Ear Of Guinea Pig Research Articles

Hearing Loss and a Cell-Based Replacement Therapy

To the Editor: We are pleased to note the appreciative comments on our recent article Functional Evaluation of a Cell Replacement Therapy in the Inner Ear (1). A cell-based replacement strategy has been proposed and investigated in recent years to substitute degenerated hair cells and spiral ganglion neurons for hearing loss, one of the major health problems in the world (2-6). However, this strategy is still in its infancy, and a number of questions need to be addressed. The selection of donor cells for transplantation is one of the critical issues. Embryonic stem (ES) cells or derived neural progenitors (7) and neural stem cells (NSCs) (8) have been found to survive and differentiate into neurons after transplantation into the inner ear of adult mammals. In an in vitro model, NSCs derived from the mice brain showed the ability to differentiate into cells expressing hair cell and neuron-specific proteins (9). In contrast to many of the candidate cells that have been explored, stem cells or progenitor cells derived from the inner ear should be more appropriate to adapt to the inner ear (10-12). The survival of implanted cells is a key issue for a cell-based strategy because it 1) determines transplantation efficacy; 2) provides the necessary time for stem cell to differentiate into hair cells or neurons; and 3) provides the time for stem cell to migrate and become integrated into the host auditory system. However, the survival rate of implanted cells is still extremely low. Approximately 0.05% of embryonic mouse NSCs survived when they were allografted transplanting into adult mouse inner ear (13). Using a stereologic method, we collected all the sections from the cochlea and counted the surviving NSCs. We found that approximately 0.04 to 0.07% implanted adult mouse NSCs survived after xenografted implantation into the inner ear of adult guinea pigs (14). Embryonic stem cells survived better in the inner ear but were still less than 1% (14). This is clearly a major limitation to the efforts using a cell therapy for restoring inner ear function (15). The low survival rate may attribute to the microenvironment in the inner ear that lacks growth factors and neurotrophins required for the survival of exogenous cells. To increase the survival of implanted cells, neurotrophins have been infused into the inner ear simultaneously with the implantation of neuronal tissue (15) or ES cells (7). To further stimulate the survival and integration of exogenous cells, we implanted embryonic mouse dorsal root ganglion neurons, a better survival model for inner ear regeneration strategy, into the inner ear. Although no significance was observed based on electrically evoked auditory brainstem responses measurement, this approach provides a good model to test the integration and the function of the implanted cells. To test what growth factors are optimal for promoting the survival of stem cells, the coculture model may be applied to culture the stem cells and sensory hair cell epithelium in the modified medium. However, to demonstrate whether stem cell-derived cells have the potential to replace the function of degenerated hair cells and neurons, an in vivo model must be used to implant the stem cells into the animals, supply with the appropriate small molecules, and test the hearing function. With the combination of stem cell-based replacement strategy and cochlear implant, we proposed and designed a Biological-EAR model, which may provide a new treatment option for hearing loss in the future (Fig. 1) (14).FIG. 1: Schematic diagram showing the Biological-EAR model. With the combination of stem cell-based replacement approach and cochlear implant, the sound will be converted into electric signals that will be perceived by the implanted cells and, in turn, be sent directly to the central auditory neurons in the brainstem, thus bypassing the degenerated hair cells and neurons.Zhengqing Hu, M.D., Ph.D.* Mats Ulfendahl, Ph.D.† *Department of Otolaryngology-HNS Wayne State University School of Medicine Detroit, Michigan, U.S.A. and †Center for Hearing and Communication Research and Department of Clinical Neuroscience Karolinska Institute Stockholm, Sweden

Expression pattern of aquaporin 4 and 5 in the middle ear of guinea pigs with secretory otitis media

Conclusions: Our study suggests that aquaporins 4 and 5 (AQP4 and AQP5) in the middle ear cavity may play a vital role in the homeostasis of the tubotympanum and in the course of the accumulation of the effusion in secretory otitis media (SOM). Objective: To explore the pathological change in water homeostasis in the middle ear in SOM and to observe the expression and regulation of AQP4 and AQP5 in the middle ear cavity in SOM. Materials and methods: Reverse transcriptase polymerase chain reaction (RT-PCR) and Western blotting were used to detect AQP4 and AQP5 in the bullae of animal models of SOM and normal animals. The expression patterns of AQP4 and AQP5 in the SOM group were compared with those in the normal group. Results: RT-PCR and immunoblot analyses revealed that mRNAs encoding AQP4 and AQP5 were expressed in the middle ear membrane of the guinea pigs in both groups; AQP4 was also detected as 33 kDa protein in both groups. Quantitative analysis of RT-PCR and Western blotting revealed that expression of AQP4 and AQP5 was higher in the SOM group than in the control group.

