Expression and Neurotransmitter Association of the Synaptic Calcium Sensor Synaptotagmin in the Avian Auditory Brain Stem

In the avian auditory brain stem, acoustic timing and intensity cues are processed in separate, parallel pathways via the two division of the cochlear nucleus, nucleus angularis (NA) and nucleus magnocellularis (NM). Differences in excitatory and inhibitory synaptic properties, such as release probability and short-term plasticity, contribute to differential processing of the auditory nerve inputs. We investigated the distribution of synaptotagmin, a putative calcium sensor for exocytosis, via immunohistochemistry and double immunofluorescence in the embryonic and hatchling chick brain stem (Gallus gallus). We found that the two major isoforms, synaptotagmin 1 (Syt1) and synaptotagmin 2 (Syt2), showed differential expression. In the NM, anti-Syt2 label was strong and resembled the endbulb terminals of the auditory nerve inputs, while anti-Syt1 label was weaker and more punctate. In NA, both isoforms were intensely expressed throughout the neuropil. A third isoform, synaptotagmin 7 (Syt7), was largely absent from the cochlear nuclei. In nucleus laminaris (NL, the target nucleus of NM), anti-Syt2 and anti-Syt7 strongly labeled the dendritic lamina. These patterns were established by embryonic day 18 and persisted to postnatal day 7. Double labeling immunofluorescence showed Syt1 and Syt2 were associated with Vesicular Glutamate Transporter 2 (VGluT2), but not Vesicular GABA Transporter (VGAT), suggesting these Syt isoforms were localized to excitatory, but not inhibitory, terminals. These results suggest that Syt2 is the major calcium binding protein underlying excitatory neurotransmission in the timing pathway comprising NM and NL, while Syt2 and Syt1 regulate excitatory transmission in the parallel intensity pathway via cochlear nucleus NA.

Effect of Unilateral Acoustic Trauma on Neuronal Firing Activity in the Inferior Colliculus of Mice

Neural hyperactivity induced by sound exposure often correlates with the development of hyperacusis and/or tinnitus. In laboratory animals, hyperactivity is typically induced by unilateral sound exposure to preserve one ear for further testing of hearing performance. Most ascending fibers in the auditory system cross into the superior olivary complex and then ascend contralaterally. Therefore, unilateral exposure should be expected to mostly affect the contralateral side above the auditory brain stem. On the other hand, it is well known that a significant number of neurons have crossing fibers at every level of the auditory pathway, which may spread the effect of unilateral exposure onto the ipsilateral side. Here we demonstrate that unilateral sound exposure causes development of hyperactivity in both the contra and ipsilateral inferior colliculus in mice. We found that both the spontaneous firing rate and bursting activity were increased significantly compared to unexposed mice. The neurons with characteristic frequencies at or above the center frequency of exposure showed the greatest increase. Surprisingly, this increase was more pronounced in the ipsilateral inferior colliculus. This study highlights the importance of considering both ipsi- and contralateral effects in future studies utilizing unilateral sound exposure.

The difference between Chirp & Click stimulation in Diagnostic Auditory Brainstem Response in assessment of hearing among age group between 1-10 years Iraqi children

Background: Aim: To compare the response of human auditory brain stem evoked by clicks stimuli and chirps. Patients and Methods: A study of cross-sectional design was chosen to evaluate the objective of the study. Children between 1-10 years were enrolled from the attendants of the Dept. of Surgery and Audiology, Al-Jamhoori Teaching Hospital, Ministry of Health /Nineveh health Directorate, and the outpatient clinics in al-alwiyah teaching hospital for children and done in the privet clinics of the researchers. The data collection extended over the period from 2019 January to 2020 August. A total number of 70 children involved in the study according to the parents’ complaints, full history taken and the clinical examination by otoscopy. The probable conductive problem excluded by using the Tympanometry. Moreover, free field test was done before chirp and click. Paired t-test was used for the statistical analysis. Results: The males represent (44.3%) and the females (55.7%). The mean age of children included was 49 months ± 27.7 SD. Wave V of the chirp shows lower latency means in all intensities in comparison with that of click stimuli. While waves I and III, show longer latency as the intensity go down, but the differences between chirp and click are insignificant. Wave V amplitudes getting lower values as the intensity decreasing in both chirp and click and become significantly higher than that of click. Wave I and III show decreasing amplitudes with the decreasing intensity in both chirp and click, with higher amplitudes in click in comparing with that of chirp, which are insignificant statistically down to below 70 dBnHL. Conclusions: The chirp stimuli are highly significant and more efficient from the click in the detection of hearing loss among the children regarding both latency and amplitude particularly at wave V.

