Bone conduction activation through soft tissues following complete immobilization of the ossicular chain, stapes footplate and round window

Classically it has been thought that bone conduction activation at the mastoid leads to relative motion between the stapes footplate and the oval window due to inertial and to compression (distortion) mechanisms. However, several recent clinical findings and experimental manipulations may point to additional mechanisms. These manipulations were extended in the present study. In ten fat sand rats, following obliteration of one ear, auditory nerve brainstem evoked response (ABR) thresholds were recorded in response to broad band click stimuli, either air conducted (AC) through insert earphones or bone conducted (BC) delivered directly to the exposed skull bone. Following this, the entire ossicular chain, stapes footplate and round window were completely immobilized with super glue, leading to a mean AC threshold elevation of 44 dB, but to a mean BC threshold change (elevation) of only 3.5 dB. In this state of complete immobilization, the bone vibrator was applied to a pool of saline in the surgical area and ABR was elicited with a mean threshold which was not significantly different from that of the BC threshold. When the bone vibrator was then applied to the eye without touching the bone at the orbit, the resulting ABR threshold was about 20 dB greater than the BC threshold. In conclusion, BC stimulation can activate the cochlea without two mobile windows. Furthermore, the cochlea can be activated by a fluid pathway and by application of a bone vibrator to non-osseous sites (soft tissue conduction).     

Basic and clinical physiology of the inner ear receptors and their neural pathways in the brain

The six receptors of the inner ear (cochlea, two otolith organs and three semicircular canals) share a common transduction unit made up of a sensory hair cell, a first order sensory neuron and the synapse between them. Displacement of the stereocilia in a particular direction leads to excitation of the hair cell and activation of the neuron. Electrical and mechanical reflections of these stages of transduction can be recorded non-invasively in humans and in animals. These include cochlear microphonic potentials, otoacoustic emissions, auditory and vestibular evoked potentials. The ability to record these activities can be used to track the development of inner ear function in the fetus and neonate and to study the effects of various ototoxic agents (e.g. noise) and drugs.     

Auditory nerve and brain stem responses in homozygous jaundiced gunn rats

Summary In humans, functional evidence based on recording cochlear microphonic, auditory nerve, and brain stem responses has shown that the site of lesion in hearing loss following neonatal hyperbilirubinemia is the auditory nerve (with sparing of the hair cells). Structural damage to the central nervous system (CNS) including the cochlear nuclei has been demonstrated in adult, homozygous Gunn rats which develop hyperbilirubinemia shortly after birth. In an attempt to use the Gunn rat as an experimental model for bilirubin-induced CNS damage, auditory nerve and brain stem responses (ABR) were recorded in jaundiced (homozygous) and non-jaundiced (heterozygous) Gunn rats and in Sabra (Wistar) rats. All of the rats including the jaundiced Gunn rats had normal ABR and responded behaviorally to sound stimuli. These results suggest that the adult jaundiced Gunn rat retains auditory function and in this way differs from human patients in whom neonatal jaundice has lead to hearing loss. Therefore, the adult homozygous Gunn rat probably cannot serve as a model for hearing loss due to hyperbilirubinemia.     

Mechanism of cochlear excitation at low intensities

In order to assess the mechanisms of cochlear activation, the cochlear fluids of one cochlea of a guinea-pig (I) were coupled to those of a cochlea of a second guinea-pig (II) by means of a saline-filled narrow bore tube, the ends of which were placed in the fluids around the opened round windows of both cochleae, thus joining the two cochleae from two different animals into a single, larger, unsealed fluid system. In response to air-conducted sound stimulation of cochlea I, auditory nerve-brainstem evoked responses could be recorded in animal II, not only when the coupling tube was filled with saline, but also when it was filled with ultrasound gel (viscosity 100,000 greater than that of water), when there was a very large hole encompassing a relatively large expanse of the cochlear shell of animal I, and even when animal I was no longer alive. The necessary control experiments were performed. Therefore, it is suggested that at low stimulus intensities, the passive, incoming basilar membrane traveling wave may not activate the cochlea. Instead the fluid pressures (condensation/rarefactions) induced in the cochlear fluids by vibrations of the stapes footplate may be adequate to directly activate the outer hair cells, which then generate an active component of basilar membrane displacement.     

