Takeshi Tanimoto

The Nippon Dental University, Tokyo, Tokyo-to, Japan

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Publications (41)126.17 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: The aim of the present study was to determine whether acetazolamide (AZ) contributes to the inhibition of the fast inactivating transient K+ current (IA) in adult rat nodose ganglion (NG) neurons. We have previously shown that pretreatment with either AZ or 4-AP attenuated or blocked the CO2-induced inhibition of slowly adapting pulmonary stretch receptors in in vivo experiments. The patch-clamp experiments were performed by using the isolated NG neurons. In addition to this, the RT-PCR of mRNA and the expression of voltagegated K+ (Kv) 1.4, Kv 4.1, Kv 4.2, and Kv 4.3 channel proteins from nodose ganglia were examined. We used NG neurons sensitive to the 1 mM AZ application. The application of 1 mM AZ inhibited the IA by approximately 27% and the additional application of 4-AP (1 mM) further inhibited IA by 48%. The application of 0.1 μM α-dendrotoxin (α-DTX), a slow inactivating transient K+ current (ID) blocker, inhibited the baseline IA by approximately 27%, and the additional application of 1 mM AZ further decreased the IA by 51%. In current clamp experiments, AZ application (1 mM) increased the number of action potentials due to the decreased duration of the depolarizing phase of action potentials and/or due to a reduction in the resting membrane potential. Four voltage-gated K+ channel proteins were present, and most (80–90%) of the four Kv channels immunoreactive neurons showed the co-expression of carbonic anhydrase-II (CA-II) immunoreactivity. These results indicate that the application of AZ causes the reduction in IA via the inhibition of four voltagegated K+ channel (Kv) proteins without affecting ID.
    CNS & Neurological Disorders - Drug Targets (Formerly Current Drug Targets - CNS & Neurological Disorders) 01/2011; 17:66-79. · 3.77 Impact Factor
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    ABSTRACT: The aim of the present study was to determine whether acetazolamide (AZ) contributes to the inhibition of the fast inactivating transient K(+) current (I(A) ) in adult rat nodose ganglion (NG) neurons. We have previously shown that pretreatment with either AZ or 4-AP attenuated or blocked the CO(2) -induced inhibition of slowly adapting pulmonary stretch receptors in in vivo experiments. The patch-clamp experiments were performed by using the isolated NG neurons. In addition to this, the RT-PCR of mRNA and the expression of voltage-gated K(+) (Kv) 1.4, Kv 4.1, Kv 4.2, and Kv 4.3 channel proteins from nodose ganglia were examined. We used NG neurons sensitive to the 1 mM AZ application. The application of 1 mM AZ inhibited the I(A) by approximately 27% and the additional application of 4-AP (1 mM) further inhibited I(A) by 48%. The application of 0.1 μM α-dendrotoxin (α-DTX), a slow inactivating transient K(+) current (I(D) ) blocker, inhibited the baseline I(A) by approximately 27%, and the additional application of 1 mM AZ further decreased the I(A) by 51%. In current clamp experiments, AZ application (1 mM) increased the number of action potentials due to the decreased duration of the depolarizing phase of action potentials and/or due to a reduction in the resting membrane potential. Four voltage-gated K(+) channel proteins were present, and most (80-90%) of the four Kv channels immunoreactive neurons showed the co-expression of carbonic anhydrase-II (CA-II) immunoreactivity. These results indicate that the application of AZ causes the reduction in I(A) via the inhibition of four voltage-gated K(+) channel (Kv) proteins without affecting I(D).
