• The Korean Journal of Physiology and Pharmacology
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• v.8 no.3
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• pp.133-140
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• 2004

The purpose of the present study was to elucidate the possible involvement of the medial vestibular nucleus (MVN) and inferior vestibular nucleus (IVN) following acute hypotension in the vestibuloautonomic reflex through vestibulosolitary or vestibuloventrolateral projections. Acute hypotension-induced cFos expression was assessed in combination with retrograde cholera toxin B subunit (CTb) tract tracing. After injection of CTb into the solitary region, CTb-labeled neurons were located prominently around the lateral borders of the caudal MVN and medial border of the IVN. The superior vestibular nucleus also had a scattered distribution of CTb-labeled neurons. After injection of CTb toxin into the unilateral VLM, the distributions of CTb-labeled neurons in the MVN and IVN were similar to that observed after injection into the solitary region, although there were fewer CTb-labeled neurons. In the caudal MVN, about 38% and 13% of CTb-labeled neurons were double-labeled for cFos after injection of CTb into the solitary region and the VLM, respectively. In the IVN, 14% and 7% of CTb-labeled neurons were double-labeled for cFos after injection of CTb into the solitary region and the VLM, respectively. Therefore, the present study suggests that acute arterial hypotension may result in activation of vestibulosolitary pathways that mediate behavioral and visceral reflexes, and vestibuloventrolateral medullary pathways that indirectly mediate vestibulosympathetic responses.

• The Korean Journal of Physiology and Pharmacology
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• v.7 no.2
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• pp.59-63
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• 2003

The medial vestibular nucleus (MVN) neurons are controlled by excitatory synaptic transmission from the vestibular afferent and commissural projections, and by inhibitory transmission from interneurons. Spontaneous synaptic currents of MVN neurons were studied using whole cell patch clamp recording in slices prepared from 13- to 17-day-old rats. The spontaneous inhibitory postsynaptic currents (sIPSCs) were significantly reduced by the $GABA_A$ antagonist bicuculline ($20{\mu}M$), but were not affected by the glycine antagonist strychnine ($1{\mu}M$). The frequency, amplitude, and decay time constant of sIPSCs were $4.3{\pm}0.9$ Hz, $18.1{\pm}2.0$ pA, and $8.9{\pm}0.4$ ms, respectively. Spontaneous excitatory postsynaptic currents (sEPSCs) were mediated by non-NMDA and NMDA receptors. The specific AMPA receptor antagonist GYKI-52466 ($50{\mu}M$) completely blocked the non-NMDA mediated sEPSCs, indicating that they are mediated by an AMPA-preferring receptor. The AMPA mediated sEPSCs were characterized by low frequency ($1.5{\pm}0.4$ Hz), small amplitude ($13.9{\pm}1.9$ pA), and rapid decay kinetics ($2.8{\pm}0.2$ ms). The majority (15/21) displayed linear I-V relationships, suggesting the presence of GluR2-containing AMPA receptors. Only 35% of recorded MVN neurons showed NMDA mediated currents, which were characterized by small amplitude and low frequency. These results suggest that the MVN neurons receive excitatory inputs mediated by AMPA, but not kainate, and NMDA receptors, and inhibitory transmission mediated by $GABA_A$ receptors in neonatal rats.

• The Korean Journal of Physiology and Pharmacology
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• v.21 no.6
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• pp.675-686
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• 2017

