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Biomedical subjects

B A Bohne

Publications and source records attributed to B A Bohne.

At least 19 recordsLinked to original sources
PubMed2000

Noise damage in the C57BL/CBA mouse cochlea.

The present study was designed to determine the response to noise of the auditory system of a genetically well-defined laboratory mouse in preparation for examining the effect of noise on mice with specific genetic mutations. The mice were C57BL/CBA F1 hybrids. Eight mice served as non-noise-exposed controls and 39 mice were exposed for 1-24 h to an octave band of noise with a center frequency of 2, 4 or 8 kHz and a sound pressure level of 100-120 dB. Auditory brainstem response thresholds were measured pre-exposure and several times post-exposure (i.e., 0-27 days) to determine the magnitude of the temporary threshold shift (TTS) and permanent threshold shift (PTS). After fixation by cardiac perfusion, the cochleas from each mouse were embedded in plastic, dissected into quarter turns of the cochlear duct and analyzed quantitatively. Immediately post-exposure, all mice had sizable TTSs at the tested frequencies (i.e., 3-50 kHz). At this time, two mice were killed. Thresholds of the other 37 mice recovered somewhat in the first 4 days post-exposure. One mouse fully recovered from its TTS; 10 mice were left with PTSs at all frequencies; 26 mice recovered at some frequencies but not others. Most mice with PTSs for 30-50 kHz had focal losses of inner and outer hair cells in the basal 20% of the organ of Corti, often with degeneration of adjacent myelinated nerve fibers in the osseous spiral lamina. On the other hand, mice with PTSs for the lower frequencies (i.e., 3-20 kHz) had stereocilia disarray without significant hair cell losses in the second and first turns. Considerable variability was found in the magnitude of hair cell losses in those mice that received identical noise exposures, despite their genetic homogeneity.

Animals↗
PubMed2000

An anatomically based frequency-place map for the mouse cochlea.

An anatomically based frequency-place map was created for the mouse using C57BL/CBA F1 hybrids by matching noise-induced lesions in the organ of Corti with permanent hearing losses as determined by auditory brainstem response (ABR) thresholds. Twenty-six mice developed 'notched' ABR threshold shifts after exposure to an octave band of noise with a center frequency of 2 kHz at 120 dB SPL for 24 h, 4 kHz at 110 dB SPL for 4 h or 8 kHz at 100 dB SPL for 1 or 2 h. ABR thresholds were determined at several intervals post-exposure until thresholds stabilized (14-27 days). Once thresholds had stabilized, the mice were killed and their cochleas were prepared for phase-contrast microscopic examination as plastic-embedded flat preparations. Hair cell loss, stereocilia damage, and myelinated nerve fiber degeneration as a function of percentage distance from the cochlear apex were determined. Frequency-position matches could be made for 22 of the 26 mice by correlating areas of hair cell loss/stereocilia damage with permanent changes in ABR thresholds. These frequency-position data were fitted with the equation: % Distance from apex=56.6 log (f(Hz))-179.1; r(2)=0.810. This frequency-place function agrees well with Ehret's (1975) theoretical function based on critical bands and masked auditory thresholds.

Animals↗
PubMed2000

Histopathological differences between temporary and permanent threshold shift.