Noise and hypoxia induced temporary threshold shifts in rats studied by ABR

Rats were exposed for 2 h either to 115 dB SPL noise, to 5% oxygen in nitrogen (hypoxia) or to both hypoxia and noise. Auditory nerve-brainstem evoked responses (ABR) to 80 dB HL clicks and threshold were recorded prior to exposure, immediately (5-10 min) after the exposure, 2 h after and 2 weeks after the exposure. The findings in each experimental animal were compared to those in the control (non-exposed) group and to those in the other groups. Thresholds were elevated in each of the experimental groups, but these were temporary threshold shifts, since 2 weeks following the exposure, threshold had returned to normal. Latencies (wave I and the IV-I interpeak latency difference- (IPLD] were prolonged in the groups exposed to hypoxia (hypoxia alone and hypoxia + noise). These results are discussed in view of possible mechanisms of these noise and hypoxia induced temporary threshold shifts.     

ABR threshold is a function of blood oxygen level

In order to determine if there is a relation between auditory threshold and oxygen availability, cats were anesthetized, paralyzed and ventilated with room air and with hypoxic gas mixtures. Auditory nerve-brain stem evoked response (ABR) thresholds and arterial blood oxygen levels [partial pressures (PaO2) and percent saturation (SaO2)] were determined. The ABR threshold was unchanged as long as PaO2 was above 30 mm Hg (SaO2 greater than 45%). Below PaO2 20 mmHg (SaO2 less than 25%) the animal was not viable. Between these values, the hypoxia caused ABR threshold elevations which were reversible when the animal was again respirated with room air. ABR threshold was an inverse function of blood O2 level with an approximate 3.05 dB elevation for every mmHg decrease in PaO2 (2.89 dB/% SaO2). These findings are probably due to hypoxia induced depression of the endocochlear potential. Since ABR could be recorded in premature human neonates after at least 28 weeks gestation and since the human fetus in utero is also hypoxic, these results indicate that the fetus (greater than 28 weeks gestational age) has a sensorineural hearing loss in addition to a conductive loss.     

Green energy by recoverable triple-oxide mesostructured perovskite photovoltaics

Perovskite solar cells have developed into a promising branch of renewable energy. A combination of feasible manufacturing and renewable modules can offer an attractive advancement to this field. Herein, a screen-printed three-layered all-nanoparticle network was developed as a rigid framework for a perovskite active layer. This matrix enables perovskite to percolate and form a complementary photoactive network. Two porous conductive oxide layers, separated by a porous insulator, serve as a chemically stable substrate for the cells. Cells prepared using this scaffold structure demonstrated a power conversion efficiency of 11.08% with a high open-circuit voltage of 0.988 V. Being fully oxidized, the scaffold demonstrated a striking thermal and chemical stability, allowing for the removal of the perovskite while keeping the substrate intact. The application of a new perovskite in lieu of a degraded one exhibited a full regeneration of all photovoltaic performances. Exclusive recycling of the photoactive materials from solar cells paves a path for more sustainable green energy production in the future.

