Exogenous BDNF and Chondroitinase ABC Consisted Biomimetic Microenvironment Regulates Survival,Migration and Differentiation of Human Neural Progenitor Cells Transplanted into a Rat Auditory Nerve

Current putative regeneration oriented studies express possible role of stem cell based implantation strategy in the restoration of fundamental perception of hearing. The present work utilizes a rat auditory nerve (AN) directed transplantation of human neural progenitor cells (HNPCs) as a cell replacement therapy for impaired auditory function. Groups of b-bungarotoxin induced auditory function compromised female rats were used to transplant HNPCs in the nerve trunk. In the treatment groups, brain derived neurotrophic factor (BDNF), peptide amphiphile nanofiber bioactive gel (Bgel) and Chondroitinase ABC (ChABC), a digestive enzyme that cleaves the core of chondroitin sulphate proteoglycans, were added along with HNPCs while the control groups were with PA inert gel (Igel) and devoid of ChABC. Six weeks post transplantation survival, migration, and differentiation of HNPCs were studied and compared. The groups treated with BDNF and Bgel showed improved survival and differentiation of transplanted HNPCs while the ChABC treated group showed significant migration of HNPCs along the AN and elongation of neuronal fibers along the nerve towards the cochlear nucleus (CN) which was characterized by immunocytochemical markers for human Nuclei (HuN), human mitochondria (HuM) and neuronal β-tubulin (Tuj1). These findings show that addition of BDNF and ChABC consisted Bgel environment facilitated HNPC survival, migration and differentiation along the transplanted rat AN towards the CN. This transplantation strategy provides unique experimental validation for futuristic role of cell based biomaterial consisted neurotrophic factor application in clinically transferable treatment of sensorineural hearing loss (SNHL) along with cochlear implants (CI).

Auditory nerve preservation and regeneration in man:relevance for cochlear implantation

Human hearing relies on 15,000 hair cells （HCs） or mecha- noreceptors sited in a 34 mm long helical shaped epithelial ridge. There may be several explanations for their vulner- ability in man and regrettably, they do not regenerate. Ap- proximately 35,000 bipolar neurons have their soma situated in the modiolus of the cochlea. Human afferents consist of two separate systems; one is represented by the large type I cells innervating the inner HCs （IHCs, n = 3,400） and the other one by the small type Ⅱcells innervating the outer HCs （OHCs, n = 12,000）. Type I spiral ganglion neurons （SGNs） constitute 96% of the afferent nerve population. Unlike in other mammals, their somas together with the pre- and post-somatic segments are unmyelinated. Type II nerve cell soma and fibers are unmyelinated.

Ouabain-Induced Auditory Nerve Degeneration in Congenic Ly5.1 Mice

The Ly5.1 mouse,also termed B6.SJL-Ptprca Pepcb/BoyJ,is a congenic strain widely used as a recipient in animal studies of bone marrow transplant.Our previous study documented that a majority of type I spiral ganglion neurons (SGNs) in the apical turns of Ly5.1 mice are unmyelinated and aggregate into neuronal clusters,similar to the spiral ganglion in the human ear.Ouabain,a well known Na-K ATPase inhibitor,has been shown to induce neuronal degeneration in a variety of neural tissues including the adult gerbil and CBA/CaJ mouse spiral ganglion.Here,functional and pathological changes of the auditory nerves in young-adult Ly5.1 mice were examined at 3,7 and 14 days after ouabain exposure.Similar to observations in CBA/CaJ mice,ouabain application selectively removed type I SGNs,resulting in an immense decline of the auditory nerve function.Hyperplasia of glial cells was seen in the injured auditory nerves at 7 days after ouabain exposure.Our data indicate that the 'human-like' features of unmyelinated type I SGNs have no protective impact on the fate of SGNs after ouabain exposure.Cells incorporating bromodeoxyuridine (BrdU) and expressing Sox2 were also counted in the auditory nerves of control and ouabain-treated ears.The number of Sox2+ glial cells significantly increased at 3 and 7 days post-treatment.Interestingly,the highest density of BrdU+ cells appeared in the apical turn of the injured auditory nerve shortly after ouabain exposure,suggesting that the pattern of SGN loss at the apical turn in Ly5.1 mouse may have some impact on the reaction of non-neuronal cells in response to acute ototoxic drug exposure in the auditory nerve.