Dose-Dependent Sustained Release of Dexamethasone in Inner Ear Cochlear Fluids Using a Novel Local Delivery Approach

The thermo-reversible triblock copolymer poloxamer 407 was investigated as a drug delivery vehicle for micronized dexamethasone into the middle and inner ears of guinea pigs. The study characterized the gelation and in vitro release kinetics of poloxamer formulations. In vivo, the pharmacokinetic profile of formulations containing varying concentrations of poloxamer and dexamethasone was examined following intratympanic administration. Significant drug levels within the perilymph were observed for at least 10 days, while systemic exposure was minimal. The sustained-release kinetics profile could be significantly modulated by varying the concentrations of both poloxamer and dexamethasone. Assessment of auditory function revealed a small transient shift in hearing threshold, most probably of conductive nature, which resolved itself within a week. No significant histological changes of the round window membrane or cochlea could be noted. Poloxamer 407 thus represents an effective and safe delivery system to achieve sustained release of dexamethasone to the inner ear.

Analysis of the cytoprotective effect of amifostine on the irradiated inner ear of guinea pigs: an experimental study

A radiacao pode causar lesao na orelha interna podendo provocar surdez sensorio-neural e inclusive levar a anacusia. A amifostina e uma substância citoprotetora seletiva de tecidos sadios, amplamente utilizada durante a radio e quimioterapia de tumores malignos. OBJETIVO: O objetivo deste estudo experimental foi verificar se existe efeito antioxidante e radioprotetor da amifostina no orgao de Corti de cobaias albinas irradiadas em regiao de cabeca e pescoco. MATERIAL E METODO: O estudo realizado envolveu quatro grupos de animais: um grupo foi submetido a irradiacao em dose unica de 350cGy. Dois grupos receberam a mesma dose de radiacao, porem receberam doses de 100 e 200mg/kg de amifostina, 30 minutos antes da irradiacao. Um grupo recebeu apenas amifostina, na dose de 200mg/Kg. Todas as cobaias foram sacrificadas 30 dias apos o experimento e suas bulas retiradas para estudo em microscopio de varredura. RESULTADO: O grau de lesao das celulas ciliadas externas foi menor nos dois grupos que receberam a amifostina que no grupo apenas irradiado. Nao foi encontrada diferenca de protecao entre os grupos que receberam doses de 100 e 200mg/kg de amifostina. Nao houve lesao no grupo que recebeu apenas amifostina. CONCLUSAO: Amifostina mostrou ser um radioprotetor do orgao de Corti de cobaias albinas irradiadas.

Change in Cochlear Response in an Animal Model of Otitis Media with Effusion

Our previous studies confirm that middle ear mobility is reduced in the presence of otitis media with effusion (OME). Variations in middle ear function may result in changes in cochlear response in OME ears. With the long-term goal of evaluating cochlear function in OME ears, the aim of this study was to measure the displacement of the basilar membrane (BM) in guinea pig ears with OME. Vibrations of the BM at the apex and basal turn were measured in an in vitro preparation extracted 3 and 14 days after injection of lipopolysaccharide in the middle ear of guinea pigs. The results show that the displacement sensitivity of the BM at the apex and the basal turn to sound pressure in the ear canal was reduced up to 25 dB at their characteristic frequencies, respectively. Cochlear gain with respect to umbo movement was also changed in ears with OME in both groups. This study provides data for analysis of the change of BM vibration in a guinea pig OME model.

Analysis of the Cytoprotective Effect of Amifostine on the Irradiated Inner Ear of Guinea Pigs: An Experimental Study

SummaryRadiation can cause damage to the inner ear, from a simple hearing loss all the way to profound deafness. Amifostine is a cytoprotective substance extensively used during radio-chemotherapy for malignant tumors.Aimthe objective of the present investigation was to establish the antioxidant and radioprotective effects of amifostine on the organ of Corti of albino guinea pigs irradiated in the head and neck region.Materials and MethodsAn experimental study conducted on four groups of guinea pigs were used; One group received only amifostine, one group was submitted to a single dose of 350 cGy and the other two were similarly irradiated but received amifostine doses of 100 or 200 mg/kg. All animals were slaughtered 30 days after the experiment, their bullae were removed and the damaged outer hair cells were counted.ResultThe extent of injury was lower in the outer hair cells of the two groups treated with amifostine compared to the group that was only irradiated. There was no difference between the group treated with 100 and 200 mg/kg of amifostine. The group that received only amifostine had no cochlear damage.ConclusionAmifostine is an effective cytoprotective substance in the Organ of Corti of irradiated guinea pigs.

