Biomedical subjects

E Borg

Publications and source records attributed to E Borg.

At least 91 records · Page 5Linked to original sources

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↗

PubMed1987

Morphological and electrophysiological study of the inner ear and the central auditory pathways following whole body fetal irradiation.

Pregnant CBA/CBA mice were whole body irradiated with 2 Gy on the 13th or 16th day of gestation, respectively. The exposed fetuses were raised to an age of 21 postnatal days. Auditory brainstem recordings of threshold levels showed a considerable elevation independent of if irradiation had been performed on either the 13th gestational day or the 16th gestational day. In exposed animals a latency difference occurs in the peaks that increases from peak 1 to peak 5, measuring in peak 5 up to 1.16 ms. Also the peak-to-peak length of waves 1-5 increases in irradiated animals. Scanning electron microscopy of the cochleae showed varying degrees of stereociliary derangement of both outer and inner hair cells, particularly in cochleae where irradiation had been performed on the 13th gestational day, but not loss of hair cells. Light microscopic analysis of auditory brainstem nuclei revealed normal conditions except that in inner ears exposed on the 16th gestational day the flocculus was fused to the lateral surface of the anterior ventral cochlear nucleus. It is concluded that the elevated threshold levels in irradiated animals are most likely due to pathological changes in the peripheral receptor organ whereas the increased latencies and the increased peak-to-peak length likewise reflect functional changes in the brainstem auditory nuclei.

Animals↗

PubMed1987

Age-related hair cell loss in spontaneously hypertensive and normotensive rats.

In the spontaneously hypertensive (SH) rat, a hereditary form of hypertension and widespread vascular abnormalities develop. In the present study the inner ear degeneration pattern in SH and normotensive (N) rats not exposed to noise was investigated and correlated with frequency-specific auditory brainstem response (ABR) thresholds. Rats of both strains were found to have a spontaneous loss of apical hair cells, but this was slightly more pronounced in SH. In SH rats, but not in those of the N strain, there was an age-related progressive loss of outer hair cells in the region 3-5 mm from the stapes, and a slight additional loss at the most basal end. According to available frequency maps, the hair cell loss should correspond to hearing loss between 6 and 24 kHz. In the SH rats hearing loss was not observed in the whole of this range, only at 16 and 20 kHz. It cannot be determined to what extent the localized spontaneous loss of hair cells is caused by vascular factors and what other mechanisms are involved, but vascular factors probably only play a minor role.

Age Factors↗

PubMed1987

Loss of hair cells and threshold sensitivity during prolonged noise exposure in normotensive albino rats.

The relation between hearing loss and loss of hair cells after prolonged exposure to a simulated industrial noise environment was determined in normotensive albino rats. Hearing loss was assessed behaviorally by a conditioned suppression technique and electrophysiologically by auditory brainstem response to pulses of 1/3 octave filtered full cycle sine waves. The ears were analyzed in surface preparations and the hair cells counted. Sixty-two ears from 46 animals were analyzed after 1, 3, 7, and 15 months of exposure. A hearing loss of up to approximately 30 dB was consistently found with minimal loss of hair cells. Between 30 and 60 dB hearing loss there was a fair correspondence between loss of function and loss of hair cells. After 15 months exposure a relatively larger loss of hair cells was observed than expected from decrease of threshold sensitivity. The results indicate the existence of a systematic although not directly proportional relation between hair cell loss and loss of sensitivity during prolonged noise exposure. It is suggested that the correlation between hearing loss and hair cell loss is influenced, e.g., by duration and level of exposure, degree of hearing loss, and location along the basilar membrane.

Animals↗

PubMed1987

Pure tone overstimulation changes the micromechanical properties of the inner hair cell stereocilia.