The structural changes associated with noise-induced temporary threshold shift (TTS) were compared to the damage associated with permanent threshold shift (PTS). A within-animal paradigm involving survival-fixation was used to minimize problems with data interpretation from interanimal variability in response to noise. Auditory brainstem response thresholds for clicks and tone pips were determined pre- and 1-2 h post-exposure in 11 chinchillas. The animals were exposed for 24 h to an octave band of noise with a center frequency of 4 kHz and a sound pressure level of 86 dB. Three animals (0/0-day) had both cochleas terminal-fixed 2-3 h post-exposure. Two animals (27/27-day) had threshold shifts determined every other day for 1 week, every week thereafter, and underwent terminal-fixation of both cochleas 27 days after exposure. Six animals (0/n-day) had threshold shifts determined in both ears upon removal from the noise; their left cochlea was then survival-fixed 2-3 h post-exposure. Threshold shifts were determined in their right ear every 2-3 days until their hearing either returned to pre-exposure values or stabilized at a reduced level at which time their right cochlea was terminal-fixed (4-13 days post-exposure). All cochleas were prepared as plastic-embedded flat preparations. Missing hair cells were counted and supporting cells and nerve fibers were evaluated throughout the organ of Corti using phase-contrast microscopy. Post-exposure, all animals had moderate TTSs in their left and right ears which averaged 43 dB for 4-12 kHz. In the 0/0-day animals, the only abnormality which correlated with TTS was a buckling of the pillar bodies. In the 0/n-day animals, their left cochlea (survival-fixed 2-3 h post-exposure) had outer hair cell (OHC) stereocilia which were not embedded in the tectorial membrane in the region of the TTS whereas OHC stereocilia were embedded in the tectorial membrane throughout the cochleas of non-noise-exposed, survival-fixed controls. Three of six right cochleas (terminal-fixed 4-13 days post-exposure) from the 0/n-day animals developed a PTS and two of these cochleas had focal losses of inner and outer hair cells and afferent nerve fibers at the corresponding frequency location. The other cochlea with PTS had buckled pillars in the corresponding frequency region. These results suggest that with moderate levels of noise exposure, buckling of the supporting cells results in an uncoupling of the OHC stereocilia from the tectorial membrane which results in a TTS. The mechanisms resulting in TTS appear to be distinct from those that produce permanent hair cell damage and a PTS.

Acoustic Stimulation↗
PubMed2000

Degeneration in the cochlea after noise damage: primary versus secondary events.

PURPOSE: To determine if noise damage in the organ of Corti is different in the low- and high-frequency regions of the cochlea. MATERIALS AND METHODS: Chinchillas were exposed for 2 to 432 days to a 0.5 (low-frequency) or 4 kHz (high-frequency) octave band of noise at 47 to 95 dB sound pressure level. Auditory thresholds were determined before, during, and after the noise exposure. The cochleas were examined microscopically as plastic-embedded flat preparations. Missing cells were counted, and the sequence of degeneration was determined as a function of recovery time (0-30 days). RESULTS: With high-frequency noise, primary damage began as small focal losses of outer hair cells in the 4-8 kHz region. With continued exposure, damage progressed to involve loss of an entire segment of the organ of Corti, along with adjacent myelinated nerve fibers. Much of the latter loss is secondary to the intermixing of cochlear fluids through the damaged reticular lamina. With low-frequency noise, primary damage appeared as outer hair cell loss scattered over a broad area in the apex. With continued exposure, additional apical outer hair cells degenerated, while supporting cells, inner hair cells, and nerve fibers remained intact. Continued exposure to low-frequency noise also resulted in focal lesions in the basal cochlea that were indistinguishable from those resulting from exposure to high-frequency noise. CONCLUSIONS: The patterns of cochlear damage and their relation to functional measures of hearing in noise-exposed chinchillas are similar to those seen in noise-exposed humans. Thus, the chinchilla is an excellent model for studying noise effects, with the long-term goal of identifying ways to limit noise-induced hearing loss in humans.

Animals↗
PubMed1999

High-resolution mapping of tlt, a mouse mutant lacking otoconia.

The ability to sense gravity is enhanced by an extracellular structure that overlies the macular sensory epithelium. This complex consists of high density particles, otoconia, embedded within a gelatinous membrane. The tilted mouse specifically lacks otoconia, yet has no other detectable anatomic lesions. Furthermore, the penetrance of the tilted phenotype is nearly 100%. This mouse provides a model to identify genes that are involved in the development and function of vestibular otoconia. Using SSLP markers, we have mapped the tilted (tlt) gene on mouse Chromosome (Chr) 5 between D5Mit421 and D5Mit353/D5Mit128/D5Mit266/D5Mit267 by analysis of the progeny of an intersubspecific F2 intercross. We also mapped the fibroblast growth factor receptor 3 (Fgfr3) gene, a potential candidate for tlt, and the Huntington's disease homolog (Hdh) gene to D5Mit268, approximately 4.3 centiMorgans (cM) from the tilted locus. This study excludes both Fgfr3 and Hdh as candidate genes for tlt and identifies closely linked microsatellite markers that will be useful for the positional cloning of tlt.