Elevating world temperatures along climatic model predictions (1) hasten the need for the global economy to move toward green renewable energy production. On the photovoltaic branch, organic (2), inorganic (3, 4), and photosynthetic (5) light harvesters were investigated extensively. In recent years, organic–inorganic perovskite solar cells (PSCs) have been breaking efficiency records (6). Perovskites are a widely diverse and tunable class of materials (7), possessing high charge diffusion length characteristics under illumination. The attractive qualities and surge of development have made the PSCs, especially fully printable panels (8), prominent candidates for large-scale commercialization (9). Simultaneously, much effort has been made to stabilize perovskite''s intrinsic properties (10) through the research of different compositions and fabrication methods. These efforts include the introduction of hole conductor–free configurations (11), two-dimensional perovskite compositions (12), and, recently, the usage of methylammonium-free compounds (13). In a typical PSC structure, the perovskite layer is situated between an electron-transporting layer (ETL) on the one side and a hole-transporting material (HTM) on the other side. Traditionally, a metal contact is evaporated onto the HTM as a cathode, sealing the basic functional structure of the cell. The alignment of the electronic structure of the functional layers enables the ETL to effectively block the diffusion of holes from the perovskite and the HTM to block electrons from reaching the cathode. HTM-free configurations eliminate the HTM layer between the light absorber and the cathode and rely on the ETL alone to induce anisotropic average diffusion of the charges as a photocurrent. Since HTMs are commonly expensive and prone to degradation over time, HTM-free configurations contribute to the cells'' durability and tenability and significantly lower their cost. One such configuration utilizes a porous carbon layer as the cathode of the cell (14), allowing the perovskite precursor solution to percolate through the pores and crystalize inside the structure.Here, a triple-layered structure of sintered nanoparticles (NPs) was designed as a general scaffold for various perovskite compositions and deposition methods. The rigid and stable, screen-printed oxide nanoparticle films form layers which manifest electronic attributes similar to their building blocks. The general structure of the scaffold includes a porous electron-conducting NP layer and a porous NP cathode, separated by a porous insulating NP layer. Though the use of alternative conductive NPs is plausible, indium tin oxide (ITO) particles were chosen as the cathodic material in this work. This conductive metal oxide material can endure more extreme chemical and thermal conditions than most other nanoparticles can. The virtue of such oxides lies in their strong structure and inert chemical behavior toward oxygen and water. NPs of the closely related metal oxide fluorine-doped tin oxide (FTO) are possible candidates for the substitution of ITO as the cathodic material in the future, with economic advantages appealing for commercialization. Widely used in the field of PSCs, mesoporous TiO₂ (mpTiO₂) possesses the ability to efficiently receive and conduct electrons from the conduction band of the perovskite and thus serves as the ETL in the structure. Since charge separation in PSCs arises from light absorption in the perovskite, continuity and connectivity of the perovskite material must be maintained, along with complete insulation between the anodic and cathodic parts of the cell. Screen-printed mesoporous ZrO₂ (mpZrO₂) was used here as an ideal material choice for the insulating layer. All three mentioned layers were successively printed and sintered atop a transparent FTO-coated glass photoanode to complete a full scaffold configuration of FTO/mpTiO₂/mpZrO₂/mpITO. The perovskite solution can then be applied directly onto the cathode contact, subsequently forming a three-dimensional polycrystalline network of perovskite in the cavities between the scaffold NPs. The ITO contact provides direct electron injection to the perovskite under illumination, and at this point the cell’s full structure is complete, without the need for any additional steps. Here, the deposition of (MA_0.15FA_0.85)PbI₃ perovskite is demonstrated, along with an optical, morphological, electronic, and photovoltaic characterization of the cells. These scalable solar cells exhibited high short-circuit currents, impressive stability, and the unique possibility of recycling by removing and reapplying damaged or degraded perovskite.     

Semicircular canal fenestration - improvement of bone- but not air-conducted auditory thresholds

