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Biomedical subjects

E Borg

Publications and source records attributed to E Borg.

At least 19 recordsLinked to original sources
PubMed1992

Auditory degeneration after exposure to toluene in two genotypes of mice.

Two inbred strains of mice, CBA/Ca (with a moderate hearing loss starting late in life) and C57BL/6J (with an early onset of spontaneous auditory degeneration), were exposed to toluene by inhalation (1000 ppm, 12 h/day, 7 days) at either 1 or 6 months of age. Thresholds of auditory brainstem response (ABR) were measured 3-5 days after exposure and assessed repeatedly up to the age of 16 months (C57) or 23 months (CBA). Both strains of mice exposed to toluene at 1 month of age showed a mild loss of sensitivity at a high frequency (31.5 kHz) shortly after exposure. With increasing age, toluene exposure had little effect on the aging process of the auditory system in CBA mice but accelerated age-related hearing loss in C57 mice. The results indicate that toluene exposure can aggravate auditory deterioration only in mice with a strong genetic predisposition to spontaneously precocious age-related hearing loss.

Administration, Inhalation↗
PubMed1992

Analysis of the coil generated impulse noise in extracranial magnetic stimulation.

An intense impulse noise artifact is generated by the coil used in extracranial magnetic stimulation (EMS) of the brain and cranial nerves. In this study we measured and analyzed the sound pressure level (SPL), spectral content, wave form, and time course of the magnetic coil acoustic artifact (MCAA) impulse noise in the sound field and in the ear canal of life-size models of the human cranium. Two different clinical magnetic stimulators and coils were used. Sound field measurements from both coils showed the MCAA to be a transient impulse noise with a rapid rise-time, brief duration, broad acoustic spectrum, and high intensity. Measurements made on models of the human head with the magnetic coils positioned at selected standard clinical positions for EMS, particularly the peripheral facial nerve, auricle and mastoid areas, indicated that the MCAA may reach sound pressure levels that exceed noise damage-risk criteria limits for sensorineural hearing loss. The maximum peak energy in the acoustic spectrum of the MCAA measured in the ear canal of the model heads was from 2 to 5 kHz, the range of highest sensitivity in human ears. Ear protectors were found to attenuate the SPL of the MCAA, reaching the ear canal of the model heads by 15-22 dB SPL, and were recommended for use by patients and subjects exposed to EMS.

Brain↗
PubMed1992

Stage dependent development of intraocular cochlear grafts.

The intraocular grafting technique was employed to test whether the peripheral hearing organ, the cochlea, is capable of survival and an organized development in total isolation from the temporal bone. Rat cochleae obtained from gestation day 16, postnatal day 1 and 7 were chosen for transplantation into the anterior chamber of the eye of adult Sprague-Dawley rats. The grafts were maintained in the anterior chamber for 6, 10, or 15 weeks survival time. The salient features of this study is that 1) cochlear structures survive and, 2) the cochlear structures develop beyond their pre-grafted stage as determined from light and electron micrographs. In the present study, the grafts obtained at gestation day 16 (GD 16) and postnatal day 1 gave a much higher rate of survival and development than the postnatal day 7 grafts. In addition, grafts maintained for either 6 or 10 weeks had a better survival rate than those grafts left for 15 weeks. It is estimated from light and electron micrographs that the gestation day 16 otocysts that were maintained for 10 weeks, developed to the equivalent of a postnatal day 10 cochlea. The grafts obtained from postnatal day one rats developed to the equivalent of approximately 14 days after birth. Interestingly, in the absence of synaptic contact, the inner and outer hair cells were capable of survival, differentiation and maturation. It remains to be determined if the spiral ganglion cells require additional neurotrophic factors for survival in the anterior chamber of the eye.

Animals↗
PubMed1992

Sound perception induced by extracranial magnetic stimulation in deaf patients.

Two profoundly hard-of-hearing and deaf patients were examined by non-invasive extracranial magnetic stimulation (EMS) in an effort to determine whether EMS could evoke auditory sensations. The patients were fitted with standard earplugs and were stimulated at the auricle, the mastoid and the temporal lobe area. The threshold of auditory sensation (TAS) was determined at each stimulus position and found to be approximately 20-40% of the maximum EMS level (2.0 Tesla). The TAS was generally lowest in mastoid stimulation, but was variable, and dependent on the angle and position of the stimulating coil relative to the skull. Middle-ear muscle reflex (MEMR) tests performed by EMS of the auricle, mastoid and temporal lobe area contralateral to the probe ear were negative. It was concluded that EMS of the auditory system, particularly the mastoid area, can evoke auditory sensations in cochlea-deaf ears, and that this technique deserves further study as a non-invasive procedure for evaluating potential cochlear implant patients in conjunction with electrostimulation.