Therapeutic effects of heme oxygenase-1 on psoriasiform skin lesions in guinea pigs

Heme oxygenase-1 (HO-1) has been shown to exert immunosuppressive, anti-inflammatory, anti-apoptotic and anti-proliferative effects. Its unique positive effects indicate that this enzyme might be a potential therapeutic target for psoriasis. To determine the effect of pharmacologic up-regulation of HO-1 on psoriasis, we generated a guinea pig model of psoriasiform skin lesions using propranolol induction. In this in vivo model, the 3-week propranolol challenge generated the psoriasiform pathological changes on the ears of guinea pigs. And then, guinea pigs were intraperitoneally injected with 5 mg/kg cobalt protoporphyrin (CoPP), a potent HO-1 inducer, 20 mg/kg zinc protoporphyrin, an inhibitor of HO-1, or PBS as controls, once a week from 9 weeks of age to 14 weeks old. CoPP induced notably HO-1 expression at both mRNA and protein levels. Moreover, CoPP treatment led to a significant reduction of the psoriasiform histopathological changes and remarkable amelioration of the psoriasiform skin lesions, compared with PBS treatment, with a concomitant reduction in proliferating cell nuclear antigen expression. Additionally, CoPP treatment resulted in a decreased TNF-alpha and significantly increased IL-10 release. Our results suggest that HO-1 induction therapy ameliorates the psoriasiform skin lesions by suppressing keratinocyte hyperproliferation and attenuating production of inflammatory responses.

The Configuration and Attachment of the Utricular and Saccular Maculae to the Temporal Bone

High-resolution X-ray microtomography (micro-CT) was used to show the spatial configuration of the membranous labyrinth of the fixed guinea pig and human inner ear. Whole temporal bones were en bloc stained in 2% osmium tetroxide for 2 days or more to allow the osmium to attach to the membranes of the inner ear, and then scanned with a Skyscan 1172 micro-CT with highest resolution of 8 microns. The scans were segmented and reconstructed. The findings for guinea pigs and humans are similar. The saccular macula is closely attached to the curved medial wall of the temporal bone, but in both human and guinea pig the utricular macula is attached to the temporal bone only at the anterior region of the macula, and, as others have reported previously, much of the caudal area of the utricular macula is tenuously supported by a thin membrane, just above the dorsal margin of the stapes. This tenuous support may have important consequences for the sensing of forces by the utricular macula. Combining information from a dissected human horizontal canal with CT images allows an estimate of the orientation of the horizontal canal crista in human subjects, data which are necessary for treatment of benign paroyxsmal positional vertigo of the horizontal canal. The very high resolution achieved by micro-CT shows that reconstruction from inadequately sampled CT data produces images that are not anatomically correct, so that canal deformations and aplasias may appear to be present.