Auditory stimulation can, under certain circumstances, activate the vestibular end organs and this is facilitated by fenestration of a semicircular canal (SCC). Several fenestrated profoundly deaf patients reported improvements in their bone- (BC) but not air-conducted (AC) thresholds. Bone conduction auditory thresholds have been reported to be better than normal in several patients with thinning or absence of bone over a SCC (dehiscence). This phenomenon was carefully studied in the fat sand rat (Psammomys obesus) by recording auditory brainstem evoked responses to BC and AC auditory stimulation, before and after SCC fenestration. Fenestration would be expected to decrease the pressure difference across the cochlear partition, causing a reduction in the amplitude of the classical base to apex input traveling wave, and should therefore lead to an elevation in AC and BC thresholds. Instead, BC thresholds decreased (i.e. improved) following fenestration (by 7.0+/-4.2 dB; P<0.005), while AC thresholds did not change. Thus the cochlea becomes more sensitive to BC, but not AC, stimulation in the presence of a SCC fenestration. This may be due to the removal by the fenestration of a factor impeding BC cochlear responses, or by the addition of a facilitating factor. The result that the SCC fenestration did not affect AC threshold provides support for the concept that at low intensities the outer hair cells are directly activated by components of the fluid pressures surrounding them, which alternate at audio-frequencies. These cochlear fluid audio-frequency pressures are induced by stapes footplate movement and not by a base to apex input traveling wave. The audio-frequency pressures would not be affected by SCC fenestration. The outer hair cell motility thus induced somehow excites the inner hair cells and the auditory nerve fibers. At low intensities the outer hair cell motility causes localized displacement at the appropriate position on the basilar membrane.     

The neonate has a temporary conductive hearing loss due to fluid in the middle ear

Postnatal functional changes in the activity of the ear and auditory pathway in neonatal guinea pigs [from day of birth (postnatal day, PND = 0), PNDs 1-4, 7 and then weekly up to 7 weeks] were studied as a model of maturation of hearing in human neonates. On the day of birth there were signs of a conductive hearing loss: negative middle ear pressure, auditory nerve brainstem evoked response (ABR) threshold elevation, ABR wave 1 latency prolongation and low amplitude otoacoustic emissions. The conductive hearing loss is probably a result of the (amniotic) fluid found in the neonatal middle-ear cavity. Over the next PNDs, this conductive hearing loss was resolved. In order to confirm this neonatal conductive hearing loss and its resolution, saline was instilled into the middle ear of guinea pigs. This induced signs of a conductive hearing loss similar to those seen in the neonatal guinea pigs which disappeared with clearance of this fluid. Therefore it may be concluded that most of the changes in auditory function seen over the first PNDs are due to absorption of amniotic fluid from the middle-ear cavity.     

Effect of high-dose cisplatin on auditory brainstem responses and otoacoustic emissions in laboratory animals

OBJECTIVE: The role of transient evoked otoacoustic emissions (TEOAE) and distortion product otoacoustic emissions (DPOAE) as early indicators of cisplatin-induced ototoxicity in three different rodent species--the guinea pig. the albino rat, and the fat sand rat (Psammomys obesus)--was investigated. In addition, an attempt was made to determine which of the three rodent species is most susceptible to cisplatin-induced ototoxicity as measured by auditory brainstem responses (ABR), BACKGROUND: There have been numerous clinical and experimental reports on cisplatin-induced ototoxicity, but to the authors' best knowledge, there has been no comparative report on the short-term effects of cisplatin on OAE measured with commercially available equipment between different rodent species. METHODS: Cisplatin was systemically administered as a single high dose (12 mg/kg intraperitoneally) to all three species, and the ototoxic effects were measured before and 3 days after the injection of cisplatin in the same animals, using ABR, TEOAE, and DPOAE. RESULTS: The ABR thresholds were significantly elevated in the guinea pigs and the albino rats but not in the sand rats. Significant depression of TEOAE energy and DPOAE amplitude occurred only in the guinea pigs. The depression of the DPOAE was greater than that of the TEOAE. The guinea pigs showed the greatest degree of ototoxicity (depression of ABR and OAE). CONCLUSIONS: Among the three rodent species, the guinea pig has the potential to be used as a sensitive animal model in studies of cisplatin ototoxicity. The study also showed that the recordings of TEOAE and DPOAE, in addition to ABR, are sensitive techniques for the assessment of cisplatin-induced ototoxicity.