Role of peripheral vestibular receptors in the control of blood pressure following hypotension.

Hypotension is one of the potential causes of dizziness. In this review, we summarize the studies published in recent years about the electrophysiological and pharmacological mechanisms of hypotension-induced dizziness and the role of the vestibular system in the control of blood pressure in response to hypotension. It is postulated that ischemic excitation of the peripheral vestibular hair cells as a result of a reduction in blood flow to the inner ear following hypotension leads to excitation of the central vestibular nuclei, which in turn may produce dizziness after hypotension. In addition, excitation of the vestibular nuclei following hypotension elicits the vestibulosympathetic reflex, and the reflex then regulates blood pressure by a dual-control (neurogenic and humoral control) mechanism. In fact, recent studies have shown that peripheral vestibular receptors play a role in the control of blood pressure through neural reflex pathways. This review illustrates the dual-control mechanism of peripheral vestibular receptors in the regulation of blood pressure following hypotension.

Dual control of the vestibulosympathetic reflex following hypotension in rats.

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.

Reactive oxygen species increase neuronal excitability via activation of nonspecific cation channel in rat medullary dorsal horn neurons.

The caudal subnucleus of the spinal trigeminal nucleus (medullary dorsal horn; MDH) receives direct inputs from small diameter primary afferent fibers that predominantly transmit nociceptive information in the orofacial region. Recent studies indicate that reactive oxygen species (ROS) is involved in persistent pain, primarily through spinal mechanisms. In this study, we aimed to investigate the role of xanthine/xanthine oxidase (X/XO) system, a known generator of superoxide anion (O2·-), on membrane excitability in the rat MDH neurons. For this, we used patch clamp recording and confocal imaging. An application of X/XO (300 µM/30 mU) induced membrane depolarization and inward currents. When slices were pretreated with ROS scavengers, such as phenyl N-tert-butylnitrone (PBN), superoxide dismutase (SOD), and catalase, X/XO-induced responses decreased. Fluorescence intensity in the DCF-DA and DHE-loaded MDH cells increased on the application of X/XO. An anion channel blocker, 4,4-diisothiocyanatostilbene-2,2-disulfonic acid (DIDS), significantly decreased X/XO-induced depolarization. X/XO elicited an inward current associated with a linear current-voltage relationship that reversed near -40 mV. X/XO-induced depolarization reduced in the presence of La3+, a nonselective cation channel (NSCC) blocker, and by lowering the external sodium concentration, indicating that membrane depolarization and inward current are induced by influx of Na+ ions. In conclusion, X/XO-induced ROS modulate the membrane excitability of MDH neurons, which was related to the activation of NSCC.

Activation of the thalamic parafascicular nucleus by electrical stimulation of the peripheral vestibular nerve in rats.

The parafascicular nucleus (PFN) of the thalamus is a primary structure in the feedback circuit of the basal ganglia-thalamo-cortical system, as well as in the neural circuit of the vestibulo-thalamo-striatal pathway. We investigated the characteristics of the functional connectivity between the peripheral vestibular system and the PFN in rats. A single electrical stimulation was applied to the horizontal semicircular canal nerve in the peripheral vestibular end-organs. This resulted in polysynaptic local field potentials (LFPs) in the PFN, which were composed of long-lasting multiple waves. The LFPs were prominently seen contralateral to the stimulation site. The PFN LFPs were suppressed by transient chemical de-afferentation of peripheral vestibular activity using a 5% lidocaine injection into the middle ear. The spontaneous firing rate of the single units increased after electrical stimulation to the horizontal canal nerve in a frequency-dependent manner. The induction of cFos protein was more prominent in the contralateral PFN than in the ipsilateral PFN following horizontal semicircular canal nerve stimulation. The functional vestibulo-parafascicular connection is a neural substrate for the transmission of vestibular sensory information to the basal ganglia.

Functional Connections of the Vestibulo-spino-adrenal Axis in the Control of Blood Pressure Via the Vestibulosympathetic Reflex in Conscious Rats.

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.

Effect of glutamate on the vestibulo-solitary projection after sodium nitroprusside-induced hypotension in conscious rats.

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.

Analysis of the Baroreceptor and Vestibular Receptor Inputs in the Rostral Ventrolateral Medulla following Hypotension in Conscious Rats.

