Jaro-Journal of the Association for Research in Otolaryngology最新文献

Purpose: The goal of this research was to determine where in the organ of Corti (ooC) sound-induced, longitudinal vibrations occur, and how they depend on the health of the cochlea.

Methods: Sound-evoked vibrations of the ooC in the cochlea's middle turn of adult anesthetized gerbils were measured using optical coherence tomography (OCT). Vibratory responses, evoked with acoustic tone complexes, were recorded at multiple, closely spaced (20 μm), tonotopic locations which changed the "viewing angle" of the vertical OCT beam re. the longitudinal motion. After spatial alignment of the responses, within-ooC regions exhibiting sound-induced longitudinal motion were identified from a conspicuous 180° phase flip.

Results: Longitudinal motion was restricted to the outer hair cells (OHC), Deiters' cells and the tunnel of Corti (i.e., the ooC's "core"). They were frequency and level-independent but did depend on the ear's metabolic state; after death, they disappeared.

Conclusion: There can be little doubt about the presence of longitudinal motions within the cochlea. Their disappearance postmortem and spatially restricted occurrence suggest these longitudinal vibrations arise from active processes within the OHC. Whether this involves cycle-by-cycle feedback or some other, as-of-yet undetermined, mechanism remains to be resolved.

Purpose: To assess system properties of the human auditory system, such as cochlear gain, frequency selectivity, and their dependence on frequency and level, it is essential to examine the interrelation of various readouts. By measuring and analyzing otoacoustic emission (OAE) and auditory brainstem response (ABR) latencies, among others, predictions of cochlear models and applicability of properties such as the minimum-phase principle, level dependence of latencies, or related changes of the gain of a presumed positive-feedback mechanism can be investigated.

Methods: Here, we present measurements of the latency of the nonlinear-distortion component of pulsed distortion-product otoacoustic emissions (DPOAE) ( $f_2$ = 1-14 kHz, $L_2$ = 25-85 dB SPL) in 20 ears (12 female, 8 male). This yields a direct estimate of intracochlear traveling-wave build-up by recording the time elapsed between the $f_2$ primary stimulus and the distortion-product pulse response. Thus, this technique does not require deriving latency from phase gradients of the coherent-reflection component of different frequencies, as is done using swept-tone DPOAE or SFOAE.

Results: At low stimulus levels ( $L_2$ = 35 dB), DPOAE latency was 13 ms at $f_2$ = 1 kHz, exponentially to  2 ms at $f_2$ = 12-14 kHz. In periods of the corresponding frequency, this rose from $\approx$ 13 periods at 1 kHz to $\ge$ 25 periods above 6 kHz. Between 3 and 6 kHz, latency showed a steeper rise, departing from a pure exponential relation. Level dependence of latencies varied among subjects, with changes ranging from -2 to -12% per 10 dB level increase. Test-retest reliability of latency determination with pulsed DPOAE was excellent.

Conclusion: For frequencies above 1 kHz and up to 14 kHz, OAE latency data align with a scaling law of $\approx$ 0.3 dB/dB. A transition region between 3 and 6 kHz shows scaling in some ears approaching 1 dB/dB, violating local scaling symmetry. Although comparison with ABR literature reveals some unresolved discrepancies, latencies of pulsed DPOAE allow a way to estimate cochlear tuning properties.

Purpose: Delivery of therapeutics to the inner ear is complicated by their inaccessible location and the presence of the blood-labyrinth barrier that restricts most blood-borne compounds from entering the inner ear. This study addresses the challenge of optimal delivery in treating inner ear disease, focusing on magnetic targeting gene therapy using adeno-associated virus (AAV).

