Neuromodulation Through Magnetic Fields Irradiation with AT-04 Improves Hyperalgesia in a Rat Model of Neuropathic Pain via Descending Pain Modulatory Systems and Opioid Analgesia.

Neuromodulation through magnetic fields irradiation with ait® (AT-04), a device that irradiates a mixed alternating magnetic fields (2 kHz and 83.3 MHz), has been shown to have high efficacy for fibromyalgia and low back pain in our previous clinical trials. The aim of this study was to elucidate the underlying analgesic mechanism of the AT-04 using the partial sciatic nerve ligation (PSL) model as an animal model of neuropathic pain. AT-04 was applied to PSL model rats with hyperalgesia and its pain-improving effect was verified by examining mechanical allodynia using the von Frey method. The results demonstrated a significant improvement in hyperalgesia in PSL model rats. We also examined the involvement of descending pain modulatory systems in the analgesic effects of AT-04 using antagonism by serotonin and noradrenergic receptor antagonists. These antagonists significantly reduced the analgesic effect of AT-04 on pain in PSL model rats by approximately 50%. We also measured the amount of serotonin and noradrenaline in the spinal fluid of PSL model rats using microdialysis during AT-04 treatment. Both monoamines were significantly increased by magnetic fields irradiation with AT-04. Furthermore, we evaluated the involvement of opioid analgesia in the analgesic effects of AT-04 using naloxone, the main antagonist of the opioid receptor, and found that it significantly antagonized the effects by approximately 60%. Therefore, the analgesic effects of AT-04 in PSL model rats involve both the endogenous pain modulation systems, including the descending pain modulatory system and the opioid analgesic system.

Acute spatial spread of NO-mediated potentiation during hindpaw ischaemia in mice.

KEY POINTS: Neuropathic pain spreads spatially beyond the injured sites, and the mechanism underlying the spread has been attributed to inflammation occurring in the spinal cord. However, the spatial spread of spinal/cortical potentiation induced by conduction block of the peripheral nerves can be observed prior to inflammation. In the present study, we found that spreading potentiation and hypersensitivity acutely induced by unilateral hindpaw ischaemia are nitric oxide (NO)-dependent and that NO is produced by ischaemia and quickly diffuses within the spinal cord. We also found that NO production induced by ischaemia is not observed in the presence of an antagonist for group II metabotropic glutamate receptors (mGluRs) and that neuronal NO synthase-positive dorsal horn neurons express group II mGluRs. These results suggest strongly that NO-mediated spreading potentiation in the spinal cord is one of the trigger mechanisms for neuropathic pain. ABSTRACT: Cortical/spinal responses to hindpaw stimulation are bilaterally potentiated by unilateral hindpaw ischaemia in mice. We tested the hypothesis that hindpaw ischaemia produces nitric oxide (NO), which diffuses in the spinal cord to induce spatially spreading potentiation. Using flavoprotein fluorescence imaging, we confirmed that the spreading potentiation in hindpaw responses was induced during ischaemia in the non-stimulated hindpaw. This spreading potentiation was blocked by spinal application of l-NAME, an inhibitor of NO synthase (NOS). Furthermore, no spreading potentiation was observed in neural NOS (nNOS) knockout mice. Spinal application of an NO donor was enough to induce cortical potentiation and mechanical hypersensitivity. The spatial distribution of NO during unilateral hindpaw ischaemia was visualized using 4-amino-5-methylamino-2',7'-difluorofluorescein (DAF-FM). An increase in fluorescence derived from the complex of DAF-FM with NO was observed on the ischaemic side of the spinal cord. A similar but smaller increase was also observed on the contralateral side. Somatosensory potentiation after hindpaw ischaemia is known to be inhibited by spinal application of LY354740, an agonist of group II metabotropic glutamate receptors (mGluRs). We confirmed that the spinal DAF-FM fluorescence increases during hindpaw ischaemia were not observed in the presence of LY354740. We also confirmed that approximately half of the nNOS-positive neurons in the superficial laminae of the dorsal horn expressed mGluR2 mRNA. These results suggest that disinhibition of mGluR2 produces NO which in turn induces a spreading potentiation in a wide area of the spinal cord. Such spreading, along with the consequent non-specific potentiation in the spinal cord, may trigger neuropathic pain.