The effect of glycerol on the guinea-pig hydropic ear

The effect of glycerol on the guinea-pig hydropic ear

Expression of Aquaporin-2 in the Inner Ear of Water-Deprived Guinea Pigs

Background and ObjectivesZZAlthough the role of aquaporin-2 (AQP2) in the kidney has been well defined, its role in the inner ear remains to be determined. The present study was to investigate the effect of water deprivation on the expression of AQP2 in the inner ear. Materials and MethodZZHealthy male guinea pigs weighing 250 g were used. The experimental group underwent water restriction and the control underwent water loading with sucrose-containing water for 3 days. Concentrations of plasma arginine-vasopressin (AVP ) were determined and electrocochleography (ECoG) recordings were made. An RT-PCR, real-time PCR and Westernblotting analysis were used for quantitative analysis of AQP2 mRNA and AQP2 protein expression. Immunohistochemistry was also used to evaluate the distribution of AQP2 water channel proteins in the inner ear. ResultsZZAQP2 was mainly expressed in the epithelium of endolymphatic sac, spiral limbus, spiral ligament and stria vascularis of scala media. The concentrations of plasma AVP were 9.2± 0.8 pg/mL in the experimental group and 0.78±0.3 pg/mL in the control. The summation potential/ action potential (SP/AP) ratio in ECoG was markedly increased in the experimental group (0.55 in the experimental and 0.29 in the control). RT-PCR and real time PCR as well as Western blot analysis showed that the level of AQP2 mRNA and protein in the cochlea and endolymphactic sac of the water-deprived group was significantly higher than those in the control group. ConclusionZZThese data suggest that AQP2 is one of the important water channels in fluid homeostasis in the inner ear. Moreover, the volume of endolymphatic space can be increased via AVP-AQP2 system in response to water deprivation. Korean J Otorhinolaryngol-Head Neck Surg 2009;52:572-8 Key WordsZZAquaporin 2·Endolymphatic hydrops·Arginine vasopressin·Inner ear.

Expression pattern of aquaporin 4 and 5 in the middle ear of guinea pigs with secretory otitis media

Expression pattern of aquaporin 4 and 5 in the middle ear of guinea pigs with secretory otitis media

Unilateral intra-perilymphatic infusion of substance P enhances ipsilateral vestibulo-ocular reflex gains in the sinusoidal rotation test

Previous studies have reported localization of substance P (SP) within the inner ear and that SP exists abundantly within vestibular endorgans. While SP's functional role in the inner ear remains unclear, SP can act as a neuromodulator in the CNS and directly influences neuronal excitability. We hypothesized that SP might influence neuronal excitability within the vestibular periphery. The present study used the sinusoidal rotation test to investigate the influence of SP after its local application in the guinea pig unilateral inner ear. A tiny hole was made adjacent to the round window in the right ears of Hartley white guinea pigs that had normal tympanic membranes and Preyer reflexes. An osmotic pump infused SP (10(-4)M, 10(-3)M, and 10(-2)M), neurokinin-1 (NK-1) receptor antagonist (10(-3)M) alone, or SP (10(-3)M)+NK-1 receptor antagonist (10(-3)M) through this hole, with rotation tests performed before, and 12h and 24h after the treatment. Results were used to calculate the vestibulo-ocular reflex (VOR) gains. After administration of 10(-3)M and 10(-2)M SP, significant increases in the VOR gains were noted at 12h after treatment, with these gains disappearing by 24h after treatment. This increase was not observed when there was simultaneous NK-1 receptor antagonist administration. There were also no changes in the VOR gains noted after administration of 10(-4)M SP or the NK-1 receptor antagonist alone. These results indicate the possibility that SP may act on vestibular endorgans as an excitatory factor via the NK-1 receptors.

Ototoxicity and otoprotection in the inner ear of guinea pigs using gentamicin and amikacin: ultrastructural and functional aspects

SummaryOtotoxicity is still a challenge to medicine. The discovery of self-protecting endogenous mechanisms of the outer hair cells associated with their functional and ultra-structural assessment methods has opened new horizons in the understanding and controlling of these mechanisms. Aim: this paper aimed at establishing whether or not underdoses of gentamicin could protect the inner ear against the harmful effects of amikacin, based on these protection mechanisms and determine if the otoacoustic emission amplitudes could be associated with the level of hair cell integrity. Materials and Methods: Experimental study. We used 31 guinea pigs. They were injected with saline solution, gentamicin and amikacin, alone and in combinations -intramuscular injections - during 12, 30 and 42 days. The otoacoustic emissions were recorded in the beginning and at the end of the experiment, comparing it with the cochlear integrity study carried out by electron microscopy. Results: gentamicin underdoses did not protect the inner ear against amikacin toxicity; the reduction in otoacoustic emissions was strongly associated with an increase in hair cell lesions. Conclusion: these findings help understand inner ear otoprotection and ototoxicity. Establishing the correlation between the emissions amplitude an cell integrity plays an important role in the follow up of hair cell damage, with possible monitoring of ototoxicity caused by drugs in humans.

