Cochlear Spiral Ganglion Cells Research Articles

Effects of Noise Damage on the Purinergic Signal of Cochlear Spiral Ganglion Cells in Guinea Pigs.

To observe the expression changes of P2 protein in cochlear spiral ganglion cells before and after noise injury, and to explore the relationship between the changes of purinergic receptors in spiral ganglion cells and noise-induced hearing loss, so that the signal transduction of purinergic receptors can be used to treat SNHL The target point provides a theoretical basis. The experimental animals were randomly divided into normal and experimental groups. The experimental group was given 120dB white noise continuous exposure for 10days and 3h a day. The auditory brainstem response was measured before and after the noise exposure. After the noise exposure, the two groups of animals were collected. Do immunofluorescence staining, western blot, fluorescence real-time quantitative PCR to observe the expression of P2 protein. The average hearing threshold of the animals in the experimental group increased to 38.75 ± 6.44dB SPL after 7days of noise exposure, and the high-frequency hearing loss was lower and severe; the average hearing threshold increased to 54.38 ± 6.80dB SPL after 10days of noise exposure, and the hearing loss at 4kHz was relatively high. Light; Frozen sections of cochlear spiral ganglion cells and staining of isolated spiral ganglion cells found that P2X2, P2X3, P2X4, P2X7, P2Y2, and P2Y4 proteins were all expressed in cochlear spiral ganglion cells before noise exposure. Among them, P2X3 expression increased and P2X4, the down-regulation of P2Y2 expression was statistically significant (P < 0.05); Western blot and real-time quantitative PCR detection results showed that the expression of P2X3 was significantly increased after noise exposure than before noise exposure (P < 0.05), and P2X4 and P2Y2 were expressed after noise exposure The amount was significantly lower than before noise exposure (P < 0.05). (Figure. 4). After noise exposure, the expression of P2 protein is upregulated or downregulated. By affecting the Ca2+ cycle, the transmission of sound signals to the auditory center is blocked, which provides a theoretical basis for the signal transduction of purinergic receptors to become a target for the treatment of SNHL.

Direct Cochlear Recordings in Humans Show a Theta Rhythmic Modulation of Auditory Nerve Activity by Selective Attention.

The architecture of the efferent auditory system enables prioritization of strongly overlapping spatiotemporal cochlear activation patterns elicited by relevant and irrelevant inputs. So far, attempts at finding such attentional modulations of cochlear activity delivered indirect insights in humans or required direct recordings in animals. The extent to which spiral ganglion cells forming the human auditory nerve are sensitive to selective attention remains largely unknown. We investigated this question by testing the effects of attending to either the auditory or visual modality in human cochlear implant (CI) users (3 female, 13 male). Auditory nerve activity was directly recorded with standard CIs during a silent (anticipatory) cue-target interval. When attending the upcoming auditory input, ongoing auditory nerve activity within the theta range (5-8 Hz) was enhanced. Crucially, using the broadband signal (4-25 Hz), a classifier was even able to decode the attended modality from single-trial data. Follow-up analysis showed that the effect was not driven by a narrow frequency in particular. Using direct cochlear recordings from deaf individuals, our findings suggest that cochlear spiral ganglion cells are sensitive to top-down attentional modulations. Given the putatively broad hair-cell degeneration of these individuals, the effects are likely mediated by alternative efferent pathways compared with previous studies using otoacoustic emissions. Successful classification of single-trial data could additionally have a significant impact on future closed-loop CI developments that incorporate real-time optimization of CI parameters based on the current mental state of the user.SIGNIFICANCE STATEMENT The efferent auditory system in principle allows top-down modulation of auditory nerve activity; however, evidence for this is lacking in humans. Using cochlear recordings in participants performing an audiovisual attention task, we show that ongoing auditory nerve activity in the silent cue-target period is directly modulated by selective attention. Specifically, ongoing auditory nerve activity is enhanced within the theta range when attending upcoming auditory input. Furthermore, over a broader frequency range, the attended modality can be decoded from single-trial data. Demonstrating this direct top-down influence on auditory nerve activity substantially extends previous works that focus on outer hair cell activity. Generally, our work could promote the use of standard cochlear implant electrodes to study cognitive neuroscientific questions.

