Outer hair cell driven reticular lamina mechanical distortion in living cochleae.

Cochlear distortions afford researchers and clinicians a glimpse into the conditions and properties of inner ear signal processing mechanisms. Until recently, our examination of these distortions has been limited to measuring the vibration of the basilar membrane or recording acoustic distortion output in the ear canal. Despite its importance, the generation mechanism of cochlear distortion remains a substantial task to understand. The ability to measure the vibration of the reticular lamina in rodent models is a recent experimental advance. Surprising mechanical properties have been revealed. These properties merit both discussion in context with our current understanding of distortion, and appraisal of the significance of new interpretations of cochlear mechanics. This review focusses on some of the recent data from our research groups and discusses the implications of these data on our understanding of vocalization processing in the periphery, and their influence upon future experimental directions. This article is part of the Special Issue Outer hair cell Edited by Joseph Santos-Sacchi and Kumar Navaratnam.

Identification of hub prognosis-associated oxidative stress genes in skin cutaneous melanoma using integrated bioinformatic analysis.

OBJECTIVE: Oxidative stress (OS) significantly correlates with cancer progression. However, targeting OS has not been considered as a therapeutic strategy in skin cutaneous melanoma (SKCM) due to a lack of systematical studies on validated biomarkers. The work presented here aimed to identify hub prognosis-associated OS genes in SKCM and generated an effective predictive model. PATIENTS AND METHODS: Gene expression profiles of SKCM samples and normal skin tissues were obtained from the Genotype-Tissue Expression (GTEx) and The Cancer Genome Atlas (TCGA) databases to identify differentially expressed OS genes. The validation cohort was obtained from the Gene Expression Omnibus (GEO) database. RESULTS: Thirteen hub prognosis-associated OS genes were recognized and incorporated into the prognostic risk model. Our constructed model was significantly associated with overall survival of SKCM patients as well as was shown to be associated with cancer progression. Our prognostic risk model was found to improve the accuracy of diagnostics, as shown using both TCGA and GEO cohorts. Both hub gene expression and risk score were used to generated nomograms that displayed favorable discriminatory abilities for SKCM. CONCLUSIONS: Overall, our study presents a model that may provide novel insights into the prognosis and survival of SKCM patients, as well as the development of individualized treatment therapy.

Group I metabotropic glutamate receptors in spiral ganglion neurons contribute to excitatory neurotransmissions in the cochlea.

Evidence has accumulated over the years supporting glutamate as the primary neurotransmitter used by hair cells in afferent cochlear neurotransmission. Besides acting on ionotropic glutamate receptors, glutamate also activates second messenger systems via G-protein-coupled metabotropic glutamate receptors (mGluRs) to modulate neuronal excitability. However, it is unclear whether mGluRs participate in cochlear neurotransmission. We present evidence directly supporting a functional role for group I metabotropic glutamate receptors (mGluRIs) in spiral ganglion (SG) neurons. The presence of mGluRI and downstream G-protein subunits was demonstrated by molecular biology and immunolabeling methods. Direct activation of mGluRIs in cultured SG neurons resulted in transient increases of intracellular Ca(++) concentration and transient inward currents that gave rise to firings of multiple action potentials. These responses showed mGluRI pharmacological specificity and quickly desensitized. We next examined changes in cochlear function after noise exposure as a result of pharmacologically manipulating cochlear glutamate neurotransmission. These in vivo tests showed that blocking non-N-methyl-D-aspartic acid glutamate receptors was sufficient to eliminate compound action potentials of the auditory nerve, and pharmacologically inhibiting mGluRIs in the cochlea did not significantly affect the hearing threshold. In contrast, blocking mGluRIs lowered the amplitude of compound action potentials at louder sound levels and reduced the noise-induced temporary threshold shift. Our results suggest that although mGluRIs did not initiate fast excitatory cochlear neurotransmission, their activation contributed to the growth of excitatory responses of the cochlea. As a result, the cochlea was more resistant to noise-induced temporary hearing losses without the activation of mGluRIs in SG neurons.