Neurosteroid dehydroepiandrosterone sulphate enhances pain transmission in rat spinal cord dorsal horn.

BACKGROUND: The neurosteroid dehydroepiandrosterone sulphate (DHEAS) activates the sigma-1 receptor, inhibits gamma-aminobutyric acid A (GABAA) and glycine receptors, and induces hyperalgesic effects. Although its effects have been studied in various tissues of the nervous system, its synaptic mechanisms in nociceptive pathways remain to be elucidated. METHODS: The threshold of mechanical hypersensitivity and spontaneous pain behaviour was assessed using the von Frey test in adult male Wistar rats after intrathecal administration of DHEAS. We also investigated the effects of DHEAS on synaptic transmission in the spinal dorsal horn using slice patch-clamp electrophysiology. RESULTS: Intrathecally administered DHEAS elicited dose-dependent mechanical hyperalgesia and spontaneous pain behaviours (withdrawal threshold: saline; 51.0 [20.1] g, 3 µg DHEAS; 14.0 [7.8] g, P<0.01, 10 µg DHEAS; 6.9 [5.2] g, 15 min after administration, P<0.001). DHEAS at 100 µM increased the frequency of miniature postsynaptic currents in the rat dorsal spinal horn; this increase was extracellular Ca2+-dependent but not sigma-1 and N-methyl-d-aspartate receptor-dependent. DHEAS suppressed the frequency of miniature inhibitory postsynaptic currents in a GABAA receptor- and sigma-1 receptor-dependent manner. CONCLUSIONS: These results suggest that DHEAS participates in the pathophysiology of nociceptive synaptic transmission in the spinal cord by potentiation of glutamate release and inhibition of the GABAA receptor.

The endogenous agonist, ß-alanine, activates glycine receptors in rat spinal dorsal neurons.

ß-alanine is a structural analog of glycine and γ-aminobutyric acid (GABA) and is thought to be involved in the modulation of nociceptive information at the spinal cord. However, it is not known whether ß-alanine exerts its effect in substantia gelatinosa (SG) neurons of the spinal dorsal horn, where glycine and GABA play an important role in regulating nociceptive transmission from the periphery. Here, we investigated the effects of ß-alanine on inhibitory synaptic transmission in adult rat SG neurons using whole-cell patch-clamp. ß-alanine dose-dependently induced outward currents in SG neurons. Current-voltage plots revealed a reversal potential at approximately -70 mV, which was close to the equilibrium potential of Cl-. Pharmacological analysis revealed that ß-alanine activates glycine receptors, but not GABAA receptors. These results suggest that ß-alanine hyperpolarizes the membrane potential of SG neurons by activating Cl- channels through glycine receptors. Our findings raise the possibility that ß-alanine may modulate pain sensation through glycine receptors.

Acetaminophen Metabolite N-Acylphenolamine Induces Analgesia via Transient Receptor Potential Vanilloid 1 Receptors Expressed on the Primary Afferent Terminals of C-fibers in the Spinal Dorsal Horn.

BACKGROUND: The widely used analgesic acetaminophen is metabolized to N-acylphenolamine, which induces analgesia by acting directly on transient receptor potential vanilloid 1 or cannabinoid 1 receptors in the brain. Although these receptors are also abundant in the spinal cord, no previous studies have reported analgesic effects of acetaminophen or N-acylphenolamine mediated by the spinal cord dorsal horn. We hypothesized that clinical doses of acetaminophen induce analgesia via these spinal mechanisms. METHODS: We assessed our hypothesis in a rat model using behavioral measures. We also used in vivo and in vitro whole cell patch-clamp recordings of dorsal horn neurons to assess excitatory synaptic transmission. RESULTS: Intravenous acetaminophen decreased peripheral pinch-induced excitatory responses in the dorsal horn (53.1 ± 20.7% of control; n = 10; P < 0.01), while direct application of acetaminophen to the dorsal horn did not reduce these responses. Direct application of N-acylphenolamine decreased the amplitudes of monosynaptic excitatory postsynaptic currents evoked by C-fiber stimulation (control, 462.5 ± 197.5 pA; N-acylphenolamine, 272.5 ± 134.5 pA; n = 10; P = 0.022) but not those evoked by stimulation of Aδ-fibers. These phenomena were mediated by transient receptor potential vanilloid 1 receptors, but not cannabinoid 1 receptors. The analgesic effects of acetaminophen and N-acylphenolamine were stronger in rats experiencing an inflammatory pain model compared to naïve rats. CONCLUSIONS: Our results suggest that the acetaminophen metabolite N-acylphenolamine induces analgesia directly via transient receptor potential vanilloid 1 receptors expressed on central terminals of C-fibers in the spinal dorsal horn and leads to conduction block, shunt currents, and desensitization of these fibers.

