Wavelet transform of single-trial vestibular short-latency evoked potential reveals temporary reduction in signal detectability and temporal precision following noise exposure.

The vestibular short-latency evoked potential (VsEP) reflects the activity of irregular vestibular afferents and their target neurons in the brain stem. Attenuation of trial-averaged VsEP waveforms is widely accepted as an indicator of vestibular dysfunction, however, more quantitative analyses of VsEP waveforms could reveal underlying neural properties of VsEP waveforms. Here, we present a time-frequency analysis of the VsEP with a wavelet transform on a single-trial basis, which allows us to examine trial-by-trial variability in the strength of VsEP waves as well as their temporal coherence across trials. Using this method, we examined changes in the VsEP following 110 dB SPL noise exposure in rats. We found detectability of head jerks based on the power of wavelet transform coefficients was significantly reduced 1 day after noise exposure but recovered nearly to pre-exposure level in 3 - 7 days and completely by 28 days after exposure. Temporal coherence of VsEP waves across trials was also significantly reduced on 1 day after exposure but recovered with a similar time course. Additionally, we found a significant reduction in the number of calretinin-positive calyces in the sacculi collected 28 days after noise exposure. Furthermore, the number of calretinin-positive calyces was significantly correlated with the degree of reduction in temporal coherence and/or signal detectability of the smallest-amplitude jerks. This new analysis of the VsEP provides more quantitative descriptions of noise-induced changes as well as new insights into potential mechanisms underlying noise-induced vestibular dysfunction. Significance Statement: Our study presents a new method of VsEP quantification using wavelet transform on a single-trial basis. It also describes a novel approach to determine the stimulus threshold of the VsEP based on signal-detection theory and Rayleigh statistics. The present analysis could also be applied to analysis of auditory brain stem response (ABR). Thus, it has the potential to provide new insights into the physiological properties that underlie peripheral vestibular and auditory dysfunction.

Noise overstimulation of young adult UMHET4 mice accelerates age-related hearing loss.

Many factors contribute to hearing loss commonly found in older adults. There can be natural aging of cellular elements, hearing loss previously induced by environmental factors such as noise or ototoxic drugs as well as genetic and epigenetic influences. Even when noise overstimulation does not immediately cause permanent hearing loss it has recently been shown to increase later age-related hearing loss (ARHL). The present study further investigated this condition in the UMHET4 mouse model by comparing a small arms fire (SAF)-like impulse noise exposure that has the greatest immediate effect in more apical cochlear regions to a broadband noise (BBN) exposure that has the greatest immediate effect in more basal cochlear regions. Both noise exposures were given at levels that only induced temporary auditory brainstem response (ABR) threshold shifts (TS). Mice were noise exposed at 5 months of age followed by ABR assessment at 6, 12, 18, 21, and 24 months of age. Mice that received the SAF-like impulse noise had accelerated age-related TS at 4 kHz that appeared at 12 months of age (significantly increased compared to no-noise controls). This increased TS at 4 kHz continued at 18 and 21 months but was no longer significantly greater at 24 months of age. The SAF-like impulse noise also induced a significantly greater mean TS at 48 kHz, first appearing at 18 months of age and continuing to be significantly greater than controls at 21 and 24 months. The BBN induced a different pace and pattern of enhanced age-related ABR TS. The mean TS for the BBN group first became significantly greater than controls at 18 months of age and only at 48 kHz. It remained significantly greater than controls at 21 months but was no longer significantly greater at 24 months of age. Results, therefore, show different influences on ARHL for the two different noise exposure conditions. Noise-induced enhancement appears to provide more an acceleration than overall total increase in ARHL.

Transient peripheral vestibular hypofunction measured with vestibular short-latency evoked potentials following noise exposure in rats.

