The cochlear auditory epithelium contains two types of sound receptors, inner hair cells (IHCs) and outer hair cells (OHCs). Mouse models for labelling juvenile and adult IHCs or OHCs exist; however, labelling for embryonic and perinatal IHCs or OHCs are lacking. Here, we generated a new knock-in Fgf8^P2A-3×GFP/+ (Fgf8^GFP/+) strain, in which the expression of a series of three GFP fragments is controlled by endogenous Fgf8 cis-regulatory elements. After confirming that GFP expression accurately reflects the expression of Fgf8, we successfully obtained both embryonic and neonatal IHCs with high purity, highlighting the power of Fgf8^GFP/+. Furthermore, our fate-mapping analysis revealed, unexpectedly, that IHCs are also derived from inner ear progenitors expressing Insm1, which is currently regarded as an OHC marker. Thus, besides serving as a highly favorable tool for sorting early IHCs, Fgf8^GFP/+ will facilitate the isolation of pure early OHCs by excluding IHCs from the entire hair cell pool.
Animals ; Mice ; Hair Cells, Auditory, Inner ; Cochlea/metabolism* ; Hair Cells, Auditory, Outer/metabolism* ; Disease Models, Animal ; Fibroblast Growth Factor 8/metabolism*

OBJECTIVES: To investigate the otoprotective effects of mouse nerve growth factor (mNGF) in A/J mice. METHODS: The mice at postnatal day 7 (P7) were randomly separated into a mNGF treated group (mNGF group) and a distilled water (for injection) treated group (control group). The mNGF dissolved in distilled water or distilled water alone was given to the mice once every other day from P7 by intramuscular injection in the hips. The otoprotective effects of mNGF in A/J mice were observed in a time course manner. The thresholds of auditory-evoked brainstem response (ABR) were tested from the age of the 3rd to the 8th week. Sections of the inner ears were stained by hematoxylin and eosin, and spiral ganglion neurons (SGNs) were observed at the age of the 3rd, the 6th,and the 8th week. Counts of whole mount outer hair cells (OHCs) in the cochleae were made at the age of 8 weeks. Expression of apoptosis related genes was determined by quantitative real-time polymerase chain reaction and Western blotting. RESULTS: ABR thresholds of the mNGF group were significantly lower than those of the control group at the age of the 6th and the 8th week. Moreover, the mNGF preserved OHC and SGN in the mouse cochleae in this period. Further experiments showed that the expression of caspase genes (including caspase-3) was inhibited in the mouse inner ears in the mNGF group. CONCLUSION: The mNGF improves hearing in A/J mice by preserving SGN and OHC in the cochleae.
Animals ; Apoptosis ; Blotting, Western ; Brain Stem ; Cochlea ; Ear, Inner ; Eosine Yellowish-(YS) ; Hair Cells, Auditory, Outer ; Hearing* ; Hematoxylin ; Hip ; Injections, Intramuscular ; Mice* ; Nerve Growth Factor* ; Neurons ; Real-Time Polymerase Chain Reaction ; Spiral Ganglion ; Water

OBJECTIVETo study the pathological alteration of the cochlear microcirculation and the role of endothelin (ET) in the process of the noise-induced injury of inner ear.

METHODSThirty rats were randomly divided into five groups: control group and 1, 4, 8, 15 d noise exposure groups (115 dB, white noise, 8 h daily). The cilium of hair cell was observed by scanning electron microscope, the cochlear microcirculation was determined by stretched preparation of the stria vascularis. The level of ET in plasma was measured through radio-immunity. The distribution of ET-1, ETA, ETB, in cochlea were detected through immunohistochemistry staining.

RESULTSIn the 4, 8, 15 d group, severe ischemia appeared on the capillary of stria vascularis and the cilium of hair cell displayed significantly disorder. The level of ET in plasma rose temporarily in the 4 d group. ET-1 activity distributed widely in the rat cochlea, there was no significant difference between the control group and the noise exposure groups. ETA expressed in the plasma of the intermediate cells and the capillary walls in the stria vascularis. The control group and the 1 d group showed weak positive staining, while the 4, 8, 15 d groups showed strong positive. The ETB, activity distributed on the endothelial cells of the capillary of stria vascularis and the alteration of the staining intensity was similar to the manifestation of ETA.

CONCLUSIONSSevere disturbance of the cochlear circulation occurred during the course of the noise injury to the inner ear. At the same time, the activity of the ET system of the cochlea stepped up significantly. It coincided with the ischemia of the stria vascularis. These findings suggest that ET may play an important role in the process of the cochlear microcirculation disorder caused by noise.