The effect of permanent noise-induced hearing loss on the auditory brainstem response (ABR) and the micromechanical properties of cochlear hair cell stereocilia in guinea pigs was investigated. The threshold of movement of the stereocilia was measured by applying force from a fluid filled pipette. After exposure to a 1.0 kHz pure tone signal at 105 dB(A) for 72 h the threshold of the ABR was broadly elevated by approximately 50 dB. Inner hair cell stereocilia showed a decrease in threshold while the outer hair cell stereocilia bundles remained unaltered. This effect was localized to the 13-15 mm distance from the stapes corresponding to the region of maximal stimulation. The effect was recorded within 1 h of exposure and remained constant with exposures up to 7 days. Following a one month recovery period from sound exposure, normal threshold values of stereocilia movement were observed, indicating recovery. At this time, swelling of the afferent dendrites beneath the inner hair cells was observed throughout the cochlea together with approximately 30% scattered loss of outer hair cells in the 13 to 15 mm region. The ABR showed some recovery (approximately 20 dB), yet a threshold shift remained.

Acoustic Stimulation↗

PubMed1985

Structure and function of the adult cochlea following prenatal irradiation.

The structure and function of the cochlea of the CBA/CBA mouse were analysed after exposure to single doses of gamma irradiation during embryonic development. Pregnant mice were exposed to 0.5, 1 and 2 Gy, respectively, on either the 12th, 13th, or 16th gestational day. Morphological analyses were performed using light microscopy, scanning electron microscopy and transmission electron microscopy while the function was measured with the auditory brainstem response (ABR) technique. The inner and outer hair cells showed pathological changes of sensory hairs and their anchoring in the cuticular plate. Cytocochleogram counting was performed classifying the morphological changes into three different severity degrees of pathology. A dose dependent pattern of irradiation induced pathology was documented. A threshold shift of about 20 dB was found after irradiation with 2 Gy. A flat loss of ABR curves occurred in animals irradiated on the 12th or 16th gestational days. If the fetuses were exposed on the 13th gestational day the high frequencies resulted in more pronounced damage than the middle and low frequencies.

Animals↗

PubMed1983

Delayed effects of noise on the ear.

The possibility that a delayed onset hearing loss may occur after noise exposure was investigated in 20 normotensive (N) and 20 spontaneously hypertensive (SH) Wistar rats. Half of the rats of each strain were first exposed to noise at 3 months of age and half were first exposed at 12 months of age. All rats were exposed for a total of 3 months to a noise of 100 dB Leq (lin) (a narrowband noise, sweeping from 3 to 30 kHz at a rate of 0.5 Hz). Hearing thresholds were determined with a behavioral technique, and also on certain selected animals by brainstem audiometry, using pulses of 1/3-octave filtered sine waves. One to two weeks after exposure to noise animals had a 30-50 dB hearing loss. The hearing loss remained stable or progressed only slightly in normotensive animals up to 12 months after end of exposure. Generally the SH animals suffered a slight additional loss of hearing over the 12 months after noise exposure. When tested at 18 months of age 3 of the 10 SH rats exposed to noise from 12 to 15 months of age suffered a hearing loss which covered the whole range of observed frequencies from 1.5 to 44 kHz and which had progressed noticeably. These results suggest that while the delayed effects of noise are normally small, exposure might trigger a pronounced hearing loss in subjects with fragile ears.

Age Factors↗

PubMed1983

Damage to sensory hairs of inner hair cells after exposure to noise in rabbits without outer hair cells.

We investigated if the noise-induced damage to the stereocilia of inner hair cells (IHCs) was dependent on the integrity of the outer hair cells (OHCs) in rabbit. Prior to the noise exposure a total loss of OHCs in the basal 1.5 to 2 turns was induced by administration of kanamycin (400 mg/kg for 10 days). This left the IHCs apparently normal as observed in the scanning electron microscope. These animals exhibited a 20-60 dB hearing loss before noise exposure. In spite of this pronounced hearing loss, the fusion and inclination of the IHC stereocilia were extensive in these noise-exposed ears. The stereocilia damage occurred at the same noise exposure and was as prominent or even more pronounced than has been noted in ears exposed to noise only. Under the assumption that kanamycin causes selective destruction of OHCs, the results can be interpreted as evidence that the OHCs facilitate the IHCs at low sound levels without being involved in the process which damages IHC stereocilia at high levels of noise.