Exposure to 120 dB sound pressure level (SPL) band-limited noise results in delayed onset latency and reduced vestibular short-latency evoked potential (VsEP) responses. These changes are still present 4 wk after noise overstimulation. Noise-induced hearing loss (NIHL) has been shown to vary in extent and duration based on the noise intensity. This study investigated whether noise-induced peripheral vestibular hypofunction (NPVH) would also decrease in extent and/or duration with less intense noise exposure. In the present study, rats were exposed to a less intense noise (110 dB SPL) but for the same duration (6 h) and frequency range (500-4,000 Hz) as used in previous studies. The VsEP was assessed 1, 3, 7, 14, 21, and 28 days after noise exposure. In contrast to 120 dB SPL noise exposure, the 110 dB SPL noise exposures produced smaller deficits in VsEP responses that fully recovered in 62% (13/21) of animals within 1 wk. These findings suggest that NPVH, a loss or attenuation of VsEP responses with a requirement for elevated stimulus intensity to elicit measurable responses, is similar to NIHL, that is, lower sound levels produce a smaller or transient deficit. These results show that it will be important to determine the extent and duration of vestibular hypofunction for different noise exposure conditions and their impact on balance.NEW & NOTEWORTHY This is the first study to show a temporary noise-induced peripheral vestibular hypofunction that recovers following exposure to continuous noise.

Rapamycin Added to Diet in Late Mid-Life Delays Age-Related Hearing Loss in UMHET4 Mice.

Our previous study demonstrated rapamycin added to diet at 4 months of age had significantly less age-related outer hair cell loss in the basal half of the cochlea at 22 months of age compared to mice without rapamycin. The present study tested adding rapamycin to diet later in life, at 14 months of age, and added a longitudinal assessment of auditory brain stem response (ABR). The present study used UMHET4 mice, a 4 way cross in which all grandparental strains lack the Cdh23753A allele that predisposes to early onset, progressive hearing loss. UMHET4 mice typically have normal hearing until 16-17 months, then exhibit threshold shifts at low frequencies/apical cochlea and later in more basal high frequency regions. ABR thresholds at 4, 12, 24, and 48 kHz were assessed at 12, 18, and 24 months of age and compared to baseline ABR thresholds acquired at 5 months of age to determine threshold shifts (TS). There was no TS at 12 months of age at any frequency tested. At 18 months of age mice with rapamycin added to diet at 14 months had a significantly lower mean TS at 4 and 12 kHz compared to mice on control diet with no significant difference at 24 and 48 kHz. At 24 months of age, the mean 4 kHz TS in rapamycin diet group was no longer significantly lower than the control diet group, while the 12 kHz mean remained significantly lower. Mean TS at 24 and 48 kHz in the rapamycin diet group became significantly lower than in the control diet group at 24 months. Hair cell counts at 24 months showed large loss in the apical half of most rapamycin and control diet mice cochleae with no significant difference between groups. There was only mild outer hair cell loss in the basal half of rapamycin and control diet mice cochleae with no significant difference between groups. The results show that a later life addition of rapamycin can decrease age-related hearing loss in the mouse model, however, it also suggests that this decrease is a delay/deceleration rather than a complete prevention.

Effects of Noise Exposure on the Vestibular System: A Systematic Review.

Despite our understanding of the impact of noise-induced damage to the auditory system, much less is known about the impact of noise exposure on the vestibular system. In this article, we review the anatomical, physiological, and functional evidence for noise-induced damage to peripheral and central vestibular structures. Morphological studies in several animal models have demonstrated cellular damage throughout the peripheral vestibular system and particularly in the otolith organs; however, there is a paucity of data on the effect of noise exposure on human vestibular end organs. Physiological studies have corroborated morphological studies by demonstrating disruption across vestibular pathways with otolith-mediated pathways impacted more than semicircular canal-mediated pathways. Similar to the temporary threshold shifts observed in the auditory system, physiological studies in animals have suggested a capacity for recovery following noise-induced vestibular damage. Human studies have demonstrated that diminished sacculo-collic responses are related to the severity of noise-induced hearing loss, and dose-dependent vestibular deficits following noise exposure have been corroborated in animal models. Further work is needed to better understand the physiological and functional consequences of noise-induced vestibular impairment in animals and humans.

Exposure to Intense Noise Causes Vestibular Loss.