Comparison of Drug Availability in the Inner Ear After Oral, Transtympanic, and Combined Administration.

Although combination of oral and transtympanic drug therapy (CT) has been proved more effective and safer for idiopathic sudden sensorineural hearing loss (ISSNHL) by some clinical trials, there are few laboratory researches on the pharmacokinetics in the inner ear following CT on account of structural limitations of the inner ear. The aim of the present study was to investigate the pharmacokinetic behaviors of CT in the inner ear of mice. Eighteen transgenic GFAP-Luc mice which express luciferase in cochlear spiral ganglion cells were divided into oral administration (OR) group, transtympanic injection route (TT) group and CT group, and luciferin was delivered into the inner ear of these mice through oral, transtympanic or combined routes, respectively. A new in vivo imaging system was used to observe luciferin/luciferase signals and the compare the pharmacokinetics of different administration routes in the inner ear of mice. Bioluminescence signals were observed in the inner ear 3.3 ± 2.6 min after CT, significantly earlier than that of OR group (15.8 ± 7.4 min). CT owned the longest reaching-peak time and largest area under the curve (AUC) among three groups. Compared to TT, CT had longer biological half-life and higher AUC value, but did not displayed stronger peak value. There were significant differences in the peak values between OR group and TT group and between OR group and CT group. This study suggests that the OR route is less effective than the TT or CT route, and combination of OR and TT can deliver more drugs into the inner ear and confer a longer therapeutic window, but cannot increase drug intensity.

Effects of estrogen on apoptosis of spiral ganglion cells in cochlea of aged C57BL/6J mice

Objective: To observe the effects of estrogen on cochlear spiral ganglia cell apoptosis in aged C57BL/6J mice, and to explore the possible mechanism of estrogen's protective effects on senile deafness. Methods: Forty C57BL/6J mice were divided into the following four groups (10 mice/group): 3 m group (3 months old group), 12 m group (12 months old sham operation group); In the 12 m OVX group (ovariectomized at 12 months), bilateral oophorectomy was performed at the age of 9 months and normal feeding was performed until the age of 12 months.The 12m OVX+E2 group (estrogen intervention group) underwent bilateral oophorectomy at 9 months of age. After the one-month washout period, mice in the other groups were treated with estrogen at the dose of 100 μg/(kg·d) by subcutaneous injection, lasting 2 months to 12 months old. Mice in the other groups were fed normally.Blood samples were collected from the tail vein at the end of the treatment in 12 m OVX+E2 group. Enzyme-linked immunosorbent assays (ELISAs) was used to determine the serum estrogen levels. Auditory brainstem response (ABR) was used to detect the changes of hearing threshold in each group.Mice were anesthetized with 2% pentobarbital sodium. Bilateral cochlea was extracted after neck amputation and paraffin-embedded sections were performed.Hematoxylin eosin (HE) staining was used to observe the morphological changes in the cochlea spiral ganglion neurons (SGN), and TUNEL staining was used to observe the apoptosis of SGN. The expression levels of Caspase-3, Bax and Bcl-2 mRNA of the apoptotic proteins in cochlear spiral ganglion were measured by real-time fluorescence quantitative PCR (QRT-PCR). Results: Compared with the 3 m group, the hearing threshold of the 12 m group was improved, the loss of spiral ganglion cells was aggravated, and the apoptosis of the cells was increased(P＜0.01). After removal of the ovaries, the hearing threshold of the mice in the 12 m OVX group was higher than that in the 12 m control group (P＜0.01), and this increased threshold was accompanied by an increased loss of spiral ganglion cells, and increased apoptosis (P＜0.01). Meanwhile, the mRNA levels of apoptotic protein Caspase-3 and Bax were increased (P＜0.01), while the mRNA level of anti-apoptotic protein Bcl-2 was decreased (P＜0.01). After exogenous estrogen was given to the 12 m OVX+E2 group, the hearing threshold was lower than that in 12 m OVX group(P＜0.01). At the same time, the apoptosis of helical ganglion cells was reduced, the mRNA levels of Caspase-3 and Bax were decreased (P＜0.01), and the Bcl-2 mRNA level was increased (P＜0.01). Conclusion: Estrogen inhibited apoptosis of cochlear spiral ganglion cells in aged C57BL/6J mice ,thus achieving a protective effect on presbycusis.