Auditory Brain Stem Response Predictors of Hearing Outcomes after Middle Fossa Resection of Vestibular Schwannomas

Objectives To analyze the relationship between preoperative and intraoperative auditory brain stem response (ABR) characteristics and hearing outcomes in patients with vestibular schwannomas (VS) undergoing hearing preservation (HP) surgery via a middle cranial fossa (MCF) approach. Design Prospective study. Setting Academic tertiary skull base referral center. Methods Pre- and postoperative pure-tone average (PTA) and word recognition score (WRS) were examined. Intraoperative ABR wave III latency, wave V latency, and amplitude were recorded. HP was defined as postoperative WRS ≥50%. Participants Adult patients with VS and WRS ≥50% who underwent MCF tumor resection between November 2017 and September 2019. Main Outcome Measures Postoperative hearing outcomes. Results Sixty patients were included. Mean tumor size was 9.2 mm (range, 3–17). HP rates were 56.7% for the cohort and 69.7% for tumors <10 mm. A complete loss of wave V was associated with an 82.9% increase in postoperative PTA (p < 0.001) and 97.2% decrease in WRS (p < 0.001), whereas a diminished wave V was correlated with 62.7% increase in PTA (p < 0.001) and 55.7% decrease in WRS (p = 0.006). A diminished or absent wave V, but not increased wave III/V latency or decreased wave V amplitude, was correlated with a decline in postoperative hearing class (r = 0.735, p < 0.001). Receiver-operating characteristic analysis demonstrated that a stable wave V has the highest accuracy in predicting HP (sensitivity of 82.6%, specificity of 84.8%). Conclusion Of the examined preoperative and intraoperative ABR characteristics, a stable wave V intraoperatively was the strongest predictor of HP after MCF resection of VS. Level of Evidence Level III.

Comparison of Auditory Brain Stem Responses and Otoacoustic Emission of Autism with Healthy Children

Background: Autism is a neurodevelopment disorder, including difficulty in establishing relationships and social interaction, difficulty in communication, performing restricted, and repetitive behaviors. The impaired reception and integration of sensory information especially auditory data are one of the main characteristics of children with autism. According to various studies, the brain stem plays a key role in the reception and integration of auditory and sensory data. Hence, this study aims to comparison auditory brain stem responses (ABR) and otoacoustic emission (OAE) of autism patients with healthy children. Materials and Methods: This case-control study was performed on 20 autism children (4-8 years old) as case group who referred to psychiatry clinics affiliated with Tabriz University of Medical Sciences and 20 healthy age-matched as the control group. The severity of autism was evaluated by the Gilliam Autism Rating Scale (GARS). Also, ABR and OAE were recorded, and all data compared with the healthy children. Results: The latencies between the waves III-V and I-V bilaterally, and wave V bilaterally and wave I in the left ear showed a significant increase in children with autism compared to the healthy group. Conclusion: This study shows that there was a reduced nerve conduction velocity in the auditory pathway of the brain stem in children with autism compared to healthy children. [GMJ.2020;9:e1937]

Can auditory brain stem response accurately reflect the cochlear function?