Hydrogen peroxide modulates synaptic transmission in ventral horn neurons of the rat spinal cord.

KEY POINTS: Excessive production of reactive oxygen species (ROS) is implicated in many central nervous system disorders; however, the physiological role of ROS in spinal ventral horn (VH) neurons remains poorly understood. We investigated how pathological levels of H2O2, an abundant ROS, regulate synaptic transmission in VH neurons of rats using a whole-cell patch clamp approach. H2O2 increased the release of glutamate and GABA from presynaptic terminals. The increase in glutamate release involved N-type voltage-gated calcium channels (VGCCs), ryanodine receptors (RyRs), and inositol trisphosphate receptors (IP3 Rs); the increase in GABA release, which inhibited glutamatergic transmission, involved IP3 R. Inhibiting N-type VGCCs and RyRs attenuates excitotoxicity resulting from increased glutamatergic activity while preserving the neuroprotective effects of GABA, and may represent a novel strategy for treating H2O2-induced motor neuron disorders resulting from trauma or ischaemia-reperfusion injury. Excessive production of reactive oxygen species (ROS) is a critical component of the cellular and molecular pathophysiology of many central nervous system (CNS) disorders, including trauma, ischaemia-reperfusion injury, and neurodegenerative diseases. Hydrogen peroxide (H2O2), an abundant ROS, modulates synaptic transmission and contributes to neuronal damage in the CNS; however, the pathophysiological role of H2O2 in spinal cord ventral horn (VH) neurons remains poorly understood, despite reports that these neurons are highly vulnerable to oxidative stress and ischaemia. This was investigated in the present study using a whole-cell patch clamp approach in rats. We found that exogenous application of H2O2 increased the release of glutamate from excitatory presynaptic terminals and γ-aminobutyric acid (GABA) from inhibitory presynaptic terminals. The increase of glutamate release was induced in part by an increase in Ca(2+) influx through N-type voltage-gated calcium channels (VGCCs) as well as by ryanodine receptor (RyR)- and inositol trisphosphate receptor-mediated Ca(2+) release from the endoplasmic reticulum (ER). In inhibitory presynaptic neurons, increased IP3 R-mediated Ca(2+) release from the ER increased GABAergic transmission, which served to rescue VH neurons from excessive release of glutamate from presynaptic terminals. These findings indicate that inhibiting N-type VGCCs or RyRs may attenuate excitotoxicity resulting from increased glutamatergic activity while preserving the neuroprotective effects of GABA, and may therefore represent a novel and targeted strategy for preventing and treating H2O2-induced motor neuron disorders.

The mu opioid receptor activation does not affect ischemia-induced agonal currents in rat spinal ventral horn.

PURPOSE: Opioid-induced spastic paraplegia after transient spinal cord ischemia during aortic surgery has been reported. Opioids modulate neurotransmission through mu (µ) opioid receptors (MORs) in the spinal ventral horn. However, their effects during ischemic insult are not understood. METHODS: The effects of the selective µ agonist [D-Ala(2),-N-Me-Phe(4), Gly(5)-ol]enkephalin (DAMGO) on ischemia-induced agonal currents were examined in the spinal lamina IX neurons of neonatal rats by using the whole-cell patch-clamp technique. Ischemia was simulated in vitro by oxygen/glucose deprivation. RESULTS: DAMGO (1 µM) produced outward currents in ~60% of spinal lamina IX neurons at a holding potential of -70 mV. Superfusion with ischemia-simulating medium elicited an agonal current. The latency was 457 ± 18 s. Despite its neuromodulatory effects, DAMGO did not significantly change the latencies of the agonal currents with (440 ± 23 s) or without (454 ± 33 s) DAMGO-induced currents. CONCLUSION: Activation of MORs does not influence ongoing ischemia-induced neuronal death. Our findings indicate that MOR agonist administration should be suitable as an anesthetic during aortic surgery.