Spiral ganglion cell degeneration-induced deafness as a consequence of reduced GATA factor activity.

Zinc-finger transcription factors GATA2 and GATA3 are both expressed in the developing inner ear, although their overlapping versus distinct activities in adult definitive inner ear are not well understood. We show here that GATA2 and GATA3 are co-expressed in cochlear spiral ganglion cells and redundantly function in the maintenance of spiral ganglion cells and auditory neural circuitry. Notably, Gata2 and Gata3 compound heterozygous mutant mice had a diminished number of spiral ganglion cells due to enhanced apoptosis, which resulted in progressive hearing loss. The decrease in spiral ganglion cellularity was associated with lowered expression of neurotrophin receptor TrkC that is an essential factor for spiral ganglion cell survival. We further show that Gata2 null mutants that additionally bear a Gata2 YAC (yeast artificial chromosome) that counteracts the lethal hematopoietic deficiency due to complete Gata2 loss nonetheless failed to complement the deficiency in neonatal spiral ganglion neurons. Furthermore, cochlea-specific Gata2 deletion mice also had fewer spiral ganglion cells and resultant hearing impairment. These results show that GATA2 and GATA3 redundantly function to maintain spiral ganglion cells and hearing. We propose possible mechanisms underlying hearing loss in human GATA2- or GATA3-related genetic disorders.

Sustained Effect of Hyaluronic Acid in Subcutaneous Administration to the Cochlear Spiral Ganglion.

The spatiotemporal distribution of drugs in the inner ear cannot be precisely evaluated because of its small area and complex structure. In the present study, we used hyaluronic acid (HA)-dispersed luciferin to image transgenic mice and to determine the effect of HA on controlled drug delivery to the cochlea. GFAP-luc mice, which express luciferase in cochlear spiral ganglion cells, were subcutaneously administered HA-luciferin (HA-sc) or luciferin dissolved in saline (NS-sc) or intraperitoneally administered luciferin dissolved in saline (NS-ip). The bioluminescence of luciferin was monitored in vivo in real time. The peak time and half-life of fluorescence emission were significantly increased in HA-sc-treated mice compared with those in NS-sc- and NS-ip-treated mice; however, significant differences were not observed in peak photon counts. We detected differences in the pharmacokinetics of luciferin in the inner ear, including its sustained release, in the presence of HA. The results indicate the clinical potential of using HA for controlled drug delivery to the cochlea.

Transactivation of human osteoprotegerin promoter by GATA-3.

Osteoprotegerin (OPG) is a key regulator of bone remodeling. Mutations in OPG are involved in a variety of human diseases. We have shown that cochlear spiral ganglion cells secrete OPG at high levels and lack of OPG causes sensorineural hearing loss in addition to the previously described conductive hearing loss. In order to study the regulation of OPG expression, we conducted a database search on regulatory elements in the promoter region of the OPG gene, and identified two potential GATA-3 binding sites. Using luciferase assays and site directed mutagenesis, we demonstrate that these two elements are GATA-3 responsive and support GATA-3 transactivation in human HEK and HeLa cells. The expression of wild type GATA-3 activated OPG mRNA and protein expression, while the expression of a dominant negative mutant of GATA-3 or a GATA-3 shRNA construct reduced OPG mRNA and protein levels. GATA-3 deficient cells generated by expressing a GATA-3 shRNA construct were sensitive to apoptosis induced by etoposide and TNF-α. This apoptotic effect could be partly prevented by the co-treatment with exogenous OPG. Our results suggest new approaches to rescue diseases due to GATA-3 deficiency – such as in hypoparathyroidism, sensorineural deafness, and renal (HDR) syndrome – by OPG therapy.

Gene transfection mediated by polyethyleneimine-polyethylene glycol nanocarrier prevents cisplatin-induced spiral ganglion cell damage.