Orthostatic hypotension (OH) is associated with symptoms including headache, dizziness, and syncope. The incidence of OH increases with age. Attenuation of the vestibulosympathetic reflex (VSR) is also associated with an increased incidence of OH. In order to understand the pathophysiology of OH, we investigated the physiological characteristics of the VSR in the disorder. We applied sodium nitroprusside (SNP) to conscious rats with sinoaortic denervation in order to induce hypotension. Expression of pERK in the intermediolateral cell column (IMC) of the T4~7 thoracic spinal regions, blood epinephrine levels, and blood pressure were evaluated following the administration of glutamate and/or SNP. SNP-induced hypotension led to increased pERK expression in the medial vestibular nucleus (MVN), rostral ventrolateral medullary nucleus (RVLM) and the IMC, as well as increased blood epinephrine levels. We co-administered either a glutamate receptor agonist or a glutamate receptor antagonist to the MVN or the RVLM. The administration of the glutamate receptor agonists, AMPA or NMDA, to the MVN or RVLM led to elevated blood pressure, increased pERK expression in the IMC, and increased blood epinephrine levels. Administration of the glutamate receptor antagonists, CNQX or MK801, to the MVN or RVLM attenuated the increased pERK expression and blood epinephrine levels caused by SNP-induced hypotension. These results suggest that two components of the pathway which maintains blood pressure are involved in the VSR induced by SNP. These are the neurogenic control of blood pressure via the RVLM and the humoral control of blood pressure via epinephrine release from the adrenal medulla.

• The Korean Journal of Physiology and Pharmacology
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• v.19 no.3
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• pp.275-281
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• 2015

Orthostatic hypotension is most common in elderly people, and its prevalence increases with age. Attenuation of the vestibulo-sympathetic reflex (VSR) is commonly associated with orthostatic hypotension. In this study, we investigated the role of glutamate on the vestibulo-solitary projection of the VSR pathway to clarify the pathophysiology of orthostatic hypotension. Blood pressure and expression of both pERK and c-Fos protein were evaluated in the nucleus tractus solitarius (NTS) after microinjection of glutamate into the medial vestibular nucleus (MVN) in conscious rats with sodium nitroprusside (SNP)-induced hypotension that received baroreceptor unloading via sinoaortic denervation (SAD). SNP-induced hypotension increased the expression of both pERK and c-Fos protein in the NTS, which was abolished by pretreatment with glutamate receptor antagonists (MK801 or CNQX) in the MVN. Microinjection of glutamate receptor agonists (NMDA or AMPA) into the MVN increased the expression of both pERK and c-Fos protein in the NTS without causing changes in blood pressure. These results indicate that both NMDA and AMPA receptors play a significant role in the vestibulo-solitary projection of the VSR pathway for maintaining blood pressure, and that glutamatergic transmission in this projection might play a key role in the pathophysiology of orthostatic hypotension.

• Biomedical Science Letters
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• v.15 no.3
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• pp.199-205
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• 2009

This study was designed to investigate direct effects of [D-$Pen^2$, D-$Pen^5$]-enkephalin, a $\delta$-opioid receptor agonist on the neuronal activity of medial vestibular nuclear (MVN) neurons by whole-cell configuration patch clamp experiments. The spike frequency of MVN neuron was increased to $9.50{\pm}0.55$ (P<0.05) and $10.56{\pm}0.66$ (P<0.05) by 5 and $10{\mu}M$ [D-$Pen^2$, D-$Pen^5$]-enkephalin from the control level of $8.05{\pm}0.55$ spikes/sec, respectively (n=18). The resting membrane potential of the neurons was increased to $-37.86{\pm}0.92$ and $-36.97{\pm}0.97$ (P<0.05) from $-38.74{\pm}1.13\;mV$ by 5 and $10{\mu}M$ [D-$Pen^2$, D-$Pen^5$]-enkephalin, respectively. The amplitude of afterhyperpolarization was decreased to $23.78{\pm}0.65$ and $21.67{\pm}0.89$ (P<0.05) from $23.73{\pm}0.53\;mV$ by 5 and $10{\mu}M$ [D-$Pen^2$, D-$Pen^5$]-enkephalin, respectively. The spike width was changed to $2.22{\pm}0.08$ and $2.24{\pm}0.07$ from $2.20{\pm}0.08\;mV$ by 5 and $10{\mu}M$ [D-$Pen^2$, D-$Pen^5$]-enkephalin, respectively. After pretreatment of naltrindole, a highly selective 8-opioid receptor antagonist, [D-$Pen^2$, D-$Pen^5$]-enkephalin did not change firing rate, resting membrane potential, afterhyperpolarization amplitude, and spike width of MVN neurons. The above experimental results suggest that [D-$Pen^2$, D-$Pen^5$]-enkephalin increases the neuronal activity of MVN neurons via inhibition of calcium-dependent potassium currents underlying the afterhyperpolarization.

