Gender-specific effects of medicinal drugs on hearing levels of older persons

As part of a large-scale study of presbyacusis, responses to a medicinal drug questionnaire from 85 female and 126 male human subjects were analyzed. Medicinal drugs were divided into 35 categories based on their pharmacologic effects. Subjects' ages ranged from 60 to 82 years. At least 10% of subjects reported taking drugs in 14 of 35 categories. Results were significantly different between female and male subjects. In men, none of the 14 categories showed a statistically significant relation to the pure-tone average (PTA) of 500, 1000, 2000, and 4000 Hz. In women, 3 of the 14 categories showed a statistically significant relation to the PTA. First, the average PTA of female subjects taking beta-adrenergic medication was 20 dB higher (poorer) than those not taking beta-adrenergic medication. Second, women taking antihistamine/cold preparations had an average PTA 9 dB higher (poorer) than those not taking antihistamine/cold preparations. Third, the average PTA of women taking calcium-channel blockers (CCBs) was 12 dB lower (better) than those not taking CCBs. In men, however, these drugs produced effects on the PTA of less than 3 dB. Differences between women and men were not explainable by differences in age or hearing level.

Hyperbaric oxygenation with corticoid in experimental acoustic trauma

Among possible therapies after acute acoustic trauma, hyperbaric oxygenation (HBO) combined with corticoid was found effective in several animal studies. Such evidence was obtained for moderate 20-25 dB losses. The aim of this study was to further assess this therapy for noise-induced hearing losses greater than previously examined. Sixty-five ears from thirty-six adult guinea pigs were used. Acoustically evoked responses from intracranial electrodes chronically implanted bilaterally into the ventral cochlear nucleus were used to assess acoustic sensitivity alterations. Trauma sound was a third-octave noise-band around 8 kHz presented bilaterally at 115 dB SPL for 45 min. One control group received no treatment, one group was treated with HBO only and another with corticoid only both starting within one day post-trauma, two groups were treated with both HBO and corticoid starting for one group within one day post-trauma, and for the second group at 6 days post-trauma. Acoustic thresholds were measured between the 6th and the 16th days after acoustic trauma. Animals treated with HBO alone or corticoid alone did not differ from controls. Combined HBO and corticoid therapy provided significant protection from noise-induced loss of auditory thresholds, especially when started one day post-exposure. Hearing loss reduction induced by HBO combined with corticoid was of similar magnitude (about 10-15 dB) as in previous studies although the induced hearing loss was considerably greater (about 40 dB instead of 20-25 dB).

Interleukin-2 affects cochlear function gradually but reversibly

Interleukin-2 (IL-2), one of the chemical mediators produced by helper T cells, activates its target cells via its receptor and induces inflammatory reactions indirectly. In this study, IL-2 was instilled into the round window niche of rats and the electrophysiological effects of inflammation on the inner ear were evaluated by a frequency-specific auditory brainstem response (ABR) technique. ABR threshold curves and intensity-latency (I-L) curves were investigated. In most cases, moderate sensorineural hearing loss (SNHL) was observed in the high-frequency areas (16-31.5 kHz). In the time course investigation of I-L curves, the responses of SNHL type appeared only 1 day after instillation (day 1) gradually becoming more prominent, to become most pronounced on days 5-7. The electrophysiological impairment was reversible within 2 weeks. Differing degrees of responsiveness of effusion production were observed following the instillation of IL-2, varying from pronounced middle ear effusion causing rather severe mixed hearing loss, to complete lack of effusion. Inflammation induced by IL-2 affects cochlear function gradually but reversibly.

Spironolactone blocks glucocorticoid-mediated hearing preservation in autoimmune mice

HYPOTHESIS

Although autoimmune sensorineural hearing loss can be effectively treated with corticosteroids, little is known about how these drugs affect cochlear function. MRL/MpJ-Faslpr autoimmune mice treated with a mineralocorticoid (aldosterone) have previously been shown to have hearing improvement equal to those treated with a glucocorticoid (prednisolone). This suggested that the restoration of hearing with steroids was the result of an effect on sodium transport rather than an antiinflammatory or immunosuppressive role. We hypothesized that corticosteroids reverse autoimmune hearing loss through the mineralocorticoid receptor and that blocking the mineralocorticoid receptor will prevent glucocorticoid effects.