Polyethyleneimine-polyethylene glycol (PEI-PEG), a novel nanocarrier, has been used for transfection and gene therapy in a variety of cells. In our previous study, we successfully carried out PEI-PEG-mediated gene transfer in spiral ganglion cells. It remains unclear whether PEI-PEG could be used for gene therapy with X-linked inhibitor of apoptosis protein (XIAP) in the inner ear. In the present study, we performed PEI-PEG-mediated XIAP gene transfection in the cochlea of Sprague-Dawley rats, via scala tympani fenestration, before daily cisplatin injections. Auditory brainstem reflex tests demonstrated the protective effects of XIAP gene therapy on auditory function. Immunohistochemical staining revealed XIAP protein expression in the cytoplasm of cells in the spiral ganglion, the organ of Corti and the stria vascularis. Reverse transcription-PCR detected high levels of XIAP mRNA expression in the cochlea. The present findings suggest that PEI-PEG nanocarrier-mediated XIAP gene transfection results in XIAP expression in the cochlea, prevents damage to cochlear spiral ganglion cells, and protects hearing.

The Effect of Controlled‐Release Hyaluronic Acid on Drug Delivery to the Cochlear Spiral Ganglion

Objectives: The spatiotemporal distribution of drugs in the inner ear has not fully been characterized because of the area’s small size and complicated compartments. In the present study, we investigate the pharmacokinetics of a small molecule conjugated with different amounts of carrier in the cochlea by using transgenic technology and the IVIS Imaging System. Methods: Luciferin, a 280 MW substrate of luciferase, was conjugated with different MW of hyaluronic acid and was subcutaneously administered to the transgenic mouse, GFAP-luc, which expresses luciferase specifically in the cochlear spiral ganglion cells. Bioluminescence produced by a chemical reaction of luciferin-luciferase was monitored using the Xenogen-IVIS 100. Results: The peak photon count decreased dose-dependently on the MW of hyaluronic acid, whereas the duration was prolonged. Conclusions: Our imaging system successfully detected differences in the pharmacokinetics of luciferin in the inner ear. The sustained-release effect of hyaluronic acid was observed and differed by its MW. The result suggests the clinical significance of hyaluronic acid for controlling drug delivery to the cochlea.

Mitochondria toxin-induced acute cochlear cell death indicates cellular activity-correlated energy consumption

The different cell types within the cochlea may have a specific contribution to the pathological changes during metabolism failure, which may provide clues for developing novel strategies for inner ear therapy. In order to evaluate activity-correlated cell death during metabolism failure in the cochlea, 3-nitropropionic acid was used to irreversibly inhibit the respiratory chain. Dose-response of the cochlear cells to 3-nitropropionic acid was analyzed in vitro. 3-Nitropropionic acid was administered onto the round window of guinea pigs. Cell death was identified by terminal transferase labeling the free 3'OH breaks in the DNA strands in vivo and propidium iodide nuclear permeation in vitro. As a result, 23.6 and 96.3 % cell death were induced by 10 and 100 mM 3-nitropropionic acid, respectively, in vitro. In the guinea pigs, 500 mM 3-nitropropionic acid induced vestibular dysfunction and severe to profound hearing losses. The cells that are the most sensitive to 3-nitropropionic acid treatment include the stria marginal and intermediate cells, epithelial cells of the Reissner's membrane, and spiral ligament fibrocytes (types II and V). Moderate sensitive cells were satellite fibrocytes of the spiral limbic central zone, osteocytes of the cochlear shell, hair cells, and spiral ganglion cells. Reduction of neurofilament in the soma and periphery processes of spiral ganglion cells occurred after the exposure. These results may be relevant to the mechanisms of injury in sudden onset sensorineural hearing loss and hazardous substance exposure-induced hearing loss.

A study of gentamicin injury mechanisms using cultured mouse cochlear spiral ganglion cells

ObjectiveTo study gentamicin injury mechanisms using postnatal mouse cochlear spiral gangcells (SGC). MethodsSGCs were isolated using a combinatorial approach of enzymatic digestion and mechanical separation from P2 ~ 6 Kunming mouse cochleae. After 4 days, cultured SGCs were fixed with 4% paraformaldehyde at room temperature for immunocytochemical examination using the methods of S–P and the monoclonal antibody against mouse neurofilament protein (Neurofilament–68/200Kda, NF–L+H). SGCs were randomly divided into a blank control group and three gentamicin treatment groups (medium gentamicin concentration at 50 mg/L, 100 mg/L and 150 mg/L respectively), SGCs were collected and examined under a transmission electron microscope after being cultured for 48 h. ResultsSGC primary culture was successful. SGC cytoplasm and neurites were dyed brownish yellow by the monoclonal mouse neurofilament protein antibody. SGCs showed classical bipolar neuron appearance. Under the transmission electron microscope,.gentamicin treated SGCs showed morphological features different compared to those in the blank control group, which might indicate apoptosis. ConclusionOur results indicate that gentamicin has direct toxic effects on cochlear SGCs in mice and the injury mechanism is closely related with apoptosis. Damage to mitochondria may play an important role in the process.