Animals↗
PubMed1999

Survival-fixation of the cochlea: a technique for following time-dependent degeneration and repair in noise-exposed chinchillas.

To minimize problems with data interpretation due to interanimal variation in susceptibility to noise, we developed a survival-fixation paradigm which involves fixing one cochlea of an experimental chinchilla at one post-exposure time and fixing the second cochlea as much as 14-24 days later. This paradigm is analytically effective because there is a high correlation in the magnitude and pattern of damage in the left and right cochleas of binaurally exposed animals. Thus, each experimental animal provides two snapshots in the degeneration and repair continua in which it can be certain that both cochleas sustained equivalent amounts of damage during the exposure. Using this technique, the time course of degeneration of different structures and cells in the organ of Corti can be determined and primary damage can be distinguished from secondary effects. The present paper discusses the issues which had to be addressed to develop this technique and provides preliminary results from chinchillas exposed to a traumatic noise.

Animals↗
PubMed1998

Long-term degeneration in the cochlear nerve and cochlear nucleus of the adult chinchilla following acoustic overstimulation.

Adult chinchillas were exposed once to an octave-band noise, centered at 4 kHz, and allowed to survive for 16 days or for 1, 2, 4, and 8 months. Axonal degeneration was mapped in the cochlear nucleus, using the Nauta-Rasmussen silver method, and related to hair cell damage and to loss of myelinated nerve fibers in the osseous spiral lamina of the cochlea. Axonal degeneration in the dorsal cochlear nucleus had already reached a peak by 16 days and disappeared after 1 month. Meanwhile, myelinated nerve fiber degeneration in the cochlea extended basally, followed 2 weeks to 2 months later by spread of axonal degeneration into the corresponding high-frequency region of the ventral cochlear nucleus. Axonal degeneration occurred early in the low-frequency region of the ventral cochlear nucleus, followed 2-4 weeks later by spread of myelinated fiber degeneration into more apical regions of the cochlea. New degeneration of axons in the cochlear nerve and in the ventral cochlear nucleus continued to occur for up to 8 months after stimulation. These findings imply that plastic changes in the central auditory pathways could play a role in the long-term effects of cochlear damage and acoustic overstimulation, possibly leading to a chronic neurodegenerative condition in the ear and in the brain.

Acoustic Stimulation↗
PubMed1998

Otoconial agenesis in tilted mutant mice.

The sense of balance is one of the phylogenetically oldest sensory systems. The vestibular organs, consisting of sensory hair cells and an overlying extracellular membrane, have been conserved throughout vertebrate evolution. To better understand mechanisms regulating vestibular development and mechanisms of vestibular pathophysiology, we have analyzed the mouse mutant, tilted (tlt), which has dysfunction of the gravity receptors. The tilted mouse arose spontaneously and has not been previously analyzed for a developmental or physiological deficit. Here we demonstrate that the tilted mouse, like the head tilt (het) mouse, specifically lacks otoconia and consequently does not sense spatial orientation relative to the force of gravity. Unlike other mouse mutations affecting the vestibular system (such as pallid, mocha and tilted head), the defect in the tilted mouse is highly penetrant, results in the nearly complete absence of otoconia, exhibits no degeneration of the sensory epithelium and has no apparent abnormal phenotype in other organ systems. We further demonstrate that protein expression in the macular sensory epithelium is qualitatively unaltered in tilted mutant mice.

Animals↗
PubMed1998

The role of micro-noise trauma in the etiology of aging-related changes in the inner ear.

