999

Somatostatin (SOM) is one of the major neuropeptides in dorsal root ganglion cells, but its role in spinal nociceptive process has not been well known. In present study we aimed to investigate the effect of SOM on the response of dorsal horn neurons to the various types of peripheral nociceptive stimuli in anesthetized cats. Using carbon-filament microelectrode, the single cell activities of wide dynamic range neurons were recorded from the lumbosacral enlargement after noxious mechanical (squeeze), thermal (radiant heat lamp) and cold (dry ice) stimulation to the receptive field. Sciatic nerve was stimulated electrically to evoke $A\;{\delta}-$ and C-nociceptive responses. SOM analogue, octreotide $(10\;{\mu}g/kg),$ was applied intravenously and the results were compared with those of morphine (2 mg/kg, MOR). Systemic SOM decreased the cellular responses to the noxious heat and the mechanical stimulation, but increased those to the cold stimulation. In the responses to the electric stimuli of sciatic nerve, $A\;{\delta}-nociceptive$ response was increased by SOM, while C-nociceptive response was decreased. On the other hand, MOR inhibited the dorsal horn cell responses to all the noxious stimuli. From the above results, it is concluded that SOM suppresses the transmission of nociceptive heat and mechanical stimuli, especially via C-fiber, while it facilitates those of nociceptive cold stimuli via $A\;{\delta}-fiber$.

• The Korean Journal of Pain
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• v.28 no.3
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• pp.185-192
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• 2015

Background: Neuropathic pain is a global clinical problem; nevertheless, nerve injury treatment methods remain limited. Olanzapine has antinociceptive and anti-nueropathic properties; however, its preventive effects have not been assessed in nerve injury models. Methods: We prepared a partial sciatic nerve ligation (Seltzer model) or sham-operated model in male Sprague-Dawley rats under isoflurane anesthesia. In a pre-treatment study, we administered olanzapine (10 mg/kg) intraperitoneally 1 h before nerve ligation. In post-treatment and dose-dependent studies, we injected 3 different doses of olanzapine intraperitoneally 1 h after nerve ligation. Mechanical allodynia was measured before and 7 days after surgery. Immunohistochemical analysis using anti-Iba-1 antibody was used to assess the effect of olanzapine at the spinal level. Results: In the pre-treatment study, median withdrawal thresholds of the normal saline groups were significantly lower than those of the sham-operated groups; however, those of the olanzapine (10 mg/kg) and sham-operated groups were not different. In the post-treatment and dose-dependent studies, the median withdrawal thresholds of the olanzapine (2.5 mg/kg) and normal saline groups were not different; however, those of the olanzapine (10 and 50 mg/kg) groups were significantly higher than those of the normal saline groups. Olanzapine did not have a significant effect on the density of Iba-1 staining. Conclusions: Olanzapine attenuated mechanical allodynia dose-dependently in the Seltzer model. This anti-allodynic effect of olanzapine was observed even when injected 1 h after nerve ligation. This effect of olanzapine appeared to be unrelated to microglia activation in the ipsilateral dorsal horn of the lumbar spinal cord.

• International Journal of Oral Biology
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• v.32 no.4
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• pp.153-160
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• 2007

The superficial dorsal horn, particularly substantia gelatinosa (SG) in the spinal cord, receives inputs from small-diameter primary afferents that predominantly convey noxious sensation. Reactive oxygen species (ROS) are toxic agents that may be involved in various neurodegenerative diseases. Recent studies indicate that ROS are also involved in persistent pain through a spinal mechanism. In the present study, whole cell patch clamp recordings were carried out on SG neurons in spinal cord slice of young rats to investigate the effects of hydrogen peroxide on neuronal excitability and excitatory synaptic transmission. In current clamp condition, tert-buthyl hydroperoxide (t-BuOOH), an ROS donor, depolarized membrane potential of SG neurons and increased the neuronal firing frequencies evoked by depolarizing current pulses. When slices were pretreated with phenyl-N-tert-buthylnitrone (PBN) or ascorbate, ROS scavengers, t-BuOOH did not induce hyperexcitability. In voltage clamp condition, t-BuOOH increased the frequency and amplitude of spontaneous excitatory postsynaptic currents (sEPSCs), and monosynaptically evoked excitatory postsynaptic currents (eEPSCs) by electrical stimulation of the ipsilateral dorsal root. These data suggest that ROS generated by peripheral nerve injury can modulate the excitability of the SG neurons via pre- and postsynaptic actions.