INTRODUCTION: The vestibular system is essential for normal postural control and balance. Because of their proximity to the cochlea, the otolith organs are vulnerable to noise. We previously showed that head jerks that evoke vestibular nerve activity were no longer capable of inducing a response after noise overstimulation. The present study adds a greater range of jerk intensities to determine if the response was abolished or required more intense stimulation (threshold shift). MATERIALS AND METHODS: Vestibular short-latency evoked potential (VsEP) measurements were taken before noise exposure and compared to repeated measurements taken at specific time points for 28 days after noise exposure. Calretinin was used to identify changes in calyx-only afferents in the sacculus. RESULTS: Results showed that more intense jerk stimuli could generate a VsEP, although it was severely attenuated relative to prenoise values. When the VsEP was evaluated 4 weeks after noise exposure, partial recovery was observed. CONCLUSION: These data suggest that noise overstimulation, such as can occur in the military, could introduce an increased risk of imbalance that should be evaluated before returning a subject to situations that require normal agility and motion. Moreover, although there is recovery with time, some dysfunction persists for extended periods.

Small Arms Fire-like noise: Effects on Hearing Loss, Gap Detection and the Influence of Preventive Treatment.

A noise-induced loss of inner hair cell (IHC) - auditory nerve synaptic connections has been suggested as a factor that can trigger the progression of maladaptive plastic changes leading to noise-induced tinnitus. The present study used a military relevant small arms fire (SAF)-like noise (50 biphasic impulses over 2.5 min at 152 dB SPL given unilaterally to the right ear) to induce loss (∼1/3) of IHC synaptic ribbons (associated with synapse loss) in rat cochleae with only minor (less than 10%) loss of outer hair cells. Approximately half of the noise-exposed rats showed poorer Gap Detection post-noise, a behavioral indication suggesting the presence of tinnitus. There was significantly greater loss of IHC ribbons in noise-exposed rats with reduced Gap Detection compared to noise-exposed rats retaining normal Gap Detection. We have previously shown systemic administration of piribedil, memantine, and/or ACEMg significantly reduced loss of IHC ribbons induced by a 3 h 4 kHz octave band 117 dB (SPL) noise. The present study examined if this treatment would also reduce ribbon loss from the SAF-like noise exposure and if this would prevent the reduced Gap Detection. As in the previous study, piribedil, memantine, and ACEMg treatment significantly reduced the noise-induced loss of ribbons, such that it was no longer significantly different from normal. However, it did not prevent development of the reduced Gap Detection indication of tinnitus in all treated noise-exposed rats, reducing the incidence but not reaching significance.

Vestibular short-latency evoked potential abolished by low-frequency noise exposure in rats.

The vestibular system plays a critical role in detection of head movements and is essential for normal postural control. Because of their anatomical proximity to the cochlea, the otolith organs are selectively exposed to sound pressure and are at risk for noise overstimulation. Clinical reports suggest a link between noise exposure and balance problems, but the structural and physiological basis for this linkage is not well understood. The goal of this study was to determine the effects of low-frequency noise (LFN) on the otolith organs by correlating changes in vestibular short-latency evoked potentials (VsEPs) with changes in saccular afferent endings following noise exposure. LFN exposure transiently abolished the VsEP and reduced the number of stained calyces within the sacculus. Although some recovery of the VsEP waveform could be observed within 3 days after noise, at 3 wk recovery was only partial in most animals, consistent with a reduced number of afferents with calyceal endings. These data show that a single intense noise exposure is capable of causing a vestibular deficit that appears to mirror the synaptic deficit associated with hidden hearing loss after noise-induced cochlear injury. NEW & NOTEWORTHY This is the first study to explore the effects of low-frequency high-intensity noise on vestibular short-latency evoked potential (VsEP) responses, which shows a linkage between attenuated noise-induced VsEPs and pathological changes to otolith organ afferents. This finding suggests a potential limitation of the VsEP for evaluation of vestibular dysfunction, since the VsEP measurement may assess the activity of a specific class rather than all afferents.

Treatment with Piribedil and Memantine Reduces Noise-Induced Loss of Inner Hair Cell Synaptic Ribbons.