METHODS

Spironolactone, a mineralocorticoid receptor antagonist, was administered to MRL/MpJ-Faslpr autoimmune mice alone or in combination with corticosteroids. The four treatment groups were: spironolactone, spironolactone + aldosterone, spironolactone + prednisolone, and untreated water controls. Auditory brainstem response (ABR) thresholds were recorded before and during treatment (2, 3, and 4 mo) to measure the effect of steroids on hearing decline.

RESULTS

Hearing in spironolactone and spironolactone + prednisolone mice showed progressive decline in hearing similar to water controls. The hearing was preserved in spironolactone + aldosterone mice, presumably as a result of the fact that aldosterone has a higher affinity for the mineralocorticoid receptor than spironolactone. Thus, aldosterone was able to maintain cochlear function with autoimmune disease progression, similar to previous reports of aldosterone treatment effects.

CONCLUSIONS

Spironolactone effectively blocked prednisolone from improving hearing in MRL/MpJ-Faslpr autoimmune mice. This offers evidence that the inner ear mineralocorticoid receptor is the therapeutic target for corticosteroids used to treat autoimmune and sudden sensorineural hearing loss. Pharmacologic treatments that selectively target the mineralocorticoid receptor may provide greater clinical benefit with fewer systemic side effects than prednisone in patients with autoimmune sensorineural hearing loss.

Effects of ketamine on response properties of neurons in the superior paraolivary nucleus of the mouse

The superior paraolivary nucleus (SPON; alternative abbreviation: SPN for the same nucleus in certain species) is a prominent brainstem structure that provides strong inhibitory input to the auditory midbrain. Previous studies established that SPON neurons encode temporal sound features with high precision. These earlier characterizations of SPON responses were recorded under the influence of ketamine, a dissociative anesthetic agent and known antagonist of N-methyl-d-aspartate glutamate (NMDA) receptors. Because NMDA alters neural responses from the auditory brainstem, single unit extracellular recordings of SPON neurons were performed in the presence and absence of ketamine. In doing so, this study represents the first in vivo examination of the SPON of the mouse. Herein, independent data sets of SPON neurons are characterized that did or did not receive ketamine, as well as neurons that were recorded both prior to and following ketamine administration. In all conditions, SPON neurons exhibited contralaterally driven spikes triggered by the offset of pure tone stimuli. Ketamine lowered both evoked and spontaneous spiking, decreased the sharpness of frequency tuning, and increased auditory thresholds and first-spike latencies. In addition, ketamine limited the range of modulation frequencies to which neurons phase-locked to sinusoidally amplitude-modulated tones.

The sensitivity to 3,3'-iminodipropionitrile differs for high- and midfrequency hearing loss in the developing rat

3,3'-Iminodipropionitrile (IDPN) has been demonstrated to produce a loss of hearing following both neonatal and adult exposures. Adult exposure induces a full spectrum hearing loss, whereas early postnatal exposure produces a high-frequency loss only. The purpose of this work was to delineate the period of development during which the rat becomes sensitive to the full ototoxic effects of IDPN. Primiparous Long Evans rats or their offspring were exposed to either saline or 300 mg/kg IDPN for three consecutive days. Ages of exposure were as follows: gestational days 15-17 or postnatal days (PND) 1-3, 5-7, 15-17, 20-22, 25-27, 30-32, 40-42, or 70-72. All animals were tested as adults for auditory thresholds to 5- and 40-kHz tones using reflex modification audiometry. Results demonstrate that adult-like susceptibility to IDPN was not reached until approximately PND 30-32. Early exposures (PND 5-22) to IDPN will induce a highfrequency selective hearing loss, sparing the lower frequency. Prenatal or early neonatal (PND 1-3) IDPN exposure resulted in a high degree of mortality (> 70%). The long period of time between the susceptible period for the high frequency (PND 5-7) and the lower frequency (PND 30-32) does not correspond to the basal to apical ontogenic profile of any one physiological or anatomical process. These data suggest either a unique site of action for IDPN in the cochlea or the possibility of two different mechanisms, one operating at early postnatal ages and one at later ages.