• Phonetics and Speech Sciences
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• v.12 no.3
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• pp.65-71
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• 2020

Feature normalization is a method to reduce the effect of environmental mismatch between the training and test conditions through the normalization of statistical characteristics of acoustic feature parameters. It demonstrates excellent performance improvement in the traditional Gaussian mixture model-hidden Markov model (GMM-HMM)-based speech recognition system. However, in a deep neural network (DNN)-based speech recognition system, minimizing the effects of environmental mismatch does not necessarily lead to the best performance improvement. In this paper, we attribute the cause of this phenomenon to information loss due to excessive feature normalization. We investigate whether there is a feature normalization method that maximizes the speech recognition performance by properly reducing the impact of environmental mismatch, while preserving useful information for training acoustic models. To this end, we introduce the mean and exponentiated variance normalization (MEVN), which is a compromise between the mean normalization (MN) and the mean and variance normalization (MVN), and compare the performance of DNN-based speech recognition system in noisy and reverberant environments according to the degree of variance normalization. Experimental results reveal that a slight performance improvement is obtained with the MEVN over the MN and the MVN, depending on the degree of variance normalization.

• The Korean Journal of Physiology and Pharmacology
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• v.5 no.2
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• pp.123-131
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• 2001

To investigate the effects of electrical stimulation on vestibular compensation, which is the recovery of vestibular symptoms following unilateral labyrinthectomy (UL), intermittent electrical stimulation was applied to the injured vestibular portion in Sprague-Dawley rats. Vestibuloocular and vestibulospinal reflexes, electrical activity and expression of c-Fos protein in medial vestibular nuclei (MVN) were measured with time following UL. Spontaneous nystagmus occurred with frequency of $2.9{\pm}0.2$ beats/sec at 2 hours after UL and disappeared after 72 hours. Electrical stimulation decreased the frequency of nystagmus significantly till 24 hours after UL. Roll head deviation was $107{\pm}9.7^{\circ}$ at 2 hours after UL and the deviation was maintained till 72 hours, but electrical stimulation decreased the deviation significantly 6 hours after UL. Resting activity of type I neurons in ipsilateral MVN to the injured vestibular side decreased significantly compared with control at 6 and 24 hours after UL, but the activity of type I neurons was recovered to control level by electrical stimulation at 24 hours after UL. Gain of type I neurons induced by sinusoidal rotation of 0.1 Hz decreased significantly till 24 hours after UL, but electrical stimulation restored the activity at 24 hours. The gain of type II neurons decreased significantly at 6 hours after UL, but electrical stimulation restored the activity. Expression of c-Fos protein was asymmetric between bilateral MVN till 24 hours after UL, but the asymmetry disappeared by electrical stimulation 6 hours after UL. These results suggest that electrical stimulation to the injured vestibular portion facilitates vestibular compensation following UL by restoration of symmetry of neuronal activity between bilateral vestibular nuclei resulting from increased activity in ipsilateral vestibular nuclei to the injured side.