Noise overstimulation can induce loss of synaptic ribbons associated with loss of Inner Hair Cell - Auditory Nerve synaptic connections. This study examined if systemic administration of Piribedil, a dopamine agonist that reduces the sound evoked auditory nerve compound action potential and/or Memantine, an NMDA receptor open channel blocker, would reduce noise-induced loss of Inner Hair Cell ribbons. Rats received systemic Memantine and/or Piribedil for 3 days before and 3 days after a 3 hour 4 kHz octave band noise at 117 dB (SPL). At 21 days following the noise there was a 26% and 38% loss of synaptic ribbons in regions 5.5 and 6.5 mm from apex, respectively, elevations in 4-, 8- and 20 kHz tonal ABR thresholds and reduced dynamic output at higher intensities of stimulation. Combined treatment with Piribedil and Memantine produced a significant reduction in the noise-induced loss of ribbons in both regions and changes in ABR sensitivity and dynamic responsiveness. Piribedil alone gave significant reduction in only the 5.5 mm region and Memantine alone did not reach significance in either region. Results identify treatments that could prevent the hearing loss and hearing disorders that result from noise-induced loss of Inner Hair Cell - Auditory Nerve synaptic connections.

Persistence, distribution, and impact of distinctly segmented microparticles on cochlear health following in vivo infusion.

Delivery of pharmaceuticals to the cochleae of patients with auditory dysfunction could potentially have many benefits from enhancing auditory nerve survival to protecting remaining sensory cells and their neuronal connections. Treatment would require platforms to enable drug delivery directly to the cochlea and increase the potential efficacy of intervention. Cochlear implant recipients are a specific patient subset that could benefit from local drug delivery as more candidates have residual hearing; and since residual hearing directly contributes to post-implantation hearing outcomes, it requires protection from implant insertion-induced trauma. This study assessed the feasibility of utilizing microparticles for drug delivery into cochlear fluids, testing persistence, distribution, biocompatibility, and drug release characteristics. To allow for delivery of multiple therapeutics, particles were composed of two distinct compartments; one containing polylactide-co-glycolide (PLGA), and one composed of acetal-modified dextran and PLGA. Following in vivo infusion, image analysis revealed microparticle persistence in the cochlea for at least 7 days post-infusion, primarily in the first and second turns. The majority of subjects maintained or had only slight elevation in auditory brainstem response thresholds at 7 days post-infusion compared to pre-infusion baselines. There was only minor to limited loss of cochlear hair cells and negligible immune response based on CD45+ immunolabling. When Piribedil-loaded microparticles were infused, Piribedil was detectable within the cochlear fluids at 7 days post-infusion. These results indicate that segmented microparticles are relatively inert, can persist, release their contents, and be functionally and biologically compatible with cochlear function and therefore are promising vehicles for cochlear drug delivery. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 104A: 1510-1522, 2016.

Hair Cell Loss, Spiral Ganglion Degeneration, and Progressive Sensorineural Hearing Loss in Mice with Targeted Deletion of Slc44a2/Ctl2.

SLC44A2 (solute carrier 44a2), also known as CTL2 (choline transporter-like protein 2), is expressed in many supporting cell types in the cochlea and is implicated in hair cell survival and antibody-induced hearing loss. In mice with the mixed C57BL/6-129 background, homozygous deletion of Slc44a2 exons 3­10 (Slc44a2(Δ/Δ)resulted in high-frequency hearing loss and hair cell death. To reduce effects associated with age-related hearing loss (ARHL) in these strains, mice carrying the Slc44a2Δ allele were backcrossed to the ARHL-resistant FVB/NJ strain and evaluated after backcross seven(N7) (99 % FVB). Slc44a2(Δ/Δ) mice produced abnormally spliced Slc44a2 transcripts that contain a frame shift and premature stop codons. Neither full-length SLC44A2 nor a putative truncated protein could be detected in Slc44a2(Δ/Δ) mice, suggesting a likely null allele. Auditory brain stem responses (ABRs) of mice carrying the Slc44a2Δ allele on an FVB/NJ genetic background were tested longitudinally between the ages of 2 and 10 months. By 6 months of age,Slc44a2(Δ/Δ) mice exhibited hearing loss at 32 kHz,but at 12 and 24 kHz had sound thresholds similar to those of wild-type Slc44a2(+/+) and heterozygous +/Slc44a2Δ mice. After 6 months of age, Slc44a2(Δ/Δ) mutants exhibited progressive hearing loss at all frequencies and +/Slc44a2(Δ) mice exhibited moderate threshold elevations at high frequency. Histologic evaluation of Slc44a2(Δ/Δ) mice revealed extensive hair cell and spiral ganglion cell loss, especially in the basal turn of the cochlea. We conclude that Slc44a2 function is required for long-term hair cell survival and maintenance of hearing.