Characterization of the effects of N-hydroxy-IDPN on the auditory, vestibular, and olfactory systems in rats

The mechanism of neurotoxicity of 3,3'-iminodipropionitrile (IDPN) has been widely debated, with either the parent compound or putative metabolites implicated in various studies. The N-hydroxylated form of IDPN (HO-IDPN) has been reported to cause the excitation with choreiform and circling (ECC) syndrome in rats at doses approximately one-eighth of that required to cause comparable signs in rats treated with IDPN. Because of the similarity of symptoms induced by HO-IDPN and IDPN, we investigated the effect of HO-IDPN on other aspects of the nervous system affected by IDPN, specifically the auditory, vestibular, and olfactory systems. In addition, ECC symptoms were quantified to replicate the previous findings. HO-IDPN was administered ip in saline for 3 consecutive days to two different cohorts of young adult male Sprague-Dawley rats. The first cohort (60, 80, 100, and 120 mg/kg; n = 2/group, except for the 120 mg/kg group, where n = 1) was used in a dose range-finding study. After making the neurobehavioral assessments, animals were sacrificed for olfactory mucosal histopathology. Based on the outcome of the first study, the second cohort (n = 10/group) received saline or HO-IDPN at 100 mg/kg/day for 3 consecutive days. Two animals from each of these groups were sacrificed for olfactory mucosal histopathology; the remaining animals were tested for neurobehavioral effects 3 weeks after the last dose. Animals in the second cohort lost approximately 8% of their pretreatment body weight. All rats receiving the 100 mg/kg/day dose of HO-IDPN (and the rat receiving 120 mg/kg/day) developed the ECC syndrome and signs of vestibular dysfunction within 4 days after the last dose. HO-IDPN caused a large decrease in the acoustic startle response and markedly elevated auditory thresholds at all frequencies tested. The threshold for the ECC syndrome and olfactory mucosal damage was 100 mg/kg. These studies extend previous findings on the neurotoxicity of HO-IDPN and point to the need for determining whether HO-IDPN is an in vivo metabolite of IDPN.

Serotonin Reuptake Inhibitors in Auditory Processing Disorders in Elderly Patients: Preliminary Results

OBJECTIVE/HYPOTHESIS

One mechanism associated with degeneration in the elderly is the decrease of neurotransmitters. In the central auditory pathway serotonin, can be found from cochlear nucleus to the auditory cortex, and it constitutes one of the most important neuromodulatory circuits in hearing processing. The present study analyzed the action of citalopram, a selective inhibitor of serotonin reuptake, in aged patients with normal to moderate sensorineural hearing loss (HL) and low performance on auditory processing.

STUDY DESIGN/METHOD

Prospective, double-blind, randomized, placebo-controlled study. Thirty-eight selected patients were randomly divided into two groups. Nineteen patients made up group A and received placebo for 60 days. Nineteen patients of Group B received 20 mg per day of citalopram for 60 days. Hearing evaluation was performed initially and after 60 days and included pure-tone audiometry, speech discrimination test (SDT), emittanciometry (acoustic impedance audiometry), identification of synthetic sentences with an ipsilateral competitive message (SSI/ICM), tests of pitch-pattern sequences (PPS), and the staggered spondaic words test (SSW).

RESULTS

Comparisons of tests of auditory processing pre- and posttreatment in each group showed a statistical improvement in performance on all tests in group B after 2 months of therapy. Comparisons pre- and posttreatment between groups showed that patients who received citalopram presented statistically significantly better results in the SSI/ICM test (P < .0001) after treatment. The same comparison in results for the PPS test and the SSW test revealed a tendency (P = .09 and 0.058, respectively) toward better performance in the group receiving citalopram.