Animals↗

PubMed1983

Ultrastructural studies of stereocilia in noise-exposed rabbits.

In rabbits with noise-induced, permanent hearing loss of more than 20 dB the stereocilia of the inner hair cells (IHCs) showed widespread signs of damage: fracturing, folding, fusion, and formation of giant hairs. Damage to the stereocilia on outer hair cells (OHCs) was much less pronounced in corresponding regions. On damaged OHCs the stereocilia were usually missing, except in the apical turn where fusion of stereocilia and formation of giant stereocilia occurred. On both IHCs and OHCs the 'neck' of the stereocilium appeared to be a site of fracture of the actin skeleton. On IHCs the actin cores of the former stereocilia were enclosed in a bulge of the apical cytoplasm to form a giant hair, with portions of the stereocilia projecting from the bulge. Inside the giant hairs profiles of the original stereocilia could be recognized, and these often retained their original circular form at least at the base of a giant hair. In the distal portion of the giant hair the actin filaments frequently formed a single thick bundle where the individual stereocilia could not be distinguished. Material had condensed between the surface membrane enclosing the former stereocilia and the actin cores. A thin kinocilium was often identified on IHCs. together with giant hairs possibly indicating a regenerative activation of the cell. It is suggested that fracture and fusion of stereocilia are due to different pathophysiological mechanisms, and that the actin of damaged cilia may undergo a slow reorganization and regeneration.

Actins↗

PubMed1983

Cochlear morphology in relation to loss of behavioural, electrophysiological, and middle ear reflex thresholds after exposure to noise.

Loss of auditory function was correlated with different pathological findings in the inner ear of the rabbit after 15 or 30 min exposure to high level broad band (2-7 kHz) noise. The ears from animals with post-exposure times ranging from 1 to 23 months were analysed by scanning electron microscopy (SEM). Complete cochleograms with quantification of loss of hair cells and damage to stereocilia were produced. Loss of function was defined by determining behavioural threshold, threshold of auditory brainstem response (ABR) to narrow-band stimuli and threshold of the middle ear muscle reflex (MER). A small scattered loss of OHCs and slight disarray of stereocilia were found in non-exposed ears of young animals, but fusion of IHC cilia was not observed. Normal auditory function was not found in any noise exposed animal with abnormal morphology. A loss of threshold sensitivity of up to about 30-40 dB was noted without loss of hair cells in the corresponding region of the cochlea. The mildest structural damage that correlated to a functional alteration consisted of damage to stereocilia of IHC. This correlated well to the MER threshold shift. In two animals a shift of MER threshold of about 20 dB was the only functional abnormality. In ears with more extensive IHC damage loss of OHCs was also found and these animals had primarily an increase in auditory threshold shift with only a small additional change in MER threshold. It is concluded that in the rabbit and with the methods used the IHC stereocilia are the structures most susceptible to damage by the noise used and that the degree of injury can be fairly well assessed by functional tests of a type that is used also routinely in the audiological clinic.

Animals↗

PubMed1983

Stapedius reflex test, brainstem audiometry and opto-vestibular tests in diagnosis of acoustic neurinomas. A comparison of test sensitivity in patients with moderate hearing loss.