The ototoxic effect of boric acid solutions applied into the middle ear of guinea pigs

This study analyzed the ototoxic effects of boric acid solutions. Boric acid solutions have been used as otologic preparations for many years. Boric acid is commonly found in solutions prepared with alcohol or distilled water but can also be found in a powder form. These preparations are used for both their antiseptic and acidic qualities in external and middle ear infections. We investigated the ototoxic effect of boric acid solutions on guinea pigs. We are unaware of any similar, previously published study of this subject in English. The study was conducted on 28 young albino guinea pigs. Prior to application of the boric acid solution under general anesthesia, an Auditory Brainstem Response (ABRs) test was applied to the right ear of the guinea pigs. Following the test, a perforation was created on the tympanic membrane of the right ear of each guinea pig and small gelfoam pieces were inserted into the perforated area. Test solutions were administered to the middle ear for 10 days by means of a transcanal route. Fifteen days after inserting the gelfoams in all of the guinea pigs, we anasthesized the guinea pigs and removed the gelfoams from the perforated region of the ear and then performed an ABRs on each guinea pig. The ABRs were within the normal range before the applications. After the application, no significant changes were detected in the ABRs thresholds in neither the saline group nor the group administered boric acid and distilled water solution; however, significant changes were detected in the ABRs thresholds of the Gentamicine and boric acid and alcohol solution groups. We believe that a 4% boric acid solution prepared with distilled water can be a more reliable preparation than a 4% boric acid solution prepared with alcohol.

The effect of anti-adhesive packing agents in the middle ear of guinea pig

The presence of adhesions after middle ear surgery is not uncommon. Fibrosis can cause conductive hearing loss and it contributes to retraction of the tympanic membrane in the post-surgery patient. The purpose of this study was to evaluate the anti-adhesive effect of Seprafilm and MeroGel in the abraded mucosa of a guinea pig's middle ear. Fifteen pathogen-free adult male albino guinea pigs weighing 250-300g each were used. Under an aseptic condition, the middle ear mucosa was abraded using a pick through a myringotomy incision. Seprafilm, MeroGel and Gelfoam, respectively, were then packed into guinea pigs' middle ear cavities. Auditory brainstem responses (ABRs) were assessed preoperatively and 3 weeks after operation. The ABR results at postoperative week 3 showed no statistically significant difference for the myringotomy and postpacking, except for the MeroGel packing. However, there was no significant threshold on the 6 weeks' postoperative ABR. The Gelfoam group demonstrated extensive fibrosis and adhesion within the bulla cavity. The Seprafilm and MeroGel groups showed no adhesion in the middle ear cleft after abrasion of the mucosa. From these results, we suggest the use of Seprafilm and MeroGel to improve the results of otosurgery.

IS N-ACETYLCYSTEINE REALLY EFFECTIVE FOR REFRACTORY EAR INFECTIONS?

To the Editor: I have read the article "N-Acetylcysteine as an Adjunct for Refractory Ear Infections" (1) with great interest, and I have also studied N-acetylcysteine (NAC) administration on the healing of acute tympanic membrane perforations in guinea pigs (2). The authors declare that no ototoxicity was observed with NAC application in the previous studies; however, Ovesen et al. (3) described increased otorrhea in their patients when NAC was used for otitis media with effusion. Kharazmi et al. (4) and Ovesen et al. (5) had showed cytotoxic effects of NAC application in a dose-dependent way in their reports. Aldavood et al. (6) had also described the toxic effects of NAC when used in corneal wound healing. Even so, in my study, NAC-treated ears of guinea pigs had serious otorrhea after tympanic membrane perforations. N-Acetylcysteine has a free radical scavenging property. It especially reduces nitric oxide (NO) levels in the damaged areas. On the other hand, NO has an ability to kill the pathogens and may play an important role in the host defense against ear infections (7). Reducing NO levels may be the reason for these reports describing cytotoxic effects of NAC (maybe it is not ototoxic but cytotoxic, as mentioned in the previous studies). Finally, I would like to ask the authors if they solved the refractory ear infections radically or if they recur after a while. If they recurred, how much time does it take for the disease to recur? After these reports and my own experience, I think this study of the authors was done with a very small amount of patients and does not carry persuasive knowledge for me. *Mehmet Eken, M.D. †Elif Esra Eken, M.D. *Kartal Dr. Lufti Kurdar Training and Research Hospital and †Sultanbeyli State Hospital Sultanbeyli, Istanbul, Turkey

Motoneurons of the stapedius muscle in the guinea pig middle ear: Afferent and efferent transmitters

The objective of the present study was to identify efferent and afferent transmitters of motoneurons of the stapedius muscle of the middle ear in order to gain more insight into the neuronal regulation of the muscle. To identify motoneurons, we injected the fluorescent neuronal tracer Fluorogold (FG) into the muscle after preparation of the middle ear in adult guinea pigs. Upon terminal uptake and retrograde neuronal transport, we observed FG in neurons located medial and ventral to the nucleus of the facial nerve ipsilateral to the injection site. Immunohistochemical studies of these motoneurons showed that the majority contains calcitonin gene-related peptide. Our data further demonstrate close spatial relationships of motoneurons to structures immunoreactive to either serotonin, substance P or neuronal nitric oxide and reveal that these neurons are under neuropeptidergic and nitrergic influence.