CONCLUSION

These preliminary results suggest that the use of citalopram can have a positive impact on auditory processes in elderly patients with low performance in auditory process.

Investigation of the ototoxic effects of interferon alpha2A on the mouse cochlea

This prospective randomized study investigates the possible toxic effects of interferon (IFN) alpha2A on the mouse cochlea. Thirty-six albino Swiss mice that were randomly assigned to 3 groups underwent baseline auditory brain stem response testing bilaterally to objectively assess baseline hearing levels. The first group received a single dose of 50,000 units, and the second group received 100,000 units of IFN-alpha2A intraperitoneally, whereas the third group was given no medication. Repeat auditory brain stem response testing revealed a significant rise in mean baseline peak equivalent sound pressure level thresholds in the groups that received IFN (P < 0.001). Histologically, the cochleae of mice that received IFN had a decreased number of fibroblasts in the spiral limbus, as well as prominent cytoplasmic vacuolation of these cells, compared with control animals. Loss of hair cells was not observed. It is possible that reversible biochemical and metabolic changes in the cochlea, rather than morphologic abnormalities, manifest IFN ototoxicity.

Effects of diazepam and triazolam on auditory and visual thresholds and reaction times in the baboon

Adult male baboons were trained on a psychophysical procedure that measured detection thresholds and reaction times for pure tone and white light stimuli. Intramuscular injections of diazepam or triazolam were given 30 min before session onset; stimulus intensity was randomly varied from trial to trial, and four to five estimates of sensory thresholds and reaction times were obtained throughout each session. Diazepam produced dose-related elevations of both auditory and visual thresholds and reaction times. Effects of a single high dose of diazepam were apparent 4-5 days after administration. Triazolam was approximately 100 times more potent than diazepam in elevating reaction times and visual thresholds, but did not elevate auditory thresholds. There were no residual effects of triazolam on the day after dosing. These results suggest that diazepam and triazolam produce qualitatively similar effects on basic psychophysical function, but that they can be differentiated on the basis of sensory modality changes and post-drug recovery time.

Effects of chronic carbon disulfide inhalation on sensory and motor function in the rat

Chronic carbon disulfide (CS2) exposure produces debilitating motor, sensory and neuropsychiatric consequences in humans. Sensory, especially auditory, tests have been considered for indexing early intoxication. This study examines effects of chronic CS2 exposure in rat upon auditory and neuromuscular function using reflex modulation audiometry to test the feasibility of using pure tone detection thresholds as such an index. This method is sensitive to the differential effects of toxicants upon acoustic and neuromuscular functioning. Rats were tested before, during and after five or 12 weeks of 500 ppm CS2 inhalation, six h/day, five days/week. Neuromuscular integrity, reflected by baseline startle amplitude, decreased 50% after five weeks and 67% following 12 weeks of CS2 exposure; recovery to 70% of preexposure values occurred on the fourth postexposure week. Twelve weeks of CS2 inhalation had no significant effect upon acoustic thresholds. Pure tone detection thresholds, therefore, do not appear adequate to index early CS2 exposure levels in the rat, as severe neuromuscular compromise occurred at a time when acoustic thresholds remained stable.

Protection against acoustic trauma by direct application of D-methionine to the inner ear

CONCLUSION

The findings from this study extend the use of the local application of D-methionine (D-met) to protect against acoustic trauma and demonstrate that D-met slowly diffuses from the perilymph.

OBJECTIVES

The objectives of the study were to determine the effect of D-met on auditory function and morphology after acoustic trauma and to measure the concentration of D-met in perilymph.

METHODS

Auditory thresholds were determine before, immediately after, and 24 h after acoustic trauma. Cochleae were analyzed using immunocytochemistry for c-Fos, TUJI, and cytochrome c. The concentration of D-met was determined from perilymph.

