Activity-Dependent Neurodegeneration and Neuroplasticity of Auditory Neurons Following Conductive Hearing Loss in Adult Mice.

We examined the functional and structural changes of auditory neurons (ANs) in adult mice after conductive hearing loss (CHL). Earplugs (EPs) were bilaterally inserted in male 8-week-old mice for 4 weeks [EP(+) group] and subsequently removed for 4 weeks [EP(+/-) group]. We examined the control mice [EP(-) group] with no EPs inserted at 12 weeks. The auditory brainstem response (ABR) was measured to determine the cochlear function before and after EP insertion, after EP removal, and at 4 weeks following EP removal. We examined the cochleae for hair cell (HC) and spiral ganglion neuron survival, synaptic and neural properties, and AN myelination. There was a significant elevation of the ABR threshold across all tested frequencies after EP insertion. After removing the occlusion, these threshold shifts were fully recovered. Compared with the EP(-) mice, the EP(+) mice showed a significant decrease in the ABR peak 1 amplitude and a significantly prolonged latency at all tested frequencies. There was no significant effect of auditory deprivation on the survival of HCs and ANs. Conversely, auditory deprivation caused significant damage to the synapses and myelin and a significant decrease in the AN size. Although functional changes in the ABR amplitude and latency did not fully recover in the EP(+/-) mice, almost all anatomical changes were fully recovered in the EP(+/-) mice; however, cochlear synapses only showed partial recovery. These results suggest that auditory activities are required to maintain peripheral auditory synapses and myelination in adults. The auditory deprivation model allows for assessment of the mechanisms of synaptopathy and demyelination in the auditory periphery, and synaptic and myelin regeneration in sensorineural hearing loss.

Effects of tympanic membrane perforation, middle ear cavity volume, and mastoid aeration on hearing impairment.

AIMS: To investigate the effects of the location and size of tympanic membrane (TM) perforation and middle ear cavity volume on conductive hearing loss in patients with TM perforation. METHODS: Data were collected via a retrospective medical chart review. RESULTS: We enrolled 128 patients with a mean age of 45.6 ± 10.1 years. The mean perforation size was 21.2 ± 8.6% of the TM area, and the mean air-bone gap (ABG) was 20.2 ± 8.6 dB HL on pure tone audiometry. Patients were divided into two groups based on mean ABG. Patients with a large ABG had a significantly larger TM perforation area and smaller mastoid volume. The TM perforation was most commonly located in the central section. However, regression analyses showed that the proportion of the perforated TM area was the only independent predictor of a large ABG (odds ratio, 1.053; 95% confidence interval, 1.022-1.085; p = 0.001). When we analyzed the frequencies in which hearing loss occurred due to TM perforation, we confirmed that hearing loss occurred mainly in the low-frequency range. CONCLUSION: In patients with TM perforation, conductive hearing loss occurs mainly at low frequencies and in proportion to the size of the TM perforation.

Multiple synostoses syndrome: Clinical report and retrospective analysis.

Multiple synostoses syndrome (SYNS1; OMIM# 186500) is a rare autosomal dominant disorder reported in a few cases worldwide. We report a Chinese pedigree characterized by proximal symphalangism, conductive hearing loss, and distinctive facies. We examined the genetic cause and reviewed the literature to discuss the pathogeny, treatment, and prevention of SYNS1. Audiological, ophthalmological, and radiological examinations were evaluated. Whole-exome sequencing (WES) was performed to identify mutations in the proband and her parents. Sanger sequencing was used to verify the results for the proband, parents, and grandmother. The literature on the genotype-phenotype correlation was reviewed. The patient was diagnosed with multiple synostoses syndrome clinically. WES and bioinformatic analysis revealed a novel missense mutation in the NOG gene, c.554C>G (p.Ser185Cys), cosegregated in this family. The literature review showed that the phenotype varies widely, but the typical facies, conductive hearing loss, and proximal symphalangism occurred frequently. All reported mutations are highly conserved in mammals based on conservation analysis, and there are regional hot spots for these mutations. However, no distinct genotype-phenotype correlations have been identified for mutations in NOG in different races. Regular systematic examinations and hearing aids are beneficial for this syndrome. However, the outcomes of otomicrosurgery are not encouraging owing to the regrowth of bone. This study expanded the mutation spectrum of NOG and is the first report of SYNS1 in a Chinese family. Genetic testing is recommended as part of the diagnosis of syndromic deafness. A clinical genetic evaluation is essential to guide prevention, such as preimplantation genetic diagnosis.