• The Korean Journal of Physiology
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• v.23 no.2
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• pp.409-420
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• 1989

Extracellular recordings were made from the spinal neurons in the lumbar enlargement of 16 cats before and during electrical stimulation of the radial nerve ipsilaterally and contralaterally. Only neurons activated by remote nerve stimulation (RNS) were included in sample. All the cell classes of spinal neurons which received afferents message from the skin and/or muscles were activated by RNS except LT cells. Approximately three quaters of cells activated by RNS had an inhibitory receptive field (RF) on the ipsilateral hindlimb and two thirds of RNS-activated neurons showed spontaneous activity. The most of these RNS-activated cells seemed to be in deep dorsal horn and in ventral horn as well. Stimulation of contralateral radial nerve produced activation of spinal neurons almost same degree as by ipsilateral nerve stimulation. The optimal stimulation parameters of radial nerve for activation of spinal cells were 5Hz-0.5 msec-2V while threshold stimulus for activation was approximately 0.18 V. Following close intra-arterial injection of $K^+$ ion excitability of RNS-activated neuron was increased in 4 of 8 cells whereas it was decreased in 2 of 8 cells. The results indicate that there are some spinal neurons in the lumbar enlargement of cats that can be activated by forelimb afferent $(A{\beta}\;&\;A{\delta})$ inputs.

• Journal of the Korean Association of Oral and Maxillofacial Surgeons
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• v.33 no.3
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• pp.227-237
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• 2007

Microglial cell activation is known to contribute to neuropathic pain following spinal sensory nerve injuries. In this study, I investigated its mechanisms in the case of trigeminal sensory nerve injuries by which microglial cell and p38 mitogen-activated protein kinase (p38 MAPK) activation in the medullary dorsal horn (MDH) would contribute to the facial pain hypersensitivity following mandibular nerve transection (MNT). And also investigated the changes of trigeminal ganglion neurons and ERK, p38 MAPK manifestations. Activation of microglial cells was monitored at 1, 3, 7, 14, 28 and 60 day using immunohistochemical analyses. Microglial cell activation was primarily observed in the superficial laminae of the MDH. Microglial cell activation was initiated at postoperative 1 day, maximal at 3 day, maintained until 14 day and gradually reduced and returned to the basal level by 60 days after MNT. Pain hypersensitivity was also initiated and attenuated almost in parallel with microglial cell activation pattern. To investigate the contribution of the microglial cell activation to the pain hypersensitivity, minocycline, an inhibitor of microglial cell activation by means of p38 MAPK inhibition, was administered. Minocycline dose-dependently attenuated the development of the pain hypersensitivity in parallel with inhibition of microglial cell and p38 MAPK activation following MNT. Mandibular nerve transection induced the activation of ERK, but did not p38 MAPK in the trigeminal ganglion. These results suggest that microglial cell activation in the MDH and p38 MAPK activation in the hyperactive microglial cells play an important role in the development of facial neuropathic pain following MNT. The results also suggest that ERK activation in the trigeminal ganglion contributes microglial cell activation and facial neuropathic pain.