RESULTS

Protection against acoustic trauma (immediately and 24 h post trauma) on auditory brainstem thresholds was found at a time when the concentration of D-met in perilymph showed a fivefold increase above basal levels. The local application of D-met to the guinea pig cochlea results in elevated D-met concentrations that are maintained in the perilymph for at least 24 h.

Efeito do metilfenidato no processamento auditivo em crianças e adolescentes com transtorno do deficit de atenção/hiperatividade

OBJETIVO: Comparar o desempenho em teste de avaliação do processamento auditivo (PA) num grupo de crianças e adolescentes com transtorno do déficit de atenção e hiperatividade (TDAH) pré e pós-metilfenidato. MÉTODO: Foram aplicados testes comportamentais padronizados de avaliação do PA em 29 indivíduos com TDAH na faixa etária de 7 a 15 anos, de ambos os sexos. Utilizou-se um grupo de comparação de 29 indivíduos sem déficit de atenção, com e sem transtornos de aprendizado. RESULTADOS: O grupo com TDAH apresentou desempenho nos testes de PA semelhante ao grupo controle sem transtornos do aprendizado sendo seus resultados ainda melhores na ocasião pós-medicação. O grupo sem déficit de atenção e com problemas de aprendizagem apresentou o pior desempenho nos testes de PA e o grupo sem déficit de atenção e sem problemas de aprendizagem foi o que apresentou o melhor desempenho. CONCLUSÃO: O teste de PA não permitiu diferenciar portadores de TDAH de controles pareados; o metilfenidato se associou a melhora do desempenho nos testes de PA nos portadores de TDAH.

Effects of noise and salicylate on auditory evoked-response thresholds in the chinchilla

The combined effects of noise and sodium salicylate on auditory sensitivity were examined in the chinchilla. Sensitivity was monitored by recording the evoked response recorded with an electrode implanted in the inferior colliculus. Sodium salicylate (300 mg/kg/day), an octave band of noise centered at 500 Hz (80 or 105 dB SPL), or both of these agents were delivered for 15 days. Threshold testing was performed at 7 frequencies before, during, and after exposure to the ototraumatic agent(s). The salicylate alone caused an average temporary threshold shift of less than 10 dB and essentially no permanent shift. Animals exposed to noise alone had temporary and permanent threshold shifts which were not significantly different from those observed in animals exposed to noise plus salicylate. The data suggest that a single daily injection of sodium salicylate, resulting in peak serum salicylate concentrations of 28 to 34 mg% 2 to 4 hours after delivery, does not exacerbate the temporary or permanent threshold shifts induced by 15-day, 24-hour-per day exposure to either a moderate- or high-level, low-frequency noise. A second series of experiments utilizing a higher dose of salicylate (450 mg/kg/day) was not completed due to a high mortality rate among subjects that received salicylate and were exposed to noise. This result was consistent with other recent examinations of the interaction of these agents.

Effects of aspirin on human auditory filters

Auditory filter shapes were measured in eight male volunteers with normal hearing, using a notched-noise forward-masking paradigm and a signal frequency of 4 kHz. The measurements were made under three conditions: after listeners had taken eight doses of three 320 mg aspirin tablets every six hours; after an identical schedule of placebo ingestion; and one week after testing in the first two conditions had been completed. Half of the listeners did the placebo condition first, and half did the aspirin condition first. Aspirin and placebo were administered double-blind, and testing took place approximately one hour after the last dose. Filter shapes were significantly broader in the aspirin condition than in the placebo and post-test conditions, indicating that even a modest dose affects auditory frequency selectivity. Two-point measures of growth of masking did not differ significantly between conditions.

Investigation of ototoxic effects of Taxol on a mice model

OBJECTIVE

To investigate the effects of taxol on the inner ear in a mice model.