Tophaceous Gout of the Middle Ear: Case Reports and Review of the Literature.

Tophaceous gout of the middle ear is a rare occurrence that presents as a granular white-colored mass. It is frequently misdiagnosed as cholesteatoma or tympanosclerosis in patients who otherwise may not manifest any clinical or biochemical signs of gout. While uncommon, it can lead to clinically significant disease such as conductive hearing loss. The present report describes 2 cases of middle ear gouty tophi initially mistaken for another entity. Both patients underwent surgery, and the diagnosis of gout was revealed after final histopathological analysis. A review of the literature is also presented.

Conductive Hearing Loss Has Long-Lasting Structural and Molecular Effects on Presynaptic and Postsynaptic Structures of Auditory Nerve Synapses in the Cochlear Nucleus.

UNLABELLED: Sound deprivation by conductive hearing loss increases hearing thresholds, but little is known about the response of the auditory brainstem during and after conductive hearing loss. Here, we show in young adult rats that 10 d of monaural conductive hearing loss (i.e., earplugging) leads to hearing deficits that persist after sound levels are restored. Hearing thresholds in response to clicks and frequencies higher than 8 kHz remain increased after a 10 d recovery period. Neural output from the cochlear nucleus measured at 10 dB above threshold is reduced and followed by an overcompensation at the level of the lateral lemniscus. We assessed whether structural and molecular substrates at auditory nerve (endbulb of Held) synapses in the cochlear nucleus could explain these long-lasting changes in hearing processing. During earplugging, vGluT1 expression in the presynaptic terminal decreased and synaptic vesicles were smaller. Together, there was an increase in postsynaptic density (PSD) thickness and an upregulation of GluA3 AMPA receptor subunits on bushy cells. After earplug removal and a 10 d recovery period, the density of synaptic vesicles increased, vesicles were also larger, and the PSD of endbulb synapses was larger and thicker. The upregulation of the GluA3 AMPAR subunit observed during earplugging was maintained after the recovery period. This suggests that GluA3 plays a role in plasticity in the cochlear nucleus. Our study demonstrates that sound deprivation has long-lasting alterations on structural and molecular presynaptic and postsynaptic components at the level of the first auditory nerve synapse in the auditory brainstem. SIGNIFICANCE STATEMENT: Despite being the second most prevalent form of hearing loss, conductive hearing loss and its effects on central synapses have received relatively little attention. Here, we show that 10 d of monaural conductive hearing loss leads to an increase in hearing thresholds, to an increased central gain upstream of the cochlear nucleus at the level of the lateral lemniscus, and to long-lasting presynaptic and postsynaptic structural and molecular effects at the endbulb of the Held synapse. Knowledge of the structural and molecular changes associated with decreased sensory experience, along with their potential reversibility, is important for the treatment of hearing deficits, such as hyperacusis and chronic otitis media with effusion, which is prevalent in young children with language acquisition or educational disabilities.

Case 226: Oval Window Atresia.