[Efficacy of repeated subcostal transversus abdominis plane blocks with 0.2% lidocaine via 18-gauge intravenous catheters for patients undergoing abdominal aortic aneurism surgery].

BACKGROUND: There is an increasing number of patients scheduled for abdominal aortic aneurysm resection in whom epidural anesthesia cannot be performed because of concomitant antiplatelet/anticoagulant therapy. Instead of epidural anesthesia for postoperative analgesia in such patients it is possible to use repeated bilateral subcostal transversus abdominis plane (TAP) blocks. METHODS: Four patients receiving antiplatelet/anticoagulant therapy for abdominal aortic aneurysm resection under general anesthesia were studied. After the completion of surgery and before emergence from anesthesia 18-gauge intravenous catheters were inserted bilaterally into subcostal TAP and 100 ml (50 ml on each side) of 0.2% lidocaine with 1/500,000 epinephrine were injected via the catheters twice daily until the second postoperative day. Pain intensity was assessed using a 0-10 numerical rating scale at rest and during movement, before and after each block. RESULTS: Numerical pain ratings at rest and during movement decreased after each block, and good analgesia was obtained. No complications such as nausea, vomiting or infection were observed in the postoperative period. CONCLUSIONS: These findings suggest that repeated bilateral subcostal TAP blocks with 0.2% lidocaine performed via 18-gauge intravenous catheters provide good postoperative analgesia after abdominal aortic aneurysm resection.

No evidence for the development of acute analgesic tolerance during and hyperalgesia after prolonged remifentanil administration in mice.

BACKGROUND: Acute opioid tolerance (AOT) and opioid-induced hyperalgesia (OIH) are undesirable effects of opioids that have been reported in both animals and humans. However, the development of AOT and OIH in cases of potent, short-acting µ-opioid receptor agonist remifentanil administration remains controversial. It has been suggested that the emergence of AOT and OIH by remifentanil could be dose and infusion duration dependent, i.e., low dose and short infusions may lead to negative results. In this study, we determined whether AOT and OIH could be elicited by prolonged, continuous administration of remifentanil at maximally tolerable doses in C57BL/6 mice. RESULTS: The analgesic effects of continuously administered remifentanil [by short (1 h) and prolonged (4 h) intraperitoneal infusions] were studied. These experiments involved repeated measurements of thermal thresholds during remifentanil administration. Therefore, particular attention was paid to prevent cumulative tissue injury, which could mimic pronociceptive effects of remifentanil. To exclude the possibility of pseudoAOT during infusion, we used brief cooling of all ipsilateral hindpaws that exhibited analgesic response. Thermal thresholds remained steadily elevated over a 1-h period during continuous administration at infusion rates of 120, 180, and 240 mg/kg/h, which indicated no AOT development. To exclude the possibility of pseudoOIH after infusion, intact contralateral hindpaws were used for all postinfusion threshold measurements. Thermal thresholds at each infusion rate returned to the baseline values within 15 min after the termination of the administration. They did not decrease below the baseline values during 1 h following infusion, which indicated no OIH development. Similar threshold dynamics were also observed for thermal and mechanical testing modalities in animals infused at 120 mg/kg/h for 4 h as well as in animals with rapidly attained and maintained maximum analgesia for 3 h. CONCLUSIONS: These results suggest that neither intra-infusion AOT nor postinfusion OIH develops in mice receiving continuous remifentanil when the possibility of cumulative tissue injury mimicking AOT or OIH is carefully avoided.

[Antagonistic action of local anesthetics except at the sodium channel].