Input signals originating from baroreceptors and vestibular receptors are integrated in the rostral ventrolateral medulla (RVLM) to maintain blood pressure during postural movement. The contribution of baroreceptors and vestibular receptors in the maintenance of blood pressure following hypotension were quantitatively analyzed by measuring phosphorylated extracellular regulated protein kinase (pERK) expression and glutamate release in the RVLM. The expression of pERK and glutamate release in the RVLM were measured in conscious rats that had undergone bilateral labyrinthectomy (BL) and/or sinoaortic denervation (SAD) following hypotension induced by a sodium nitroprusside (SNP) infusion. The expression of pERK was significantly increased in the RVLM in the control group following SNP infusion, and expression peaked 10 min after SNP infusion. The number of pERK positive neurons increased following SNP infusion in BL, SAD, and BL+SAD groups, although the increase was smaller than seen in the control group. The SAD group showed a relatively higher reduction in pERK expression when compared with the BL group. The level of glutamate release was significantly increased in the RVLM in control, BL, SAD groups following SNP infusion, and this peaked 10 min after SNP infusion. The SAD group showed a relatively higher reduction in glutamate release when compared with the BL group. These results suggest that the baroreceptors are more powerful in pERK expression and glutamate release in the RVLM following hypotension than the vestibular receptors, but the vestibular receptors still have an important role in the RVLM.

Effect of Vestibulosympathetic Reflex and Baroreflex on Expression of pERK in the Nucleus Tractus Solitarius following Acute Hypotension in Conscious Rats.

Control of blood pressure is maintained by the interaction between the arterial baroreflex and vestibulosympathetic reflex during postural changes. In this study, the contributions of vestibular receptors and baroreceptors to the maintenance of blood pressure following acute hypotension were compared in terms of phosphorylated extracellular regulated protein kinase (pERK) expression in the nucleus tractus solitaries (NTS). Expression of pERK in the NTS was measured in conscious rats that had undergone bilateral labyrinthectomy (BL) and/or sinoaortic denervation (SAD) 5, 10, 20, and 40 min following acute hypotension induced by sodium nitroprusside (SNP) infusion. Expression of pERK increased significantly in the NTS in the control group following SNP infusion, and the expression peaked at 10 min after SNP infusion. The number of pERK positive neurons increased following SNP infusion in BL, SAD, and BL+SAD groups, although the increase was smaller than in control group. The BL group showed a relatively higher reduction in pERK expression than the SAD group, and the pERK expression in the NTS was localized to the caudal portion of the nuclei in the BL and SAD groups. These results suggest that the vestibular receptors may play a key role in maintaining blood pressure following acute hypotension; thus, the vestibular system may contribute to compensate for orthostatic hypotension.

Comparative analysis of vestibular receptor and baroreceptor inputs to the nucleus tractus solitarius following acute hypotension in conscious rats.

Blood pressure is maintained by the interaction between the arterial baroreflexes and the vestibulo-cardiovascular reflexes during postural changes. In this study, the influence of the vestibular receptors on the maintenance of blood pressure following acute hypotension was quantitatively compared with the role of baroreceptors in terms of c-Fos protein expression in the nucleus tractus solitarius (NTS). Expression of c-Fos protein in the NTS was measured in conscious rats that had undergone bilateral labyrinthectomy (BL) and/or sinoaortic denervation (SAD). Expression of c-Fos protein increased significantly in the NTS in the sham group after sodium nitroprusside (SNP) administration. However, the BL, SAD, and SAD+BL groups showed significant decreases in c-Fos protein expression compared to that of the sham group. The SAD group showed relatively more reduction in c-Fos protein expression than the BL group, and the SAD+BL group showed the least expression among the three experimental groups. The c-Fos protein expression in the NTS following acute hypotension was localized to the caudal portions of the nuclei in the BL and SAD groups. These results suggest that the role of vestibular receptors in maintaining blood pressure following acute hypotension is less potent than that of the baroreceptors but more potent than other afferent inputs in conscious rats. In addition, afferent signals for maintaining blood pressure originating from the vestibular receptors and the baroreceptors may converge in the caudal portion of the NTS.

Vulnerability of the vestibular organs to transient ischemia: implications for isolated vascular vertigo.

