In order to know the effects of caloric stimulation on neuronal firing in medial vestibular nuclei (MVN) by middle ear irrigation, the middle ear was irrigated with ice (4 degrees C), hot (44 degrees C), and warm (37 degrees C) water, and the firing rate of MVN neuron was extracellularly recorded. The results showed that the firing rate of MVN neuron was changed by caloric stimulation, and the majority of MVN neurons showed excitation by irrigation with hot water and inhibition by ice water (type A). The neuronal firing was recovered immediately after the cessation of the stimulation. I It was concluded that the neuronal firing rate in MVN was changed by caloric stimulation in middle ear cavity. The response was different in various neurons.
Cold ; Ear, Middle ; Electrophysiology ; Endolymph/physiology ; Heat ; Irrigation ; Neurons/classification ; Neurons/physiology ; Rats, Wistar ; Vestibular Nerve/*physiology ; Vestibular Nuclei/*physiology

The capability of the central vestibular system in utilizing cues arising from the inner ear determines the ability of animals to acquire the sense of head orientations in the three-dimensional space and to shape postural movements. During development, neurons in the vestibular nucleus (VN) show significant changes in their electrophysiological properties. An age-dependent enhancement of membrane excitability is accompanied by a progressive increase in firing rate and discharge regularity. The coding of horizontal and vertical linear motions also exhibits developmental refinement in VN neurons. Further, modification of cell surface receptors, such as glutamate receptors, of developing VN neurons are well-orchestrated in the course of maturation, thereby regulating synaptic efficacy and spatial coding capacity of these neurons in local circuits. Taken together, these characteristic features of VN neurons contribute to developmental establishment of space-centered coordinates within the brain.
Animals ; Ear, Inner ; physiology ; Electrophysiological Phenomena ; Movement ; Neurons ; physiology ; Rats ; Receptors, Cell Surface ; physiology ; Vestibular Nuclei ; physiology

Vestibular compensation is an important model for developing the prevention and intervention strategies of vestibular disorders, and investigating the plasticity of the adult central nervous system induced by peripheral injury. Medial vestibular nucleus (MVN) in brainstem is critical center for vestibular compensation. Its neuronal excitability and sensitivity have been implicated in normal function of vestibular system. Previous studies mainly focused on the changes in neuronal excitability of the MVN in lesional side of the rat model of vestibular compensation following the unilateral labyrinthectomy (UL). However, the plasticity of sensitivity of bilateral MVN neurons dynamically responding to input stimuli is still largely unknown. In the present study, by using qPCR, whole-cell patch clamp recording in acute brain slices and behavioral techniques, we observed that 6 h after UL, rats showed a significant deficit in spontaneous locomotion, and a decrease in excitability of type B neurons in the ipsilesional rather than contralesional MVN. By contrast, type B neurons in the contralesional rather than ipsilesional MVN exhibited an increase in response sensitivity to the ramp and step input current stimuli. One week after UL, both the neuronal excitability of the ipsilesional MVN and the neuronal sensitivity of the contralesional MVN recovered to the baseline, accompanied by a compensation of spontaneous locomotion. In addition, the data showed that the small conductance Ca²⁺-activated K⁺ (SK) channel involved in the regulation of type B MVN neuronal sensitivity, showed a selective decrease in expression in the contralesional MVN 6 h after UL, and returned to normal level 1 week later. Pharmacological blockage of SK channel in contralateral MVN to inhibit the UL-induced functional plasticity of SK channel significantly delayed the compensation of vestibular motor dysfunction. These results suggest that the changes in plasticity of the ipsilesional MVN neuronal excitability, together with changes in the contralesional MVN neuronal sensitivity, may both contribute to the development of vestibular symptoms as well as vestibular compensation, and SK channel may be an essential ionic mechanism responsible for the dynamic changes of MVN neuronal sensitivity during vestibular compensation.
Animals ; Locomotion ; Neurons/physiology* ; Patch-Clamp Techniques ; Rats ; Vestibular Nuclei/metabolism* ; Vestibule, Labyrinth