Acoustic Impedance Tests↗
PubMed1991

Acoustic trauma in extracranial magnetic brain stimulation.

The effects of the magnetic coil acoustic artifact (MCAA) associated with extracranial magnetic field stimulation (EMFS) of the brain were studied in normal hearing rabbits. Spectral and intensity analyses showed that the MCAA is a high intensity transient signal with peak energy between 2 and 5 kHz, and peak amplitudes in the first 100-200 mu sec. At EMFS levels of 50-100% of maximum output (2.0 Tesla), the corresponding MCAA levels were 131-142 dB sound pressure level (peak hold) at the outer ear and amplified by the external meatus to reach 145-157 dB sound pressure level (SPL) at the position of the tympanic membrane in rabbits. Measurements of the acoustic middle ear muscle reflex (AMR) in non-anesthetized rabbits indicated that exposure to EMFS levels of 50-100% resulted in correspondingly increasing compound threshold shifts (CTS) and permanent threshold shifts (PTS) in the unprotected ears of the experimental animals. Auditory brain-stem responses (ABR) measures on the same and additional animals corroborated these findings. Morphological studies showed evidence of substantial cochlear trauma at EMFS levels as low as 50%, with increasing severity up to 100% EMFS. Morphological examination of inner ear structures following exposure to the MCAA in the acute preparation (fixed within hours after exposure) showed ruptures between pillar cells and a detached organ of Corti. Preparations examined 3 or more weeks after exposure showed damaged pillar cells, a widespread loss of outer hair cells, fused and fractured inner hair cell stereocilia, and kinocilium outgrowth on inner hair cells. Although this extremely short impulse contains approximately 2 orders of magnitude less acoustic energy than a continuous noise exposure of 131 dB for 15 min, it is substantially more injurious to the cochlea. The present findings suggest that the acoustic artifact produced by the EMFS coil in some clinical instruments may pose a potential risk for temporary and permanent hearing loss in patients and clinicians when held in close proximity to the unprotected ear. Initial studies suggest that the magnetic field alone did not appear to cause permanent hearing impairment. We recommend the use of ear protectors for the patient and clinician during EMFS as a precautionary measure to prevent possible hearing loss from the MCAA.

Animals↗
PubMed1991

Age-related loss of auditory sensitivity in two mouse genotypes.

Frequency-specific auditory brainstem responses (ABR) (frequency range 2-31.5 kHz) were used to describe age-dependent alterations in frequency sensitivity in CBA/ca (to 30 months) and C57BL/6J (to 16 months) mouse genotypes. The two strains displayed an age-related loss similar to that of humans, with a primary decline in high-frequency sensitivity. CBA mice showed a slow, yet gradual decrease in sensitivity to high- followed by low-frequency until 18 months of age and a rapid deterioration at all frequencies thereafter. C57 mice demonstrated precocious aging in auditory sensitivity in an unsteady rather than gradual manner. By testing the same individuals on repeated occasions it was shown that, for C57 mice, the degenerative process was more precipitous with three phases, and that the individual variability was larger than that of CBA mice. It is suggested that the two mouse genotypes can be used to express the different aspects of human presbycusis in individual variability and modes of gradual or staggered progression.

Aging↗
PubMed1991

Mechanoacoustic properties of the tympanic membrane: a study on isolated Mongolian gerbil temporal bones.

In order to study the mechanical properties of the tympanic membrane in diseased ears, we have designed and evaluated an experimental tympanometric model. Isolated temporal bones of healthy Mongolian gerbils were studied with a Grason-Stadler 1723 typanometer in two-component admittance measurements with probe tones of 220 and 660 Hz. The normal tympanometric curve is described, and the validity and reproducibility of the model are assessed. The morphology of the gerbil tympanic membrane is described and compared with those of other species. Various alterations were produced in the middle ear, and it was found that tympanometry showed high sensitivity for tympanic membrane stiffness but not for mass changes. The condition of the pars flaccida did not significantly influence admittance, which was also resistant to osmotic challenge to the membrane. Ossicular chain disruption caused an increased admittance, whereas malleus fixation, without affecting the tympanic membrane itself, caused a pronounced reduction. The tympanometric patterns during tympanic membrane mass increase, and with hypertrophic myringeal scars and perforations were also determined. We conclude that tympanometry in the in vitro middle ear of gerbils offers possibilities for studying changes of the tympanic membrane physiology in disease.

Acoustic Impedance Tests↗
PubMed1990

Stapedius reflex thresholds in relation to tails of auditory nerve fiber frequency tuning curves.