METHODS

This study was performed on 112 ears of 56 albino Swiss mice. All animals underwent baseline auditory brainstem response (ABR) testing bilaterally and baseline Peak Equivalent Sound Pressure Levels (PESPLs) were obtained. The mice were randomly assigned to seven groups consisting of one control and six study groups. The control group received no medications while the mice in groups 1-6 received 1 x 60, 1 x 20, 2 x 20, 3 x 20, 4 x 20 and 5 x 20 mg/kg taxol intraperitoneally. Control ABR assessments were performed 3 weeks after the last dose. The animals were then sacrificed while still anaesthetised and the bullae (cochleae included) were dissected from their temporal bones. Haematoxylin-eosin and Masson's trichrome stains were used to demonstrate connective tissue, and periodic acid Schiff (PAS) stain was used to highlight epithelial elements.

RESULTS

Significant decreases in the hearing levels were observed in all the groups which received taxol. No correlation was observed between the dose given and the degree of hearing loss. The sections from the control group showed no histopathologic abnormalities while the sections from the study groups demonstrated vacuolisation in the epithelial cells of the spiral limbus, and the stria vascularis, vacuolisation of the fibroblasts and decreasing the number of the fibroblasts in the spiral limbus.

CONCLUSION

Taxol causes mild to moderate sensorineural hearing loss in mice. Histopathologically, there were degenerative changes in the cochlea resembling the ones that take place in salisylate and interferon alpha 2a ototoxicity which are thought to be reversible. There was no sensory cell loss. The hearing loss begins with doses less than or equal to 20mg/kg and is not dose dependent after this dose. Hearing monitorisation with audiologic evaluation is strongly recommended before and during the use of the drug in human subjects.

Similar half-octave TTS protection of the cochlea by xylazine/ketamine or sympathectomy

Cochlear efferents, sympathetic control and stress conditions have been shown to influence sound-induced hearing loss. These factors are also known to be modified by sedation/anesthesia. We tested here the effect of sedation/anesthesia on temporary threshold shift (TTS) compared to that in the same awake animals. The effect of sympathectomy was also tested. We employed awake guinea pigs with a chronically implanted electrode on the round window of each of the cochleae. Each ear was tested for its sensitivity to TTS induced by a 1 min or a 10 min exposure to an 8 kHz pure tone at 96 dB sound pressure level. After an intramuscular injection of xylazine or ketamine together with xylazine, TTS at half-octave frequencies was reduced compared to that in awake animals. The second half-octave frequencies were less affected. This specific pattern of protection was also observed here after surgical ablation of a superior cervical ganglion. The data lead to the speculation that protection from TTS under sedation/anesthesia might be due to diminished sympathetic influence. Xylazine is a pre-synaptic alpha2-adrenoreceptor agonist which blocks noradrenaline release from the sympathetic system. Ketamine is a N-methyl-D-aspartic acid receptor antagonist which could reduce glutamate excitotoxicity as well as reduce sympathetic activity.

Topical gentamicin and ethacrynic acid: effects on cochlear function

OBJECTIVE

To determine whether concurrent intravenous administration of the loop diuretic ethacrynic acid potentiates the toxicity of the aminoglycoside antibiotic gentamicin applied topically on the round window.

STUDY DESIGN

The authors studied the effects on cochlear sensitivity of co-administered intracardiac ethacrynic acid (40 mg/kg) and high-dose topical gentamicin solution (100%) applied to the round window. Comparisons were made with animals receiving ethacrynic acid plus systemic gentamicin (100 mg/kg); topical gentamicin alone; systemic gentamicin alone; and intravenous ethacrynic acid alone.

METHODS

Experiments were carried out on pigmented guinea pigs weighing 400 to 500 g. Changes in cochlear function were characterized by monitoring shifts in compound action potential (CAP) thresholds by use of chronic indwelling electrodes implanted at the round window, vertex, and contralateral mastoid.

RESULTS

After 20 days animals receiving ethacrynic acid in combination with topical gentamicin to the round window failed to demonstrate a significant deterioration in cochlear sensitivity, whereas all animals receiving systemic gentamicin plus ethacrynic acid experienced profound increases in CAP thresholds.