In order to know the effects of caloric stimulation on neuronal firing in medial vestibular nuclei (MVN) by middle ear irrigation, the middle ear was irrigated with ice (4 degrees C), hot (44 degrees C), and warm (37 degrees C) water, and the firing rate of MVN neuron was extracellularly recorded. The results showed that the firing rate of MVN neuron was changed by caloric stimulation, and the majority of MVN neurons showed excitation by irrigation with hot water and inhibition by ice water (type A). The neuronal firing was recovered immediately after the cessation of the stimulation. I It was concluded that the neuronal firing rate in MVN was changed by caloric stimulation in middle ear cavity. The response was different in various neurons.
Animals ; Cold Temperature ; Ear, Middle ; Electrophysiology ; Endolymph ; physiology ; Female ; Hot Temperature ; Male ; Neurons ; classification ; physiology ; Rats ; Rats, Wistar ; Therapeutic Irrigation ; Vestibular Nerve ; physiology ; Vestibular Nuclei ; physiology

OBJECTIVETo establish the visual patch clamp whole-cell recording technique and study the properties and functional significance of muscarinic receptor-mediated currents in rat medial vestibular nucleus neurons (MVNn).

METHODSBrain slices containing the MVN were prepared from fifteen Wistar rats. By combining infrared differential interference contrast (IR-DIC) technique and CCD-Camera system with visual patch clamp whole-cell recording technique, twenty healthy neurons were located and muscarinic receptor-mediated currents in rat MVNn were observed and analyzed.

RESULTSVisual patch clamp technique can be used to make direct localization and to make sure of active neuron. In MVNn, a comparison of the current-voltage relationships before and during the application of muscarine, which revealed an increase in the slope of the I-V curve and the reversal potential for this response lay at (-88.4 +/- 4.9) mV (x +/- s), indicates that the activation of muscarinic cholinergic receptors leads to a decrease in potassium current. The test in the voltage sensitivity of the muscarine-induced response, which showed that the effect had a linear current-voltage relationship and reversed at (-86.7 +/- 3.5) mV, indicates that the potassium current blocked by muscarine corresponds to the voltage-insensitive leak potassium current.

CONCLUSIONSVisual patch clamp technique, which was considered better than blind patch clamp technique, can improve the success of sealing process. By the analysis of muscarinic receptor-mediated currents, the data provide support that muscarinic cholinergic mechanisms play a prominent role in the modulation of the excitability of MVNn and also offer a new idea for the efficacy of anticholinergic drugs.

Animals ; Electrophysiological Phenomena ; Neurons ; physiology ; Patch-Clamp Techniques ; Rats ; Rats, Wistar ; Receptors, Muscarinic ; physiology ; Vestibular Nuclei ; physiology

OBJECTIVETo study human vestibular cerebral representations by combining right-sided ice-water stimulation at 0 degree C with blood oxygenation level dependent functional magnetic resonance imaging (BOLD-fMRI) and to evaluate the value of this method in the functional localization of human vestibular cortex.

METHODSTwenty right-handed volunteers (12 men and 8 women) received unilateral irrigation of the right external auditory meatu for 15 s with 15 ml of water at 0 degrees C during fMRI in complete darkness. The functional imaging of brain cortex was acquired with a 1.5-T MRI scanner (Signa Infinity Twin + Excite; General Electric Co., USA). The successive functional images from each subject were analyzed as a group with statistical parametric mapping software (SPM 99).

RESULTSUltimately, data obtained from 17 subjects were analyzed (3 subjects were eliminated from data because of head movement exceeding 2 mm). The group analysis showed bilateral (particularly left-sided) cortical activation, associated with caloric stimulus involving in temporoparietal junction extending into the posterior insula, supramarginal gyrus in the inferior parietal lobe, precuneus, supplementary motor area (SMA), the ventrolateral portion of the occipital lobe, cuneus and lingual gyrus, superior temporal gyrus and cingular cortex.

CONCLUSIONSIce-water stimulation at 0 degree C in fMRI reveals a widespread cortical network involved in vestibular signal processing in human. As the functional localization of vestibular cortex could be determined precisely, ice-water stimulation at 0 degree C in fMRI would hold great promise as a sensitive and reproducible tool for the research in human vestibular cortex.