The aim of this study was to elucidate the mechanism of isolated vascular vertigo by determining selective and relative ischemic vulnerability of the vestibular structures using a global hypoperfusion model in rats. Sprague-Dawley male rats weighing 330-350 g were subjected to transient global ischemia of the brain using a 4-vessel-occlusion (4VO) model. After permanent occlusion of both vertebral arteries (VA) using electrocauterization, both common carotid arteries (CCAs) were occluded for 5-20 min with ligation. One hour after reperfusion of the CCAs, the animals were sacrificed and subjected to c-Fos staining of the entire cerebellum, brainstem, and vestibular ganglion. The rats in the sham group received the same surgical procedures except the vessel ligation. With 4VO for 5-15 min, both the sham and experimental groups showed a weak and scarce c-Fos expression in the medial vestibular nucleus (MVN), neuron Y, and cochlear nucleus. After 4VO for 20 min, only the MVN began to show a significant difference in the number of c-Fos positive neurons between the experimental and sham groups (33.7±17.7 vs.7.1±5.1, Wilcoxon rank test, p=0.005). With 4VO for up to 20 min, c-Fos positive neurons were not found in other areas of the brainstem and cerebellum, including the superior, lateral, and spinal vestibular nuclei, the vestibular ganglion, the cerebellar cortex, and the deep cerebellar nuclei. The vestibular structures appear to be vulnerable to ischemia more than any other structures in the brainstem and cerebellum. Of the vestibular structures, the MVN is most vulnerable to ischemic insults in rats. These findings are consistent with the common findings of vertigo as an initial and isolated symptom of posterior circulation ischemia in human.

Temporal changes of calbindin expression in the nodulus following unilateral labyrinthectomy in rats.

Following unilateral vestibular deafferentation, many of the oculomotor and postural symptoms, such as spontaneous ocular nystagmus and head tilt, gradually abate over time in a process known as 'vestibular compensation'. Although many experimental studies have indicated a role for the cerebellum during vestibular compensation, the effects of unilateral labyrinthectomy (UL) on cerebellar function and the role of cerebellum in post-lesional plasticity remain unclear. Thus, we investigated the temporal changes of calbindin expression in the ipsilateral and contralateral nodulus to the lesion side during vestibular compensation following UL in rats. Change of calbindin expression in the nodulus was measured by immunohistochemistry at 2, 6, 24 and 48hr following UL. The staining intensity of calbindin-positive Purkinje cells in the ipsilateral and contralateral nodulus to the lesion side was found to decrease 6hr after UL compared with the control and asymmetric calbindin expression between ipsilateral and contralateral nodulus 24hr after UL. Forty-eight hours after UL, calbindin expression returned to the control level, and asymmetric expression in both noduli also subsided. It is suggested that the regulation of calbindin expression may facilitate synaptic plasticity by adjusting the efficacy of biochemical responses of Purkinje cells according to the changes in neuronal activity in the vestibular nuclear complex during the early phase of vestibular compensation. Thus, the results revealed that the nodulus has a role during vestibular compensation through Purkinje cells.

Additive role of the vestibular end organ and baroreceptors on the regulation of blood pressure in rats.

Contribution of the vestibular end organ to regulation of arterial pressure was quantitatively compared with the role of baroreceptors in terms of baroreflex sensitivity and c-Fos protein expression in the rostral ventrolateral medulla (RVLM). Baroreflex sensitivity and c-Fos protein expression in the RVLM were measured in conscious rats that had undergone bilateral labyrinthectomy (BL) and/or baroreceptor unloading. BL attenuated baroreflex sensitivity during intravenous infusion of sodium nitroprusside (SNP), but did not significantly affect the sensitivity following infusion of phenylephrine (PE). Baroreflex sensitivity became positive following sinoaortic denervation (SAD) during infusion of PE and attenuated sensitivity during infusion of SNP. Baroreflex sensitivity also became positive following double ablation (BL+SAD) during infusion of PE, and attenuated sensitivity during infusion of SNP. c-Fos protein expression increased significantly in the RVLM in the sham group after SNP administration. However, the BL, SAD, and SAD+BL groups showed significant decreases in c-Fos protein expression compared with that in the sham group. The SAD group showed more reduced c-Fos protein expression than that in the BL group, and the SAD+BL group showed less expression than that in the SAD group. These results suggest that the vestibular system cooperates with baroreceptors to maintain arterial pressure during hypotension but that baroreceptors regulate arterial pressure during both hypotension and hypertension. Additionally, afferent signals for maintaining blood pressure from the vestibular end organs and the baroreceptors may be integrated in the RVLM.

Mechanism of glutamate receptor for excitation of medial vestibular nucleus induced by acute hypotension.