Local anesthetics block impulses in peripheral nerves through the inhibition of voltage-gated sodium channels. However, the effects of local anesthetics may be more complex. It has been reported that local anesthetics not only block the impulses in nerve roots, but could also interact with many membrane phospholipids and proteins, including various receptors, and thereby affect a variety of cellular activities. In fact, there is evidence indicating that local anesthetics could inhibit NMDA-induced glutamatergic transmission in the spinal cord. Therefore, NMDA receptor antagonism of local anesthetics may have the possibility to prevent the patients from developing chronic pain. Furthermore, local anesthetics might have the possibility to prevent cancer cell proliferation like NMDA receptor antagonists. Local anesthetics have also been reported to have an inhibitory effect on other ion channel-coupled receptors, including 5-HT3, GABA, glycine, and nicotinic ACh receptors. Recently, the interaction between local anesthetics and TRPV1 agonist has attracted the attention because they raise the possibilities of producing analgesic effect without affecting motor or other sensory functions. The effects of local anesthetics may have some aspects which have not been clarified. Further investigations will be required to fully understand the actions of local anesthetics.

Milnacipran inhibits glutamatergic N-methyl-D-aspartate receptor activity in spinal dorsal horn neurons.

BACKGROUND: Antidepressants, which are widely used for treatment of chronic pain, are thought to have antinociceptive effects by blockade of serotonin and noradrenaline reuptake. However, these drugs also interact with various receptors such as excitatory glutamatergic receptors. Thermal hyperalgesia was induced by intrathecal injection of NMDA in rats. Paw withdrawal latency was measured after intrathecal injection of antidepressants. The effects of antidepressants on the NMDA and AMPA-induced responses were examined in lamina II neurons of rat spinal cord slices using the whole-cell patch-clamp technique. The effects of milnacipran followed by application of NMDA on pERK activation were also investigated in the spinal cord. RESULTS: Intrathecal injection of milnacipran (0.1 µmol), but not citalopram (0.1 µmol) and desipramine (0.1 µmol), followed by intrathecal injection of NMDA (1 µg) suppressed thermal hyperalgesia. Milnacipran (100 µM) reduced the amplitude of NMDA (56 ± 3 %, 64 ± 5 % of control)-, but not AMPA (98 ± 5 %, 97 ± 5 % of control)-mediated currents induced by exogenous application and dorsal root stimulation, respectively. Citalopram (100 µM) and desipramine (30 µM) had no effect on the amplitude of exogenous NMDA-induced currents. The number of pERK-positive neurons in the group treated with milnacipran (100 µM), but not citalopram (100 µM) or desipramine (30 µM), followed by NMDA (100 µM) was significantly lower compared with the NMDA-alone group. CONCLUSIONS: The antinociceptive effect of milnacipran may be dependent on the drug's direct modulation of NMDA receptors in the superficial dorsal horn. Furthermore, in addition to inhibiting the reuptake of monoamines, glutamate NMDA receptors are also important for analgesia induced by milnacipran.

Effect of xenon on excitatory and inhibitory transmission in rat spinal ventral horn neurons.

BACKGROUND: The minimum alveolar concentration is determined in the spinal cord rather than in the brain. Xenon inhibits glutamatergic excitatory synaptic transmission in the dorsal horn neurons. However, its actions in the ventral horn neurons have not been investigated. METHODS: The effects of 50 or 75% xenon on excitatory and inhibitory synaptic transmission were examined in the spinal lamina IX neurons of neonatal rats by using a whole cell patch clamp technique. RESULTS: Fifty percent xenon inhibited the α-amino-3-hydroxy-5-methyl-4-isoxazole-4-propionic acid-induced currents (amplitudes = 72 ± 9% and integrated area = 73 ± 13% of the control values), and α-amino-3-hydroxy-5-methyl-4-isoxazole-4-propionic acid receptor-mediated electrically evoked excitatory postsynaptic currents (amplitudes = 69 ± 13% of the control values). Seventy-five percent xenon similarly inhibited α-amino-3-hydroxy-5-methyl-4-isoxazole-4-propionic acid-induced currents. However, xenon had no effect on the N-methyl-D-aspartate-induced currents or N-methyl-D-aspartate receptor-mediated electrically evoked excitatory postsynaptic currents. Xenon decreased the amplitude, but not the frequency, of miniature excitatory postsynaptic currents. There were no discernible effects on the currents induced by γ-aminobutyric acid or glycine or on miniature inhibitory postsynaptic currents. CONCLUSIONS: Xenon inhibits α-amino-3-hydroxy-5-methyl-4-isoxazole-4-propionic acid receptor-mediated glutamatergic excitatory transmission in the spinal lamina IX neurons via a postsynaptic mechanism. In contrast, there are no substantial effects on N-methyl-D-aspartate receptor-mediated or inhibitory synaptic transmission. The suppressive effects on excitatory synaptic transmission in the ventral horn neurons partly account for the mechanism behind xenon's ability to produce immobility in response to noxious stimuli and to determine the minimum alveolar concentration.