Adult ; Brain Mapping ; Cerebral Cortex ; anatomy & histology ; physiology ; Ear, Inner ; Female ; Humans ; Magnetic Resonance Imaging ; methods ; Male ; Vestibular Nuclei ; anatomy & histology ; physiology ; Young Adult

OBJECTIVETo investigate modulation of gamma-aminobutyric acid (GABA) and its receptors on medial vestibular nucleus neurons in vivo.

METHODSTwenty-six male Wistar rats were used. gamma-aminobutyric acid, bicuculline (BIC, gamma-aminobutyric acid A receptor antagonist) and 2-hydroxysaclofen (SAC, gamma-aminobutyric acid B receptor antagonist) were microiontophoresed on medial vestibular nucleus (MVN) neurons to determine the effects of gamma-aminobutyric acid and its antagonists on the neuronal firing rates of medial vestibular nucleus in rats in vivo.

RESULTSMicroiontophoretic application of y-aminobutyric acid at 10, 30, 50 nA electric current produced inhibitory responses on 42 MVN neurons, these responses were dose-dependent decreases, firing rates (x +/- s) of MVN neurons decreased form (14.8 +/- 5.6) times/s to (8.7 +/- 3.4) times/s, (4.1 +/- 1.6) times/s and (2.2 +/- 1.1) times/s respectively; microiontophoretic application of bicuculline in 37 MVN neurons, 86.5% (32/37) neurons produced excitatory responses, 13.5% (5/37) neurons didn't response, firing rates of MVN neurons increased form (15.3 +/- 6.3) times/s to (16.8 +/- 7.1) times/s, (25.9 +/- 10.1) times/s and (32.7 +/- 11.3) times/s respectively at 10, 30, 50 nA electric current, which were dose-dependent increases, and the inhibitory responses of gamma-aminobutyric acid on MVN neurons were blocked by bicuculline completely; however, microiontophoretic application of 2-hydroxysaclofen didn't produced responses as bicuculline did.

CONCLUSIONSModulation of gamma-aminobutyric acid on medial vestibular nucleus neurons was mediated by y-aminobutyric acid A receptor in vivo.

Animals ; Electrophysiology ; Male ; Neurons ; drug effects ; physiology ; Rats ; Rats, Wistar ; Receptors, GABA ; metabolism ; Vestibular Nuclei ; cytology ; drug effects ; physiology ; gamma-Aminobutyric Acid ; pharmacology

In order to understand whether some special amino acids in the medial vestibular nucleus (MVN) of rats are involved in the regulation of blood pressure, we used microdialysis technique and high performance liquid chromatography (HPLC) to measure the changes of glutamate and taurine in this central area. Acute hypotension was induced by hemorrhage from the femoral artery. It was observed that the basal release of glutamate and taurine in the MVN was stable about 90 min after the beginning of microdialysis. The basal release of glutamate was (18.96 +/- 0.27) pmol/sample (8 mul), and that of taurine was (7.73 +/- 0.05) pmol/sample (8 mul). Glutamate release increased (P<0.05) and taurine release reduced (P<0.05) in the MVN in the hemorrhage-induced acute hypotensive rats. Nevertheless, these changes were not observed in the hemorrhage-induced acute hypotensive rats which were pretreated by infusing 2% lidocaine into the middle ear or 100 mg arsanilic acid into the tympanic cavity. These results suggest that the hemorrhage-induced acute hypotention can influence the activity of the neurons in the MVN by the afferent impulses from vestibular organ, and that some special amino acid transmitters in the MVN are involved in this process.
Animals ; Blood Pressure ; physiology ; Glutamic Acid ; metabolism ; Hypotension ; metabolism ; physiopathology ; Male ; Microdialysis ; methods ; Rats ; Rats, Wistar ; Taurine ; metabolism ; Vestibular Nuclei ; metabolism ; physiopathology