    CNS Neuroscience & Therapeutics 03/2010; 17(1):66-79. · 4.46 Impact Factor
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    ABSTRACT: Voltage-gated K+ (Kv) channels are one of the important physiological regulators of the membrane potentials in excitable cells, including sensory ganglion neurons. The aim of the present study was to investigate whether temporomandibular joint (TMJ) inflammation alters expression of Kv channel subtype 1.4 (Kv1.4) of trigeminal ganglion (TRG) neurons innervating TMJ relating allodynia (pain caused by normally innoxious stimulation), by using both behavioral and immunohistochemical techniques. TMJ inflammation was induced by injection of Complete Freund's Adjuvant (CFA) into the rat TMJ. The threshold for escape from mechanical stimulation applied to the orofacial area in TMJ inflamed rats was significantly lower than that in naïve rats. TMJ afferents were identified by fluorogold (FG) labeling. The mean numbers of Kv1.4-/neurofilament (NF) 200(myelinated fiber marker) positive- and negative-immunoreactivities FG-labeled small-/medium-diameter TRG neurons in inflamed rats were significantly decreased when compared with those in the naïve rats. These findings suggest that TMJ inflammation reduces the expression of Kv1.4 subunits in the small-/medium sized (Adelta-/C-) TRG neurons and this may contribute to trigeminal inflammatory allodynia in TMJ disorder. These results lead us to suggest that Kv channel openers may be a potential therapeutic agents for prevention of mechanical allodynia.
    European journal of pain (London, England) 03/2008; 12(2):189-95. · 3.37 Impact Factor
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    ABSTRACT: Peripheral nerve injury activates satellite cells to produce interleukin 1beta (IL-1beta) which mediates inflammation and hyperalgesia. This study investigated the hypothesis that activation of satellite glial cells modulates the excitability of trigeminal ganglion (TRG) neurons via IL-1beta following inflammation. Inflammation was induced by injection of complete Freund's adjuvant (CFA) into the whisker pad area. The threshold for escape from mechanical stimulation applied to the whisker pad in inflamed rats was significantly lower than that in control. Two days post-CFA injection, the mean percentage of TRG neurons encircled by glial fibrillary acidic protein (GFAP)-/IL-1beta-immunoreactive cells was significantly increased compared to controls. GFAP and IL-1beta immunoreactivities were coexpressed in the same cells. Fluorogold (FG) labeling identified the site of inflammation. The number of FG-labeled IL-receptor type I (IL-1RI) TRG neurons in inflamed rats was significantly greater than in controls. In FG-labeled small TRG neurons, the size of IL-1beta (1 nM) induced-depolarization in inflamed rats was larger than in controls. IL-1beta application significantly increased firing rates evoked by depolarizing pulses in the neurons of inflamed rats, compared to controls. The response to IL-1beta was abolished by treatment with the IL-1RI antagonist. These results suggest that activation of satellite glial cells modulates the excitability of small-diameter TRG neurons via IL-1beta following inflammation, and that the upregulation of IL-1RI in the soma may contribute to the mechanism underlying inflammatory hyperalgesia. Therefore IL-1beta blockers are potential therapeutic agents for prevention of trigeminal hyperalgesia.
    Pain 06/2007; 129(1-2):155-66. · 5.64 Impact Factor
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    ABSTRACT: We examined whether 8-bromo-cAMP (8-Br-cAMP)-induced modification of tetrodotoxin-resistant (TTX-R) sodium current in neonatal rat nodose ganglion neurons is mediated by the activation of protein kinase A (PKA) and/or protein kinase C (PKC). In 8-Br-cAMP applications ranging from 0.001 to 1.0mM, 8-Br-cAMP at 0.1mM showed a maximal increase in the peak TTX-R Na(+) (Nav1.8) current and produced a hyperpolarizing shift in the conductance-voltage (G-V) curve. The PKC inhibitor bisindolylmaleimide Ro-31-8425 (Ro-31-8425, 0.5microM) decreased the peak Nav 1.8 current. The Ro-31-8425-induced modulation of the G(V)(1/2) baseline (a percent change in G at baseline V1/2) was not affected by additional 8-Br-cAMP application (0.1mM). The maximal increase in Nav 1.8 currents was seen at 0.1microM after the application of a PKC activator, phorbol 12-myristate 13-acetate (PMA) and forskolin. The PMA-induced increase in Nav 1.8 currents was not significantly affected by additional 0.1mM 8-Br-cAMP application. Intracellular application of a PKA inhibitor, protein kinase inhibitor (PKI, 0.01mM), inhibited the baseline Nav 1.8 current, significantly attenuated the 8-Br-cAMP-and PMA-induced increase in the peak Nav 1.8 current, and caused a significant increase in the slope factor of the inactivation curve. The PKI application at a higher concentration (0.5mM) greatly inhibited the PMA (0.1microM)-induced increase in the peak Nav 1.8 current amplitude and further enhanced the Ro-31-8425-induced decrease in the current. These results suggest that the 8-Br-cAMP-induced increase in Nav 1.8 currents may be mediated by activation of both PKA and PKC.