Autoregulation of cochlear blood flow in the hydropic guinea pig.

Previous data suggest that regulation of cochlear blood flow (CBF) may be abnormal in the hydropic guinea pig. The purpose of this study was to employ the technique of anterior inferior cerebellar artery (AICA) occlusion to measure CBF autoregulation in experimental endolymphatic hydrops. This study also addresses the role of the cochlear sympathetic neural innervation and nitric oxide in CBF regulation with hydrops. In anesthetized guinea pigs, CBF was measured with a laser Doppler flowmeter probe while the AICA was intermittently occluded with a microvascular occluder. The CBF response was measured in normal, 6-week, and 12-week chronically hydropic animals. The gain factors (0 = no autoregulation, 1 = complete autoregulation) for 1-min occlusion were 0.95 +/- 0.16 (control), 0.77 +/- 0.28 (6 week, P = 0.164), and 0.67 +/- 0.25 (12 week, P = 0.037). NG-nitro-L-arginine methyl ester (L-NAME), a competitive inhibitor of nitric oxide synthase, was infused intravenously to assess basal nitric oxide (an endogenous vasodilator) production in the hydropic ear. With infusion of L-NAME, CBF was reduced by 9.16 +/- 11%, 10.7 +/- 10% (P = 0.87), and 16.6 +/- 18% (P = 0.95), in the control, 6-week, and 12-week animals, respectively. In a separate group of 12-week hydropic animals, the left superior cervical ganglion (SCG) was anesthetized with lidocaine, and AICA occlusions were performed pre- and post-blockade. Prior to blocking the SCG, the gain was 0.712 +/- 0.02 and afterwards 0.708 +/- 0.051 (P = 0.93). The above results show that there was a statistically significant reduction in CBF autoregulation in the 12-week hydropic animals. There was no difference in basal nitric oxide production in normal versus hydropic animals nor was there a change in autoregulation following blockade of the SCG. These data provide clear evidence for reduced CBF autoregulation in experimental endolymphatic hydrops.

Hydrops-induced changes in cochlear blood flow.

Laser Doppler flowmetry was used to assess cochlear blood flow (CBF) in the hydropic ear in four experiments. 1) The increase in CBF elicited by local electrical stimulation of the cochlea in the hydropic ear was compared to that observed in normal controls. The magnitude of the evoked CBF change was reduced by approximately 30% in the hydropic ear compared to the normal ear. 2) The reduction in CBF evoked by direct electrical stimulation of the superior cervical ganglion was reduced by approximately one third in the hydropic ear compared to a normal ear. 3) Rhythmic (flux motion or vasomotion) variations in CBF, observed in association with lower blood pressure and thought to extend the autoregulatory range in an organ system, were reduced or eliminated in the hydropic ear. 4) The autoregulatory response to a decreased perfusion pressure, produced by decreased cardiac output, was clearly reduced relative to control in the hydropic ear. These findings represent the first report of significant CBF changes with hydrops. They are consistent with reports of increased sensitivity of the hydropic ear to trauma and stress and may be relevant considerations in the treatment of hydrops in humans.

Studies of inner ear blood flow in animals and human beings.