A 6-year-old girl presented with bilateral hearing loss. Her otologic, birth, and family histories were limited, given that she was adopted, but her parents reported that she had had difficulty hearing and speaking ever since they adopted her at 2 years of age. Her parents denied a history of acute otitis media, otorrhea, otalgia, vertigo, autophony, or tinnitus since her adoption. At 2.5 years of age, a diagnosis of hearing loss was made, and she was given hearing aids. Her parents believed that she had been doing well with both receptive and expressive language since she had received the hearing aids. At examination, she had small bilateral preauricular skin tags and normal pinna. Her external auditory canals were of a normal caliber bilaterally, with no otorrhea or lesions. The tympanic membranes were translucent and mobile at pneumatic otoscopy. There was no evidence of a middle ear lesion, nor was there a Schwartz sign. She had no nystagmus or vertigo at pneumatic otoscopy. Audiometry was performed and revealed moderate to severe conductive hearing loss bilaterally, with a mixed component present at 2000 KHz. She had normal bilateral middle ear pressure at tympanometry. Thin-section computed tomography (CT) of the temporal bone was performed.

Remodelling at the calyx of Held-MNTB synapse in mice developing with unilateral conductive hearing loss.

Structure and function of central synapses are profoundly influenced by experience during developmental sensitive periods. Sensory synapses, which are the indispensable interface for the developing brain to interact with its environment, are particularly plastic. In the auditory system, moderate forms of unilateral hearing loss during development are prevalent but the pre- and postsynaptic modifications that occur when hearing symmetry is perturbed are not well understood. We investigated this issue by performing experiments at the large calyx of Held synapse. Principal neurons of the medial nucleus of the trapezoid body (MNTB) are innervated by calyx of Held terminals that originate from the axons of globular bushy cells located in the contralateral ventral cochlear nucleus. We compared populations of synapses in the same animal that were either sound deprived (SD) or sound experienced (SE) after unilateral conductive hearing loss (CHL). Middle ear ossicles were removed 1 week prior to hearing onset (approx. postnatal day (P) 12) and morphological and electrophysiological approaches were applied to auditory brainstem slices taken from these mice at P17-19. Calyces in the SD and SE MNTB acquired their mature digitated morphology but these were structurally more complex than those in normal hearing mice. This was accompanied by bilateral decreases in initial EPSC amplitude and synaptic conductance despite the CHL being unilateral. During high-frequency stimulation, some SD synapses displayed short-term depression whereas others displayed short-term facilitation followed by slow depression similar to the heterogeneities observed in normal hearing mice. However SE synapses predominantly displayed short-term facilitation followed by slow depression which could be explained in part by the decrease in release probability. Furthermore, the excitability of principal cells in the SD MNTB had increased significantly. Despite these unilateral changes in short-term plasticity and excitability, heterogeneities in the spiking fidelity among the population of both SD and SE synapses showed similar continuums to those in normal hearing mice. Our study suggests that preservations in the heterogeneity in spiking fidelity via synaptic remodelling ensures symmetric functional stability which is probably important for retaining the capability to maximally code sound localization cues despite moderate asymmetries in hearing experience.

Giant cell tumors of the skull base: case series and current concepts.

OBJECTIVE: To study the clinical features, tumor characteristics and outcomes of giant cell tumors (GCTs) in the skull base based on long-term follow-up. We also report the largest series of GCTs in the temporal bone and the lateral skull base. MATERIALS AND METHODS: A retrospective study was conducted of all GCTs managed at the Gruppo Otologico, a quaternary referral skull base institute, in Italy from 1993 to 2013. The clinical features, investigations, surgical management and follow-up were recorded. The surgical approaches used were infratemporal fossa approach (ITFA) type B and D and middle cranial fossa (MCF) approaches. RESULTS AND OBSERVATIONS: A total of 7 patients with GCTs of the skull base were treated at our institution. The principal complaints were hearing loss reported in 6 (85.71%) patients, tinnitus in 5 (71.43%) and swelling in 3 (42.9%). Pure-tone audiometry showed conductive hearing loss in 5 (71.43%) patients. High-resolution CT scan and MRI with gadolinium enhancement were done in all patients. Radiology showed involvement of the ITF and middle ear in 6 (85.71%) patients each, temporomandibular joint in 4 (57.14%) patients, invasions of the squamous part of the temporal bone, mastoid, MCF and greater wing of sphenoid in 3 (42.9%) patients each and the petrous bone in 2 (28.6%) patients. ITFA type B was applied as an approach for tumor removal in 5 (71.43%) patients, including a case where an additional MCF approach was employed, and ITFA type D and the transmastoid approach were applied in 1 (14.3%) patient each. Total tumor removal and successful cure was achieved in 6 (85.71%) patients. Subtotal removal leading to recurrence and eventual mortality was the result in 1 (14.3%) patient. CONCLUSIONS: A thorough knowledge of the anatomy of the skull base and the various skull base approaches is necessary to tackle GCTs. ITFA type B and D combined with MCF approaches provide good exposure of the tumor with minimal postoperative sequelae and good locoregional control. Recurrence due to either subtotal removal or suboptimal treatment may have disastrous consequences for the patient.