Animals ; Cochlea ; pathology ; Ear, Inner ; pathology ; Endothelins ; blood ; Hair Cells, Auditory ; pathology ; Hearing Loss, Noise-Induced ; blood ; pathology ; Male ; Microcirculation ; Rats ; Rats, Sprague-Dawley ; Stria Vascularis ; pathology

BACKGROUND AND OBJECTIVES: Endolymphatic hydrops has been considered as an important histologic substrate of Meniere's disease. A permanent displacement of basilar membrane (BM) by increased endolymphatic pressure has been thought to be an explanation for hearing change. Direct observation of histological sections of temporal bones, however, suggested that stereocilia and tectorial membrane decoupling is more associated with pressure induced by mechanical deformation of the organ of Corti rather than with the displacement of BM. METERIALS AND METHOD: 26 cochleae from 13 female pigmented ginea pigs were harvested. One cochlea per each animal was injected with artificial perilymph. The other one was used as control. After fixation, followed by embedding and mid-modiolar sectionning, specimens were observed with a microscope. Morphometric parameters of each row and turn of the organ of Corti were measured and quantified. RESULTS: The average area and height of the organ of Corti were significantly smaller in the apical turn of the experimental group (p<0.05). The lengths of outer hair cell and Deiters cell in the apical turn were also significantly reduced in the experimental group (p<0.05). The angle between the outer hair cell and Deiters cell was smaller in the apex and in the 3rd turn of the experimental group (p<0.05). CONCLUSION: Results show that compression and deformation of the organ of Corti, especially in the apical turn, is a prominent feature in the acute endolymphatic hydrops model. We suggest that the deformation of organ of Corti is the primary cause of hydrops that induce the decoupling of tectorial membrane and stereocilia rather than the displacement of BM.
Animals ; Basilar Membrane ; Cochlea ; Edema ; Endolymphatic Hydrops* ; Female ; Guinea Pigs ; Hair ; Hearing ; Humans ; Meniere Disease ; Organ of Corti* ; Perilymph ; Stereocilia ; Swine ; Tectorial Membrane ; Temporal Bone

BACKGROUND AND OBJECTIVES: Nitric oxide (NO) is an inorganic, gaseous free radical that carries a variety of messages between cells. The histochemical demonstration of neuronal betaNADPH-d is the demonstration of the presence of NOS. The purpose of this study was to identify the existence of NOS and the difference of the expression of betaNADPH-d in mouse and gerbil cochleae. MATERIALS AND METHODS: Each of the eight cochleae of Mongolian gerbil (Meriones unguiculatus) and mice (CJU/A) were fixed by cardiac perfusion with 4% paraformaldehyde in 0.1M phosphate buffer solution. The en-bloc cochleae were incubated after decalcification, and stained with betaNADPH-d and counterstained with acid fuchsin. The relative intensity of staining was decided in the same location of cochlea. RESULTS: Most supporting cells were strongly stained except Claudius cells and Boettcher's cells in gerbil. However, Boettcher's cells were strongly stained in mice. Outer hair cells, inner hair cells, basial membrane and lining cells of spiral limbus were strongly stained. Interdental cells of spiral limbus, inner border cells and intermediate cells of stria vascularis were moderately stained. Tectorial membrane and amorphous layer of basial membrane were not stained. CONCLUSION: Using betaNADPH-d staining, this study documents the presence of nitric oxide synthase in mice and gerbil cochleae and the difference of staining between two species.
Animals ; Cochlea* ; Gerbillinae* ; Hair ; Membranes ; Mice* ; Neurons ; Nitric Oxide ; Nitric Oxide Synthase ; Perfusion ; Rosaniline Dyes ; Stria Vascularis ; Tectorial Membrane

OBJECTIVES: Apoptosis may play an important role in the mechanism underlying the GJB2 gene conditional knockout (cCx26) mice cochlear cell death. The objective of this study was to explore the the damage mode of the outer hair cells (OHCs) and its real time point of apoptosis and provide information to further explore the role of apoptosis in the happening of hearing loss in cCx26 mice. METHODS: Cochleae from mice at various developmental stages (P8, P12, and P21) were dissected out and first used to be observed under the scanning electron microscope (SEM). Basilar membranes from mice at P8, P14, P18, and P21 were stained by fluorescein isothiocyanate-conjugated phalloidin and propidium iodide (PI) and examined under confocal microscope. RESULTS: The loss of OHCs of cCx26 knockout mice was first set between P12 and P21 under SEM. Whole mount phalloidin and PI staining revealed that obvious apoptotic appearance of the OHCs surface morphology was observed at P18. CONCLUSION: Typical apoptotic morphology was found in the OHCs in the organ of Corti of the cCx26 mice at P18. This may provide information to further study the role of apoptosis in the occurrence of hearing loss of cCx26 mice.
Animals ; Apoptosis ; Basilar Membrane ; Cell Death ; Cochlea ; Connexins ; Electrons ; Fluorescein ; Hair ; Hair Cells, Auditory, Outer ; Hearing Loss ; Hearing Loss, Sensorineural ; Mice ; Mice, Knockout ; Organ of Corti ; Phalloidine ; Propidium