CONCLUSIONS

This study supports the contention that ethacrynic acid potentiates aminoglycoside ototoxicity by facilitating the entry of the antibiotics from the systemic circulation into the endolymph. In addition, this study answers important clinical concerns regarding the safety of the use of topical aminoglycoside agents in combination with loop diuretics.

Tetraethylammonium effects on cochlear potentials in the guinea pig

Voltage-dependent K+ channels in the basolateral membrane of hair cells in guinea-pig cochlea might contribute to the non-linear current-voltage relationships in these hair cells and, thereby, to generation of the extracellular summating potential (SP). To evaluate the role of K+ channels in the generation of the SP the perilymphatic perfusion technique was used to introduce the K(+)-channel blocker tetraethylammonium (TEA) into the cochlea. Sound-evoked cochlear potentials were measured subsequently. Without blocking nerve activity TEA induced reversible shifts of the SP in the negative direction, irrespective of whether we recorded from scala vestibuli or scala tympani. Shifts in the negative direction were probably due to TEA acting directly on the afferent fibres, since removal of nerve activity by the potent Na(+)-channel blocker tetrodotoxin (TTX) prevented TEA from shifting the SP in the negative direction. Once nerve activity had been removed by TTX, administration of TEA caused a small decrease in the magnitude of the SP, both in scala vestibuli and in scala tympani, irrespective of its polarity. The decrease was significant for the highest test frequencies only (8-12 kHz), and completely reversible. The rapidly activated K+ channel in the inner hair cell (IHC) is probably blocked by TEA and this blocking might be responsible for the small decrease in magnitude of the SP. The asymmetric contribution from this K+ channel to the IHC's current-voltage relationship seems to be only partly responsible for the generation of the SP, since blocking of this K+ channel with TEA caused relatively small decreases in the amplitude of the SP. TEA did not affect the endocochlear potential.

Onset and offset responses from inferior colliculus and auditory cortex to paired noisebursts: inner hair cell loss

Thirteen adult chinchillas were anesthetized with ketamine/acepromazine and tungsten electrodes were placed in the right inferior colliculus (IC) and auditory cortex (AC). A reference electrode was implanted in the anterior cranium. Following a recovery period, AC and IC responses to left ear stimulation were obtained from unanesthetized animals resting in a passive restraint inside a sound-attenuating booth. After the first recording, the animals were injected with carboplatin (75 mg/kg). Four to five weeks later, a second recording was made. Stimuli were 50 ms duration (0 ms rise and fall time), 80 dB SPL noiseburst pairs. In one group of seven animals, the gap time varied from 1 to 64 ms. In a second group of six animals, the gap time ranged from 0.25 to 64 ms in order to determine gap threshold. The responses were amplified (10000x) and filtered from 10 to 3000 Hz. Each response was the average of 100 stimulus presentations. The dependent variables were the latency of the initial positive peak and the amplitude of the response from initial positive peak to the following negativity. Following the second recording, all animals were sacrificed, the cochleas harvested, and cochleograms were obtained by counting outer hair cells (OHCs) and inner hair cells (IHCs). For the onset response to the second noiseburst of each pair, response amplitudes decreased and latencies increased with decreasing gap time. For a 64 ms gap time, the IC response approached the latencies and amplitudes seen for the onset response to the single noiseburst or first noiseburst in the pair (herein called "baseline" values), while the AC response latency approached baseline values, but AC amplitude did not. Interestingly, the offset responses to the first noiseburst were not present at gaps of less than 8 ms, while the onset responses to the second noiseburst were typically present at gaps of 1-2 ms. Cochleograms revealed a normal (or near-normal) complement of OHCs, and IHC loss averaging roughly 30-40% in apical regions and increasing to 60-70% in more basal regions (compared to normative data). Following carboplatin, the latencies of IC onset responses were delayed by several tenths of a millisecond, with the greatest pre- versus post-carboplatin latency shift occurring at short noiseburst gaps. AC response latencies were largely unaffected by carboplatin. IC onset response amplitudes were reduced following carboplatin, while AC onset responses were similar to pre-carboplatin values. IC offset response latencies to the first noiseburst were increased post-carboplatin, while AC offset response latencies varied little from pre-carboplatin values. IC and AC offset response amplitudes to the first noiseburst were decreased post-carboplatin.