The mu opioid receptor modulates neurotransmission in the rat spinal ventral horn.

BACKGROUND: Opioids inhibit excitatory neurotransmission and produce antinociception through µ opioid receptors (MORs). Although MORs are expressed in the spinal ventral horn, their functions and effects are largely unknown. Therefore, we examined the neuromodulatory effects of µ opioids in spinal lamina IX neurons at the cellular level. METHODS: The effects of the selective µ agonist [D-Ala(2),-N-Me-Phe(4), Gly(5)-ol]enkephalin (DAMGO) on synaptic transmission were examined in spinal lamina IX neurons of neonatal rats using the whole-cell patch-clamp technique. RESULTS: DAMGO produced outward currents in 56% of the lamina IX neurons recorded, with a 50% effective concentration of 0.1 µM. Analysis of the current-voltage relationship revealed a reversal potential of approximately -86 mV. These currents were not blocked by tetrodotoxin but were inhibited by Ba(2+) or a selective µ antagonist. Moreover, the currents were suppressed by the addition of Cs(+) and tetraethylammonium or guanosine 5'-[ß-thio]diphosphate trilithium salt to the pipette solution. In addition, DAMGO decreased the frequency of spontaneous excitatory and inhibitory postsynaptic currents, and these effects were unaltered by treatment with tetrodotoxin. CONCLUSION: Our results suggest that DAMGO hyperpolarizes spinal lamina IX neurons by G protein-mediated activation of K(+) channels after activation of MORs. Furthermore, activation of MORs on presynaptic terminals reduces both excitatory and inhibitory transmitter release. Although traditionally opioids are not thought to affect motor function, the present study documents neuromodulatory effects of µ opioids in spinal lamina IX neurons, suggesting that MORs can influence motor activity.

Zaltoprofen inhibits bradykinin-mediated enhancement of glutamate receptor activity in substantia gelatinosa neurons.

BACKGROUND: Zaltoprofen, a propionic acid derivative of nonsteroidal anti-inflammatory drugs, has been proposed to inhibit the nociception mediated by bradykinin. Here, I attempted to clarify the molecular mechanisms underlying the blocking effect of zaltoprofen on bradykinin-mediated enhancement of excitatory glutamatergic transmission in the superficial dorsal horn of the spinal cord. METHODS: The effects of zaltoprofen on the response to exogenous administration of α-amino-3-hydroxy-5-methyl-4-isoxazole-4-propionic acid (AMPA) currents were examined in lamina II neurons of adult rat spinal cord slices using the whole-cell patch-clamp technique. RESULTS: AMPA currents were significantly enhanced by preapplication of bradykinin (10 µM). However, zaltoprofen (1, 10 µM) and a nonselective cyclooxygenase (COX)-1 and COX-2 inhibitor, ibuprofen, blocked the bradykinin-mediated enhancing effect. The inhibitory effect of ibuprofen, but not zaltoprofen, was removed by adding prostaglandin E(2). Furthermore, the inhibitory effect of zaltoprofen was removed in the presence of protein kinase C (PKC) activator, whereas the effect of zaltoprofen was still present in the presence of phospholipase C activator. CONCLUSIONS: These findings suggest that the antinociceptive effect of zaltoprofen may block the augmenting effect of bradykinin on AMPA currents through inhibition of protein kinase C activation, without affecting COX in the superficial dorsal horn.