This article reviews current studies on inner ear blood flow, discusses their relevance to the maintenance of normal homeostasis of the inner ear, reports for the first time clear changes in fundamental properties of cochlear blood flow in the chronic hydropic ear, and describes the potential of applying laser Doppler flowmetry technology to the measurement of inner ear blood flow in human beings. Studies of the guinea pig in which perfusion pressure is varied demonstrate a broad range of autoregulatory capabilities of the inner ear vasculature. Gain factors range from 0.76 and higher for recovery for less than 1 minute of modified perfusion pressure. This is significantly greater than reports obtained for brain autoregulation. In a series of four investigations of cochlear blood flow in the hydropic ear in guinea pigs, a decreased responsiveness to electrical stimulation and direct stimulation of the superior cervical ganglia was found, indicating a change in sympathetic control of cochlear tone. Reduced vasomotion was observed, and autoregulatory capabilities were reduced. In human investigations, changes in cochlear blood flow were demonstrated with direct electrical stimulation of the round window and warm water irrigation of the ear canal, but not with carbogen breathing. Increased cochlear blood flow was observed with increased systemic blood pressure, and a remarkable decrease in cochlear blood flow was observed with the application of 1:10,000 epinephrine to the round window. These observations indicate the potential for development of laser Doppler flowmetry technology in the diagnosis and treatment of inner ear vascular disorders, and the animal investigations suggest that changes may occur in the chronic hydropic ear that compromise autoregulation and thus increase the sensitivity of the hydropic ear to other stress factors. Treatments can be found to modify such changes in vascular tone.

Neuronal regulation of cochlear blood flow in the guinea-pig.

1. Previous studies have shown that electrical stimulation (ES) of the guinea-pig cochlea causes a neurally mediated increase in cochlear blood flow (CBF). It is known that the centrifugal neuronal input to the cochlea comes through the perivascular sympathetic plexus from the cervical sympathetic chain and along the vestibular nerve (VN) from the periolivary area of the brainstem. Both of these neuronal systems are distributed topographically in the cochlea. 2. In order to study the neural origins of ES-evoked CBF increase, laser Doppler flowmetry was used to test the following hypotheses. (a) The response is regional, that is, limited to the area of the cochlea stimulated. To test this we performed differential ES of the cochlear turns. CBF was measured from either the third or the first turn. (b) The response is mediated via autonomic receptors within the cochlea. To study this, we applied atropine, succinylcholine and idazoxan locally to the cochlea. (c) The response is influenced by neuronal input via the sympathetic cervical chain (SC) and components of the VN. We stimulated and sectioned the SC, and sectioned the VN, to test this hypothesis. 3. We observed that the CBF response was topographically restricted to the stimulated region. Locally applied muscarinic or nicotinic antagonists (atropine and succinylcholine respectively) did not affect the response. However, local idazoxan (an alpha 2-blocker) eliminated the response. Locally applied adrenaline and SC stimulation modified the dynamic range of the response. SC sectioning enhanced the responsiveness of the cochlear vasculature to ES. The VN section caused a temporary decrease in CBF and elimination of the ES-evoked CBF response. 4. We conclude that the release of dilating agents is topographical with respect to ES current flow, the ES-evoked CBF increase is peripherally mediated via alpha 2-receptors, and the response is influenced by input via the SC. The elimination of the response by VN sectioning proximal to the brainstem indicated that fibres of the VN mediate the CBF increase during direct cochlear ES. The data suggest that these fibres may be the efferent limb of a neural loop involved with the regulation of CBF. Such a system could provide a mechanism for the rapid increase in CBF with organ stress.

Cochlear flux motion and arterial pressure reduction in guinea pig.

Vasomotion, as a fundamental phenomenon of microvessels, exists in the cochlea of guinea pig. In the current study, the vasomotion and its relation to arterial pressure reduction was studied in the guinea pig cochlea, using laser Doppler flowmetry (LDF). Blood pressure (BP) in 25 guinea pigs was manipulated by a mechanical occluder placed around the descending aorta or the inferior vena cava. Before thoracotomy and artificial respiration, BP was 55.5 +/- 10.9 mmHg and no flux motion occurred. Vasomotion became evident when BP was significantly lower (28.2 +/- 7.2 mmHg) than the mean BP after thoracotomy (37.3 +/- 8.3 mmHg) (t = 4.1536, p < 0.05). Vasomotion appeared during both continuous hypotension and brief BP decreases caused by mechanical occlusion. During periods of continuous flux motion, both increase and decrease in BP could weaken or abolish it. The pressure provoking the vasomotion was different for each animal but the pressure range for a given animal was relatively stable. Mean frequency and amplitude of flux motion were 3.8 +/- 0.6 cycles per min and 20.8 +/- 7.1% of the baseline. A negative linear relationship was found between amplitude and frequency. Oscillations of LDF signal indicate that there is a synchronization of contraction and relaxation of cochlear microvessels or of the larger supplying vessels to the cochlea. Manipulation of BP possibly initiates the fluctuating change in vascular tone by influencing the activity of pacemaker or feedback mechanisms of cochlear vascular smooth muscles.(ABSTRACT TRUNCATED AT 250 WORDS)