Operative findings of conductive hearing loss with intact tympanic membrane and normal temporal bone computed tomography.

Despite recent technological advances in diagnostic methods including imaging technology, it is often difficult to establish a preoperative diagnosis of conductive hearing loss (CHL) in patients with an intact tympanic membrane (TM). Especially, in patients with a normal temporal bone computed tomography (TBCT), preoperative diagnosis is more difficult. We investigated middle ear disorders encountered in patients with CHL involving an intact TM and normal TBCT. We also analyzed the surgical results with special reference to the pathology. We reviewed the medical records of 365 patients with intact TM, who underwent exploratory tympanotomy for CHL. Fifty nine patients (67 ears, eight bilateral surgeries) had a normal preoperative TBCT findings reported by neuro-radiologists. Demographic data, otologic history, TM findings, preoperative imaging findings, intraoperative findings, and pre- and postoperative audiologic data were obtained and analyzed. Exploration was performed most frequently in the second and fifth decades. The most common postoperative diagnosis was stapedial fixation with non-progressive hearing loss. The most commonly performed hearing-restoring procedure was stapedotomy with piston wire prosthesis insertion. Various types of hearing-restoring procedures during exploration resulted in effective hearing improvement, especially with better outcome in the ossicular chain fixation group. In patients with CHL who have intact TM and normal TBCT, we should consider an exploratory tympanotomy for exact diagnosis and hearing improvement. Information of the common operative findings from this study may help in preoperative counseling.

Asymmetry in Cortical Thickness of the Heschl's Gyrus in Unilateral Ear Canal Atresia.

HYPOTHESIS: Unilateral congenital conductive hearing impairment in ear canal atresia leads to atrophy of the gray matter of the contralateral primary auditory cortex or changes in asymmetry pattern if left untreated in childhood. BACKGROUND: Unilateral ear canal atresia with associated severe conductive hearing loss results in deteriorated sound localization and difficulties in understanding of speech in a noisy environment. Cortical atrophy in the Heschl's gyrus has been reported in acquired sensorineural hearing loss but has not been studied in unilateral conductive hearing loss. METHODS: We obtained T1w and T2w FLAIR MRI data from 17 subjects with unilateral congenital ear canal atresia and 17 matched controls. Gray matter volume and thickness were measured in the Heschl's gyrus using Freesurfer. RESULTS: In unilateral congenital ear canal atresia, Heschl's gyrus exhibited cortical thickness asymmetry (right thicker than left, corrected p = 0.0012, mean difference 0.25 mm), while controls had symmetric findings. Gray matter volume and total thickness did not differ from controls with normal hearing. CONCLUSION: We observed cortical thickness asymmetry in congenital unilateral ear canal atresia but no evidence of contralateral cortex atrophy. Further research is needed to understand the implications of this asymmetry on central auditory processing deficits.

Auditory system involvement in late onset Pompe disease: a study of 20 Italian patients.

