Cochlear implantation leads to many structural changes within the cochlea which can impair residual hearing. In patients with preserved low-frequency hearing, a delayed hearing loss can occur weeks-to-years post-implantation. We explore whether stiffening of the basilar membrane (BM) may be a contributory factor in an animal model. Our objective is to map changes in morphology and Young's modulus of basal and apical areas of the BM after cochlear implantation, using quantitative nanomechanical atomic force microscopy (QNM-AFM) after cochlear implant surgery. Cochlear implantation was undertaken in the guinea pig, and the BM was harvested at four time-points: 1 day, 14 days, 28 days and 84 days post-implantation for QNM-AFM analysis. Auditory brainstem response thresholds were determined prior to implantation and termination. BM tissue showed altered morphology and a progressive increase in Young's modulus, mainly in the apex, over time after implantation. BM tissue from the cochlear base demonstrated areas of extreme stiffness which are likely due to micro-calcification on the BM. In conclusion, stiffening of the BM after cochlear implantation occurs over time, even at sites far apical to a cochlear implant.

Deiters cells extend from the basilar membrane to the reticular lamina and, together with pillar cells and outer hair cells, structurally define the micro-architecture of the organ of Corti. Studying vibrotome sections of the mouse organ of Corti with confocal and scanning electron microscopy we found that the basal pole of every Deiters cell, independently of their position in the organ of Corti and along the cochlear spiral, attached to the basilar membrane within a 15.1 ± 0.3 μm-wide stripe running the length of the cochlear spiral adjacent to the row of outer pillar cells. All Deiters cells' basal poles had similar diameter and general morphology, and distributed on the stripe in a precise arrangement with a center-to-center distance of 7.1 ± 0.3 μm between neighbor cells of the same row and 5.9 ± 0.4 μm for neighbor cells in adjacent rows. Complete detachment of Deiters cells revealed an elliptical imprint on the top surface of the basilar membrane consisting of a smaller central structure with a very smooth surface surrounded by a rougher area, suggesting the presence of two different anchoring junctions. These previously unidentified morphological features of Deiters cells could be critical for the mechanical response of the organ of Corti.

Noise exposure leads to an increase in the macrophage population. This increment is thought to be caused by the transformation of infiltrated monocytes into macrophages rather than by proliferation of the cochlear resident macrophages. However, studies on infiltrated monocytes in the cochlea are scarce. Thus, we aimed to investigate the infiltration of monocytes and their transformation into macrophages after noise exposure.

The detection of different frequencies in sound is accomplished with remarkable precision by the basilar membrane (BM), an elastic, ribbon-like structure with graded stiffness along the cochlear spiral. Sound stimulates a wave of displacement along the BM with maximal magnitude at precise, frequency-specific locations to excite neural signals that carry frequency information to the brain. Perceptual frequency discrimination requires fine resolution of this frequency map, but little is known of the intrinsic molecular features that demarcate the place of response on the BM. To investigate the role of BM microarchitecture in frequency discrimination, we deleted extracellular matrix protein emilin 2, which disturbed the filamentous organization in the BM. Emilin2 -/- mice displayed broadened mechanical and neural frequency tuning with multiple response peaks that are shifted to lower frequencies than normal. Thus, emilin 2 confers a stiffness gradient on the BM that is critical for accurate frequency resolution.