    Neuropharmacology 04/2007; 52(3):904-24. · 4.11 Impact Factor
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    ABSTRACT: The effect of iontophoretic application of the 5-HT3 receptor agonist, phenylbiguanide (PBG), on the excitation of the trigeminal spinal nucleus oralis (TSNO) neurons to tooth-pulp (TP) stimulation was examined. The PBG application inhibited the TP-evoked TSNO neuronal excitation, and this inhibition was completely blocked by co-application of a GABAA receptor antagonist, bicuculline. The results suggest that the activation of 5-HT3 receptors elicits GABA release in the TSNO.
    Brain Research 10/2006; 1109(1):70-3. · 2.88 Impact Factor
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    ABSTRACT: The aim of the present study was to determine whether there is a convergence of inputs from tooth pulp (TP) and the superior sagittal sinus (SSS) on rat C1 spinal neurons, and to examine the effects of iontophoretically applied N-methyl-D: -aspartate (NMDA) and non-NMDA receptor antagonists on the SSS-evoked activity of C1 neurons. Extracellular single unit-recordings were made from 20 C1 units responding to TP electrical stimulation with a constant temporal relationship to a digastric electromyogram signal, using a multibarrel electrode in pentobarbital-anesthetized rats. Ninety percent of C1 neurons (18/20) responding to TP stimulation also responded to the SSS stimulation. These neurons were considered to be SSS-afferent inputs from Adelta-fibers (5.8 +/- 0.6 m/s; n = 18), based on the calculation of nerve conduction velocity. After the iontophoretic application (30, 50, and 70 nA) of an NMDA receptor blocker (5R-10S)-(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d] cycloheptene-5,10-imine hydrogen maleate (MK801) or a non-NMDA receptor blocker (6-cyano-7-nitroquinoxaline-2,3-dione) (CNQX), the mean number of spikes responding to the SSS stimulation significantly decreased (30, 50, and 70 nA; P < 0.05). These results suggest that there is a convergence of inputs from SSS and TP afferents on C1 neurons; it is possible that both NMDA and non-NMDA receptors located on C1 neurons may be targets for the treatment of the trigeminal referred pain associated with migraine.
    Odontology 10/2006; 94(1):22-8. · 1.58 Impact Factor
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    ABSTRACT: The aim of the present study was to test the hypothesis that activation of α2-adrenoreceptors modulates the excitability of C1 neurons having convergent inputs from both the tooth pulp (TP) and the superior sagittal sinus (SSS), by using the microiontophoretic techniques of drug application and immunohistochemical approaches. Extracellular single-unit recordings were made from 38 C1 neurons responding to electrical stimulation of TP under pentobarbital-anesthetized rats. Seventy-one percent of C1 neurons (27/38) that responded to TP stimulation also responded to electrical stimulation of the SSS. In these neurons, l-glutamate-evoked C1 neuronal discharge firings were increased in a dose-dependent manner. The mean glutamate-evoked firing rates were dose-dependently inhibited after microiontophoretic application of clonidine (α2-adrenoreceptor/imidazoline I1 receptor agonist). The inhibition of glutamate-evoked C1 mean firings by clonidine was antagonized by the co-application of idazoxan (α2-adrenoreceptor/imidazoline I2 receptor antagonist), yohimbine (α2-adrenoreceptor) but not the α1-adrenoreceptor antagonist, prazosin with affinity for α2B- and α2C-adrenoreceptors. The mean spontaneous discharge frequencies were significantly inhibited by the microiontophoretic application of clonidine and this inhibition was reversed by the co-application of idazoxan, yohimbine. Microiontophoresis of clonidine also resulted in a reduction of TP-/SSS-evoked activity and this effect was reversed by the co-application of yohimbine. Immunoreactivity for α2A-adrenoreceptor was found in the superficial layers of I–III in the C1 region. These results suggest that α2-adrenoreceptor agonist clonidine inhibits the excitability of C1 neurons having convergent inputs from TP and SSS afferents, and that the activation of α2A-adrenoreceptors onto C1 dorsal horn neurons may contribute as a useful therapeutic target for the alleviation of trigeminal referred pain associated with migraine and tooth pain.