Eleven chinchillas between 1 and 2.4 years of age had the malleus/incus complex removed from one middle ear and then lived in the Washington University animal facilities for 4 years post-surgery. Each animal had one ear (termed ambient-noise) in which the conductive apparatus was intact; the other ear (termed noise-protected) had a 50-60 dB conductive hearing loss. The background sound level in the animal facility was 59 dBA with periodic brief sounds up to 102 dBA. After the 4-year experimental period, both ears were fixed, embedded in plastic and dissected for microscopic examination as flat preparations. The quantitative and qualitative findings in the noise-protected ears were compared to those in the ambient-noise ears. Both groups of ears sustained losses of sensory and supporting cells throughout the organ of Corti. A variable amount of age pigment was found to have accumulated in the outer hair cells and all supporting cells. In the noise-protected ears, inner hair cell loss ranged from 1.0 to 3.1% and averaged 1.7 +/- 0.8%; outer hair cell loss ranged from 1.8 to 6.4% and averaged 3.6 +/- 1.2%. In the ambient-noise ears, inner hair cell loss ranged from 0.7 to 2.8% and averaged 1.6 +/- 0.7%; outer hair cell loss ranged from 1.3 to 5.4% and averaged 3.6 +/- 1.2%. Within-animal comparison of cell losses in the noise-protected and ambient-noise ears revealed no significant difference between the two groups. It is concluded that long-term exposure to micro-noise does not accelerate the spontaneous loss of sensory cells which occurs with aging. Although not quantified, there was no obvious difference in the amount or cellular distribution of age pigment in the two groups. Thus, it appears that the formation of age pigment in the ear is the result of the cells' basic metabolic processes rather than the wear and tear from sensory transduction.

Aging↗
PubMed1997

New growth of axons in the cochlear nucleus of adult chinchillas after acoustic trauma.

This study determined the effect of acoustic overstimulation of the adult cochlea on axons in the cochlear nucleus. Chinchillas were exposed to an octave-band noise centered at 4 kHz at 108 dB sound pressure level for 1.75 h. One chinchilla was never exposed to the noise, and several others had one ear protected by an ear plug or prior removal of the malleus and incus. Exposure of unprotected ears caused loss of inner and outer hair cells and myelinated nerve fibers, mostly in the basal half of the cochlea. Cochlear nerve fiber degeneration, ipsilateral to the exposed ears, was traced to regions of the cochlear nucleus representing the damaged parts of the cochlea. In silver impregnations of a deafferented zone in the posteroventral cochlear nucleus, the concentration of axons decreased by 43% after 1 month and by 54% after 2 months. However, by 8 months, the concentration of thinner axons, with diameters of less than 0.46 microm, increased by 46-90% over that at 2 months. The concentration of axons with larger diameters did not change. Between 2 and 8 months small axonal endings appeared next to neuronal cell bodies. This later increase of thinner axons and endings is consistent with a reactive growth of new axons of relatively small diameter. The emergence of small perisomatic boutons suggests that the new axons formed synaptic endings, which might contribute to an abnormal reorganization of the central auditory system and to the pathological changes that accompany acoustic overstimulation.

Animals↗
PubMed1997

Neuronal and transneuronal degeneration of auditory axons in the brainstem after cochlear lesions in the chinchilla: cochleotopic and non-cochleotopic patterns.

Terminal axonal degeneration in the brain following cochlear lesions was studied with the Nauta-Rasmussen method. Losses of hair cells and myelinated cochlear fibers were assessed. The cochleotopic map projected, from apex to base, on the ventral-to-dorsal axes of the cochlear nuclei. The cochleotopic correspondence was better for loss of cochlear nerve fibers and inner hair cells, than for outer hair cells. Cochlear fibers were traced to all parts of the cochlear nucleus, including the small-cell shell, also to cell-group Y and the flocculus. Terminal axonal degeneration in nuclei of the superior olivary complex, lateral lemniscus, and inferior colliculus was interpreted as transynaptic, since degenerated axons could not be traced to these locations from the cochlear nerve or trapezoid body. Moreover, biotinylated dextran amine injection in the basal turn of scala media of a normal cochlea labeled cochlear nerve fibers projecting to the high-frequency regions of the cochlear nuclei and to the flocculus, but not to more central auditory nuclei. This is the first detailed account of transynaptic degeneration in the ascending auditory pathway resulting from cochlear damage in an adult mammal. These findings are consistent with a dystrophic process depending on hair-cell loss and/or direct damage to cochlear nerve fibers.