Cochlea ; Humans ; Macrophages ; Stria Vascularis

Labyrinthitis ossificans (LO) is a pathologic formation of fibrosis and new bone within the lumen of the otic capsule. The LO is a challenging issue in cochlear implantation since obliteration and obstruction of the cochlea make electrode insertion through scala tympani (classic route) difficult. Moreover, tympanomastoidectomy for resolution of chronic otitis media is also simultaneously considered for tympanogenic LO with severe to profound hearing loss because ossification could progress in case of staged or delayed implantation after initial tympanomastoidectomy. We report a patient with tympanogenic LO, who received subtotal petrosectomy with simultaneous cochlear implantation via scala vestibuli instead of the scala tympani for hearing rehabilitation.
Cochlea ; Cochlear Implantation* ; Cochlear Implants* ; Ear, Inner* ; Electrodes ; Fibrosis ; Hearing ; Hearing Loss ; Humans ; Labyrinthitis* ; Otitis Media ; Rehabilitation ; Scala Tympani ; Scala Vestibuli*

OBJECTIVETo investigate the related parameters of the temporal bone structure for determining the position of implanting electrode into the scala tympani in cochlear implantation surgery through the facial recess and epitympanum approach.

METHODSIn a surgical simulation experiment, 20 human temporal bones were studied and measured to determine the related parameters of the temporal bone structure.

RESULTSThe distance 5.91∓0.29 mm between the short process of the incus and the round window niche, 2.11∓0.18 mm between the stapes and the round window niche, 6.70∓0.19 mm between the facial nerve in the perpendicular paragraph and the round window niche, 2.22∓0.21 mm from the pyramidal eminence to the round window, and 2.16∓0.14 mm between the stapes and the round window. The minimal distance between the implanting electrode and the vestibular window was 2.12∓0.19 mm. The distance between the cochleariform process and the round window niche was 3.79∓0.17 mm. The position of the cochlear electrode array insertion into the second cochlear turn was 2.25∓0.13 mm under the stapes. The location of the cochlear electrode array insertion into the second cochlear turn was 2.28∓0.20 mm inferior to the pyramidal eminence.

CONCLUSIONThese parameters provide a reference value to determine the different positions of cochlear electrode array insertion into the scale tympani in different patients.

Adult ; Cochlea ; anatomy & histology ; surgery ; Cochlear Implantation ; Cochlear Implants ; Ear, Middle ; anatomy & histology ; surgery ; Female ; Humans ; Male ; Round Window, Ear ; anatomy & histology ; surgery ; Scala Tympani ; anatomy & histology ; surgery

OBJECTIVES: Morphological studies on presbycusis, or age-related hearing loss, have been performed in several different strains of mice that demonstrate hearing loss with auditory pathology. The C57BL/6 (C57) mouse is a known model of early onset presbycusis, while the CBA mouse is characterized by relatively late onset hearing loss. We performed this study to further understand how early onset hearing loss is related with the aging process of the cochlea. METHODS: We compared C57 cochlear pathology and its accompanying apoptotic processes to those in CBA mice. Hearing thresholds and outer hair cell functions have been evaluated by auditory brainstem response (ABR) recordings and distortion product otoacoustic emission (DPOAE). RESULTS: ABR recordings and DPOAE studies demonstrated high frequency hearing loss in C57 mice at P3mo of age. Cochlear morphologic studies of P1mo C57 and CBA mice did not show differences in the organ of Corti, spiral ganglion, or stria vascularis. However, from P3mo and onwards, a predominant early outer hair cell degeneration at the basal turn of the cochlea in C57 mice without definitive degeneration of spiral ganglion cells and stria vascularis/spiral ligament, compared with CBA mice, was observed. Additionally, apoptotic processes in the C57 mice also demonstrated an earlier progression. CONCLUSION: These data suggest that the C57 mouse could be an excellent animal model for early onset 'sensory' presbycusis in their young age until P6mo. Further studies to investigate the intrinsic or extrinsic etiologic factors that lead to the early degeneration of organ of Corti, especially in the high frequency region, in C57 mice may provide a possible pathological mechanism of early onset hearing loss.
Aging ; Animals ; Apoptosis ; Cochlea ; Evoked Potentials, Auditory, Brain Stem ; Hair ; Hearing ; Hearing Loss ; Ligaments ; Mice ; Mice, Inbred CBA ; Models, Animal ; Organ of Corti ; Presbycusis ; Spiral Ganglion ; Stria Vascularis