    Experimental Brain Research 09/2006; 174(2):210-220. · 2.22 Impact Factor
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    ABSTRACT: The aim of the present study was to investigate the effect of temporomandibular joint inflammation on the excitability of trigeminal root ganglion neurons innervating the temporomandibular joint using a perforated patch-clamp technique. Inflammation was induced by injection of complete Freund's adjuvant into the rat temporomandibular joint. The threshold for escape from mechanical stimulation in the temporomandibular joint-inflamed rats was significantly lower than that in control rats. Fluorogold labeling was used to identify the trigeminal root ganglion neurons innervating the site of inflammation. When voltage-clamp (V(h)=-60 mV) conditions were applied to these Fluorogold-labeled small diameter trigeminal root ganglion neurons (<30 mum), voltage-dependent transient K(+) current densities were significantly reduced in the inflamed rats compared with controls. In addition, the voltage-dependence of inactivation of the voltage-dependent transient K(+) current was negatively shifted in the labeled temporomandibular joint-inflamed trigeminal root ganglion neurons. Furthermore, temporomandibular joint inflammation significantly reduced the threshold current and significantly increased action potential firings evoked at two-fold threshold in the Fluorogold-labeled small trigeminal root ganglion neurons. Application of 4-aminopyridine (0.5mM) to control trigeminal root ganglion neurons mimicked the changes in the firing properties observed after complete Freund's adjuvant treatment. Together, these results suggest that temporomandibular joint inflammation increases the excitability of trigeminal root ganglion neurons innervating temporomandibular joint by suppressing voltage-dependent transient K(+) current via a leftward shift in the inactivation curve. These changes may contribute to trigeminal inflammatory allodynia in temporomandibular joint disorder.
    Neuroscience 01/2006; 138(2):621-30. · 3.12 Impact Factor
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    ABSTRACT: The combined effects of ouabain (Na(+)-K(+) ATPase inhibitor) and hyperinflation (inflation volume=three tidal volumes) on slowly adapting pulmonary stretch receptors (SARs) were studied before and after administration of nifedipine (an L-type Ca(2+) channel blocker) and KB-R7943 (a reverse-mode Na(+)-Ca(2+) exchanger blocker) in anesthetized, artificially ventilated rabbits after bilateral vagotomy. Before ouabain administration, hyperinflation stimulated SAR activity. After 20 min of ouabain administration (30 microg/kg) the SARs increased discharge rates in normal inflation. Under these conditions, hyperinflation initially stimulated SAR activity but subsequently inhibited the activity at peak inflation. Additional administration of 60 microg/kg ouabain (total dose=90 microg/kg) caused a further stimulation of SAR activity, but 20 min later both normal inflation and hyperinflation resulted in a greater inhibition of the receptor activity. The hyperinflation-induced SAR inhibition in the presence of ouabain (30 microg/kg) was not significantly altered by administration of either nifedipine (2 and 4 mg/kg) or KB-R7943 (1 and 3 mg/kg). In another series of experiments, we further examined the combined effects of ouabain and hyperinflation in veratridine (a Na(+) channel opener, 40 microg/kg)-treated animals. After recovery from the veratridine effect on SAR activity, which vigorously stimulated the receptor activity, ouabain treatment (30 microg/kg) that silenced the receptor activity at peak inflation greatly inhibited hyperinflation-induced SAR stimulation. These results suggest that hyperinflation-induced SAR inhibition in the presence of ouabain may be related to a Na(+) overload, but not to a Ca(2+) influx via activation of L-type Ca(2+) channels, in the SAR endings.
