Role of trophic factors in the development, survival and repair of primary auditory neurons

Cell Transplantation and Neuroengineering Approach for Spinal Cord Injury Treatment: A Summary of Current Laboratory Findings and Review of Literature

Spinal cord injury (SCI) can cause severe traumatic injury to the central nervous system (CNS). Current therapeutic effects achieved for SCI in clinical medicine show that there is still a long way to go to reach the desired goal of full or significant functional recovery. In basic medical research, however, cell transplantation, gene therapy, application of cytokines, and biomaterial scaffolds have been widely used and investigated as treatments for SCI. All of these strategies when used separately would help rebuild, to some extent, the neural circuits in the lesion area of the spinal cord. In light of this, it is generally accepted that a combined treatment may be a more effective strategy. This review focuses primarily on our recent series of work on transplantation of Schwann cells and adult stem cells, and transplantation of stem cell-derived neural network scaffolds with functional synapses. Arising from this, an artificial neural network (an exogenous neuronal relay) has been designed and fabricated by us—a biomaterial scaffold implanted with Schwann cells modified by the neurotrophin-3 (NT-3) gene and adult stem cells modified with the TrkC (receptor of NT-3) gene. More importantly, experimental evidence suggests that the novel artificial network can integrate with the host tissue and serve as an exogenous neuronal relay for signal transfer and functional improvement of SCI.

Keynote review: The auditory system, hearing loss and potential targets for drug development

There is a huge potential market for the treatment of hearing loss. Drugs are already available to ameliorate predictable, damaging effects of excessive noise and ototoxic drugs. The biggest challenge now is to develop drug-based treatments for regeneration of sensory cells following noise-induced and age-related hearing loss. This requires careful consideration of the physiological mechanisms of hearing loss and identification of key cellular and molecular targets. There are many molecular cues for the discovery of suitable drug targets and a full range of experimental resources are available for initial screening through to functional analysis in vivo. There is now an unparalleled opportunity for translational research.

Effect of cochlear integrity on cochlear nucleus neuron glucose metabolism in aged adult broiler chickens

Abrupt removal of excitatory input is devastating to post-synaptic neurons in normally functioning sensory systems. In both mammalian and avian auditory systems, abrupt temporary or permanent experimental deafferentation stimulates a cascade of changes in central auditory structures that can result in neuron death. Effects of naturally occurring progressive deafferentation on central auditory structure and function have not been fully described. Extensive naturally occurring cochlear damage is found in some aged chickens, despite their regenerative capacity, providing the opportunity to examine the effects of this type of deafferentation on the avian cochlear nucleus (nucleus magnocellularis, NM). Previous evaluation of NM oxidative metabolism using cytochrome oxidase histochemistry revealed that naturally occurring cochlear damage results in down-regulated metabolism in corresponding regions of NM. It is unknown how progressive hair cell damage and loss affects NM glucose uptake. Here, NM glucose metabolism is assessed using 2-deoxyglucose uptake as a marker for metabolic activity in the presence of normal, mildly damaged, severely damaged, and totally damaged cochlear hair cells. Results indicate that while severe and total cochlear damage significantly decrease NM oxidative metabolism, only total damage results in significantly decreased NM glucose metabolism. Results are discussed in the context of functional reorganization and trophic support.

Neuroprotective effects of brain-derived neurotrophic factor (BDNF) on hearing in experimental pneumococcal meningitis

Bacterial meningitis is still one of the most common causes of acquired profound sensorineural deafness in children despite antibiotic treatment. We investigated the neuroprotective effects of brain-derived neurotrophic factor on hearing function in experimental bacterial meningitis. We implanted stainless steel tubes into both cerebral ventricles of Sprague-Dawley rats aged 21 days. Bacterial meningitis was induced by inoculating a strain of serotype III Streptococcus pneumoniae into the cisterna magna. Six micrograms per day of brain-derived neurotrophic factor (groups 1 and 3) or albumin (groups 2 and 4) was injected into the cerebral ventricles 24 hours after or before infection, respectively, for a duration of 7 days. Additionally, all rats received antibiotic subcutaneous treatment starting 24 hours after infection for 7 days. Brainstem auditory evoked potentials were recorded 24 hours before and 24 hours after infection and after 7 days of treatment with brain-derived neurotrophic factor or placebo and antibiotics, respectively, to determine hearing threshold. Our results showed that the hearing thresholds of animals in each group increased significantly 24 hours after infection compared with the results recorded 24 hours before infection (P < .01). After 7 days of treatment with brain-derived neurotrophic factor, brainstem auditory evoked potential responses recurred in 16 ears when stimulated at 75 dB hearing level in groups 1 and 3. Their hearing thresholds significantly decreased compared with the control group 2 (P < .05) and group 4 (P < .01). However, 13 of 14 ears absent brainstem auditory evoked potential responses could still not be identified at 75 dB hearing level in control groups 2 and 4. The improvement of the hearing thresholds in group 3 (treated before infection) was greater than that of group 1 (treated after infection) (P < .05), but there was no significant difference found between the control groups before and after infection (P > .05). Our study supports the hypothesis that the administration of exogenous brain-derived neurotrophic factor can be effective in preventing or treating hearing loss following bacterial meningitis.

Regulation of axonal growth and guidance by the neurotrophin family of neurotrophic factors

1. The neurotrophins play an important role during development to stimulate and guide axonal growth for the establishment of a correctly wired and functional neural system. Neurotrophins can also regulate adult nervous system plasticity by promoting neuronal survival and stimulating nerve regrowth following injury. 2. Therefore, the potential exists for these neurotrophic factors to be used as therapeutic agents for the treatment of neurodegenerative disorders. However, in order to realize the full capacity of neurotrophic factors as therapeutic agents, it is important to understand the mechanisms by which they elicit their survival and regenerative effects. 3. The present paper reviews some of the ways in which neurotrophins regulate axonal growth and guidance.