Animals↗
PubMed1997

Degeneration of axons in the brainstem of the chinchilla after auditory overstimulation.

The patterns of axonal degeneration following acoustic overstimulation of the cochlea were traced in the brainstem of adult chinchillas. The Nauta-Rasmussen method for axonal degeneration was used following survivals of 1-32 days after a 105 min exposure to an octave-band noise with a center frequency of 4 kHz and a sound pressure level of 108 dB. Hair-cell and myelinated nerve-fiber loss were assessed in the cochlea. The cochleotopic pattern of terminal degeneration in the ventral cochlear nucleus correlated with the sites of myelinated fiber and inner-hair-cell loss: this correlation was less rigorous with outer-hair-cell loss, especially in the dorsal cochlear nucleus. These results are consistent with a dystrophic process with a slow time course depending on hair-cell loss and/or direct cochlear nerve-fiber damage. However, in a number of cases with no damage in the apical cochlea, fine fiber degeneration occurred with a faster course in low-frequency regions in the dorsal cochlear nucleus and, transynaptically, in a non-cochleotopic pattern in the superior olive and inferior colliculus. These findings suggest that neuronal hyperactivity plays a role in the central degeneration following acoustic overstimulation, possibly by an excitotoxic process.

Acoustic Stimulation↗
PubMed1997

Processing and analyzing the mouse temporal bone to identify gross, cellular and subcellular pathology.

A technique has been developed for preparing the mouse temporal bone for histopathological examination: first, as a whole mount to detect any gross malformations of the bony or membranous labyrinths; second, in dissected segments to localize damage in the different sensory organs and to quantify sensory- and supporting-cell losses; and finally, in semi-thick and thin sections to identify and characterize subcellular pathology. Examples are given of the successful application of this technique to mice with very different inner-ear problems, including those with an abnormally short cochlear spiral, a defective lateral semicircular canal, abnormal otoliths over the saccular macula, an increased susceptibility to noise damage and those which lack fibroblast growth factor receptor 3.

Animals↗
PubMed1997

Time course of nerve-fiber regeneration in the noise-damaged mammalian cochlea.

The time course of events which are essential for nerve-fiber regeneration in the mammalian cochlea was determined using a group of chinchillas that had been exposed for 3.5 hr to an octave band of noise with a center frequency of 4 kHz and a sound pressure level of 108 dB. The animals recovered from 40 min (0 days) to 100 days at which times their inner ears were fixed and the organs of Corti prepared for phase-contrast and bright-field microscopy as plastic-embedded flat preparations. Selected areas identified in the flat preparations were semi-thick and thin sectioned at radial or tangential angles for examination by bright-field and transmission electron microscopy. The following time-ordered events appeared critical for nerve-fiber regeneration: (1) The area of the basilar membrane in which regeneration had a possibility of occurring showed signs of severe injury. Outer hair cells degenerated first followed by outer pillars, inner pillars, inner hair cells and other supporting cells; (2) Myelinated nerve fibers in the osseous spiral lamina became fragmented, starting at the distal ends of the fibers. This degeneration gradually extended back to Rosenthal's canal; (3) Fibrous processes, originating from Schwann-like cells in the osseous spiral lamina, extended laterally on the basilar membrane; (4) Schwann cells lined up medial to the habenulae perforata in the areas of severest damage, apparently ready to migrate through the habenulae onto the basilar membrane; (5) Schwann-cell nuclei appeared on the basilar membrane beneath the developing layer of squamous epithelium which was in the process of replacing the degenerated portion of the organ of Corti; (6) Regenerated nerve fibers with thin myelin sheaths or a simple investment of Schwann cell cytoplasm appeared in areas of total loss of the organ of Corti; and (7) The myelin sheaths on the regenerated nerve fibers gradually became thicker.