    Life Sciences 12/2005; 78(1):112-20. · 2.56 Impact Factor
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    ABSTRACT: The aim of this study was to investigate whether under in vivo conditions, temporomandibular joint (TMJ) inflammation alters the excitability of Abeta-trigeminal root ganglion (TRG) neuronal activity innervating the facial skin by using extracellular electrophysiological recording with multibarrel-electrodes. Complete Freund's adjuvant (CFA) was injected into the rat TMJ. Threshold for escape from mechanical stimulation applied to the whisker pad area in inflamed rats (2 days) was significantly lower than that in control rats. A total of 36 Abeta-TRG neurons responding to electrical stimulation of the whisker pad was recorded in pentobarbital-anesthetized rats. The number of Abeta-TRG neurons with spontaneous firings and their firing rate in TMJ inflamed rats were significantly larger than those in control rats. The firing rates of their spontaneous activity in the Abeta-TRG neurons were current-dependently decreased by local iontophoretic application of an NK1 receptor antagonist (L-703,606) in inflamed, but not non-inflamed rats. Their spontaneous activities were current-dependently increased by local iontophoretic application of substance P (SP) in control and inflamed rats. The mechanical response threshold of Abeta-TRG neurons in inflamed rats was significantly lower than that in control rats. The mechanical response threshold in inflamed rats after iontophoretic application of L-703,606 was not different from that in control rats. These results suggest that TMJ inflammation modulate the excitability of Abeta-TRG neurons innervating the facial skin via paracrine mechanism due to SP released from TRG neuronal cell body. Such a SP release may play an important role in determining the trigeminal inflammatory allodynia concerning the temporomandibular disorder.
    Pain 09/2005; 116(3):375-85. · 5.64 Impact Factor
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    ABSTRACT: 1 The aim of the present study was to investigate which EP receptor subtypes (EP1-EP4) act predominantly on the modification of the tetrodotoxin-resistant Na+ current (I(NaR)) in acutely isolated neonatal rat nodose ganglion (NG) neurones. 2 Of the four EP receptor agonists ranging from 0.01 to 10 muM, the EP2 receptor agonist (ONO-AE1-259, 0.1-10 microM) and the EP4 receptor agonist (ONO-AE1-329, 1 microM) significantly increased peak I(NaR). The responses were associated with a hyperpolarizing shift in the activation curve. 3 Neither the EP1 receptor agonist ONO-DI-004 nor the EP3 receptor agonist ONO-AE-248 significantly modified the properties of I(NaR). 4 In PGE2 applications ranging from 0.01 to 10 microM, 1 microM PGE2 produced a maximal increase in the peak I(NaR) amplitude. The PGE2 (1 microM)-induced increase in the GV(1/2) baseline (% change in G at baseline V(1/2)) was significantly attenuated by either intracellular application of the PKA inhibitor PKI or extracellular application of the protein kinase C inhibitor staurosporine (1 microM). However, the slope factor k was not significantly altered by PGE2 applications at 0.01-10 microM. In addition, the hyperpolarizing shift of V(1/2) by PGE2 was not significantly altered by either PKI or staurosporine. 5 In other series of experiments, reverse transcription-polymerase chain reaction (RT-PCR) of mRNA from nodose ganglia indicated that all four EP receptors were present. 6 The NG contained many neuronal cell bodies (diameter <30 microm) with intense or moderate EP2, EP3, and EP4 receptor-immunoreactivities. 7 These results suggest that the PGE2-induced modification of I(NaR) is mainly mediated by activation of both EP2 and EP4 receptors.