The cochlear basilar membrane (CBM) contains inner hair cells and outer hair cells that convert sound waves into electrical signals and transmit them to the central auditory system. Cochlear aging, the primary reason of age-related hearing loss, can reduce the signal transmission capacity. There is no ideal in vitro aging model of the CBM. In this study, we cultured the CBM, which was dissected from the cochlea of the C57BL/6 mice 5 days after birth, in a medium containing 20 mg/mL, 40 mg/mL, or 60 mg/mL D-galactose (D-gal). Compared with the control group, the levels of senescence-associated β-galactosidase were increased in a concentration-dependent manner in the CBM of the D-gal groups. In addition, levels of the mitochondrial superoxide and patterns of an age-related mitochondrial DNA3860-bp deletion were significantly increased. The ATP levels and the membrane potential of the mitochondrial were significantly decreased in the CBM of the D-gal groups compared with the control group. Furthermore, in comparison with the control group, damaged hair cell stereocilia and a loss of inner hair cell ribbon synapses were observed in the CBM of the D-gal groups. A loss of hair cells and activation of caspase-3-mediated outer hair cell apoptosis were also observed in the CBM of the high-dose D-gal group. These insults induced by D-gal in the CBM in vitro were similar to the ones that occur in cochlear natural aging in vivo. Thus, we believe that this is a successful in vitro aging model using cultured CBM. These results demonstrate the effects of mitochondrial oxidative damage on presbycusis and provide a reliable aging model to study the mechanisms of presbycusis in vitro.

No abstract available

The basilar membrane (BM) of the mammalian cochlea constitutes a spiraling acellular ribbon that is intimately attached to the organ of Corti. Its graded stiffness, increasing from apex to the base of the cochlea provides the mechanical basis for sound frequency analysis. Despite its central role in auditory signal transduction, virtually nothing is known about the BM's structural development. Using polarized light microscopy, the present study characterized the architectural transformations of freshly dissected BM at time points during postnatal development and maturation. The results indicate that the BM structural elements increase progressively in size, becoming radially aligned and more tightly packed with maturation and reach the adult structural signature by postnatal day 20 (P20). The findings provide insight into structural details and developmental changes of the mammalian BM, suggesting that BM is a dynamic structure that changes throughout the life of an animal.

We proposed a piezoelectric artificial basilar membrane (ABM) composed of a microelectromechanical system cantilever array. The ABM mimics the tonotopy of the cochlea: frequency selectivity and mechanoelectric transduction. The fabricated ABM exhibits a clear tonotopy in an audible frequency range (2.92-12.6 kHz). Also, an animal model was used to verify the characteristics of the ABM as a front end for potential cochlear implant applications. For this, a signal processor was used to convert the piezoelectric output from the ABM to an electrical stimulus for auditory neurons. The electrical stimulus for auditory neurons was delivered through an implanted intra-cochlear electrode array. The amplitude of the electrical stimulus was modulated in the range of 0.15 to 3.5 V with incoming sound pressure levels (SPL) of 70.1 to 94.8 dB SPL. The electrical stimulus was used to elicit an electrically evoked auditory brainstem response (EABR) from deafened guinea pigs. EABRs were successfully measured and their magnitude increased upon application of acoustic stimuli from 75 to 95 dB SPL. The frequency selectivity of the ABM was estimated by measuring the magnitude of EABRs while applying sound pressure at the resonance and off-resonance frequencies of the corresponding cantilever of the selected channel. In this study, we demonstrated a novel piezoelectric ABM and verified its characteristics by measuring EABRs.

Age-related hearing loss (ARHL) is the most common sensory degenerative disease and can significantly impact the quality of life in elderly people. A previous study using GeneChip miRNA microarray assays showed that the expression of miR-29a changes with age, however, its role in hearing loss is still unclear. In this study, we characterized the cochlear phenotype of miR-29a knockout (miR-29a-/-) mice and found that miR-29a-deficient mice had a rapid progressive elevation of the hearing threshold from 2 to 5 months of age compared with littermate controls as measured by the auditory brainstem response. Stereocilia degeneration, hair cell loss and abnormal stria vascularis (SV) were observed in miR-29a-/- mice at 4 months of age. Transcriptome sequencing results showed elevated extracellular matrix (ECM) gene expression in miR-29a-/- mice. Both Gene Ontology (GO) annotation and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis revealed that the key differences were closely related to ECM. Further examination with a transmission electron microscope showed thickening of the basilar membrane in the cochlea of miR-29a-/- mice. Five Col4a genes (Col4a1-a5) and two laminin genes (Lamb2 and Lamc1) were validated as miR-29a direct targets by dual luciferase assays and miR-29a inhibition assays with a miR-29a inhibitor. Consistent with the target gene validation results, the expression of these genes was significantly increased in the cochlea of miR-29a-/- mice, as shown by RT-PCR and Western blot. These findings suggest that miR-29a plays an important role in maintaining cochlear structure and function by regulating the expression of collagen and laminin and that the disturbance of its expression could be a cause of progressive hearing loss.