Auditory brain stem response (ABR) is more commonly used to evaluate cochlear lesions than cochlear compound action potential (CAP). In a noise-induced cochlear damage model, we found that the reduced CAP and enhanced ABR caused the threshold difference. In a unilateral cochlear destruction model, a shadow curve of the ABR from the contralateral healthy ear masked the hearing loss in the destroyed ear.

Imaging of Auditory Brain Stem Implants

Auditory brain stem implants are infrequently encountered neuroprosthetic devices used for auditory rehabilitation in deaf patients with pathology between the cochlea and cochlear nuclei who would not benefit from cochlear implantation. This article reviews the device, the relevant anatomy, audiologic performance, operative approaches, and conditions in which auditory brain stem implants are indicated. The imaging appearance of auditory brain stem implants, including optimal lead positioning, and imaging safety considerations of the device are also discussed. Knowledge of the device can assist the radiologist in detecting postoperative complications and component malpositioning and in providing safe and effective imaging practices in patients with indwelling auditory brain stem implants.Learning Objective: To describe the auditory brain stem implant device, identify optimal lead positioning, and list indications for auditory brain stem implant placement.

Auditory Brainstem Evoked Response Patterns in the Neonatal Intensive Care Unit

Objective Delayed maturation of auditory brainstem pathway in neonates admitted to the neonatal intensive care unit (NICU) may lead to misdiagnosis of children with normal peripheral hearing and inappropriate use of amplification devices. The aim of this study is to determine the pattern of auditory brain stem response in neonates admitted to the NICU for proper hearing assessment in this high-risk population. Study Design This prospective study was conducted on 1,469 infants who were admitted to the NICU, of which 1,423 had one or more risk factors for permanent congenital hearing loss and were screened with automated auditory brain stem response (AABR). A total of 60 infants were referred for diagnostic ABR analysis after failure on AABR screening. The control group comprised 60 well-baby nursery neonates with no risk factors for PCHL. Results Mean values of absolute latencies of waves III and V; interpeak latencies I–III, III–V, and I–V; amplitude of waves I, and V; and I/V amplitude ratio at 90 dBnHL measured for the right and left ears at 1 and 3 months of age show significant difference in NICU neonates compared with controls (p < 0.05). All the diagnostic ABR measurements significantly improved at the age of 3 months (p < 0.001) except wave I absolute latency of both groups (p > 0.05). Significant correlations were found between ABR readings at the age of 1 and 3 months and the gestational age of the NICU neonates (p < 0.05). Conclusion Diagnostic ABR findings in NICU neonates suggested delayed maturation of the auditory brainstem pathway with a great impact of gestational age on this maturation. Auditory maturational changes were observed at 3 months of age of patient and control groups.

Within-Subject Analysis of Auditory Brain Stem Responses in Adults With Unilateral Tinnitus

Tinnitus affects about 10% of population worldwide. Most patients present with some degrees of hearing impairment, while others remain normal. The aim of this study was to analyze the latency and amplitude of auditory brain stem response (ABR) waveforms in patients with unilateral tinnitus. The tinnitus ears and non-tinnitus ears were compared for each patient. Sixty-seven patients with single-sided tinnitus were enrolled, including 26 male and 41 female patients with a mean age of 54.4 (age ranged from 22 to 79). Eighteen patients had bilateral normal hearing, while 49 patients had some degree of sensorineural hearing. The ABR waveforms were retrospectively analyzed in terms of waves I, III, and V absolute latency, as well as waves I-III, waves II-V, and waves I-V latency intervals, amplitude, and amplitude ratio (III/I, V/I). Statistical analyses were performed within patients. There was no significant ABR difference between the tinnitus and non-tinnitus ears with regard to all the wave latencies and amplitudes in our patients (all P values >0.1). Our result that ABR changes were not found between tinnitus and non-tinnitus ears implies that tinnitus does not simply originate from the defect of the peripheral auditory system. It conforms to the contemporary theory that a higher level of the brain is involved in the generation of tinnitus.