    British Journal of Pharmacology 06/2005; 145(4):503-13. · 5.07 Impact Factor
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    ABSTRACT: The aim of this study was to test the hypothesis that temporomandibular joint (TMJ) inflammation alters the excitability of trigeminal root ganglion (TRG) neurons innervating the facial skin, by using behavioral, electrophysiological, molecular, and immunohistochemical approaches. Complete Freund's adjuvant (CFA) was injected into the rat TMJ to produce inflammation. The threshold for escape from mechanical stimulation applied to the orofacial area in TMJ-inflamed rats was significantly lower than that in naïve rats. The TRG neurons innervating the inflamed TMJ were labeled by 2% Fluorogold (FG) injection into the TMJ. The number of FG-labeled substance P (SP)-immunoreactive neurons in the inflamed rats was significantly increased compared with that in the naïve rats. On the other hand, medium- and large-diameter TRG neurons (>30 microm) innervating the facial skin were labeled by FG injection into the facial skin. In the FG-labeled cutaneous TRG neurons, the occurrence of SP (100 nM) induced membrane depolarization in inflamed rats (medium: 73.3%, large : 85.7%) was larger than that in the naïve rats (medium: 29.4%, large : 0%). In addition, SP application significantly increased the firing rate evoked by depolarizing pulses in the neurons of inflamed rats compared with those of naïve rats. Quantitative single-cell RT-PCR analysis showed the increased expression of mRNA for the NK1 receptor in FG-labeled TRG neurons in inflamed rats compared with that in naive rats. The numbers of SP and NK1 receptors/neurofilament 200 positive immunoreactive TRG neurons innervating the facial skin (FG-labeled) in the inflamed rats were significantly increased compared with those seen in naïve rats. These results suggest that TMJ inflammation can alter the excitability of medium- and large-diameter TRG neurons innervating the facial skin and that an increase in SP/NK1 receptors in their soma may contribute to the mechanism underlying the trigeminal inflammatory allodynia in the TMJ disorder.
    Journal of Neurophysiology 06/2005; 93(5):2723-38. · 3.30 Impact Factor
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    ABSTRACT: The co-expression of carbonic anhydrase II (CAII) with the voltage-gated potassium channel subtype 1.4 (Kv1.4) or the vanilloid receptor (TRPV1) was examined in adult rat trigeminal ganglion (TG) neurons by using the immunofluorescence method. The small-diameter Kv.1.4-positive TG neurons co-expressed CAII immunoreactivity (47%). Most TRPV1-positive TG neurons (79%) had the CAII immunoreactivity, but showed a lack of immunoreactivity for a neurofilament protein (NF200), a maker of large TG neurons with myelinated axons. The fact that CAII-immunoreactive TG neurons revealed a common expression of both Kv1.4 and TRPV1 leads us to suggest that CAII may be one of the nociceptive neuronal markers.
    Brain Research 06/2005; 1044(2):262-5. · 2.88 Impact Factor
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    ABSTRACT: The purpose of the present study was to determine whether modulation of the trigeminal spinal nucleus oralis (TSNO) neurons related to tooth-pulp (TP)-evoked jaw-opening reflex (JOR) after electrical stimulation of the sciatic nerve (SN) is mediated by the descending serotonergic (5-HT(3)) inhibitory system activated by inhibitory GABAergic interneurons. In 30 anesthetized rats, the activity of TSNO neurons (87.5%, 35/40) and all digastric muscle electromyograms (dEMG, n=30) in response to TP stimulation (at an intensity of 3.5 times the threshold for JOR) were inhibited by conditioning stimulation of the SN (5.0 mA x 0.5 ms, 1 Hz, conditioning-test intervals; 50 ms). The inhibitory effects were significantly attenuated after intravenous administration of the 5-HT(3) receptor antagonist ICS 205-930 (n=6). Using multibarrel electrodes, iontophoretic application of ICS 205-930 into the TSNO significantly reduced the SN stimulation-induced inhibition of TP-evoked TSNO neuronal excitation (n=6), and in the same neurons, iontophoretic application of the GABA(A) receptor antagonist bicuculline into the TSNO greatly inhibited their effect. On the other hand, we found the expression of 5-HT(3) receptor immunoreactive neurons in the TSNO. These results suggest that SN stimulation may activate the descending serotonergic (5-HT(3)) inhibitory system through activation of inhibitory GABAergic interneurons, which inhibit excitatory responses of the TSNO neurons to TP stimulation.