Refractory Positional Vertigo With Apogeotropic Horizontal Nystagmus After Labyrinthitis: Surgical Treatment and Identification of Dysmorphic Ampullae.

OBJECTIVES: To describe the rationale, intraoperative details, and histopathologic findings discovered when treating an unusual case of apogeotropic horizontal canal positional vertigo with a transmastoid labyrinthectomy. PATIENT: A single case report. INTERVENTION: Therapeutic. MAIN OUTCOME MEASURES: Resolution of apogeotropic nystagmus and improvement of positional vertigo. RESULTS: The apogeotropic variant of horizontal canal positional vertigo can be a difficult entity to treat. This report describes a patient who developed profound sensorineural hearing loss and vertigo after an acute left labyrinthitis. Ten months later, she developed vertigo with apogeotropic positional nystagmus involving the left horizontal semicircular canal. Particle repositioning maneuvers and vestibular physical therapy were unsuccessful. In addition, she developed intermittent positional vertigo affecting the ipsilateral vertical semicircular canals. Given the persistence of her vertigo, multiple canal involvement, and patient preference for definitive treatment, a transmastoid labyrinthectomy was performed. Intraoperatively, the ampulla of the horizontal canal as well as that of the other canals was grossly abnormal as later confirmed on histology. After surgery, her apogeotropic nystagmus and vertigo resolved, and her balance ability gradually improved to a highly functional level. CONCLUSION: This case illustrates a unique form of positional vertigo that developed and persisted after acute labyrinthitis. Conservative measures were unsuccessful and a transmastoid labyrinthectomy documented dense inflammatory tissue involving all three ampullae. We postulate that the post-labyrinthitic inflammatory changes resulted in mass loading of the membranous ampullae, causing abnormal nystagmus patterns and positional vertigo, which resolved after the labyrinthectomy.

Disruption of lateral olivocochlear neurons with a dopaminergic neurotoxin depresses spontaneous auditory nerve activity.

Neurons of the lateral olivocochlear (LOC) system project from the auditory brainstem to the cochlea, where they synapse on radial dendrites of auditory nerve fibers. Selective LOC disruption depresses sound-evoked auditory nerve activity in the guinea pig, but enhances it in the mouse. Here, LOC disruption depressed spontaneous auditory nerve activity in the guinea pig. Recordings from single auditory nerve fibers revealed a significantly reduced proportion of fibers with the highest spontaneous firing rates (SRs) and an increased proportion of neurons with lower SRs. Ensemble activity, estimated using round window noise, also decreased after LOC disruption. Decreased spontaneous activity after LOC disruption may be a consequence of reduced tonic release of excitatory transmitters from the LOC terminals in guinea pigs.

OTO-201: nonclinical assessment of a sustained-release ciprofloxacin hydrogel for the treatment of otitis media.

HYPOTHESIS: OTO-201 can provide sustained release to the middle ear and effectively treat otitis media, when compared with FDA-approved ciprofloxacin otic drop formulations. BACKGROUND: There is an unmet medical need for antibiotic therapy that can provide a full course of treatment from a single administration by an otolaryngologist at the time of tympanostomy tube placement, obviating the need for twice daily multiday treatment with short-acting otic drops. METHODS: Studies in guinea pigs and chinchillas were conducted. OTO-201 was administered as a single intratympanic injection and compared with the twice daily multi-day treatment with Ciprodex or Cetraxal otic drops. RESULTS: OTO-201 demonstrated sustained release of ciprofloxacin in the middle ear compartment for days to approximately 2 weeks depending on the dose. The substantial C(max) values and steady drug exposure yielded by OTO-201 were in contrast to the pulsatile short lasting exposure seen with Ciprodex and Cetraxal. OTO-201 was also effective in a preclinical chinchilla model of Streptococcus pneumoniae-induced otitis media. The degree of cure was comparable to that afforded by Ciprodex and Cetraxal. There was no evidence of middle or inner ear pathology in guinea pigs treated with OTO-201, unlike Ciprodex and Cetraxal, which both demonstrated mild cochlear ototoxicity. No adverse effects of the poloxamer 407 vehicle were noted. CONCLUSION: Intratympanic injection of OTO-201 constitutes an attractive treatment option to twice daily multiday dosing with ciprofloxacin ear drops for the treatment of otitis media, as evidenced by superior middle ear drug exposure, efficacy in an acute otitis media model, safety of administration, and convenience of a single dose regimen.