Reduction of spinal cord ischemia/reperfusion injury with simvastatin in rats.

BACKGROUND: Surgery of the thoracic or thoracoabdominal aorta may cause spinal cord ischemia and subsequent paraplegia. However, conventional strategies for preventing paraplegia due to spinal cord ischemia provide insufficient protection and cause additional side effects. We hypothesized that simvastatin, a drug recently shown to be neuroprotective against brain ischemia/reperfusion, would be neuroprotective in a rat spinal cord ischemia/reperfusion model. METHODS: Rats were randomly assigned to simvastatin, vehicle, or sham-surgery (sham) groups (n = 6 per group). Simvastatin (10 mg/kg) or vehicle was administered subcutaneously once daily for 7 days before aortic balloon occlusion, and once at 24 hours after reperfusion. Spinal cord ischemia was induced by balloon inflation of a 2F Fogarty catheter in the thoracic aorta, and the proximal mean arterial blood pressure was maintained at 40 mm Hg for 12 minutes. The sham group received the same operation without inflation of the balloon. Ischemic injury was assessed by hindlimb motor function using the Motor Deficit Index score at 6 to 48 hours after ischemic reperfusion, and histological assessment of the spinal cord was performed 48 hours after reperfusion. RESULTS: The Motor Deficit Index scores at 24 and 48 hours after reperfusion were significantly improved in the simvastatin group compared with the vehicle group (P = 0.021 and P = 0.023, respectively). Furthermore, there were significantly more normal motor neurons in the simvastatin group than in the vehicle group (P = 0.037). The percentage area of white matter vacuolation was significantly smaller in the simvastatin group than in the vehicle group (P = 0.030). CONCLUSIONS: Simvastatin treatment can attenuate hindlimb motor dysfunction and histopathological changes in spinal cord ischemia/reperfusion injury in rats.

[Case of airway management by laryngeal mask airway for a child with laryngeal web undergoing adenotonsillectomy].

We report a case of airway management by laryngeal mask airway (LMA) for a 4-year-old boy with laryngeal web undergoing adenotonsillectomy. Although the patient had no symptoms of airway stenosis, we detected a subglottic laryngeal web during the preoperative examination. The opening orifice of the laryngeal web was estimated to be too small for intubation, and we chose to manage the airway with LMA and spontaneous respiration. Using the LMA and Davis-Crowe mouth gag, we were able to provide the surgeon with the same exposure as with intubation while effectively managing the airway.

[Anesthetic mechanisms in the spinal cord].

The essential elements of anesthesia are : hypnosis, amnesia, analgesia, immobility, and inhibition of untoward reflexes. The spinal cord is responsible for the latter three. Suppression of excitatory transmission and stimulation of inhibitory transmission are the anesthetic mechanisms in the spinal cord. Each anesthetic, however, has a unique effect on the transmission systems in the spinal cord. Some exclusively suppress excitatory transmission or stimulate inhibitory transmission, and others have a dual effect. The minimum alveolar/anesthetic concentration (MAC) is spinally mediated. Furthermore neurons in the ventral horn of spinal cord seem to be more depressed by anesthetics than neurons in the dorsal horn of the spinal cord. The ventral spinal cord also has relation to spinal cord ischemia. Investigation of the neuroprotective effect against spinal ischemia as well as the anesthetic effect in the ventral spinal cord is a very important subject of research.

Serotonin Plays a Key Role in the Development of Opioid-Induced Hyperalgesia in Mice.