Methods: The investigation explores three AAV serotypes (AAV2 Quad Mut, AAV2 pANC80L65, and AAV9 PHP.eB) delivered systemically, tagged with a brain-derived nerve growth factor (BDNF) transgene and GFP reporter protein, and captured with superparamagnetic nanoparticles. External magnets target AAV delivery to the Left ear of both male and female Long Evans rats. After 2 weeks, we evaluated tropism and transduction in both cochleae and assessed distribution in other major organs (heart, lung, liver, kidney, spleen, and brain) using immunohistochemistry, real-time polymerase chain reaction, and enzyme-linked immunosorbent assays. Six animals were used for each experimental group.

Results: Immunofluorescence analysis demonstrated the qualitative distribution of AAVs in sensory cells and spiral ganglion neurons (SGN) in both ears. A significant increase in BDNF gene expression in the targeted left ear of rats administered AAV2 Quad Mut was observed. A single dose of magnetic targeting of AAV2 Quad Mut effectively transduced SGN and enhanced BDNF expression, leading to the restoration of ouabain-induced SGN loss and hearing loss (HL).

Conclusion: These findings indicate the potential of magnetic targeting to direct gene therapy following systemic delivery, paving the way for future applications in the treatment of HL.

Purpose: In preclinical research, animals are used to perform clinical experiments. The use of large animals with human-like anatomies and structural size appears to be essential. For auditory function research, we needed to identify an animal model whose dimensions are close to those of the human inner ear for future research. In the present study, we investigated measurements of the human and sheep inner ear using 3 T Magnetic Resonance Imaging (MRI) to evaluate the suitability of a sheep model for studying the inner ear.

Methods: Inner ears were compared between 8 ears from 4 normal humans (women) and 8 ears from 4 normal sheep (female). Cranial MRI of both species' cochleae were acquired and analyzed, with specific measurements for key anatomical features, including the cochlea length and width, the length and width of the inner auditory canal, the number of spiral turns of the cochlea and the cochlea volume. The size ratios between sheep and human cochlear structures were calculated and compared.

Results: Overall cochlear dimensions of the sheep were approximately 2/3 that of human cochleae across most measurements, except for the internal auditory canal. The internal auditory canal of the sheep was 1/3 of the size of that in humans. The number of spiral turns in the cochlea was equivalent between the two species.

Conclusion: Given the proportionally similar dimensions to humans, the sheep cochlea appears to be a promising model for inner ear research, specifically to develop pathological models, to study the pathophysiological mechanisms of inner ear diseases, and/or to improve treatment with implantable prostheses.

Purpose: Present-day cochlear implants (CIs) can deliver usable speech reception in quiet surroundings. Most CI users, however, show impaired sensitivity to temporal fine structure, which hampers their use of pitch contours and spatial cues to segregate competing talkers. In previous short-term animal studies, we used intraneural (IN) electrodes to stimulate pathways originating from various cochlear turns. Neurons in the inferior colliculus synchronized to apical stimulation at higher rates than to stimulation of the middle-to-basal pathways that are stimulated primarily by today's CIs. Here, we use non-invasive recordings to test the safety and efficacy of up to 6 months of IN implantation and stimulation in cats.

Methods: Deafened cats (ten female, two male) were implanted with IN and/or conventional CI electrodes. The IN electrodes were single activated-iridium shanks that targeted apical-turn fibers. Scalp recordings were made from sedated animals at 2-3-week intervals. Auditory brainstem responses to single electrical pulses (eABR) tracked sensitivity and growth of responses. Frequency following responses to electrical pulse trains (eFFR) assessed brainstem temporal transmission at varying pulse rates.

Results: Thresholds for eABR were lower for IN than for CI stimulation, dynamic ranges were wider, and (by inference) spread of activation was more restricted. The eFFR evaluated at latencies comparable to those of inferior-colliculus spikes synchronized at maximum pulse rates averaging > 360 pulses/s for IN compared to ~ 240 pulses/s for CI stimulation. The eABR thresholds and eFFR cutoff rates were stable out to 6 months after implantation.

Conclusions: The results demonstrate the safety and efficacy of chronic IN stimulation in an animal model. In a future clinical device, an IN electrode could augment cochlear-implant performance by enhancing temporal acuity, thereby improving speech reception amid competing sounds.