To understand the neurochemical mechanisms underlying the vestibular compensation, we determined the levels of amino acids such as aspartate, glutamate, glutamine, glycine, taurine, alanine in the medial vestibular nucleus (MVN) following unilateral labyrinthectomy (UL), by using in vivo brain microdialysis and high-performance liquid chromatography technique. Rats were pretreated by infusing 2% lidocaine 1.2 mL or 10 mg arsanilic acid into the tympanic cavity to obstruct uni-periphery vestibular organ, and then the levels of amino acids were determined in MVN of normal control and ipsilateral or contralateral lesional (ipsi-/contra-lesional) rats. In the control experiment, the levels of aspartate, glutamate, glutamine, glycine, taurine, and alanine were (6.15 +/- 0.59), (18.13 +/- 1.21), (33.73 +/- 1.67), (9.26 +/- 0.65), (9.56 +/- 0.77) and (10.07 +/- 0.83) pmol/8 muL sample, respectively. The concentrations of aspartate and glutamate decreased, while the concentration of taurine increased in the ipsi-lesional MVN of rats 10 min after infusing 2% lidocaine into middle ear to obstruct uni-periphery vestibular organ. Whereas the concentration of glutamate increased, the concentrations of glycine and alanine decreased in the contra-lesional MVN, accompanied by imbalances of glutamate, glycine and alanine in the bilateral nuclei. In contrast, the levels of glutamate and alanine decreased, the level of glutamine increased in the ipsi-lesional MVN, and the level of glutamate decreased in the contra-lesional MVN of rats 2 weeks after infusing 10 mg arsanilic acid into the tympanic cavity to obstruct uni-periphery vestibular organ. Furthermore, the level of glutamine in the ipsi-lesional MVN was obviously higher than that in the contra-lesional MVN. These results demonstrate that an imbalance of different amino acids appeared in bilateral MVN after UL, and this imbalance decreased after the development of vestibular compensation. Whereas the imbalance of glutamine release in bilateral nuclei appeared after vestibular compensation.
Amino Acids ; metabolism ; Animals ; Aspartic Acid ; metabolism ; Ear, Inner ; physiology ; surgery ; Glutamic Acid ; metabolism ; Male ; Rats ; Rats, Wistar ; Taurine ; metabolism ; Vestibular Nuclei ; metabolism ; physiopathology

To understand whether some amino acids in the medial vestibular nucleus (MVN) of conscious rats are involved in the regulation of blood pressure, microdialysis technique and high performance liquid chromatography (HPLC) were used to measure the changes of gamma-aminobutyric acid (GABA) and glycine (Gly) in this central area. Wistar rats (250-350 g) were randomly divided into three experimental groups: the control group with intact labyrinths; the ipsilateral MVN of unilateral labyrinthectomy (UL); contralateral MVN of the UL. Acute hypotension was induced by intravenous infusion of sodium nitroprusside (SNP). Unilateral chemical labyrinthectomy was performed 14 days before the start of the experiment to eliminate afferent signals from the peripheral vestibular receptors in the inner ear. Blood pressure decreased by 30% after SNP injection. In the control group, GABA and Gly release reduced to 43.53%+/-6.58% (P<0.01) and 62.24%+/-7.51% (P<0.01) respectively in the MVN following SNP-induced acute hypotension in conscious rats. In the contralateral MVN of UL, GABA and Gly release also reduced to 45.85%+/-17.27% (P<0.01) and 73.30%+/-3.00% (P<0.01) respectively following SNP-induced acute hypotension in conscious rats. In contrast, in the ipsilateral MVN of UL, GABA and Gly releases were not changed following SNP-induced acute hypotension in conscious rats. These results suggest that the SNP-induced acute hypotension may influence the activity of the neurons in the MVN by the afferent impulses from the peripheral vestibular organ, and that GABA and Gly may be involved in this process.
Acute Disease ; Animals ; Chromatography, High Pressure Liquid ; Ear, Inner ; physiology ; surgery ; Glycine ; metabolism ; Hypotension ; metabolism ; physiopathology ; Male ; Microdialysis ; Random Allocation ; Rats ; Rats, Wistar ; Vestibular Nuclei ; metabolism ; physiology ; gamma-Aminobutyric Acid ; metabolism