Brainstem auditory evoked potential combined with high resolution cranial base CT can optimize the diagnosis of auditory nerve injury

Purpose:Auditory nerve injury is one of the most common nerve injury complications of skull base fractures.However,there is currently a lack of auxiliary examination methods for its direct diagnosis.The purpose of this study was to find a more efficient and accurate means of diagnosis for auditory nerve injury.Methods:Through retrospectively analyzing the results of brainstem auditory evoked potential(BAEP)and high-resolution CT(HRCT)in 37 patients with hearing impairment following trauma from January 1,2018 to July 31,2020,the role of the two inspection methods in the diagnosis of auditory nerve injury was studied.Inclusion criteria were patient had a clear history of trauma and unilateral hearing impairment after trauma;while exclusion criteria were:(1)severe patient with a Glasgow coma scale score<5 because these patients were classified as severe head injury and admitted to the intensive care unit,(2)patient in the subacute stage admitted 72 h after trauma,and(3)patient with prior hearing impairment before trauma.According to Goodman's classification of hearing impairment,the patients were divided into low/medium/severe injury groups.In addition,patients were divided into HRCT-positive and negative groups for further investigation with their BAEP results.The positive rates of BEAP for each group were observed,and the results were analyzed by Chi-square test(p<0.05,regarded as statistical difference).Results:A total of 37 patients were included,including 21 males and 16 females.All of them were hospitalized patients with GCS score of 6-15 at the time of admission.The BAEP positive rate in the medium and severe injury group was 100%,which was significantly higher than that in the low injury group(27.27%)(p<0.01).The rate of BEAP positivity was significantly higher in the HRCT-positive group(20/30,66.7%)than in the HRCT-negative group(1/7,14.3%)(p<0.05).Twenty patients(54.05%)were both positive for BEAP and HRCT test,and considered to have auditory nerve damage.Six patients(16.22%)were both negative for BEAP and HRCT test,and 10 patients(27.03%)were BAEP-negative but HRCT-positive:all the 16 patients were considered as non-neurological injury.The rest 1 case(2.70%)was BAEP-positive but HRCT-negative,which we speculate may have auditory nerve concussion.Conclusion:By way of BAEP combining with skull base HRCT,we may improve the accuracy of the diagnosis of auditory nerve injury.Such a diagnostic strategy may be beneficial to guiding treatment plans and evaluating prognosis.

Temporal sequential correlation analysis on compoundaction potentials of the auditory nerve versus the stimulating AM-sound envelope

Compound action potentials of the auditory nerve in response to amplitude modulating tones were recorded in guinea pigs with electrode implanted to the exit of the internal auditory meatus and temporal sequential correlation between the responses and the modulators was studied in a paradigm of systematically changing acoustic parameters. Three kinds of modulators were used. continuous or burst sinusoids of fixed frequency (in the range of 40 Hz-5 kHz), short bursts of sinusoids with changing frequency and short segments of speech signal. Ranges of parametric variation were 500 Hz-20 kHz for carrier frequency, 5%-95% for modulation depth and 20 dB-90 dB SPL for intensity. For continuous or burst sinusoidal modulators of fixed frequencies, the correlation coefficient (r) remained quite high in most parametric conditions, ranging from 0.80 to 0.95. It became smaller mainly in instances of decreased response amplitude on account of unfavourable parameters. For burst modulators of changing frequency, r varied around 0.66-0.86. When segments of speech signal served as the modulators, significant correlation (r around 0.50 ) also existed, indicating the validity of the timing mode of information encoding for speech sound at the cochlear nerve level. Some theoretical and technical points in studying the timing mechanism of audition is discussed.