• International Journal of Oral Biology
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• v.37 no.1
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• pp.17-23
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• 2012

Recent studies indicate that reactive oxygen species (ROS) are critically involved in persistent pain primarily through spinal mechanisms, and that mitochondria are the main source of ROS in the spinal dorsal horn. To investigate whether mitochondrial ROS can induce changes in membrane excitability on spinal substantia gelatonosa (SG) neurons, we examined the effects of mitochondrial electron transport complex (ETC) substrates and inhibitors on the membrane potential of SG neurons in spinal slices. Application of ETC inhibitors, rotenone or antimycin A, resulted in a slowly developing and slight membrane depolarization in SG neurons. Also, application of both malate, a complex I substrate, and succinate, a complex II substrate, caused reversible membrane depolarization and enhanced firing activity. Changes in membrane potential after malate exposure were more prominent than succinate exposure. When slices were pretreated with ROS scavengers such as phenyl-N-tert-buthylnitrone (PBN), catalase and 4- hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPOL), malate-induced depolarization was significantly decreased. Intracellular calcium above $100{\mu}M$ increased malateinduced depolarization, witch was suppressed by cyclosporin A, a mitochondrial permeability transition (MPT) inhibitor. These results suggest that enhanced production of spinal mitochondrial ROS can induce nociception through central sensitization.

• The Korean Journal of Pharmacology
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• v.29 no.1
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• pp.33-41
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• 1993

Central analgesic effect of capsaicin was assessed by the tail flick reflex (TFR) test, using male Sprague-Dawley rats under anesthesia with pentobarbital sodium (induction with 40 mg/kg and maintenance with $4{\sim}8\;mg/kg/hr$). Level of norepinephrine in the spinal cord was also measured. Capsaicin, $35{\sim}150\;{\mu}g$, was injected intrathecally, and the TFR latency was measured before, 10, 30, and 60 minutes after the drug administration. TFR latency was increased 100% or more immediately by intrathecal capsaicin, from 2.9 seconds to the maximum of 7.0 seconds at 10 minute after the drug; P<0.01. The increase in TFR latency was maintained during the course of experiment of 2 hours. Concomitant reduction of NE content in the spinal cord was observed; from 16 ng/mg protein to 7 ng/mg protein. On the other hand, subcutaneous injection of capsaicin of 50 mg/kg did not change the TFR latency although the NE content reduced similarly to the case of intrathecal injection. Pretreatment of the animal with 0.5 mg/kg of MK-801 reversed the increase of TFR latency and NE reduction induced by intrathecal capsaicin. These results suggest that capsaicin causes analgesia at the spinal cord level by activating the excitatory amino acid-NE-dorsal horn interneurons axis of the descending inhibitory pain modulation pathway.

• The Korean Journal of Physiology and Pharmacology
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• v.21 no.4
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• pp.371-376
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• 2017

The caudal subnucleus of the spinal trigeminal nucleus (medullary dorsal horn; MDH) receives direct inputs from small diameter primary afferent fibers that predominantly transmit nociceptive information in the orofacial region. Recent studies indicate that reactive oxygen species (ROS) is involved in persistent pain, primarily through spinal mechanisms. In this study, we aimed to investigate the role of xanthine/xanthine oxidase (X/XO) system, a known generator of superoxide anion ($O_2{^-}$), on membrane excitability in the rat MDH neurons. For this, we used patch clamp recording and confocal imaging. An application of X/XO ($300{\mu}M/30mU$) induced membrane depolarization and inward currents. When slices were pretreated with ROS scavengers, such as phenyl N-tert-butylnitrone (PBN), superoxide dismutase (SOD), and catalase, X/XO-induced responses decreased. Fluorescence intensity in the DCF-DA and DHE-loaded MDH cells increased on the application of X/XO. An anion channel blocker, 4,4-diisothiocyanatostilbene-2,2-disulfonic acid (DIDS), significantly decreased X/XO-induced depolarization. X/XO elicited an inward current associated with a linear current-voltage relationship that reversed near -40 mV. X/XO-induced depolarization reduced in the presence of $La^{3+}$, a nonselective cation channel (NSCC) blocker, and by lowering the external sodium concentration, indicating that membrane depolarization and inward current are induced by influx of $Na^+$ ions. In conclusion, X/XO-induced ROS modulate the membrane excitability of MDH neurons, which was related to the activation of NSCC.