The acoustic stapedius reflex (ASR) threshold on non-anesthetized rabbits was compared to some measures of the single auditory nerve fiber activity of rabbits. The observations were made on normal-hearing animals, with some additional data from noise-exposed individuals. The results showed that the ASR threshold was reached at a sound level above saturation of discharge rate for individual neurons at their characteristic frequency (CF) in normal animals. It was found, on the other hand, that the ASR threshold measured across frequencies from 0.25 to 12.0 kHz were at a level similar to that of the tails of the frequency tuning curves (FTCs). Cochlear lesions-induced changes in FTC tail levels were paralleled by changes in ASR threshold levels. The raise of ASR threshold was, however, somewhat larger than the raise of the tails which might be explained by the significant relative decrease in the total number of units found in the frequency region corresponding to the lesion. There was also a decrease in the high spontaneous rate (SR) compared to the low and medium SR fibers for higher frequencies. It is concluded that the FTC tails can be a major eighth-nerve correlate to ASR activation.

Acoustic Stimulation↗
PubMed1990

Hearing loss from the acoustic artifact of the coil used in extracranial magnetic stimulation.

The stimulating coil used in extracranial magnetic field stimulation (EMFS) emits a high intensity impulse sound artifact that causes permanent threshold shifts in the unprotected ears of experimental animals. At magnetic stimulation levels of 50 to 100%, the magnetic coil acoustic artifact (MCAA) ranged from 145 to 157 dB peak sound pressure level at the eardrum. The magnetic field alone did not appear to cause hearing impairment since no threshold shifts were observed in ears that were plugged with ear protectors during exposure to the MCAA. These findings suggest that the acoustic artifact produced by EMFS in the clinic may pose some risk for hearing loss in patients and clinicians when held in close proximity to the unprotected ear. We recommend the use of ear protectors for the patient and clinician during EMFS as a precautionary measure to prevent hearing loss.

Animals↗
PubMed1989

Noise level, inner hair cell damage, audiometric features, and equal-energy hypothesis.

Rabbits were exposed to 2- to 7-kHz noise either for a short duration at a high sound-pressure level (15 or 30 min at 115 dB SPL), or a long duration at a low level (512 h at 85 dB SPL). The high-level exposure produced a hearing loss in the frequency range 2-6 kHz, whereas the low-level exposure gave maximum hearing loss at 12-20 kHz. The 115-dB exposure caused significantly more damage to inner hair cells than the 85-dB exposure. The implications of the present results for evaluating audiograms, equal-energy hypothesis, risk criteria, and subjective auditory features are pointed out.

Animals↗
PubMed1989

Acoustic middle ear reflexes in laboratory animals using clinical equipment: technical considerations.

Acoustic middle ear muscle reflexes (AMR) were examined in nonanesthetized rabbits using clinical oto-impedance devices to determine the feasibility of utilizing clinically available instruments in studies of laboratory animals, particularly with regard to parameters such as probe tone frequency and intensity. The Karolinska Sjukhuset clinical impedance instrument and the Madsen Electronics ZO174 standard clinical impedance meter were used. The results of this study show that reliable AMRs and tympanograms can be obtained from rabbits with both clinical instruments. Probe tone frequencies in the range of 800-1,200 Hz were most effective for eliciting tympanograms and the AMR in rabbits. The probe tone level was also found to be an important factor, with the most reliable sound pressure level being around 70 dB SPL, and below that of the reflex threshold. Both clinical instruments recorded AMR threshold elevations in animals with 7th-nerve and cochlear lesions. AMR decay was observed at 8 and 12 kHz, but no decay was seen in normal-hearing animals up to 4 kHz, suggesting that this frequency may be suitable for detecting and measuring pathological decay in the rabbit. The overall results suggest that standard oto-impedance instruments with a probe tone frequency of 1,000 Hz may be used effectively in experimental studies of several aspects of the AMR in laboratory animals, such as rabbits.

Acoustic Impedance Tests↗
PubMed1989

Auditory stimulation brain map.

The topography of auditory evoked potentials (AEPs) was studied in 12 neurologically normal, adult, right-handed subjects of either sex. The AEPs were recorded with seventeen active electrodes in response to 500 Hz tone bursts with a level of 75 dB HL presented either to the left or the right ear. AEP brain maps were obtained with the BRAIN ATLAS III system. A region of maximum negativity was obtained corresponding to N1 at vertex and defined as focus of N1 (FN1). The reproducibility within and between sessions of FN1 was studied and found to be good for most of the subjects. The interindividual variability was moderate and the centre of FN1 on the map was localized 7 mm in front of the vertex electrode and 8.4 and 8.0 mm to the contralateral side of the vertex electrode upon stimulation of the left and the right ear, respectively. The approximate position of the skull surface is obtained by multiplication by a factor of 3. It was concluded that a standardized test session including six single maps based on 50 stimuli each gives an average map with identifiable and reproducible focus. The basis seems to be fulfilled to use the brain map in further analysis on clinical material.