Animals↗
PubMed1996

Skeletal overgrowth and deafness in mice lacking fibroblast growth factor receptor 3.

Fibroblast growth factor receptor 3 (Fgfr3) is a tyrosine kinase receptor expressed in developing bone, cochlea, brain and spinal cord. Achondroplasia, the most common genetic form of dwarfism, is caused by mutations in FGFR3. Here we show that mice homozygous for a targeted disruption of Fgfr3 exhibit skeletal and inner ear defects. Skeletal defects include kyphosis, scoliosis, crooked tails and curvature and overgrowth of long bones and vertebrae. Contrasts between the skeletal phenotype and achondroplasia suggest that activation of FGFR3 causes achondroplasia. Inner ear defects include failure of pillar cell differentiation and tunnel of Corti formation and result in profound deafness. Our results demonstrate that Fgfr3 is essential for normal endochondral ossification and inner ear development.

Achondroplasia↗
PubMed1995

Regenerated nerve fibers in the noise-damaged chinchilla cochlea are not efferent.

Nerve-fiber regeneration in the chinchilla cochlea following a traumatic noise exposure was systematically described by Bohne and Harding (1992). However, their study did not determine the origin of the regenerated nerve fibers (RNFs). In the present study, 23 chinchillas were exposed for 12 h to a 0.5 kHz octave band of noise at 120 dB SPL. After a 3-month or 1-year recovery period, their right cochleas were incubated to demonstrate acetylcholinesterase (AChE) activity and then briefly counterstained with Neutral Red or OsO4. Their left cochleas were fixed with OsO4 and dissected using a combined organ of Corti (OC)/modiolus technique that preserved both structures for high-resolution microscopy. All cochleas were prepared as plastic-embedded flat preparations. Damage was located in the basal two-thirds of the cochlea and generally consisted of multiple lesions in the OC, often involving total degeneration of one or more OC segments (i.e., OC wipeouts). The OC wipeouts were separated from one another by areas which contained some identifiable cells of the OC (i.e., OC remnants). Most RNFs were found in OC wipeouts adjacent to OC remnants. In those animals (83%) with significant OC damage, 13 (100%) 3-month-recovery chinchillas had 1-96 RNFs while 6 (86%) 1-year-recovery chinchillas had 7-62 RNFs. In the AChE-stained cochleas, none of the RNFs were AChE-positive, but normal AChE-positive fibers were found in the undamaged apical turn. A variable number of surviving spiral ganglion cells was present in those regions of Rosenthal's canal that had originally innervated the missing hair cells in the OC wipeouts and remnants. It is concluded that RNFs are not part of the efferent cochlear system and therefore, most likely belong to the afferent system.

Acetylcholinesterase↗
PubMed1995

Heterozygosity mapping of partially congenic lines: mapping of a semidominant neurological mutation, Wheels (Whl), on mouse chromosome 4.

We identified a semidominant, chemically induced, mouse mutation with a complex array of abnormal behaviors including bidirectional circling and hyperactivity, abnormal circadian rhythmicity and abnormal responses to light. In this report, we genetically and phenotypically characterized the circling/waltzing component of the abnormal behavior. We mapped the locus controlling this trait by heterozygosity mapping of partially congenic lines carrying the mutagenized chromosome outcrossed to different inbred strains for three generations. Analysis of 68 PCR-based markers in 13 affected individuals indicated that the mutant locus, named Wheels (Whl), resides in the subcentromeric portion of mouse chromosome 4. The statistical evaluation of data obtained by heterozygosity mapping validates this efficient mapping approach. Further characterization of the Whl mutation demonstrated that Whl/Whl homozygotes die during embryonic life and that the penetrance of circling behavior depends on genetic background. Morphological analysis of the inner ears of Whl/+ mice revealed a variable number of abnormalities in the sensory and nonsensory portions of their semicircular canals. Abnormalities ranged from slight atrophy of one or more cristae to complete absence of the lateral crista and canal. The molecular characterization of the gene disrupted in the Whl mutation will provide insight into developmental mechanisms involved in inner ear formation.

Animals↗