Netrin-1-mediated axon guidance in mouse embryonic stem cells overexpressing neurogenin-1.

Stem cell therapy holds great promise for treating neurodegenerative disease, but major barriers to effective therapeutic strategies remain. A complete understanding of the derived phenotype is required for predicting cell response once introduced into the host tissue. We sought to identify major axonal guidance cues present in neurons derived from the transient overexpression of neurogenin-1 (Neurog1) in mouse embryonic stem cells (ESCs). Neurog1 upregulated the netrin-1 axon guidance receptors DCC (deleted in colorectal cancer) and neogenin (NEO1). Quantitative polymerase chain reaction results showed a 2-fold increase in NEO1 mRNA and a 36-fold increase in DCC mRNA in Neurog1-induced compared with control ESCs. Immunohistochemistry indicated that DCC was primarily expressed on cells positive for the neuronal marker TUJ1. DCC was preferentially localized to the cell soma and growth-cones of induced neurons. In contrast, NEO1 expression showed less specificity, labeling both TUJ1-positive and TUJ1-negative cells as well as uninduced control cells. Axonal outgrowth was directed preferentially toward aggregates of HEK293 cells secreting a recombinant active fragment of netrin-1. These data indicate that DCC and NEO1 are downstream products of Neurog1 and may guide the integration of Neurog1-induced ESCs with target cells secreting netrin-1. Differential expression profiles for netrin receptors could indicate different roles for this guidance cue on neuronal and non-neuronal cells.

Induction of heat shock proteins by hyperthermia and noise overstimulation in hsf1 -/- mice.

Diverse cellular and environmental stresses can activate the heat shock response, an evolutionarily conserved mechanism to protect proteins from denaturation. Stressors activate heat shock transcription factor 1 (HSF1), which binds to heat shock elements in the genes for heat shock proteins, leading to rapid induction of these important molecular chaperones. Both heat and noise stress are known to activate the heat shock response in the cochlea and protect it from subsequent noise trauma. However, the contribution of HSF1 to induction of heat shock proteins following noise trauma has not been investigated at the molecular level. We evaluated the role of HSF1 in the cochlea following noise stress by examining induction of heat shock proteins in Hsf1 ( +/- ) control and Hsf1 ( -/- ) mice. Heat stress rapidly induced expression of Hsp25, Hsp47, Hsp70.1, Hsp70.3, Hsp84, Hsp86, and Hsp110 in the cochleae of wild-type and Hsf1 ( +/- ) mice, but not in Hsf1 ( -/- ) mice, confirming the essential role of HSF1 in mediating the heat shock response. Exposure to broadband noise (2-20 kHz) at 106 dB SPL for 2 h produced partial hearing loss. Maximal induction of heat shock proteins occurred 4 h after the noise. In comparison to heat stress, noise stress resulted in lower induced levels of Hsp25, Hsp70.1, Hsp70.3, Hsp86, and Hsp110 in Hsf1 ( +/- ) mice. Induction of these heat shock proteins was attenuated, but not completely eliminated, in Hsf1 ( -/- ) mice. These same noise exposure conditions induced genes for several immediate early transcription factors and maximum induction occurred earlier than for heat shock proteins. Thus, additional signaling pathways and transcriptional regulators that are activated by noise probably contribute to induction of heat shock proteins in the cochlea.

Nestin-expressing cells in the developing, mature and noise-exposed cochlear epithelium.