Glycogen storage disease type II (GSD II), also known as Pompe disease, is an autosomal recessive inherited disorder caused by a reduced activity of acid alpha glucosidase (GAA). Two different clinical entities have been described: rapidly fatal infantile and late onset forms. Hearing loss has been described in classic infantile Pompe patients but rarely in late onset cases. The main purpose of this study was to investigate the involvement of the auditory system in a cohort of Italian patients with late onset GSD II. We have enrolled 20 patients, 12 males and 8 females. The auditory system assessment included speech and pure tone audiometry, impedance audiometry and auditory brainstem responses (ABR). A combined interpretation of those tests allowed us to define the origin of the hearing impairment (sensorineural, conductive or mixed). Clinically, all patients but one denied subjective hearing disturbances. On the other hand, audiological evaluation revealed that 21/40 patient ears (52.5%) had a hearing impairment: 57% had a sensorineural deficit, 33% showed a conductive hearing loss whereas 10% presented with a mixed pattern. Our study revealed that, in this group of GSDII late onset patients, the auditory system impairment was more frequently present than thought with a prominent cochlear involvement. Our results emphasize the importance of a routinely auditory function evaluation in all forms of Pompe disease.

Mutations in the NOG gene are commonly found in congenital stapes ankylosis with symphalangism, but not in otosclerosis.

Human noggin (NOG) is a responsible gene for multiple synostosis syndrome (SYNS1) and proximal symphalangism (SYM1), two conditions that are recently known to be within a wider range of clinical manifestations of stapes ankylosis with symphalangism. This study was performed to determine the range of phenotype caused by NOG mutations, using Japanese patients with various phenotypes including sporadic inherited SYM1, dominantly inherited SYM1, stapes ankylosis with broad thumb and toes (Teunissen and Cremer syndrome). In addition, 33 patients with typical otosclerosis (without symphalangism) were studied. Direct sequencing analysis disclosed three novel mutations of the NOG gene in three SYM1 families. None of the otosclerosis patients without symphalangism had NOG mutations, indicating that NOG mutations may be restrictively found within patients with various skeletal abnormalities. These results together with the literature review indicated that there are no clear genotype-phenotype correlations for NOG mutations. With regard to surgical outcome, most of the patients in these three families with NOG mutations showed remarkable air-bone gap recovery after stapes surgery. Molecular genetic testing is useful to differentiate syndromic stapes ankylosis from otosclerosis, and even mild skeletal anomalies can be a diagnostic indicator of NOG-associated disease.

Comparison of ear-canal reflectance and umbo velocity in patients with conductive hearing loss: a preliminary study.

OBJECTIVE: The goal of the present study was to investigate the clinical utility of measurements of ear-canal reflectance (ECR) in a population of patients with conductive hearing loss in the presence of an intact, healthy tympanic membrane and an aerated middle ear. We also sought to compare the diagnostic accuracy of umbo velocity (VU) measurements and measurements of ECR in the same group of patients. DESIGN: This prospective study comprised 31 adult patients with conductive hearing loss, of which 14 had surgically confirmed stapes fixation due to otosclerosis, 6 had surgically confirmed ossicular discontinuity, and 11 had computed tomography and vestibular evoked myogenic potential confirmed superior semicircular canal dehiscence (SCD). Measurements on all 31 ears included pure-tone audiometry for 0.25 to 8 kHz, ECR for 0.2 to 6 kHz using the Mimosa Acoustics HearID system, and VU for 0.3 to 6 kHz using the HLV-1000 laser Doppler vibrometer (Polytec Inc, Waldbronn, Germany). We analyzed power reflectance |ECR| as well as the absorbance level = 10 × log10(1 - |ECR|). All measurements were made before any surgical intervention. The VU and ECR data were plotted against normative data obtained in a companion study of 58 strictly defined normal ears (). RESULTS: Small increases in |ECR| at low-to-mid frequencies (400-1000 Hz) were observed in cases with stapes fixation, while narrowband decreases were seen for both SCD and ossicular discontinuity. The SCD and ossicular discontinuity differed in that the SCD had smaller decreases at mid-frequency (∼1000 Hz), whereas ossicular discontinuity had larger decreases at lower frequencies (500-800 Hz). SCD tended to have less air-bone gap at high frequencies (1-4 kHz) compared with stapes fixation and ossicular discontinuity. The |ECR| measurements, in conjunction with audiometry, could successfully separate 28 of the 31 cases into the three pathologies. By comparison, VU measurements, in conjunction with audiometry, could successfully separate various pathologies in 29 of 31 cases. CONCLUSIONS: The combination of |ECR| with audiometry showed clinical utility in the differential diagnosis of conductive hearing loss in the presence of an intact tympanic membrane and an aerated middle ear and seems to be of similar sensitivity and specificity to measurements of VU plus audiometry. Additional research is needed to expand upon these promising preliminary results.

