Determinants of Response Pattern of Cochlear Nucleus Neuron:a Study Based on the Model

Objective: Neurons in the cochlear nucleus show different response patterns to the short tone bursts. Because of the limitations of animal experiments, it is hard to explore the principle. Therefore, using a model to simulate CN neurons will be a feasible way. Methods: Based on the initial model mentioned in the previous study, we proposed an improved CN model in MATLAB R2012b. Results: By modifying the parameters of the model we found the interchanges among "primary-like", "chopper",and "onset" response patterns. Furthermore, we simulated the "pauser" response pattern by adding an extra input in our model. Conclusion: The results indicate that the synaptic integrations and the input modes can give rise to different characteristics of CN neurons, which eventually determine the response patterns of CN neurons.

Histological and Physiological Investigation of Channelrhodopsin-2 and Halorhodopsin in the Dorsal Cochlear Nucleus

We have delivered viral vectors containing either Chop2 fused with GFP, Channelrhodopsin-2 （ChR2）, or Halorhodopsin （HaloR） fused with mCherry （to form light gated cation channels or chloride pumps, respectively）, into the dorsal cochlear nucleus （DCN）. One to eighteen months later we examined the CN and inferior colliculus （IC） for evidence of virally transfected cells and processes. Production of ChR2 and HaloR was observed throughout the DCN. Rhodopsin localization within neurons was determined, with elongate, fusiform and giant cells identified based on morphology and location within the DCN. Production of ChR2 and HaloR was found at both the injection site as well as in regions projecting to and from the DCN. Light driven neuronal activity in the DCN was dependent upon the wavelength and intensity of the light, with only the appropriate wavelength resulting in activation and higher intensity light resulting in more neuronal activity. Transfecting cells via viral delivery of rhodopsins can be useful as a tract tracer and as a neuronal marker to delineate pathways. In the future rhodopsin delivery and activation may be developed as an alternative to electrical stimulation of neurons.

Frequency Selectivity Behaviour in the Auditory Midbrain： Implications of Model Study

By numerical simulations on frequency dependence of the spiking threshold, i.e. on the critical amplitude of periodic stimulus, for a neuron to fire, we find that bushy cells in the cochlear nuclear exhibit frequency selec- tivity behaviour. However, the selective frequency band of a bushy cell is far away from that of the preferred spectral range in human and mammal auditory perception. The mechanism underlying this neural activity is also discussed. Further studies show that the ion channel densities have little impact on the selective frequency band of bushy cells. These findings suggest that the neuronal behaviour of frequency selectivity in bushy cells at both the single cell and population levels may be not functionally relevant to frequency discrimination. Our results may reveal a neural hint to the reconsideration on the busily cell functional role in auditory information processing of sound frequency.

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).

Clinical and scientific innovations in auditory brainstem implants

The auditory brainstem implant(ABI)was originally developed to provide rehabilitation of retrocochlear deafness caused by neurofibromatosis type 2(NF2).Recent studies of the ABI have investigated outcomes in non-NF2 cohorts,such as patients with cochlear nerve aplasia or cochlear ossification and more recently,intractable tinnitus.New technologies that improve the ABI-neural tissue interface are being explored as means to improve performance and decrease side effects.Innovative discoveries in optogenetics and bioengineering present opportunities to continually evolve this technology into the future,enhancing spatial selectivity of neuronal activation in the cochlear nucleus and preventing side effects through reduction in activation of non-target neuronal circuitry.These advances will improve surgical planning and ultimately improve patients1 audiological capabilities.ABI research has rapidly increased in the 21st century and applications of this technology are likely to continually evolve.Herein,we aim to characterize ongoing clinical,basic science,and bioengineering advances in ABIs and discuss future directions of this technology.