Purpose: In the fields of both vestibular and auditory research, reliable vestibular function tests are essential. However, unlike the auditory function tests, which use standard Auditory Brainstem Response (ABR) equipment, there is no equivalent widely adopted apparatus for vestibular tests. Vestibulo-ocular reflexes (VORs) are the compensatory ocular reflexes that ensure stable vision during head motion. VORs are widely used in clinics to diagnose vestibular deficits. In the research, VORs have been used by various groups to evaluate the mouse vestibular function. However, the effectiveness of VOR tests has not been systematically evaluated with appropriate mouse models, and the lack of commercial equipment hampers its accessibility, confining vestibular testing to a select few labs.

Methods: In this study, we developed an integrated and surgery-free instrument system with both angular VOR (aVOR) and off-vertical axis rotation (OVAR) modes for evaluating mouse vestibular function. In addition, the eye rotation calibrations used in this study standardize the data between instruments. To demonstrate its validity and efficacy of the testing equipment, we evaluated four mouse models, including both genders, with peripheral vestibular deficits: 1) mice injected with the vestibulotoxic drug 3,3'-iminodiproprionitrile (IDPN, 2 mg/g and 4 mg/g, 3 male/3 female per group); 2) Critical MET-related mutant mice (Cdh23^v2J/v2J, 4 male/4 female and TMC1^-/-, 6 male/5 female); 3) Vestibular-specific mutant mice (Zpld1^-/-, 6 male/6 female, for semicircular canal dysfunction and Otop1^tlt/tlt, 3 male/2 female, for otoconia deficient); 4) Unilateral vestibular lesion (UVL) mouse model (3 male/3 female per group) where gentamicin was injected into horizontal semicircular canal.

Results: The results showed: 1) Quantification of vestibular deficits can be achieved as a daily routine; 2) Both the horizontal semicircular canal and otolith organs can be assessed, respectively; and 3) The lesion side of UVL can be identified.

Conclusion: These test results reveal the potential of our system as standard equipment for evaluating common vestibular deficits in mice.

Purpose: The mammalian cochlea has two types of low abundance and highly specialized inner (IHC) and outer (OHC) mechanosensory hair cells. Their malfunction or death is a common cause of congenital and acquired deafness. IHCs and OHCs exhibit different transcriptomes during development. We wondered how differences in gene expression are regulated at the chromatin level in developing IHCs and OHCs, and whether there were also differences in mRNA splicing between IHCs and OHCs.

Methods: We separately collected developing mouse IHCs and OHCs to identify their mRNAs and chromatin states. We examined their transcriptomes by bulk (full coverage) RNA-seq from six biological replicates each to reveal differences in gene expression and in alternative mRNA splicing. We also examined their chromatin conformation by bulk ATAC-seq from two biological replicates each to reveal open vs. closed promoter and enhancer elements. We then compared ATAC-seq with RNA-seq datasets to determine if differential chromatin accessibility can account for differential gene expression. Each biological replicate consists of hair cells pooled from multiple neonatal mice of both sexes.

Results: We found that developing IHCs and OHCs have differentially accessible promoters in many differentially expressed genes. This includes functional genes whose expression is incipient in neonatal hair cells but will be maintained throughout life, and developmental genes which are only expressed transiently. We also found that different mRNA isoforms result from alternative mRNA splicing and transcription start sites. Finally, our data reveals that cochlear hair cells utilize unique promoters and mRNA isoforms absent in other cell types.

Conclusion: Differential transcriptomes between developing hair cell types result from pre- and post-transcriptional mechanisms. The unique promoters and mRNA isoforms in cochlear HCs highlight the importance of elucidating transcriptomes and epigenomes of rare cell types. We provide a comprehensive resource for the identification of promoters and mRNA isoforms of genes expressed by neonatal IHCs or OHCs, which is publicly-accessible for visualization of any gene of interest at  https://igvviewer.s3.us-east-2.amazonaws.com/index.html .