The auditory sensory epithelium in non-mammalian vertebrates can replace lost hair cells by transdifferentiation of supporting cells, but this regenerative ability is lost in the mammalian cochlea. Future cell-based treatment of hearing loss may depend on stem cell transplantation or on transdifferentiation of endogenous cells in the cochlea. For both approaches, identification of cells with stem cell features within the mature cochlea may be useful. Here we use a Nestin-ß-gal mouse to examine the presence of Nestin positive cells in the mature auditory epithelium, and determine how overstimulation of the ear impacts these cells. Nestin positive cells were found in the apical turn of the cochlea lateral to the outer hair cell area. This pattern of expression persisted into mature age. The area of Nestin positive cells was increased after the noise lesion. This increase in area coincided with an increase in expression of the Nestin mRNA. The data suggest that cells with potential stem cell features remain in the mature mammalian cochlea, restricted to the apical turn, and that an additional set of signals is necessary to trigger their contribution to cell replacement therapy in the ear. As such, this population of cells could serve to generate cochlear stem cells for research and potential therapy, and may be a target for treatments based on induced transdifferentiation of endogenous cochlear cells.

OTO-104: a sustained-release dexamethasone hydrogel for the treatment of otic disorders.

HYPOTHESIS: To investigate whether OTO-104, a poloxamer-based hydrogel containing micronized dexamethasone for intratympanic delivery, can provide long-lasting inner ear exposure and be well tolerated. METHODS: OTO-104 was administered intratympanically to guinea pigs and sheep, and its pharmacokinetic and toxicity profiles were examined. RESULTS: After a single intratympanic injection of OTO-104 (from 0.6% to 20%, w/w), significant and prolonged exposure to dexamethasone in the inner ear was observed. Increasing the concentration of OTO-104 resulted in higher perilymph drug levels as well as a more prolonged duration of exposure. At the highest dose, therapeutic perilymph levels of dexamethasone could be sustained over 3 months in guinea pigs and more than 1 month in sheep. A toxicologic evaluation was conducted, including assessments of middle and inner ear function and physiology, as well as appraisal of local and systemic toxicity. A small and transient shift in hearing threshold was observed, most probably conductive in nature. No significant histologic changes in middle or inner ear tissues were noted. Although macroscopically mild erythema/inflammation was documented in a subset of guinea pigs treated with 20% OTO-104, the nature and the severity of these changes were not different between the poloxamer vehicle, saline, and 20% OTO-104 groups. No evidence of acute dermal toxicity, delayed hypersensitivity, or systemic adverse effects was found. CONCLUSION: OTO-104 is a novel proprietary therapeutic delivery system that can achieve prolonged, sustained release of dexamethasone within the inner ear fluids. The administration of this clinical candidate formulation via intratympanic injection is expected to be well tolerated both locally and systemically.

The intrinsic electrophysiological properties of neurons derived from mouse embryonic stem cells overexpressing neurogenin-1.

A mouse embryonic stem (ES) cell line containing an inducible transgene for the proneural gene Neurog1 has been used to generate glutamatergic neurons at a high efficiency. The present study used in vitro electrophysiology to establish the timeline for acquiring a functional neuronal phenotype in Neurog1-induced cells exhibiting a neuronal morphology. TTX-sensitive action potentials could be evoked from over 80% of the cells after only 4.5 days in vitro (DIV). These cells uniformly showed rapidly adapting responses to current injection, firing one to three action potentials at the onset of the stimulus. In the absence of Neurog1, a limited number of ES cells adopted a neuronal morphology, but these cells displayed slow calcium depolarizations rather than sodium-based spikes. Voltage-gated Na(+), K(+), and Ca(2+) currents were present in nearly all induced cells as early as 4.5 DIV. The voltage-dependent properties of these currents changed little from 4 to 12 DIV with half-activation voltage varying by <10 mV for any current type throughout the culture period. This study demonstrates that forced expression of proneural genes can induce ES cells to quickly acquire a functional neuronal phenotype with mature electrophysiological properties. Transient overexpression of Neurog1 may be used in neural repair strategies that require the rapid induction of functional neurons from pluripotent stem cells.