Two different techniques to facilitate reconstruction of the long incus process with bone cement: a feasibility study in human cadaveric temporal bones.

The purpose of this feasibility study was to evaluate two novel techniques facilitating bone cement repair of ossicular discontinuity between the incus and stapes. An isolated damage of the long incus process can be repaired using bone cement. However, bridging of a large gap between incus remnant and stapes head with bone cement is difficult, since viscous cement is not stable and the wet cement bridge may collapse. Ten fresh-frozen cadaveric human temporal bones were used. The long process of the incus was subtotally resected. A novel instrument and polylactide acid (PLA) scaffolds were applied to support ossicular reconstruction with bone cement. Stability of cement bridging was tested by checking for a round window reflex or motion of the stapes by palpating the malleus handle. Both the instrument as well as the PLA scaffolds were relatively easy to insert into the middle ear. However, bone cement adhered to the instrument irrespective of cement viscosity and contact time of the instrument with the ossicles. The bone cement plug had to be detached and sculptured. By contrast, PLA scaffolds could be used in a standardized manner and generated stable cement reconstructions. Curved PLA scaffolds were superior to straight ones. Initial results in cadaveric human temporal bones suggest that implantable PLA scaffolds might be suitable to support bone cement repair, even in very large defects of the long incus process.

Conductive hearing loss and middle ear pathology in young infants referred through a newborn universal hearing screening program in Australia.

BACKGROUND: Although newborn hearing screening programs have been introduced in most states in Australia, the prevalence of conductive hearing loss and middle ear pathology in the infants referred through these programs is not known. PURPOSE: This study was designed to (1) evaluate the prevalence of conductive hearing loss and middle ear pathology in infants referred by a newborn hearing screening program in north Queensland, (2) compare prevalence rates of conductive hearing loss and middle ear pathology in indigenous and nonindigenous infants, and (3) review the outcomes of those infants diagnosed with conductive hearing loss and middle ear pathology. RESEARCH DESIGN: Retrospective chart review of infants referred to the Audiology Department of The Townsville Hospital was conducted. STUDY SAMPLE: Chart review of 234 infants referred for one or both ears from a newborn hearing screening program in north Queensland was conducted. A total of 211 infants attended the diagnostic appointment. Review appointments to monitor hearing status were completed for 46 infants with middle ear pathology or conductive hearing loss. DATA COLLECTION AND ANALYSIS: Diagnosis of hearing impairment was made using an age-appropriate battery of audiological tests. Results were analyzed for both initial and review appointments. RESULTS: Mean age at initial diagnostic assessment was 47.5 days (SD = 31.3). Of the 69 infants with middle ear pathology during initial diagnostic assessment, 18 had middle ear pathology with normal hearing, 47 had conductive hearing loss, and 4 had mixed hearing loss. Prevalence of conductive hearing loss in the newborns was 2.97 per 1,000 while prevalence of middle ear pathology (with or without conductive hearing loss) was 4.36 per 1,000. Indigenous Australians or Aboriginal and Torres Strait Islander (ATSI) infants had a significantly higher prevalence of conductive hearing loss and middle ear pathology than non-ATSI infants (35.19 and 44.45% vs 17.83 and 28.66%, respectively). ATSI infants also showed poor resolution of conductive hearing loss over time with 66.67% of ATSI infants reviewed showing persistent conductive hearing loss compared to 17.86% of non-ATSI infants. Medical management of 17 infants with persistent conductive hearing loss included monitoring, antibiotic treatment, examination under anesthesia, and grommet insertion. CONCLUSIONS: Conductive hearing loss was found to be a common diagnosis among infants referred through screening. ATSI infants had significantly higher rates of middle ear pathology and conductive hearing loss at birth and showed poor resolution of middle ear pathology over time compared to non-ATSI infants. Future research using a direct measure of middle ear function as an adjunct to the automated auditory brainstem response screening tool to distinguish conductive from sensorineural hearing loss may facilitate prioritization of infants for assessment, thus reducing parental anxiety and streamlining the management strategies for the respective types of hearing loss.