    Brain Research Bulletin 03/2005; 65(1):31-40. · 2.94 Impact Factor
  • M Takeda, T Tanimoto, M Ito, M Nasu, S Matsumoto
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    ABSTRACT: The aim of the present study was to demonstrate the convergence of inputs from masseter muscle (MM) and tooth pulp (TP) onto C1 spinal neurons and to determine whether the afferent fibers express the functional vanilloid receptor (VR1). Extracellular single-unit recordings were made from 61 C1 units responding to TP electrical stimulation with a constant temporal relationship to a digastric electromyogram signal in pentobarbital anesthetized rats. Eighty-four percent of C1 neurons responding to TP stimulation also responded to the ipsilateral MM stimulation. Of these neurons, 61% were considered to be afferent inputs from Adelta-fibers and the remaining units (39%) were C-fibers, based on calculation of the nerve conduction velocity. Intramuscular injection of capsaicin (0.05 and 0.1%) produced a reduction in a MM-induced C1 neuronal activity in a dose-dependent manner and this effect was antagonized by pretreatment with an antagonist of VR1, capsazepine. Some of these units were also excited by noxious heat stimulation (> 43 degrees C). The trigeminal root ganglion (TRG) neurons that innervated the MM were retrogradely labeled with Fluorogold (FG) and the small-diameter FG-labeled TRG neurons expressed the immunoreactivity for VR1. After intramuscular mustard oil injection (noxious chemical stimulation), the C1 neuronal activity induced by both touch and pinch stimuli was enhanced and their receptive field sizes were significantly expanded. These changes were reversed within 15-20 min. These results suggest that there may be the convergence of noxious afferents inputs from the MM and TP afferents on the same C1 neurons in rats, and that the afferent fibers expressing the functional VR1 may contribute to the hyperalgesia and/or referred pain associated with temporomandibular joint disorder.
    Experimental Brain Research 02/2005; 160(1):107-17. · 2.22 Impact Factor
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    ABSTRACT: To test the hypothesis that vagal afferent (VA) stimulation modulates the first cervical dorsal horn (C(1)) neuron activity, which is projected by tooth pulp (TP) afferent inputs through the activation of a local GABAergic mechanism via 5-hydroxytryptamine(3) (5-HT(3)) receptors, we used the technique of microiontophoretic application of drugs. In pentobarbital-anesthetized rats, we recorded C(1) spinal neuron activity responding to TP stimulation. The TP stimulation-evoked C(1) spinal neuron excitation was inhibited by VA stimulation, and this inhibition was significantly attenuated by iontophoretic application of the 5-HT(3) receptor antagonist ICS 205-930 (3-tropanyl-indole-3-carboxylate hydrochloride [endo-8-methyl-8-azabicyclo [3.2.1] oct-3-ol indol-3-yl-carboxylate hydrochloride]) (40 nA) or the GABA(A) receptor antagonist bicuculline (40 nA). In another series of experiments, we determined that 60 nA iontophoretic application of glutamate produced a maximal increase in the C(1) spinal neuron activity at a minimal current. In 53 of 65 neurons (81.5%), VA conditioning stimulation (1.0 mA x 0.1 ms, 50 Hz for 30 s) caused a significant inhibition (35.1%) of the glutamate (60 nA) application-evoked C(1) spinal neuron excitation. Iontophoretic application of ICS 205-930 (40 nA) or bicuculline (40 nA) significantly attenuated the VA stimulation-induced inhibition of glutamate iontophoretic application (60 nA)-evoked C(1) spinal neuron excitation. These results suggest that VA stimulation-induced suppression of C(1) spinal neuron activity, responding to TP stimulation, involve 5-HT(3) receptor activation, possibly originating in the descending serotonergic inhibitory system, and postsynaptic modulation of inhibitory GABAergic neurons.