Adult↗
PubMed1988

Protection against noise trauma by pre-exposure to a low level acoustic stimulus.

Guinea pigs were pre-exposed to a low level acoustic stimulus prior to exposure to a stimulus known to yield a permanent threshold shift. This pre-treatment resulted in: 1) approximately a 20 dB reduction in the threshold shift relative to animals not pre-exposed, and 2) complete recovery from the threshold shift after 2 months.

Acoustic Stimulation↗
PubMed1988

Eighth nerve fiber firing features in normal-hearing rabbits.

Neural activity of single eighth nerve fibers was recorded with glass microelectrodes in anesthetized normal-hearing rabbits. The units had a spontaneous rate ranging from 0 to approximately 120 spikes/s. In a large number of fibers this rate was below 2 spikes/s. The frequency tuning curves (FTCs) had a tip and a tail region for fibers with a high or medium characteristic frequency (CF). For low-frequency units the FTC was more symmetrically U-shaped. The tip threshold reached the behavioral threshold and units with thresholds of up to more than 60 dB above the mean behavioral threshold were found. There was a weak negative correlation between spontaneous rate and tip threshold. Frequency selectivity, Q10, was about 2 for units with CF below 2 kHz and about 5 for those with CF above 4 kHz. The peristimulus time (PST) histogram showed an initial peak, a plateau, and poststimulus inhibition. For the majority of fibers the dynamic range was 20-30 dB. Some fibers did not reach saturation within the stimulus intensity available. The tip-to-tail distance was 50 dB for high-frequency units at one octave below CF, a matter of potential interest for further studies of animals with inner ear lesions.

Animals↗
PubMed1988

Ototoxicity of cisplatin in gynaecological cancer patients.

The ototoxic side effect of a moderate dose of cisplatin was studied by regular audiometric investigations in 186 women with gynaecologic cancer. Cisplatin was given in a dose of 50 mg/m2 body surface by intravenous infusion every 4 weeks. High-frequency hearing loss occurred in 40 patients (22%), but in no single case was a significant change observed in the frequency range of 0.5-2 kHz. Older patients showed a statistically significant greater incidence of audiometric changes, but the pretreatment audiogram was not a predictor for ototoxic changes. It is concluded that a moderate dose of cisplatin does not effect the ability to communicate.

Adult↗
PubMed1988

Auditory brain map, effects of age.

Brain maps of late auditory evoked cortical potentials were obtained with the Brain Atlas III system in school-aged children and adults. All subjects were judged as neurologically normal, right-handed, and having normal hearing. The stimulus was a 100 ms burst of 500 Hz pure tone at 75 dB HL presented separately to the left and right ear. The results showed a frontoparietal maximum of negative activity corresponding to N1 and designated as the focus of N1 (FN1). FN1 had latencies of 108 ms (left stimulation (stim] and 113 ms (right stim) and amplitudes of -6.0 microV (left stim) and -4.8 microV (right stim) in children and a latency of 90 ms and an amplitude of -6.5 microV in adults. Among the children, more had ipsilateral than contralateral FN1, usually on the right side. The distance between the centers of gravity of FN1s obtained on stimulation of the two ears was significantly smaller in the maps of children than adults (p less than 0.01). The present findings indicated that the topography of the electrical activity changes during adolescence.

Adult↗
PubMed1987

A histochemical characterization of muscle fiber types in the avian M. stapedius.

The muscle fiber types and sizes in the M. stapedius (middle ear muscle) of the domestic chicken, Gallus gallus were determined histochemically on the basis of their reactions to myofibrillar adenosine triphosphatase (mATPase), succinic dehydrogenase and NADH diaphorase. Only type II fibers were identified at pH 9.4 and 4.2. At pH 4.6 three levels of activity were seen: high, intermediate and low. With the staining techniques three subtypes of fibers for oxidative enzymes, Types II1 (highly glycolytic), II12 (intermediately glycolytic and lipolytic) and II123 (highly lipolytic) were identified. Fiber diameter was also measured for the different fiber types. The average fiber diameter was around 20 micron for each fiber type. Although similar in size, the fiber types were markedly different in their histochemical properties. These findings plus those of earlier physiological studies suggest that the M. stapedius of G. gallus is a fast twitch, muscle with fibers of similar diameter showing mainly fatigue resistance characteristics.

Adenosine Triphosphatases↗