The stapedius reflex test, brainstem audiometry and the opto-vestibular tests for identifying acoustic neurinomas (AN) were evaluated and compared in a study of 21 patients with radiologically or surgically verified AN and a pure tone average not exceeding 60 dB HL. The stapedius reflex test results were interpreted according to the criteria developed at this clinic. The stimuli for the auditory brainstem response (ABR) were 2 kHz haversine waves and 4 kHz square waves. The vestibular examination consisted of a caloric test and the recording of eye-tracking and gaze nystagmus. In the cases studied the stapedius reflex test gave 1 false-negative result and ABR none. The ENG gave 3 false-negatives whereas the results of speech discrimination tests were misleading in no fewer than 1/3 of the cases. The results of the different tests were directly correlated but correlation coefficients did not exceed 0.65. Tumours larger than 15-20 mm showed a different test pattern than those below that size: stapedius reflex response, ABR and caloric response were eliminated and all of these patients had abnormal optomotor function. It is suggested that an optimal routine test procedure should consist of a pure tone audiogram, supplemented by ABR or the stapedius reflex test. Opto-vestibular tests may be of value in a preliminary estimation of tumour size.

Audiometry↗

PubMed1983

Noise-induced hearing loss in shipyard workers with unilateral conductive hearing loss.

In a study of 6500 workers in the shipbuilding industry, 8 subjects were found to have unilateral conductive hearing impairment established before the noise exposure period and without recurrent attacks of acute or chronic infection or clinical diagnosis of otosclerosis. All subjects demonstrated a more pronounced sensorineural hearing loss at 4.0 kHz in the ear with normal middle ear function. The results show the value of even a small permanent conductive hearing loss for protection against noise-induced hearing loss. The observations are discussed in relation to the role of individual variations in sound transmission, the value of the acoustic reflex in noise-induced hearing loss and the efficiency of continuous use of hearing protectors.

Auditory Threshold↗

PubMed1982

Analysis of the avian middle ear muscle contraction by strain gauge and volume and impedance change measures.

1. Aves, unlike mammals, possess only one middle ear muscle, the stapedius. This muscle, which is innervated by a branch of the facial nerve, is exceptional in the respect that it alone exerts its effects on an entire physiological system, viz. the middle ear. 2. Measurements of the physiological effects of this muscle in situ revealed both fast and slow components: the fast component results from the active contractile machinery of the muscle while the slow component derives from certain passive, visco-elastic attachments. 3. The use of middle ear volume and impedance change measures in situ revealed a broader range of the muscle's physiological actions than was predictable by conventional strain gauge recording and/or histochemical studies.

Acoustic Impedance Tests↗

PubMed1982

Acoustic reflex after experimental lesions to inner and outer hair cells.

Chronic effects of noise or kanamycin on the acoustic intra-aural reflex in nonanesthetized rabbits were studied. The intra-aural reflex activity was simultaneously recorded in both ears upon alternate stimulation of the left and the right side. The inner ears were analyzed in scanning and transmission electronmicroscopy. Exposure to bandlimited high-level noise was found to induce extensive deformations in the sensory hairs of the inner hair cells without loss of outer hair cells. Kanamycin caused a degeneration of outer hair cells in the basal 1-2 turns without affecting the morphology of the inner hair cells. The morphological changes, as a function of the location on the basilar membrane, were compared to physiological changes, as a function of frequency. In the noise-exposed animals the threshold of the intra-aural reflex was found to be raised in a frequency range corresponding to the extent of abnormal sensory hairs of the inner hair cells. In the kanamycin-treated animals reflex changes correlated to the loss of outer hair cells. The observations were interpreted as indicating that both types of hair cells cooperate in the activation of the intra-aural reflex in rabbits.

Animals↗

PubMed1982

Auditory thresholds in rats of different age and strain. A behavioral and electrophysiological study.