Ascorbic Acid Reduces Noise‐Induced Nitric Oxide Production in the Guinea Pig Ear

Noise-induced hearing loss can be caused, among other causes, by increased nitric oxide (NO) production in the inner ear leading to nitroactive stress and cell destruction. Some studies in the literature suggest that the degree of hearing loss (HL) could be reduced in an animal model through ascorbic acid supplementation. To identify the effect of ascorbic acid on tissue-dependent NO content in the inner ear of the guinea pig, we determined the local NO production in the organ of Corti and the lateral wall separately 6 hours after noise exposure. Prospective animal study in guinea pigs. Over a period of 7 days, male guinea pigs were supplied with minimum (25 mg/kg body weight/day) and maximum (525 mg/kg body weight/day) ascorbic acid doses, and afterwards exposed to noise (90 dB sound pressure level for 1 hour). The acoustic-evoked potentials were recorded before and after noise exposure. The organ of Corti and the lateral wall were incubated differently for 6 hours in culture medium, and the degree of NO production was determined by chemiluminescence. Ascorbic acid treatment reduced the hearing threshold shift after noise exposure depending on concentration. When the maximum ascorbic acid dose was substituted, NO production was significantly reduced in the lateral wall after noise exposure and slightly reduced in the organ of Corti. Oral supplementation of the natural radical scavenger ascorbic acid reduces the NO-production rate in the inner ear in noisy conditions. This finding supports the concept of inner ear protection by ascorbic acid supplementation.

AFM and BSEM: Novel approaches to the Basilar Membrane

For over a half century, researchers have probed cochlear biophysics with increasingly sophisticated technologies. Recently, we brought two new approaches, atomic force microscopy (AFM) and backscatter electron microscopy (BSEM), to bear on the question of how basilar membrane structural variations affect mechanical responses. Hemi‐cochleae and basilar membrane segments were obtained from rat, guinea pig, and gerbil ears by temporal bone microdissection. Hemi‐cochleae in PBS or formalin were imaged in a hydrated, uncoated state (VP wet mode) in Petri dishes mounted on boutons using an Hitachi S3400 N‐1 SEM. Membrane segments were excised, trimmed of laminae and ligament remnants, and mounted on polylysine/albumin‐coated glass for AFM imaging and force measurements. Both BSEM and AFM data indicate two distinct regions consistent with softer ground substance separating relatively stiff, ordered fiber bundles oriented radially in pectinate regions. Fibers and bundles ranged 0.3 to 1 μm in diameter with elasticity values, based on a Hertzian contact model, in the hundreds of kPa range, consistent with mixed elastin and collagen. Greatest variations occurred in matrix spacing, suggesting differences are attributable largely to packing density. Middle turn ground substance spacing averaged 1.5 μm, consistent with previously reported values (Naidu and Mountain, 2007; Fung, 1993).

Influence of topical application of basic fibroblast growth factor upon inner ear

Basic fibroblast growth factor (b-FGF) has recently been shown to have a positive effect on the treatment of postoperative mastoid cavity problem, but its ototoxicity has not been investigated. To investigate the effect of b-FGF on the inner ear of guinea pigs. In groups A (n = 10) and B (n =11), b-FGF was applied into the left external auditory canal and the middle ear, respectively. The right ear served as a control. At 1 week after b-FGF administration, the endocochlear DC potential (EP) was measured, and morphology of the cochleae was examined by scanning electron microscopy. In group A, the EP values of experimental ears and controls were 90.0 +/- 8.4 (mV, mean +/- SD) and 89.4 +/- 4.3 (P > 0.05). In group B, the values were 86.5 +/- 11.4 and 87.5 +/- 6.1, respectively, (P > 0.05). Morphological findings showed no damage on the cochlear. Application of b-FGF to the external and middle ears does not seem to have an apparent risk of ototoxicity.