Brain-derived neurotrophic factor promotes cochlear spiral ganglion cell survival and function in deafened, developing cats.

Postnatal development and survival of spiral ganglion (SG) neurons depend on both neural activity and neurotrophic support. Our previous studies showed that electrical stimulation from a cochlear implant only partially prevents SG degeneration after early deafness. Thus, neurotrophic agents that might be combined with an implant to improve neural survival are of interest. Recent studies reporting that brain-derived neurotrophic factor (BDNF) promotes SG survival after deafness have been conducted in rodents and limited to relatively short durations. Our study examined longer duration BDNF treatment in deafened cats that may better model the slow progression of SG degeneration in human cochleae, and this is the first study of BDNF in the developing auditory system. Kittens were deafened neonatally, implanted at 4-5 weeks with intracochlear electrodes containing a drug-delivery cannula, and BDNF or artificial perilymph was infused for 10 weeks from a miniosmotic pump. In BDNF-treated cochleae, SG cells grew to normal size and were significantly larger than cells on the contralateral side. However, their morphology was not completely normal, and many neurons lacked or had thinned perikaryl myelin. Unbiased stereology was employed to estimate SG cell density, independent of cell size. BDNF was effective in promoting significantly improved survival of SG neurons in these developing animals. BDNF treatment also resulted in higher density and larger size of myelinated radial nerve fibers, sprouting of fibers into the scala tympani, and improvement of electrically evoked auditory brainstem response thresholds. BDNF may have potential therapeutic value in the developing auditory system, but many serious obstacles currently preclude clinical application.

Visualization of intracellular trafficking of Math1 protein in different cell types with a newly‐constructed nonviral gene delivery plasmid

In recent years, Math1 gene therapy was indicated to be the future therapy for deafness in combination with other growth factors. However, Math1 delivery using adenovirus-mediated gene delivery or electroporation was impractical. The contribution of Math1 in the combined procedure was not clearly elucidated using the existing plasmids. Nonviral gene delivery vectors are expected to be extremely safe and convenient. The present study aimed to construct the pCDNA6.2/C-EmGFP-Math1 plasmid and evaluate its transfection efficiency and intracellular trafficking of Math1 protein corresponding to transcription regulation function. After constructing the pCDNA6.2/C-EmGFP-Math1 expression plasmid, the plasmid was transfected into different cell lines and primary cochlear cells using Lipofectamine 2000. Transfection efficiencies of the plasmid were evaluated. Transfection efficiencies using liposome nanoparticles containing Math1 plasmid were also assessed. Intracellular trafficking of Math1 was monitored using confocal microscopy. Different cell types can be transfected with high transfection efficiencies by the pcDNA6.2/C-EmGFP-Math1 plasmid using Lipofectamine 2000. Liposome nanoparticles containing the Math1 plasmid expressed the gene with variable efficiencies, depending on the particle size, surface charge and PEGylation status. Unique intracellular trafficking of Math1 was demonstrated in different cell types. The newly-constructed plasmid pcDNA6.2/C-EmGFP-Math1 was suitable for nonviral gene delivery of Math1. Unique intracellular trafficking of Math1 with dynamics from the cytoplasm to the nucleus was demonstrated. The modification of mesenchymal stem cells by Math1 gene delivery and by brain-derived neurotrophic factor and glial cell line-derived neurotrophic factor treatments can potentially be applied to cell replacement for the treatment of cochlear spiral ganglion cell loss in deafness.