In the vestibular nuclei, acute hypotension induces excitation of electrical activity and expression of c-Fos protein and phosphorylated extracellular signal-regulated kinase (pERK). Expression of c-Fos protein and pERK is mediated by the excitatory neurotransmitter, glutamate. We investigated the signaling pathway of glutamate and its receptors in the vestibular nuclei following acute hypotension in conscious rats. Glutamate release and the expression of c-Fos protein in the medial vestibular nuclei (MVN) were measured by microdialysis and immunohistochemical analysis, respectively. We compared the responses of rats with unilateral labyrinthectomy to unaltered controls. Acute hypotension was induced by infusing sodium nitroprusside (SNP) into the femoral vein. In the control group, glutamate release and the expression of c-Fos protein increased in the bilateral MVN following acute hypotension. In the unilateral labyrinthectomy group, glutamate release and the expression of c-Fos protein increased in the MVN contralateral to the lesion, but did not change in the ipsilateral MVN following acute hypotension. Microinjection of NMDA or AMPA into the lateral ventricle increased the expression of c-Fos protein in the bilateral MVN of conscious intact labyrinthine rats. However, after intracerebroventricular microinjection of MK-801 or CNQX little c-Fos protein was expressed in the bilateral MVN of these rats following acute hypotension. These results suggest that in response to acute hypotension, excitatory afferent signals from the peripheral vestibular receptors release glutamate into postsynaptic neurons in the vestibular nuclei. These excitatory signals are transmitted through the NMDA receptors and AMPA receptors of glutamate in the vestibular system.

Chronic Administration of Monosodium Glutamate under Chronic Variable Stress Impaired Hypothalamic-Pituitary-Adrenal Axis Function in Rats.

The hypothalamic-pituitary-adrenal (HPA) axis is the primary endocrine system to respond to stress. The HPA axis may be affected by increased level of corticotrophin-releasing factors under chronic stress and by chronic administration of monosodium glutamate (MSG). The purpose of this study was to investigate whether chronic MSG administration aggravates chronic variable stress (CVS)-induced behavioral and hormonal changes. Twenty-four adult male Sprague-Dawley rats, weighing 200~220 g, were divided into 4 groups as follows: water administration (CON), MSG (3 g/kg) administration (MSG), CVS, and CVS with MSG (3 g/kg) administration (CVS+MSG). In addition, for the purpose of comparing the effect on plasma corticosterone levels between chronic stress and daily care or acute stress, 2 groups were added at the end of the experiment; the 2 new groups were as follows: naïve mice (n=7) and mice exposed to restraint stress for 2 h just before decapitation (A-Str, n=7). In an open field test performed after the experiment, the CVS+MSG group significant decrease in activity. The increase in relative adrenal weights in the CVS and CVS+MSG group was significantly greater than those in the CON and/or MSG groups. In spite of the increase in the relative adrenal weight, there was a significant decrease in the plasma corticosterone levels in the CVS+MSG group as compared to all other groups, except the naïve group. These results suggest that impaired HPA axis function as well as the decrease in the behavioral activity in adult rats can be induced by chronic MSG administration under CVS rather than CVS alone.

The Effects of Glutamate NMDA Receptor Antagonist MK-801 on Gastrointestinal Motility after Middle Cerebral Artery Occlusion in Rats.

This study was performed to investigate the role of glutamate neurotransmitter system on gastrointestinal motility in a middle cerebral artery occlusion (MCAO) model of rats. The right middle cerebral artery was occluded by surgical operation, and intestinal transit and geometric center as a parameter of gastrointestinal motility and expression of c-Fos protein in the insular cortex and cingulate cortex were measured at 2 and 12 h after MCAO. Intestinal transit was 66.3+/-7.5% and 62.3+/-5.7% 2 and 12 h after sham operation, respectively, and MCAO significantly decreased intestinal transit to 39.0+/-3.5% and 47.0+/-5.1% at 2 and 12 h after the occlusion, respectively (p<0.01). The geometric center was 5.6+/-0.4 and 5.2+/-0.9 at 2 and 12 h after sham operation, respectively, and MCAO significantly decreased geometric center to 2.9+/-0.8 and 3.0+/-0.3 at 2 and 12 h after the occlusion, respectively (p<0.01). In control animals, injection of atropine decreased intestinal transit to 35.9+/-5.2%, and injection of glutamate NMDA receptor antagonist, MK-801, decreased intestinal transit to 28.8+/-9.5%. Pretreatment with MK-801, a glutamate NMDA receptor antagonist, in the MCAO group decreased intestinal transit to 11.8+/-3.2%, which was significantly decreased compared to MCAO group (p<0.01). MCAO markedly increased the expression of c-Fos protein in the insular cortex and cingulate cortex ipsilateral to the occlusion 2 h after MCAO, and pretreatment with MK-801 produced marked reduction of c-Fos protein expression compared to MCAO group (p<0.01). These results suggest that modulation of gastrointestinal motility after MCAO might be partially mediated through a glutamate NMDA receptor system.