The goal of this study was to determine whether RhoA, a small GTPase, might be involved in the development of cerebral pathogenesis in diabetes. Male SD rats (n = 120) were divided into six groups: diabetic for 2, 4, 8 weeks, and an age-matched control group. Diabetes was induced by intravenous injection of streptozotocin (50 mg/kg). RhoA mRNA expression in basilar artery was measured by competitive RT-PCR. RhoA mRNA level was significantly increased in 4 weeks (184.1 +/- 28.5%, n = 7) and 8 weeks (218.7 +/- 24.5%, n = 7) after STZ injection compared to the age matched control basilar arteries (P < 0.05). Western blot was used to measure the membrane binding RhoA level to represent the activity of RhoA. We found that RhoA activity was strikingly increased in the diabetic basilar artery (n = 10 in each groups) compared to control basilar artery after STZ injection. Our data demonstrated that there was an upregulation of RhoA in the basilar artery of STZ induced diabetic rats, suggesting that RhoA might be involved in the cerebral vascular pathogenesis during diabetes mellitus.

The avian basilar papilla is tonotopically organized such that hair cells along the sensory epithelium respond best to acoustic stimulation at differing frequencies. This specificity arises due to the mechanics of the cochlea itself and intrinsic electrical properties of the hair cells. Tall hair cells show membrane voltage oscillations in response to step current injection that may allow cells to act as electrical resonators, boosting the response at the resonant frequency. These oscillations and the underlying currents have been studied in enzymatically isolated cells. This study uses a whole chick (Gallus domesticus) basilar papilla preparation where the entire epithelium and its afferent connections are intact. With this preparation, a map of changes in potassium currents of tall hair cells was produced. All cells recorded from expressed two K+ currents, a calcium-activated K+ current, I(K(Ca)), and a voltage-activated K+ current, I(K). Also, apical cells expressed an inward rectifier K+ current, I(IR). The amplitude of total outward current increases in a gradient along the tonotopic axis. Pharmacological blockers were used to separate the outward K+ currents. These experiments showed that both currents individually increase in magnitude along a gradient from apex to base. Finally, measurements of oscillation frequency in response to current steps suggest a discontinuous change in the electrical resonances at about 33% from the apex. This study demonstrates a new preparation to study the electrical properties of hair cells in more detail along the tonotopic axis of the chick basilar papilla.

Acute ischemic stroke (AIS) due to basilar artery occlusion (BAO) represents 1-4% of all ischemic strokes. BAO results in strokes associated with a high risk of a poor functional outcome and, in 86-95% of the untreated cases, it results in death because of the vital cerebral structures involved. Diagnosis can be delayed because of the variability in presenting symptoms, and acute treatment is often attempted even beyond 6 h from symptoms onset because of the high risk of a fatal prognosis.