• The Korean Journal of Physiology and Pharmacology
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• v.6 no.4
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• pp.199-205
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• 2002

The role of peripheral vestibular receptors in acute hypotension was investigated in anesthetized rats. Acute hypotension was induced by either intravenous infusion of sodium nitroprusside (SNP) or by experimental hemorrhage, and electrical activity and expression of cFos-like immunoreactive (cFL) protein were measured in the medial vestibular nuclei (MVN). Blood pressure decreased proportionately to the does of intravenous SNP and to the volume of the hemorrhage. Blood pressure decreased 10, 30, 50% for the 5, 10, $15{\mu}g/kg$ SNP injection, respectively, and also decreased 30 and 50% after 1- and 2-ml blood loss, respectively, due to hemorrhage. In animals with intact labyrinths, acute hypotension induced by either intravenous infusion of SNP or hemorrhage produced different electrical activities with three different patterns in type I and II neurons of MVN. The responses of type I neurons showed excitatory in 2/3 of recorded neurons and inhibitory or no change in 1/3 of neurons, while the responses of type II neurons showed inhibitory in 2/3 of recorded neurons and excitatory or no change in 1/3 of neurons. In unilateral labyrinthectomized animals, 2/3 of type I neurons ipsilateral to the lesion showed an inhibitory response, and 2/3 of contralateral type I neurons showed an excitatory response after the induction of acute hypotension. The response patterns of type II neurons were opposite from those of the type I neurons. After 30% decrease in blood pressure, cFL protein expressed in the bilateral vestibular nuclei of control animals with intact labyrinths. Expression of cFL protein increased significantly proportionately to the reduction of blood pressure. The unilateral labyrinthectomized animals with acute hypotension produced expression of cFL neurons in contralateral vestibular nuclei to the lesion side, but not in ipsilateral vestibular nuclei. However, cFL protein was not expressed in bilateral vestibular nuclei after acute hypotension in bilateral labyrinthectomized animals. These results suggest that the peripheral vestibular receptors might play a significant role in controlling blood pressure following acute hypotension via activation of type I neurons and inhibition of type II neurons in the vestibular nuclei.

• The Korean Journal of Physiology and Pharmacology
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• v.19 no.5
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• pp.427-434
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• 2015

Significant evidence supports the role of the vestibular system in the regulation of blood pressure during postural movements. In the present study, the role of the vestibulo-spino-adrenal (VSA) axis in the modulation of blood pressure via the vestibulosympathetic reflex was clarified by immunohistochemical and enzyme immunoassay methods in conscious rats with sinoaortic denervation. Expression of c-Fos protein in the intermediolateral cell column of the middle thoracic spinal regions and blood epinephrine levels were investigated, following microinjection of glutamate receptor agonists or antagonists into the medial vestibular nucleus (MVN) and/or sodium nitroprusside (SNP)-induced hypotension. Both microinjection of glutamate receptor agonists (NMDA and AMPA) into the MVN or rostral ventrolateral medullary nucleus (RVLM) and SNP-induced hypotension led to increased number of c-Fos positive neurons in the intermediolateral cell column of the middle thoracic spinal regions and increased blood epinephrine levels. Pretreatment with microinjection of glutamate receptor antagonists (MK-801 and CNQX) into the MVN or RVLM prevented the increased number of c-Fos positive neurons resulting from SNP-induced hypotension, and reversed the increased blood epinephrine levels. These results indicate that the VSA axis may be a key component of the pathway used by the vestibulosympathetic reflex to maintain blood pressure during postural movements.

• The Journal of the Acoustical Society of Korea
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• v.33 no.1
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• pp.68-74
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• 2014

In a previous work, we proposed a novel approach of histogram equalization using a supplement set which is composed of centroids of Fuzzy C-Means of the background utterances. The performance of the proposed method is affected by the size of the supplement set, but it is difficult to find the best size at the point of recognition. In this paper, we propose a histogram equalization using a supplement set for majority voting based speaker identification. The proposed method identifies test utterances using a majority voting on the histogram equalization methods with various sizes of supplement sets. The proposed method is compared with the conventional feature normalization methods such as CMN(Cepstral Mean Normalization), MVN(Mean and Variance Normalization), and HEQ(Histogram Equalization) and the histogram equalization method using a supplement set.