The auditory sensitivity of albino rats was determined behaviorally by conditioned suppression of licking and electrophysiologically by the auditory brain stem response (ABR). The behavioral thresholds were obtained with 10-Hz frequency-modulated tones, and the ABR with 1/1- or 1/3-octave filtered sine waves. Individual variability, reproducibility of responses and the influence of sex, age and strain were investigated. The behavioral and electrophysiological techniques were compared in animals with noise-induced high-frequency hearing losses. The results showed the highest degree of normal auditory sensitivity to be around 12-24 kHz. The variability in 20 rats was about 15 dB. In young animals, strain and sex had no influence. A deterioration in high-frequency hearing sensitivity was observed in aged hypertensive rats, whereas normotensive ones showed only minimal changes. The thresholds obtained with the electrophysiological (ABR) technique were 10-20 dB higher than those obtained behaviorally. Both techniques (behavioral and 1/3-octave ABR) assess high-frequency hearing loss equally well. It was concluded that the ABR (1/3-octave filtered sine waves) is suitable for the determination of hearing thresholds and the assessment of hearing loss, at least in the high-frequency range. The ABR technique is especially useful in long-term experiments during which thresholds are determined repeatedly.

Age Factors↗

PubMed1982

Noise-induced hearing loss in normotensive and spontaneously hypertensive rats.

Hearing loss was investigated in normotensive (N) and spontaneously hypertensive (SH) rats after prolonged exposure to a simulated industrial noise environment. Exposure was initiated in a group of young rats (3 months old) and continued up to 18 months of age, and in a group of old rats (15 months old) and followed up to 18 months of age. Hearing thresholds were determined behaviorally with a conditioned suppression technique before and after 1, 2, 3 and, for some groups, also after 15 months of exposure. A frequency-modulated noise band sweeping from 3 to 30 kHz at a frequency of 0.5 Hz was presented 10 hours daily at a level of 100 dB Leq(lin). The results showed that young N and SH rats not exposed to noise had identical hearing thresholds. Noise exposure induced a significantly greater hearing loss in SH rats than in N rats; SH animals were more susceptible to noise than were young ones; no difference was seen between males and females. The histology of the inner ears of the rats was examined by light microscopy after the end of the experiment. The young noise-exposed N rats showed no abnormal loss of hair cells in spite of the fact that they sustained hearing losses of 30-40 dB. The SH rats showed a significantly greater loss of hair cells than did the N rats. The stereocilia were found to be fused on a large number of inner hair cells in the basal turns of both N and SH animals. It was concluded that SH and N rats constitute an interesting model for the investigation of biological mechanisms behind individual differences in susceptibility to noise-induced hearing loss.

Age Factors↗

PubMed1982

Susceptibility of the sympathectomized ear to noise-induced hearing loss.

Unilaterally sympathectomiced rats were exposed to 100 dB Leq frequency-modulated noise for 1 month. Normotensive as well as spontaneously hypertensive animals (with a blood pressure of above 200 mmHg) were investigated. Auditory sensitivity was determined by auditory brainstem responses to 1/3-octave filtered sine waves in the frequency range 0.8-20.0 kHz. In addition, morphological analysis was carried out. It was found that the sympathetic innervation to the inner ear of the rat originated in, or passed through the ipsilateral superior cervical ganglion. Sympathectomy did not alter pre-exposure hearing thresholds nor influence the size of the noise-induced hearing loss either in 3 or 11 months old hypertensive rats, or in normotensive rats of 11 months. A slightly smaller loss was seen in the sympathectomized side in young normotensive rats. It was concluded that the sympathetic does not exert a protection of the inner ear against functional disturbances in hypertension, neither during basal metabolic condition nor during extreme conditions, i.e. during noxious noise exposure.

Animals↗

PubMed1982

Protective value of sympathectomy of the ear in noise.

Noise-induced hearing loss was assessed in unilaterally sympathectomized rats exposed one month to 100 dB Leq(lin) noise. The systolic blood pressure of these animals was in the range of 110-140 mmHg. Auditory sensitivity was determined electrophysiologically by brainstem response audiometry to 1/3-octave filtered clicks. The results showed that the loss of sensitivity was about 10 dB smaller (p less than 0.01) on the sympathectomized side. This observation may partially explain the individual differences in susceptibility to noise-induced hearing loss and point towards protective measures and therapeutic possibilities through manipulation of sympathetic activity in the inner ear.

Animals↗