The current study observed the effects and investigated the mechanism of remifentanil (RMF) on the isolated cerebral basilar arteries of spontaneously hypertensive rats (SHR) and Wistar‑Kyoto (WKY) rats. A pressure myograph system was used to observe and compare the effects of different concentrations of RMF (10‑10‑10‑5 mol/l) on the diameter changes of freshly isolated cerebral basilar arteries, which have been pre‑shrunk by phenylephrine (PE), an endothelium‑independent vasoconstrictor. Vascular smooth‑muscle cells of the cerebral basilar artery (BASMCs) were freshly obtained via enzymolysis. BKCa (large‑conductance calcium‑activated potassium channels) current (IBKCa) and Kv (voltage‑gated potassium channels) current (IKv) were recorded using a whole‑cell patch‑clamp technique. The changes in IBKCa and IKv produced by different concentrations of RMF (10‑10 to 10‑5 mol/l) on the two types of rats with the holding potential of ‑40 mV were observed and compared. The cerebral basilar arteries of the SHR and WKY rats were relaxed by RMF in a concentration-dependent manner (P<0.05; n=5). At the same concentration, the diastolic effect of RMF on SHR was weaker than that observed in WKY rats (P<0.05, n=5). When the rats were pre‑perfused with 10‑3 mol/l of the BKCa channel blocker tetraethylammonium (TEA), the diastolic amplitudes of RMF in SHR and WKY rats were decreased, and the fitting curves shifted down (P<0.05; n=7 and 6, respectively). However, no statistically significant difference was observed with 10‑3 mol/l of the Kv channel blocker 4‑aminopyridine (4‑AP; n=6 and 9, respectively; P>0.05). Outward currents were increased by RMF in both BASMCs of SHR and WKY rats in a voltage‑ and dose‑dependent manner (P<0.05; n=6). At the same concentration, the effect of RMF on the outward currents in BASMCs of WKY rats was stronger than that on SHR (P<0.05; n=6). The enhancing effect of RMF can be partially blocked by either 10‑3 mol/l TEA (P<0.05; n=6) or 10‑3 mol/l 4‑AP (P<0.05 or 0.01; n=6 and 9, respectively) however can be totally blocked by the mixture of TEA and 4‑AP (P<0.05, n=7). RMF served a diastolic role in the cerebral basilar arteries of rats in a dose‑dependent manner, likely by activating the BKCa and Kv channels. However, SHR demonstrated a less pronounced diastolic reaction to RMF than that observed in WKY rats.

This study aimed to assess the clinical usefulness of a direct aspiration first pass technique as a first-line strategy for mechanical thrombectomy in posterior circulation.

There is limited evidence for mechanical thrombectomy in patients with basilar artery occlusion. Despite recanalization, there are several reports on poor outcomes. Therefore, we retrospectively evaluated the outcomes and examined the predictors of mechanical thrombectomy in patients with basilar artery occlusion.

The common preconception about central nervous system neurones is that thousands of small postsynaptic potentials sum across the entire dendritic tree to generate substantial firing rates, previously observed in in vivo experiments. We present evidence that local inputs confined to a single basal dendrite can profoundly influence the neuronal output of layer V pyramidal neurones in the rat prefrontal cortical slices. In our experiments, brief glutamatergic stimulation delivered in a restricted part of the basilar dendritic tree invariably produced sustained plateau depolarizations of the cell body, accompanied by bursts of action potentials. Because of their small diameters, basolateral dendrites are not routinely accessible for glass electrode measurements, and very little is known about their electrical properties and their role in information processing. Voltage-sensitive dye recordings were used to follow membrane potential transients in distal segments of basal branches during sub- and suprathreshold glutamate and synaptic stimulations. Recordings were obtained simultaneously from multiple dendrites and multiple points along individual dendrites, thus showing in a direct way how regenerative potentials initiate at the postsynaptic site and propagate decrementally toward the cell body. The glutamate-evoked dendritic plateau depolarizations described here are likely to occur in conjunction with strong excitatory drive during so-called 'UP states', previously observed in in vivo recordings from mammalian cortices.

Serum- and glucocorticoid-inducible kinease-1 (SGK1) is a serine/threonine kinase regulated by hypotonic stimuli, which is involved in regulation of cell cycle and apoptosis. Our previous study shows that activation of volume-regulated Cl- channels (VRCCs) protects rat basilar artery smooth muscle cells (BASMCs) against hydrogen peroxide (H2O2)-induced apoptosis. In the present study, we investigated whether SGK1 was involved in the protective effect of VRCCs in BASMCs. We showed that hypotonic challenge significantly reduced H2O2-induced apoptosis, and increased SGK1 phosphorylation, but did not affect SGK1 protein expression. The protective effect of hypotonic challenge against H2O2-induced apoptosis was mediated through inhibiting mitochondria-dependent apoptotic pathway, evidenced by increased Bcl-2/Bax ratio, stabilizing mitochondrial membrane potential (MMP), decreased cytochrome c release from the mitochondria to the cytoplasm, and inhibition of the activation of caspase-9 and caspase-3. These protective effects of hypotonic challenge against H2O2-induced apoptosis was diminished and enhanced, respectively, by SGK1 knockdown and overexpression. We further revealed that SGK1 activation significantly increased forkhead box O3a (FOXO3a) phosphorylation, and then inhibited the translocation of FOXO3a into nucleus and the subsequent expression of Bcl-2 interacting mediator of cell death (Bim). In conclusion, SGK1 mediates the protective effect of VRCCs against H2O2-induced apoptosis in BASMCs via inhibiting FOXO3a/Bim signaling pathway. Our results provide compelling evidences that SGK1 is a critical link between VRCCs and apoptosis, and shed a new light on the treatment of vascular apoptosis-associated diseases, such as vascular remodeling, angiogenesis, and atherosclerosis.