Concomitant Dehiscences of the Temporal Bone: A Case-Based Study.

Otic capsule dehiscences create a pathological third window in the inner ear that results in a dissipation of the acoustic energy consequent to the lowered impedance. Superior semicircular canal dehiscence (SSCD) was identified by Minor et al in 1998 as a syndrome leading to vertigo and inner ear conductive hearing loss. The authors also reported the relation between the dehiscence and pressure- or sound-induced vertigo (Tullio's phenomenon). Prevalence rates of SSCD in anatomical studies range from 0.4% to 0.7% with a majority of patients being asymptomatic. The observed association with other temporal bone dehiscences, as well as the propensity toward a bilateral or contralateral "near dehiscence," raises the question of whether a specific local bone demineralization or systemic mechanisms could be considered. The present report regard a case of a patient with a previous episode of meningitis, with a concomitant bilateral SSCD and tegmen tympani dehiscence from the side of meningitis. The patient was affected by dizziness, left moderate conductive hearing loss, and pressure/sound-induced vertigo. Because of disabling vestibular symptoms, the patient underwent surgical treatment. A middle cranial fossa approach allowed to reach both dehiscences on the symptomatic side, where bone wax and fascia were used for repair. At 6 months from the procedure, hearing was preserved, and the vestibular symptoms disappeared.

Presynaptic GABA(B) receptors regulate experience-dependent development of inhibitory short-term plasticity.

Short-term changes in synaptic gain support information processing throughout the CNS, yet we know little about the developmental regulation of such plasticity. Here we report that auditory experience is necessary for the normal maturation of synaptic inhibitory short-term plasticity (iSTP) in the auditory cortex, and that presynaptic GABA(B) receptors regulate this development. Moderate or severe hearing loss was induced in gerbils, and iSTP was characterized by measuring inhibitory synaptic current amplitudes in response to repetitive stimuli. We reveal a profound developmental shift of iSTP from depressing to facilitating after the onset of hearing. Even moderate hearing loss prevented this shift. This iSTP change was mediated by a specific class of inhibitory interneurons, the low-threshold spiking cells. Further, using paired recordings, we reveal that presynaptic GABA(B) receptors at interneuron-pyramidal connections regulate iSTP in an experience-dependent manner. This novel synaptic mechanism may support the emergence of mature temporal processing in the auditory cortex.

Effects of location, size and shape of tympanic membrane perforations on hearing: analysis of 400 cases.

OBJECTIVE: This study aimed to evaluate the effect of size, location and shape of tympanic membrane perforations on hearing levels of a large study group treated in a tertiary referral centre. METHOD: Medical data of 458 patients with tympanic membrane perforations were evaluated. RESULTS: A total of 336 patients had normal middle-ear findings during the surgical procedures. There was a significant difference in terms of mean pure tone average and air-bone gap values between posterior-inferior and anterior-inferior perforations (p = 0.005 and p = 0.044, respectively). The mean air-bone gap value of kidney-shaped perforations was significantly higher. Posterior-superior and posterior perforations were significant indicators for ossicular chain defects (p < 0.001; odds ratio, 14.2 and p = 0.004; odds ratio, 3.4, respectively). CONCLUSION: Perforations located in the posterior-inferior quadrant caused the greatest hearing loss. The difference between posterior-inferior and anterior-superior or inferior perforations was statistically significant. Posterior perforations had a significant relationship with ossicular chain pathologies. Kidney-shaped perforations caused higher pure tone average and air-bone gap values than annular, elliptical or pinpoint perforations.