Administration of amitriptyline attenuates noise-induced hearing loss via glial cell line-derived neurotrophic factor (GDNF) induction

Antidepressant treatments have been described to induce neurotrophic factors (NTFs) and reverse the cell loss observed in rodent stress models. Amitriptyline (AT), a tricyclic antidepressant agent, has been reported in recent studies to induce glial cell line-derived neurotrophic factor (GDNF) synthesis and release in rat C6 glioblastoma cells. GDNF has shown protection against acoustic trauma in previous studies. Therefore, we investigated whether AT could induce GDNF synthesis in the cochlea and attenuate cochlea damage against acoustic trauma. We used Hartley guinea pigs and injected AT (30 mg/kg) or saline into the peritoneum. Subjects were exposed to 117 dB SPL octave band noise centered at 4 kHz for 24 h. Noise-induced hearing loss (NIHL) was assessed with auditory brain stem response (ABR) at 4, 8 and 16 kHz measured prior to the injection, 3 days and 7 days after noise exposure. For histological assessment, we observed the sensory epithelium using a surface preparation technique and assessed the quantitative hair cell (HC) damage. We evaluated GDNF synthesis with or without intense noise exposure at 3, 12 and 24 h after the administration of AT in the cochlea using Western blot analysis. GDNF expression was shown 3 h and 12 h after the injection without noise, whereas with noise the GDNF expression lasted for 24 h. The AT-administrated group showed significantly reduced ABR threshold shift and less HC damage than the saline-administrated group. These findings suggest that the administration of AT-induced GDNF levels in the cochlea and attenuated cochlea damage from NIHL.

Assessment of central auditory processing in a group of workers exposed to solvents

CONCLUSION

Despite having normal hearing thresholds and speech recognition thresholds, results for central auditory tests were abnormal in a group of workers exposed to solvents. Workers exposed to solvents may have difficulties in everyday listening situations that are not related to a decrement in hearing thresholds. A central auditory processing disorder may underlie these difficulties.

OBJECTIVE

To study central auditory processing abilities in a group of workers occupationally exposed to a mix of organic solvents.

MATERIALS AND METHODS

Ten workers exposed to a mix of organic solvents and 10 matched non-exposed workers were studied. The test battery comprised pure-tone audiometry, tympanometry, acoustic reflex measurement, acoustic reflex decay, dichotic digit, pitch pattern sequence, masking level difference, filtered speech, random gap detection and hearing-in-noise tests.

RESULTS

All the workers presented normal hearing thresholds and no signs of middle ear abnormalities. Workers exposed to solvents had lower results in comparison with the control group and previously reported normative data, in the majority of the tests.

Astragaloside IV attenuates impulse noise-induced trauma in guinea pig

CONCLUSION

These results suggest that the beneficial effect of astragaloside IV on impulse noise-induced hearing loss may be due to its ability to inhibit inducible nitric oxide synthase (iNOS) and prevent the formation of reactive nitrogen species (RNS).

OBJECTIVE

Astragaloside IV is the major active constituent of Astragalus membranaceus, which has been widely used for the treatment of diseases in China due to its antioxidant properties. iNOS and RNS are involved in damage induced by impulse noise trauma. The purpose of the present study was to investigate if astragaloside IV has the potential to reduce cochlear damage from impulse noise.

METHODS

Guinea pigs in the experimental group were administered astragaloside IV intragastrically. Auditory thresholds were assessed by sound-evoked auditory brainstem response (ABR) at click and tone bursts of 8, 16 and 32 kHz, 72 h before and after exposure to impulse noise. iNOS and nitrotyrosine were determined immunohistochemically. Hair cell damage was analyzed by scanning electron microscopy.

RESULTS

Astragaloside IV significantly reduced ABR deficits, reduced hair cell damage, and decreased the expression of iNOS and RNS formation.