Changes of some amino acid concentrations in the medial vestibular nucleus of conscious rats following acute hypotension.

Microdialysis and high performance liquid chromatography (HPLC) were used to measure the changes of certain amino acids in the medial vestibular nucleus (MVN) of conscious rats in order to understand whether those amino acids are involved in the regulation of blood pressure. Acute hypotension was induced by infusing sodium nitroprusside (SNP) into the femoral vein. In the control group, glutamate (Glu) release increased, though gamma-aminobutyric acid (GABA) and taurine (Tau) release decreased in the MVN following acute hypotension. In the unilateral labyrinthectomy group, the levels of Glu, GABA, and Tau were unchanged in the ipsilateral MVN to the lesion following acute hypotension. Furthermore, in the contralateral MVN to the lesion, Glu release increased, and GABA and Tau release decreased following acute hypotension. These results suggest that SNP-induced acute hypotension can influence the activity of neurons in the MVN through afferent signals from peripheral vestibular receptors, and that certain amino acid transmitters in the MVN are involved in this process.

Recovery of vestibulogastrointestinal symptoms during vestibular compensation after unilateral labyrinthectomy in rats.

BACKGROUND: The loss of unilateral vestibular function causes vestibulogastrointestinal symptoms that include nausea and vomiting. However, the temporal changes occurring on vestibular compensation are unclear. Thus, the temporal changes and the role of the cerebellum in the recovery of vestibulogastrointestinal symptoms after unilateral labyrinthectomy (UL) were investigated in this study. METHODS: Vestibulogastrointestinal symptoms were evaluated for intestinal transit and geometric center, whereas vestibulo-ocular symptoms were represented by spontaneous nystagmus. Expression of the c-Fos protein was observed in the vestibular nuclei. These were measured at 30 minutes and at 2, 6, and 24 hours after UL in rats. RESULTS: Intestinal transit was 66.3% +/- 7.6% in the control animals but significantly decreased to 40.7% +/- 7.8%, 46.3% +/- 6.3%, and 48.6% +/- 10.8% at 30 minutes (p < 0.01), 2 hours (p < 0.01), and 6 hours (p < 0.05) after UL, respectively. The intestinal transit showed a recovery to control levels 24 hours after UL. The geometric center was 5.6 +/- 0.4 in control animals but significantly decreased to 2.1 +/- 0.4, 2.9 +/- 0.3, and 4.0 +/- 0.3 at 30 minutes, 2 hours, and 6 hours after UL, respectively (p < 0.01). Recovery of the geometric center to control levels, 24 hours after UL, was reported. Uvulonodullectomy significantly decreased the intestinal transit and geometric center for 24 hours after surgery (p < 0.01). Moreover, UL in uvulonodullectomized animals significantly decreased the intestinal transit and geometric center for 24 hours after surgery (p < 0.01). Pretreatment of the UL animals with MK-801 significantly increased the geometric center 30 minutes after surgery (p < 0.01). Unilateral labyrinthectomy produced spontaneous nystagmus, 28.9 +/- 1.5, 23.3 +/- 1.4, 17.5 +/- 1.5, and 9.2 +/- 0.9 beats per 10 seconds at 30 minutes and at 2, 6, and 24 hours after UL, respectively. Expression of the c-Fos protein was significantly increased in the medial vestibular nuclei and inferior vestibular nuclei at 1, 2, and 6 hours after UL, and the expression was significantly decreased in animals that were pretreated with MK-801 (p < 0.01). CONCLUSION: These results suggest that the recovery of vestibulogastrointestinal symptoms is faster than that of vestibulo-ocular symptoms and that the cerebellum and glutamate have an important role to play in the recovery of symptoms after UL.

Cardioprotective effects of alpha-lipoic Acid on myocardial reperfusion injury: suppression of reactive oxygen species generation and activation of mitogen-activated protein kinase.