Purpose: The basic principle of sensorimotor gating (SMG) relies on the ability of a weak lead stimulus (such as a pre-pulse) to inhibit a startling effect of a following, more intense, abrupt stimulus-the so-called pre-pulse inhibition (PPI) paradigm. PPI has been used for near half a century as a means to investigate psychiatric disorders in which its disruption is a surrogate for altered SMG in schizophrenia. However, the blinking response is very variable, making it a poor outcome measure at the individual level. Unlike PPI, which is regulated in the lateral globus pallidus from the basal ganglia, inhibition of the startle reflex by preceding silent gaps embedded in continuous background noise is processed in the auditory cortex, making it particularly suitable for measuring cortical responses.

Methods: Here, based on the behavioral gap-pre-pulse inhibition of acoustic startle (GPIAS) stemming from animal research in tinnitus research, we present a new sensory gating (SG) paradigm using source-localized magnetoencephalography (MEG) in 26 normal hearing healthy participants (13 females, 12 males, 1 other) with a mean age of 28.4 (SD $\pm 5.8$ ), where we expose them to various levels of sound pulses in presence or absence of preceding silent gaps embedded in broadband carrier noises of either 60 or 70 dB SPL, using various interstimulus intervals (ISI: 0, 60, 120, 240 ms).

Results: We evidence a near 72.5% (SD $\pm 15.9$ ) suppression of N1 evoked response to a pulse as high as 90 dB(A) sound pressure level (SPL) when preceded by a 50 ms long silent gap in a 60 dB(A) SPL broadband carrier noise. Cortical inhibition was greatest with 240 ms ISI between gap and pulses, and about 1.5 times larger in the right transverse temporal gyrus when compared to the left hemisphere. While merely 68% of the individuals blinked at the highest pulse levels, cortical evoked responses were found in all participants.

Conclusion: Overall, we provide evidence that SG, measured by N1 cortical response to sound pulses, is reliably inhibited by preceding gaps. We propose this paradigm as an effective method to assess auditory SG through development and aging, and potentially as a method for the diagnosis of hearing disorders like tinnitus or hyperacusis.

Purpose: The stria vascularis (SV) is a secretory epithelium that maintains fluid homeostasis and generates the endocochlear potential in the cochlear duct. Multiomic studies have identified genes in the SV that could contribute to the pathogenesis of Menière's Disease (MD), a disorder defined by episodic vertigo, sensorineural hearing loss, and tinnitus. This systematic review identified genes expressed in the SV cell types (marginal, intermediate, and basal) and gap junction proteins to evaluate their pathophysiological connections to MD.

Methods: We conducted a literature search on 1293 articles relevant to MD and SV that were screened for SV genes involved in MD. Following quality assessment, 130 studies met the inclusion criteria, comprising 26 human studies, 101 animal studies, and three human-animal studies.

Results: Seven immune-related and six auditory-related genes were identified: CACNA1D, ESRRB, HGF, KCNE1, MDH1, QSOX1, and SLC12A2 (marginal cells); ACTB, TMEM176A, and TMEM176B (intermediate cells); and ACTN1, COL11A2, and GSTM1 (basal cells). Gene-set-enrichment-analysis revealed pathways involving gap-junction assembly and electrical coupling. International Mouse Phenotyping Consortium data showed Gja1 and Kcne1 knockouts have immune system abnormalities. Single-cell RNA sequencing data of the lateral wall revealed high expression of Coch, Dtna, and Prkcb in fibrocytes, Reisner's cells, and immune cells. Furthermore, TWEAK released from intermediate cells and bound to its receptor (TNFRSF12A) in the marginal cells may upregulate NF-κB inflammatory response in MD patients.

Conclusion: We hypothesize that some SV genes may contribute to the audiovestibular phenotype in MD, but most of them play a role in the altered immune response found in Sporadic MD.