    Journal of Pharmacology and Experimental Therapeutics 12/2004; 311(2):803-10. · 3.89 Impact Factor
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    ABSTRACT: After transection of the inferior alveolar nerve (IAN), the whisker pad area, which is innervated by the infraorbital nerve (ION) that was not injured, showed hypersensitivity to mechanical stimulation. Two days after IAN transection, threshold intensity for escape behavior to mechanical stimulation of the ipsilateral whisker pad area was less than 4.0 g, indicating mechanical allodynia. A total of 68 single fiber discharges were recorded from ION fibers at 3 days after IAN transection. The responses of C- and A-fibers were classified according to their conduction velocity. The C-fiber activities were not affected by IAN transection, whereas A-fiber activities were significantly enhanced by IAN transection as indicated by an increase in background activity and mechanically evoked response. Since the A-fiber responses were significantly affected by IAN transection, patch clamp recording was performed from middle to large diameter retrogradely labeled and acutely dissociated trigeminal ganglion (TRG) neurons. The I(K) (sustained) and I(A) (transient) currents were significantly smaller and hyperpolarization-activated current (I(h)) was significantly larger in TRG neurons of rats with IAN transection as compared to those of naive rats. Furthermore, current injection into TRG neurons induced high frequency spike discharges in rats with IAN transection. These data suggest that changes in K(+) current and I(h) observed in the uninjured TRG neurons reflect an increase in excitability of TRG neurons innervated by the ION after IAN transection, resulting in the development of mechano-allodynia in the area adjacent to the injured IAN innervated region.
    Pain 11/2004; 111(3):323-34. · 5.64 Impact Factor
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    ABSTRACT: The aim of the present study was to test the hypothesis that there is a convergence of afferent inputs from the temporomandibular joint (TMJ) on C1 spinal neurons responding to electrical stimulation of the tooth pulp (TP). In 14 pentobarbital anesthetized rats, the extracellular single unit activity of 31 C1 spinal neurons and the amplitude in a digastric muscle electromyogram (n = 31) increased proportionally during 1.0-3.5 times the threshold for the jaw-opening reflex (JOR). Of 31 C1 spinal neurons responsive to TP afferents, 28 (approximately 90%) were also excited by electrical stimulation of the ipsilateral TMJ capsule. All neurons tested were divided into three categories of nociceptive specific, wide dynamic range and non-responsive as to their responsiveness to mechanical stimuli (pin prick and touch) of the somatic receptive field (skin of the face, neck, jaw and upper forearm) and TMJ capsule. Nineteen (68%) of 28 C1 spinal neurons received nociceptive information from C fibers of the TMJ capsule. These results suggest that there is a convergence of noxious information from the TMJ and TP afferents on the same C1 spinal neurons, which importantly contribute to pain perception from the TMJ region.
    Life Sciences 09/2004; 75(12):1465-78. · 2.56 Impact Factor
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    ABSTRACT: Inhibitory responses of slowly adapting pulmonary stretch receptor (SAR) activity to CO(2) inhalation (maximal tracheal CO(2) concentration ranging from 9.5 to 12.5%) for approximately 60 s were examined before and after administration of acetazolamide (a carbonic anhydrase inhibitor) or 4-aminopyridine (4-AP, a K(+) channel blocker). The experiments were performed in 35 anesthetized, artificially ventilated rats after unilateral vagotomy. Sixty-eight of eighty-four SARs were inhibited by CO(2) inhalation. The SAR inhibition was attenuated by pretreatment with either acetazolamide (20 mg/kg, n = 10) or 4-AP (0.7 and 2.0 mg/kg, n = 10). In other series of experiments, stainings to show the existence of carbonic anhydrase (CA) enzymatic reaction were not found in the smooth muscle of either extrapulmonary or intrapulmonary bronchi. Protein gene product 9.5 (PGP 9.5)-immunoreactive SAR terminals to form leaflike extensions were found in the bronchioles at different diameters and were smooth-muscle-related receptors. But in the same sections, CA isozyme II-like (erythrocyte CA) immunoreactive SAR terminals were not identified. These results suggest that CO(2)-induced inhibition of SARs may be involved in the CA-dependent CO(2) hydration in addition to the activation of 4-AP sensitive K(+) currents.
    Chemical Senses 06/2004; 29(4):351-61. · 3.22 Impact Factor