Effects of the neurotrophic factors BDNF, NT-3, and FGF2 on dissociated neurons of the cochlear nucleus

Neuritin Controls Axonal Branching in Serotonin Neurons: A Possible Mediator Involved in the Regulation of Depressive and Anxiety Behaviors via FGF Signaling

Abnormal neuronal morphological features, such as dendrite branching, axonal branching, and spine density, are thought to contribute to the symptoms of depression and anxiety. However, the role and molecular mechanisms of aberrant neuronal morphology in the regulation of mood disorders remain poorly characterized. Here, we show that neuritin, an activity-dependent protein, regulates the axonal morphology of serotonin neurons. Male neuritin knock-out (KO) mice harbored impaired axonal branches of serotonin neurons in the medial prefrontal cortex and basolateral region of the amygdala (BLA), and male neuritin KO mice exhibited depressive and anxiety-like behaviors. We also observed that the expression of neuritin was decreased by unpredictable chronic stress in the male mouse brain and that decreased expression of neuritin was associated with reduced axonal branching of serotonin neurons in the brain and with depressive and anxiety behaviors in mice. Furthermore, the stress-mediated impairments in axonal branching and depressive behaviors were reversed by the overexpression of neuritin in the BLA. The ability of neuritin to increase axonal branching in serotonin neurons involves fibroblast growth factor (FGF) signaling, and neuritin contributes to FGF-2-mediated axonal branching regulation in vitro. Finally, the oral administration of an FGF inhibitor reduced the axonal branching of serotonin neurons in the brain and caused depressive and anxiety behaviors in male mice. Our results support the involvement of neuritin in models of stress-induced depression and suggest that neuronal morphological plasticity may play a role in controlling animal behavior.

Candidate Key Proteins in Tinnitus-A Bioinformatic Study of Synaptic Transmission in the Cochlear Nucleus

The aim of this study was to identify key proteins of synaptic transmission in the cochlear nucleus (CN) that are involved in normal hearing, acoustic stimulation, and tinnitus. A gene list was compiled from the GeneCards database using the keywords "synaptic transmission" AND "tinnitus" AND "cochlear nucleus" (Tin). For comparison, two gene lists with the keywords "auditory perception" (AP) AND "acoustic stimulation" (AcouStim) were built. The STRING protein-protein interaction (PPI) network and the Cytoscape data analyzer were used to identify the top two high-degree proteins (HDPs) and their high-score interaction proteins (HSIPs), together referred to as key proteins. The top1 key proteins of the Tin-process were BDNF, NTRK1, NTRK3, and NTF3; the top2 key proteins are FOS, JUN, CREB1, EGR1, MAPK1, and MAPK3. Highly significant GO terms in CN in tinnitus were "RNA polymerase II transcription factor complex", "late endosome", cellular response to cadmium ion", "cellular response to reactive oxygen species", and "nerve growth factor signaling pathway", indicating changes in vesicle and cell homeostasis. In contrast to the spiral ganglion, where important changes in tinnitus are characterized by processes at the level of cells, important biological changes in the CN take place at the level of synapses and transcription.

Exogenous neuritin restores auditory following cochlear spiral ganglion neuron denervation of gerbils

Spiral ganglion neurons (SGNs) transmit sound signals received by hair cells to the auditory center to produce hearing. The quantity and function are important for maintaining normal hearing function. Limited by the regenerative capacity, SGNs are unable to regenerate spontaneously after injury. Various neurotrophic factors play an important role in the regeneration process. Neuritin is a neurite growth factor that plays an important role in neural plasticity and nerve injury repair. In this study, we used bioinformatics analysis to show that neuritin was negatively correlated with cochlear damage. Then, we aimed to establish a cochlear spiral ganglion-specific sensorineural deafness model in gerbils using ouabain and determine the effects of exogenous neuritin protein in protecting damaged cochlear SGNs and repairing damaged auditory nerve function. The provides a new research strategy and scientific basis for the prevention and treatment of sensorineural deafness caused by the loss of SGNs. We were discovered that neuritin is expressed throughout the development of the gerbil cochlea, primarily in the SGNs and Corti regions. The expression of neuritin was negatively correlated with the sensorineural deafness induced by ouabain. In vitro and in vivo revealed that neuritin significantly maintained the number and arrangement of SGNs and nerve fibers in the damaged cochlea and effectively protected the high-frequency listening function of gerbils.

Molecular and Clinical Significance of Fibroblast Growth Factor 2 in Development and Regeneration of the Auditory System

The fibroblast growth factor 2 (FGF2) is a member of the FGF family which is involved in key biological processes including development, cellular proliferation, wound healing, and angiogenesis. Although the utility of the FGF family as therapeutic agents has attracted attention, and FGF2 has been studied in several clinical contexts, there remains an incomplete understanding of the molecular and clinical function of FGF2 in the auditory system. In this review, we highlight the role of FGF2 in inner ear development and hearing protection and present relevant clinical studies for tympanic membrane (TM) repair. We conclude by discussing the future implications of FGF2 as a potential therapeutic agent.