Provoked flux motion of cochlear blood flow measured with laser Doppler flowmetry in guinea pig.

Although progress has been made in the study of cochlear blood flow (CBF) regulation since laser Doppler flowmetry (LDF) was introduced, cochlear vasomotion has not been investigated. Therefore, the primary objective of this study was to determine if oscillatory fluctuations of CBF could be provoked. Guinea pigs were anesthetized with diazepam (5 mg/kg) and fentanyl (0.32 mg/kg). Blood pressure (BP) was recorded from a carotid artery cannula. The cochlea and pons cerebellum were ventrally exposed; the bilateral CBF and brain blood flow (BBF) or skin blood flow (SBF) were monitored by LDF. After administration of phentolamine (0.25-0.75 mg/kg, i.v.), ipsilateral CBF in 7 of 16 animals showed a 2-5 min episode of oscillation. During artificial hyperventilation, continuous oscillation of CBF was recorded (the flux motion frequency was 3.5 +/- 0.5 cycles per min and its amplitude 25.8 +/- 5.6% from baseline). The time-dependent flux change (the waveform) was the same throughout a single cochlea but different between cochleae of the same animal. Compared to BBF, CBF vasomotion frequency was lower, and amplitude larger. SBF exhibited no such motion. Flux motion could be eliminated by inhalation of pure oxygen or 5% CO2 in oxygen or by the smooth muscle relaxants, papaverine and hydralazine. Phentolamine-induced vasomotion may be due to a hypotensive perfusion pressure, and hyperventilation-enhanced vasomotion may be caused by changing blood gas concentrations and by hormonal or neuronal activity. Oxygen and CO2 inhalation slightly increased BP and this change in perfusion pressure was probably associated with weakened vasomotion.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of electrical stimulation of the superior cervical ganglion on cochlear blood flow in guinea pig.

It has been proposed that cochlear blood flow (CBF) is controlled in part by the sympathetic nervous system. In the present study the effect of electrical stimulation of the superior cervical ganglion (SCG) on CBF in guinea pigs was investigated using laser Doppler flowmetry (LDF). Animals were anesthetized with diazepam and fentanyl and the SCG was exposed. A custom-designed bipolar cuff electrode was fixed around the ganglion and 1 ms biphasic current pulses were injected at 0.15 mA to 1.5 mA, 6 Hz. Bilateral CBF was monitored, while the ganglion was stimulated for 3 or 5 min before and after the ascending sympathetic trunk and nerve branches from SCG were sectioned. Electrical stimulation of 0.5 mA caused the ipsilateral CBF (CBFi) to decrease 11.7% +/- 1.3 from the baseline (BL), while the contralateral CBF (CBFc) increased slightly due to the change in systemic blood pressure (BP). A linear relation was observed between the level of current stimulation and evoked reduction in CBF. Cervical sympathetic trunk section (between the SCG and the middle cervical ganglion) did not influence the pattern or the amplitude of CBF change in response to electrical stimulation of SCG. Sectioning the efferent fibers of the medial inferior and medial superior branch of the SCG only minimally reduced the amplitude of the CBF decrease evoked by electrical stimulation. However, sectioning the superior lateral branch abolished this decrease.(ABSTRACT TRUNCATED AT 250 WORDS)