Masashi Iwata

Rhode Island Hospital, Providence, Rhode Island, United States

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Publications (4)20.88 Total impact

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    ABSTRACT: Cerebellar dysfunction in multiple sclerosis (MS) contributes significantly to disability, is relatively refractory to symptomatic therapy, and often progresses despite treatment with disease-modifying agents. We previously observed that sodium channel Nav1.8, whose expression is normally restricted to the peripheral nervous system, is present in cerebellar Purkinje neurons in a mouse model of MS (experimental autoimmune encephalomyelitis [EAE]) and in humans with MS. Here, we tested the hypothesis that upregulation of Nav1.8 in cerebellum in MS and EAE has functional consequences contributing to symptom burden. Electrophysiology and behavioral assessment were performed in a new transgenic mouse model overexpressing Nav1.8 in Purkinje neurons. We also measured EAE symptom progression in mice lacking Nav1.8 compared to wild-type littermates. Finally, we administered the Nav1.8-selective blocker A803467 in the context of previously established EAE to determine reversibility of MS-like deficits. We report that, in the context of an otherwise healthy nervous system, ectopic expression of Nav1.8 in Purkinje neurons alters their electrophysiological properties, and disrupts coordinated motor behaviors. Additionally, we show that Nav1.8 expression contributes to symptom development in EAE. Finally, we demonstrate that abnormal patterns of Purkinje neuron firing and MS-like deficits in EAE can be partially reversed by pharmacotherapy using a Nav1.8-selective blocker. Our results add to the evidence that a channelopathy contributes to cerebellar dysfunction in MS. Our data suggest that Nav1.8-specific blockers, when available for humans, merit study in MS.
    Annals of Neurology 02/2012; 71(2):186-94. · 11.91 Impact Factor
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    ABSTRACT: Chronic neuropathic pain is associated with long-term changes at multiple levels of the neuroaxis, including in the brain, where electrical stimulation has been used to manage severe pain conditions. However, the clinical outcome of deep brain stimulation is often mixed, and the mechanisms are poorly understood. By means of electrophysiologic methods, we sought to characterize the changes in neuronal activity in the ventral posterolateral nucleus of the thalamus (VPL) in a rat model of peripheral neuropathic pain, and to reverse these changes with low-voltage, high-frequency stimulation (HFS) in the VPL. Extracellular single-unit neuronal activity was recorded in naive rats and in those with sciatic chronic constriction injury (CCI). Seven days after CCI, brush- and pinch-evoked firing, as well as spontaneous firing and afterdischarge, were significantly increased compared to naive rats. Spontaneous rhythmic oscillation in neuronal firing was also observed in rats with CCI. HFS decreased neuronal firing rates in rats with CCI up to ~50% except for spontaneous activity, whereas low-frequency stimulation had no effect. Compared to naive rats, burst firing properties (burst events, percentage of spikes in burst, and mean interburst time) were altered in rats with CCI, whereas these changes were reversed to near normal after HFS. Thermal hyperalgesia in rats with CCI was significantly attenuated by HFS. Therefore, this study demonstrates that electrical stimulation within the VPL can effectively modulate some nociceptive phenomena associated with peripheral neuropathic pain.
    Pain 09/2011; 152(11):2505-13. · 5.64 Impact Factor
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    ABSTRACT: Background / Purpose: We characterized pain-induced plasticity in the ventral posterolateral (VPL) thalamus using electrophysiology, and tested for microgliosis. Extracellular single-unit activity was recorded in naïve and neuropathic rats with sciatic chronic constriction injury (CCI). Main conclusion: At d7 after CCI, brush and pinch-evoked firing, as well as spontaneous firing and afterdischarge, were significantly increased compared to naïve rats. Spontaneous oscillation was also observed in neuropathic rats. Expression of OX-42 was increased in VPL contralateral to CCI and co-localized with phosphorylated p38MAPK (P-p38). Low-voltage high frequency stimulation (HFS; 0.5-1.5 V, 100-200 Hz) in the VPL contralateral to CCI decreased firing rates in rats with CCI up to ~50% except for spontaneous activity, whereas low frequency stimulation (20-40 Hz) had no effect. Compared to naïve rats, burst firing properties (burst events, % spikes in burst and mean interburst time) were altered in rats with CCI, whereas these changes were reversed to near normal after HFS.Thermal hyperalgesia in rats with CCI was significantly attenuated by HFS as well as by microinjection of minocycline into the VPL, whereas vehicle injection has no effect on paw withdrawal latency. Minocycline also abrogated the expression of OX-42 in the VPL after CCI.Therefore, peripheral neuropathic pain causes plasticity in the VPL which manifests as reactive microgliosis and neuronal sensitization, concomitant with neuropathic behavior. Modulation of the nociceptive circuitry can be achieved by electrical microstimulation or injection of a glial inhibitor in the VPL.
    New York Academy of Sciences 2011 - Chronic Inflammatory and Neuropathic Pain meeting; 07/2011
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    ABSTRACT: Post-synaptic density protein PSD-95 is emerging as a valid target for modulating nociception in animal studies. Based on the key role of PSD-95 in neuronal plasticity and the maintenance of pain behavior, we predicted that CN2097, a peptide-based macrocycle of nine residues that binds to the PSD-95 Discs large, Zona occludens 1 (PDZ) domains of PSD-95, would interfere with physiologic phenomena in the spinal cord related to central sensitization. Furthermore, we tested whether spinal intrathecal injection of CN2097 attenuates thermal hyperalgesia in a rat model of sciatic neuropathy. Results demonstrate that spinal CN2097 reverses hyperexcitability of wide dynamic range (WDR) neurons in the dorsal horn of neuropathic rats and decreases their evoked responses to peripheral stimuli (brush, low caliber von Frey and pressure), whereas CN5125 ("negative control") has no effect. CN2097 also blocks C-fiber long-term potentiation (LTP) in the dorsal horn, which is linked to neuronal plasticity and central sensitization. At a molecular level, CN2097 attenuates the increase in phosphorylated p38 MAPK, a key intracellular signaling pathway in neuropathic pain. Moreover, spinal injection of CN2097 blocks thermal hyperalgesia in neuropathic rats. We conclude that CN2097 is a small molecule peptide with putative anti-nociceptive effects that modulates physiologic phenomena related to central sensitization under conditions of chronic pain.
    Neuroscience 02/2010; 167(2):490-500. · 3.33 Impact Factor