Neurotrophin-3 Promotes the Neuronal Differentiation of BMSCs and Improves Cognitive Function in a Rat Model of Alzheimer's Disease

Transplantation of bone marrow-derived mesenchymal stem cells (BMSCs) has the potential to be developed into an effective treatment for neurodegenerative diseases such as Alzheimer's disease (AD). However, the therapeutic effects of BMSCs are limited by their low neural differentiation rate. We transfected BMSCs with neurotrophin-3 (NT-3), a neurotrophic factor that promotes neuronal differentiation, and investigated the effects of NT-3 gene overexpression on the differentiation of BMSCs into neurons in vitro and in vivo. We further studied the possible molecular mechanisms. We found that overexpression of NT-3 promoted the differentiation of BMSCs into neurons in vitro and in vivo and improved cognitive function in rats with experimental AD. By contrast, silencing NT-3 inhibited the differentiation of BMSCs and decreased cognitive function in rats with AD. The Wnt/β-catenin signaling pathway was involved in the mechanism by which NT-3 gene modification influenced the neuronal differentiation of BMSCs in vitro and in vivo. Our findings support the prospect of using NT-3-transduced BMSCs for the development of novel therapies for AD.

Nobiletin ameliorates isoflurane-induced cognitive impairment via antioxidant, anti-inflammatory and anti-apoptotic effects in aging rats

A recent study reported that nobiletin is an active ingredient in Fructus Aurantii immaturus and Pericarpium Citri Reticulatae, which may be capable of preventing ischemic stroke. Therefore, the present study aimed to determine the neuroprotective effects of nobiletin, and to evaluate whether it could ameliorate isoflurane‑induced cognitive impairment via antioxidant, anti‑inflammatory and anti‑apoptotic effects in aging rats. Male Sprague‑Dawley rats (age, 18 months) were used to analyze the neuroprotective effects of nobiletin. Morris water maze test was used to determine cognitive competence. Enzyme‑linked immunosorbent assay and western blot analysis were also used to quantify nuclear factor‑κB, tumor necrosis factor (TNF)‑α, IL‑1β, IL‑6, glutathione, (GSH), GSH‑peroxidase, superoxide dismutase and malondialdehyde concentration and relevant protein expression levels Cognitive competence was increased in isoflurane-treated rats following treatment with nobiletin. In addition, as expected, nobiletin exerted antioxidant, anti-inflammatory and anti‑apoptotic effects on isoflurane‑induced cognitive impairment in aging rats. Treatment with nobiletin induced the activation of phosphorylated (p)‑Akt, p‑cAMP response element binding protein (CREB) and brain‑derived neurotrophic factor (BDNF) protein expression and reduced the levels of B‑cell lymphoma 2‑associated X protein (Bax) in isoflurane‑induced rats. In conclusion, the present study demonstrated that nobiletin may ameliorate isoflurane-induced cognitive impairment through antioxidant, anti‑inflammatory and anti‑apoptotic effects via modulation of Akt, Bax, p‑CREB and BDNF in aging rats. These findings provide support for the molecular mechanisms underlying the effects of nobiletin treatment on isoflurane-induced damage.

Effects of brain-derived neurotrophic factor (BDNF) on the cochlear nucleus in cats deafened as neonates

Many previous studies have shown significant neurotrophic effects of intracochlear delivery of BDNF in preventing degeneration of cochlear spiral ganglion (SG) neurons after deafness in rodents and our laboratory has shown similar results in developing cats deafened prior to hearing onset. This study examined the morphology of the cochlear nucleus (CN) in a group of neonatally deafened cats from a previous study in which infusion of BDNF elicited a significant improvement in survival of the SG neurons. Five cats were deafened by systemic injections of neomycin sulfate (60 mg/kg, SQ, SID) starting one day after birth, and continuing for 16-18 days until auditory brainstem response (ABR) testing demonstrated profound bilateral hearing loss. The animals were implanted unilaterally at about 1 month of age using custom-designed electrodes with a drug-delivery cannula connected to an osmotic pump. BDNF (94 μg/ml; 0.25 μl/hr) was delivered for 10 weeks. The animals were euthanized and studied at 14-23 weeks of age. Consistent with the neurotrophic effects of BDNF on SG survival, the total CN volume in these animals was significantly larger on the BDNF-treated side than on the contralateral side. However, total CN volume, both ipsi- and contralateral to the implants in these deafened juvenile animals, was markedly smaller than the CN in normal adult animals, reflecting the severe effects of deafness on the central auditory system during development. Data from the individual major CN subdivisions (DCN, Dorsal Cochlear Nucleus; PVCN, Posteroventral Cochlear Nucleus; AVCN, Anteroventral Cochlear Nucleus) also were analyzed. A significant difference was observed between the BDNF-treated and control sides only in the AVCN. Measurements of the cross-sectional areas of spherical cells showed that cells were significantly larger in the AVCN ipsilateral to the implant than on the contralateral side. Further, the numerical density of spherical cells was significantly lower in the AVCN ipsilateral to the implant than on the contralateral side, consistent with the larger AVCN volume observed with BDNF treatment. Together, findings indicate significant neurotrophic effects of intracochlear BDNF infusion on the developing CN.