Opioid usage for pain therapy is limited by its undesirable clinical effects, including paradoxical hyperalgesia, also known as opioid-induced hyperalgesia (OIH). However, the mechanisms associated with the development and maintenance of OIH remain unclear. Here, we investigated the effect of serotonin inhibition by the 5-HT3 receptor antagonist, ondansetron (OND), as well as serotonin deprivation via its synthesis inhibitor para-chlorophenylalanine, on mouse OIH models, with particular focus on astrocyte activation. Co-administering of OND and morphine, in combination with serotonin depletion, inhibited mechanical hyperalgesia and astrocyte activation in the spinal dorsal horn of mouse OIH models. Although previous studies have suggested that activation of astrocytes in the spinal dorsal horn is essential for the development and maintenance of OIH, herein, treatment with carbenoxolone (CBX), a gap junction inhibitor that suppresses astrocyte activation, did not ameliorate mechanical hyperalgesia in mouse OIH models. These results indicate that serotonin in the spinal dorsal horn, and activation of the 5-HT3 receptor play essential roles in OIH induced by chronic morphine, while astrocyte activation in the spinal dorsal horn serves as a secondary effect of OIH. Our findings further suggest that serotonergic regulation in the spinal dorsal horn may be a therapeutic target of OIH. PERSPECTIVE: The current study revealed that the descending serotonergic pain-facilitatory system in the spinal dorsal horn is crucial in OIH, and that activation of astrocytes is a secondary phenotype of OIH. Our study offers new therapeutic targets for OIH and may help reduce inappropriate opioid use.

Xenon inhibits excitatory but not inhibitory transmission in rat spinal cord dorsal horn neurons.

BACKGROUND: The molecular targets for the promising gaseous anaesthetic xenon are still under investigation. Most studies identify N-methyl-D-aspartate (NMDA) receptors as the primary molecular target for xenon, but the role of alpha-amino-3-hydroxy-5-methyl-4-isoxazole-4-propionic acid (AMPA) receptors is less clear. In this study we evaluated the effect of xenon on excitatory and inhibitory synaptic transmission in the superficial dorsal horn of the spinal cord using in vitro patch-clamp recordings from rat spinal cord slices. We further evaluated the effects of xenon on innocuous and noxious stimuli using in vivo patch-clamp method. RESULTS: In vitro, xenon decreased the amplitude and area under the curve of currents induced by exogenous NMDA and AMPA and inhibited dorsal root stimulation-evoked excitatory postsynaptic currents. Xenon decreased the amplitude, but not the frequency, of miniature excitatory postsynaptic currents. There was no discernible effect on miniature or evoked inhibitory postsynaptic currents or on the current induced by inhibitory neurotransmitters. In vivo, xenon inhibited responses to tactile and painful stimuli even in the presence of NMDA receptor antagonist. CONCLUSIONS: Xenon inhibits glutamatergic excitatory transmission in the superficial dorsal horn via a postsynaptic mechanism. There is no substantial effect on inhibitory synaptic transmission at the concentration we used. The blunting of excitation in the dorsal horn lamina II neurons could underlie the analgesic effect of xenon.

Bupivacaine inhibits glutamatergic transmission in spinal dorsal horn neurons.

BACKGROUND: The local anesthetic bupivacaine is thought not only to block sodium channels but also to interact with various receptors. Here, the authors focus on excitatory glutamatergic transmission in the superficial dorsal horn of the spinal cord with respect to its importance for nociceptive processing. METHODS: The effects of bupivacaine on the response to exogenous administration of N-methyl-D-aspartate (NMDA) receptor agonists were examined in lamina II neurons of adult rat spinal cord slices using the whole-cell patch-clamp technique. RESULTS: Bupivacaine (0.5, 2 mm) dose-dependently reduced the peak amplitudes of exogenous NMDA-induced currents. However, this inhibitory effect of bupivacaine (2 mm) was not blocked by the presence of tetrodotoxin, a sodium channel blocker, or La(3+), a voltage-gated Ca+ channel blocker, and was unaffected by changes in pH conditions. Moreover, intrapipette guanosine-5'-O-(2-thiodiphosphate) (1 mm), a G-protein inhibitor, did not block the reduction of NMDA current amplitudes by bupivacaine. Similarly, lidocaine, ropivacaine, and mepivacaine also reduced the amplitudes of NMDA-induced currents. CONCLUSIONS: These findings raise the possibility that the antinociceptive effect of bupivacaine may be due to direct modulation of NMDA receptors in the superficial dorsal horn. In addition to voltage-gated sodium channels, glutamate NMDA receptors are also important for analgesia induced by local anesthetics.