Effect of brain-derived neurotrophic factor gene transfected bone-marrow mesenchymal stem cells on damaged cochlear spiral ganglion cells of guinea pigs

To investigate the protective role of brain-derived neurotrophic factor (BDNF) gene transfected bone-marrow mesenchymal stem cells (BMSC) on cochlear spiral ganglion cells (SGC) impaired by aminoglycoside antibiotics (AmAn). The differentiation of BMSC transfected by BDNF gene (BDNF-BMSC) were detected with immunohistochemical examination of Nestin, neuron-specific enolase (NSE), and glial fibrillary acid protein (GFAP) antibody in vitro. BDNF gene transfected BMSC were transplanted into the cochleae of guinea pigs deafened by amikacin, while the control groups were designed in which artificial perilymphatic fluid (APF), BMSC or BDNF gene was injected into cochleae alone. The cochleae were obtained on the week 1, 2 and 4 after injection, respectively, paraffin-embedded, and cut in a paramodiolar plane subsequently. The histopathological changes of cochleae were observed, the density of SGC was calculated by staining with HE, and the corresponding optical density (COD) was calculated with immunohistochemical staining using NSE antibody. And the protective role of various groups on the cochlear SGC were compared. The positive staining rate of BDNF gene transfected BMSC with Nestin, NSE and GFAP antibody were all higher than that of BMSC in vitro (P < 0.01). After transplantation into cochleae, the differences of SGC density and COD among various groups were all significant on the same time points (P < 0.05). The SGC density and COD of the BDNF gene transfected BMSC group were the highest. The SGC density and COD of various groups on week 4 were all obviously decreased than those on week 1 and 2 (P < 0.05). AmAn-induced SGC damage could be depressed by BMSC, BDNF gene or BDNF gene transfected BMSC transplantation into cochleae, while BDNF gene transfected BMSC showed the best protective role.

Efficient transduction of spiral ganglion cells using adenovirus type 5 vector in the rat

Conclusions: The adenovirus-5 vector specifically transduced spiral ganglion cells with high efficiency, suggesting that it is a potential gene therapeutic tool for the survival of spiral ganglion cells with secondary injury. Objectives: This study aimed to find a suitable viral vector allowing efficient transduction to spiral ganglion cells. Methods: Lentivirus, adeno-associated virus-2 and adenovirus-5 constructs habouring green fluorescence protein (GFP) gene were injected into scala tympani via the round window membrane of rat. Distribution and fluorescence intensity of GFP within the cochlea were estimated using a fluorescence microscope. Results: The GFP expressions mediated by all three viral vectors were observed in multiple cell types of the cochlea. Compared with the other two viral vectors, the adenovirus-5 vector efficiently transduced cochlear spiral ganglion cells in vivo and was still present 2 weeks after viral vector injection.

Study of protective effect on rat cochlear spiral ganglion after blast exposure by adenovirus-mediated human β-nerve growth factor gene

Objective To study whether adenovirus-mediated human β-nerve growth factor (Ad-hNGF β) gene has any protective effect on rat cochlear spiral ganglion after blast exposure. Methods Deafness was induced by blast exposure (172.0 dB) in 20 healthy rats. Seven days after blast exposure, Ad-hNGF β was infused into the perilymphatic space of 10 animals as the hNGF β/blast group, and artificial perilymph fluid (APF) was infused into the perilymphatic space of 10 animals as the APF/blast control group. An additional control group consisted of 10 healthy rats which received Ad-hNGF β target gene with no blast exposure (hNGF β/control group). Auditory functions were monitored by thresholds of auditory brain stem responses (ABR). At weeks 1, 4, and 8 postoperatively, the animals were killed, and the cochleae were removed for immunohistochemical, hematoxylin and eosin staining study. Results The ABR threshold shifts in the hNGF β/blast group were significantly smaller than that of APF/blast control group. There were no significant differences of the ABR values between before and after operation in the hNGF β/control group. Expression of Ad-hNGF β protein was detected in each turn of the cochlea in the first week, with almost equal intensity in all turns. In the fourth week, the reactive intensity decreased. In the eighth week, no reaction was detectable. The results of hematoxylin and eosin stain showed that the number of spiral ganglions in the hNGF β/blast group was significantly greater than that of the APF/blast control group in the 4th week ( P < .01). Conclusion Adenovirus-mediated human β-nerve growth factor can be expressed at a high level and for a relatively long period in the blast impaired cochlea, suggesting that Ad-hNGF β has a protective effect on rat cochlear spiral ganglion cells after blast exposure.