The mechanical and electrical responses of the mammalian cochlea to acoustic stimuli are nonlinear and highly tuned in frequency. This is due to the electromechanical properties of cochlear outer hair cells (OHCs). At each location along the cochlear spiral, the OHCs mediate an active process in which the sensory tissue motion is enhanced at frequencies close to the most sensitive frequency (called the characteristic frequency, CF). Previous experimental results showed an approximate 0.3 cycle phase shift in the OHC-generated extracellular voltage relative the basilar membrane displacement, which was initiated at a frequency approximately one-half octave lower than the CF. Findings in the present paper reinforce that result. This shift is significant because it brings the phase of the OHC-derived electromotile force near to that of the basilar membrane velocity at frequencies above the shift, thereby enabling the transfer of electrical to mechanical power at the basilar membrane. In order to seek a candidate physical mechanism for this phenomenon, we used a comprehensive electromechanical mathematical model of the cochlear response to sound. The model predicts the phase shift in the extracellular voltage referenced to the basilar membrane at a frequency approximately one-half octave below CF, in accordance with the experimental data. In the model, this feature arises from a minimum in the radial impedance of the tectorial membrane and its limbal attachment. These experimental and theoretical results are consistent with the hypothesis that a tectorial membrane resonance introduces the correct phasing between mechanical and electrical responses for power generation, effectively turning on the cochlear amplifier.

Frequency tuning in the cochlea is determined by the passive mechanical properties of the basilar membrane and active feedback from the outer hair cells, sensory-effector cells that detect and amplify sound-induced basilar membrane motions. The sensory hair bundles of the outer hair cells are imbedded in the tectorial membrane, a sheet of extracellular matrix that overlies the cochlea's sensory epithelium. The tectorial membrane contains radially organized collagen fibrils that are imbedded in an unusual striated-sheet matrix formed by two glycoproteins, alpha-tectorin (Tecta) and beta-tectorin (Tectb). In Tectb(-/-) mice the structure of the striated-sheet matrix is disrupted. Although these mice have a low-frequency hearing loss, basilar-membrane and neural tuning are both significantly enhanced in the high-frequency regions of the cochlea, with little loss in sensitivity. These findings can be attributed to a reduction in the acting mass of the tectorial membrane and reveal a new function for this structure in controlling interactions along the cochlea.

The cell membranes in the hair bundle of an auditory hair cell confront a difficult task as the bundle oscillates in response to sound: for efficient mechanotransduction, all the component stereocilia of the hair bundle must move essentially in unison, shearing at their tips yet maintaining contact without membrane fusion. One mechanism by which this cohesion might occur is counterion-mediated attachment between glycan components of apposed stereociliary membranes. Using capillary electrophoresis, we showed that the stereociliary glycocalyx acts as a negatively charged polymer brush. We found by force-sensing photomicrometry that the stereocilia formed elastic connections with one another to various degrees depending on the surrounding ionic environment and the presence of N-linked sugars. Mg(2+) was a more potent mediator of attachment than was Ca(2+). The forces between stereocilia produced chaotic stick-slip behavior. These results indicate that counterion-mediated interactions in the glycocalyx contribute to the stereociliary coherence that is essential for hearing.