BACKGROUND AND OBJECTIVES: Reactive oxygen species (ROS) and mitogen-activated protein (MAP) kinase play an important role in the development of myocardial reperfusion injury. In this study, we examined whether treatment with alpha-lipoic acid (ALA) before reperfusion could prevent myocardial reperfusion injury in vivo. MATERIALS AND METHODS: Sprague-Dawley rats were subjected to a 45-minute left anterior descending coronary artery ligation followed by 45- or 10-minute reperfusion. ALA was administered 10 minutes prior to reperfusion. The infarct size ratio of the infarct area to the ischemic area at risk, was measured based on 10, 25, 50, and 100 mg/kg of ALA, with propidium iodide (PI) fluorescence. Apoptosis was evaluated by TdT-mediated dUDP nick end labeling (TUNEL) staining. The generation of intracellular ROS was evaluated using the fluorogenic probe, dichlorodihydrofluorescein diacetate (CM-H(2)DCFDA). Western blot analysis was performed for MAP kinase (pERK 1/2 and pJNK 1/2) activity. RESULTS: The infarct size, according to ALA dose, was significantly suppressed 29.1% with ALA 25 mg/kg (p<0.0001), 41.5% with 50 mg/kg (p<0.05), and 41.4% with 100 mg/kg (p<0.05) compared to the controls (54.3%). However, the results were not significantly different with 47.2% of the ALA 10 mg/kg (p=0.192). A few apoptotic nucleoli were detected in the ALA 25 mg/kg group, but were frequently detected in the control group. The ROS generation was significantly suppressed (p<0.0001), the activity of pERK 1/2 was significantly increased (p<0.05) and the activity of pJNK 1/2 was significantly decreased (p<0.05) in the ALA 25 mg/kg group compared to the controls. CONCLUSION: The results of this study suggested that adequate doses of ALA before reperfusion was effective for the prevention of myocardial reperfusion injury in vivo. This cardioprotective activity of ALA might be associated with an anti-apoptotic effect of ALA via suppression of ROS generation, increase of pERK 1/2 and decrease of pJNK 1/2 activity.

Changes in calbindin expression within the flocculus after unilateral labyrinthectomy in rats.

The role of flocculus in vestibular compensation is still a controversial issue. Calbindin regulates intracellular signaling and has been reported to be a reliable marker of Purkinje cell. Expression of calbindin in flocculus was examined using immunohistochemistry following unilateral labyrinthectomy (UL) in rats. Both the staining intensity and number of calbindin-positive Purkinje cells in the ipsilateral flocculus to the lesion side decreased 6h after UL compared to the control and contralateral side. Forty-eight hours after UL, the expression of calbindin returned to control levels and asymmetric expression in bilateral flocculus subsided. These transient reduction of calbindin expression in the ipsilateral flocculus may reflect a decrease in the GABAergic inhibition of the floccular Purkinje cell to the ipsilateral vestibular nuclei during vestibular compensation.

Signaling pathway of glutamate in the vestibular nuclei following acute hypotension in rats.

Acute hypotension induces excitation of electrical activity and expression of c-Fos protein and phosphorylated extracellular signal-regulated kinase (pERK) in the vestibular nuclei. Expression of c-Fos protein and pERK is mediated by the excitatory neurotransmitter, glutamate. In this study, in order to investigate the signaling pathway of glutamate in the vestibular nuclei following acute hypotension, expression of the NR2B subunit of glutamate N-methyl-D-aspartate (NMDA) receptors and the GluR1 subunit of glutamate alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptors was measured by Western blotting in the medial vestibular nucleus (MVN) following acute hypotension in bilateral labyrinthectomized (BL) rats. In intact labyrinthine animals, acute hypotension increased expression of pGluR1 and pNR2B in the MVN. Expression of pGluR1 Ser831 and Ser845 peaked at 5 and 30 min after acute hypotension and expression of pNR2B peaked at 60 min after acute hypotension, respectively. In BL animals, expression of pGluR1 Ser831, pGluR1 Ser845, and pNR2B was decreased significantly compared to intact labyrinthine animals following acute hypotension. These results suggest that excitatory afferent signals from the peripheral vestibular receptors, resulting from acute hypotension, release glutamate into postsynaptic neurons in the vestibular nuclei and the excitatory signals are transmitted through the GluR1 subunit of the AMPA receptors and the NR2B subunits of the NMDA receptors in the vestibular system.