Adenovirus-mediated human β-nerve growth factor gene transfer has a protective effect on cochlear spiral ganglion after blast exposure

Objective To study whether adenovirus-mediated human β-nerve growth factor (Ad-hNGFβ) gene has any protective effect on blast hearing impairment. Methods Deafness was induced by blast exposure (172.0 dB) in 30 healthy guinea pigs. On day 7 of blast exposure, Ad-hNGFβ was infused into the perilymphatic space of 20 animals as the study group (hNGFβ group), and artificial perilymph fluid (APF) was infused into the perilymphatic space of the other 10 animals as the control group. At weeks 1, 4 and 8 after blast exposure, the animals were sacrificed and the cochleae were removed for immunohis-tochemical and HE stainings. Results Expression of Ad-hNGFβ protein was detected in each turn of the cochlea at the 1st week, with almost equal intensity in all turns. At the 4th week, the reactive intensity of the expression of Ad-hNGFβ protein decreased. At the 8th week, no expression was detectable. The results of HE staining showed that the amount of spiral ganglions in hNGFβ group was significantly greater than that of the control group at week 4 ( P < 0.01). Conclusion Ad-hNGFβ can be expressed at a high level and for a relatively long period in the blast impaired cochlea, suggesting that Ad-hNGFβ has a protective effect on cochlear spiral ganglion cells after blast exposure and the efficient gene transfer into cochlea had been achieved without toxicity.

Spontaneous Discharge Patterns in Cochlear Spiral Ganglion Cells Before the Onset of Hearing in Cats

Spontaneous neural activity has been recorded in the auditory nerve of cats as early as 2 days postnatal (P2), yet individual auditory neurons do not respond to ambient sound levels <90-100 dB SPL until about P10. Significant refinement of the central projections from the spiral ganglion to the cochlear nucleus occurs during this neonatal period. This refinement may be dependent on peripheral spontaneous discharge activity. We recorded from single spiral ganglion cells in kittens aged P3-P9. The spiral ganglion was accessed through the round window through the spiral lamina. A total of 112 ganglion cells were isolated for study in nine animals. Spike rates in neonates were very low, ranging from 0.06 to 56 spikes/s, with a mean of 3.09 +/- 8.24 spikes/s. Ganglion cells in neonatal kittens exhibited remarkable repetitive spontaneous bursting discharge patterns. The unusual patterns were evident in the large mean interval CV (CV(i) = 2.9 +/- 1.6) and burst index of 5.2 +/- 3.5 across ganglion cells. Spontaneous bursting patterns in these neonatal mammals were similar to those reported for cochlear ganglion cells of the embryonic chicken, suggesting this may be a general phenomenon that is common across animal classes. Rhythmic spontaneous discharge of retinal ganglion cells has been shown to be important in the development of central retinotopic projections and normal binocular vision. Bursting rhythms in cochlear ganglion cells may play a similar role in the auditory system during prehearing periods.

Spontaneous Generation in Early Sensory Development. Focus on “Spontaneous Discharge Patterns in Cochlear Spiral Ganglion Cells Before the Onset of Hearing in Cats”

Sensory systems are our gateways to the outside world. How are these complex systems—sensory organ and the associated brain pathways—set up during development? Molecular cues are of course essential in establishing many basic cellular characteristics and the connections between all elements of a

Optical parameter variability in laser nerve stimulation: a study of pulse duration, repetition rate, and wavelength.

Pulsed lasers can evoke neural activity from motor as well as sensory neurons in vivo. Lasers allow more selective spatial resolution of stimulation than the conventional electrical stimulation. To date, few studies have examined pulsed, mid-infrared laser stimulation of nerves and very little of the available optical parameter space has been studied. In this study, a pulsed diode laser, with wavelength between 1.844-1.873 microm, was used to elicit compound action potentials (CAPs) from the auditory system of the gerbil. We found that pulse durations as short as 35 micros elicit a CAP from the cochlea. In addition, repetition rates up to 13 Hz can continually stimulate cochlear spiral ganglion cells for extended periods of time. Varying the wavelength and, therefore, the optical penetration depth, allowed different populations of neurons to be stimulated. The technology of optical stimulation could significantly improve cochlear implants, which are hampered by a lack of spatial selectivity.