Electrophysiological study of the effect of sodium salicylate upon the cochlea

Safety Assessment of Salicylic Acid, Butyloctyl Salicylate, Calcium Salicylate, C12–15 Alkyl Salicylate, Capryloyl Salicylic Acid, Hexyldodecyl Salicylate, Isocetyl Salicylate, Isodecyl Salicylate, Magnesium Salicylate, MEA-Salicylate, Ethylhexyl Salicylate, Potassium Salicylate, Methyl Salicylate, Myristyl Salicylate, Sodium Salicylate, TEA-Salicylate, and Tridecyl Salicylate

Salicylic Acid is an aromatic acid used in cosmetic formulations as a denaturant, hair-conditioning agent, and skin-conditioning agent—miscellaneous in a wide range of cosmetic products at concentrations ranging from 0.0008% to 3%. The Calcium, Magnesium, and MEA salts are preservatives, and Potassium Salicylate is a cosmetic biocide and preservative, not currently in use. Sodium Salicylate is used as a denaturant and preservative (0.09% to 2%). The TEA salt of Salicylic Acid is used as an ultraviolet (UV) light absorber (0.0001% to 0.75%). Several Salicylic Acid esters are used as skin conditioning agents—miscellaneous (Capryloyl, 0.1% to 1%; C12–15 Alkyl, no current use; Isocetyl, 3% to 5%; Isodecyl, no current use; and Tridecyl, no current use). Butyloctyl Salicylate (0.5% to 5%) and Hexyldodecyl Salicylate (no current use) are hair-conditioning agents and skin-conditioning agents—miscellaneous. Ethylhexyl Salicylate (formerly known as Octyl Salicylate) is used as a fragrance ingredient, sunscreen agent, and UV light absorber (0.001% to 8%), and Methyl Salicylate is used as a denaturant and flavoring agent (0.0001% to 0.6%). Myristyl Salicylate has no reported function. Isodecyl Salicylate is used in three formulations, but no concentration of use information was reported. Salicylates are absorbed percutaneously. Around 10% of applied salicylates can remain in the skin. Salicylic Acid is reported to enhance percutaneous penetration of some agents (e.g., vitamin A), but not others (e.g., hydrocortisone). Little acute toxicity (LD50 in rats; >2 g/kg) via a dermal exposure route is seen for Salicylic Acid, Methyl Salicylate, Tridecyl Salicylate, and Butyloctyl Salicylate. Short-term oral, inhalation, and parenteral exposures to salicylates sufficient to produce high blood concentrations are associated primarily with liver and kidney damage. Subchronic dermal exposures to undiluted Methyl Salicylate were associated with kidney damage. Chronic oral exposure to Methyl Salicylate produced bone lesions as a function of the level of exposure in 2-year rat studies; liver damage was seen in dogs exposed to 0.15 g/kg/day in one study; kidney and liver weight increases in another study at the same exposure; but no liver or kidney abnormalities in a study at 0.167 g/kg/day. Applications of Isodecyl, Tridecyl, and Butyloctyl Salicylate were not irritating to rabbit skin, whereas undiluted Ethylhexyl Salicylate produced minimal to mild irritation. Methyl Salicylate at a 1% concentration with a 70% ethanol vehicle were irritating, whereas a 6% concentration in polyethylene glycol produced little or no irritation. Isodecyl Salicylate, Methyl Salicylate, Ethylhexyl (Octyl) Salicylate, Tridecyl Salicylate, and Butyloctyl Salicylate were not ocular irritants. Although Salicylic Acid at a concentration of 20% in acetone was positive in the local lymph node assay, a concentration of 20% in acetone/olive oil was not. Methyl Salicylate was negative at concentrations up to 25% in this assay, independent of vehicle. Maximization tests of Methyl Salicylate, Ethylhexyl Salicylate, and Butyloctyl Salicylate produced no sensitization in guinea pigs. Neither Salicylic Acid nor Tridecyl Salicylate were photosensitizers. Salicylic Acid, produced when aspirin is rapidly hydrolyzed after absorption from the gut, was reported to be the causative agent in aspirin teratogenesis in animals. Dermal exposures to Methyl Salicylate, oral exposures to Salicylic Acid, Sodium Salicylate, and Methyl Salicylate, and parenteral exposures to Salicylic Acid, Sodium Salicylate, and Methyl Salicylate are all associated with reproductive and developmental toxicity as a function of blood levels reached as a result of exposure. An exposure assessment of a representative cosmetic product used on a daily basis estimated that the exposure from the cosmetic product would be only 20% of the level seen with ingestion of a “baby” aspirin (81 mg) on a daily basis. Studies of the genotoxic potential of Salicylic Acid, Sodium Salicylate, Isodecyl Salicylate, Methyl Salicylate, Ethylhexyl (Octyl) Salicylate, Tridecyl Salicylate, and Butyloctyl Salicylate were generally negative. Methyl Salicylate, in a mouse skin-painting study, did not induce neoplasms. Likewise, Methyl Salicylate was negative in a mouse pulmonary tumor system. In clinical tests, Salicylic Acid (2%) produced minimal cumulative irritation and slight or no irritation(1.5%); TEA-Salicylate (8%) produced no irritation; Methyl Salicylate (>12%) produced pain and erythema, a 1% aerosol produced erythema, but an 8% solution was not irritating; Ethylhexyl Salicylate (4%) and undiluted Tridecyl Salicylate produced no irritation. In atopic patients, Methyl Salicylate caused irritation as a function of concentration (no irritation at concentrations of 15% or less). In normal skin, Salicylic Acid, Methyl Salicylate, and Ethylhexyl (Octyl) Salicylate are not sensitizers. Salicylic Acid is not a photosensitizer, nor is it phototoxic. Salicylic Acid and Ethylhexyl Salicylate are low-level photoprotective agents. Salicylic Acid is well-documented to have keratolytic action on normal human skin. Because of the possible use of these ingredients as exfoliating agents, a concern exists that repeated use may effectively increase exposure of the dermis and epidermis to UV radiation. It was concluded that the prudent course of action would be to advise the cosmetics industry that there is a risk of increased UV radiation damage with the use of any exfoliant, including Salicylic Acid and the listed salicylates, and that steps need to be taken to formulate cosmetic products with these ingredients as exfoliating agents so as not to increase sun sensitivity, or when increased sun sensitivity would be expected, to include directions for the daily use of sun protection. The available data were not sufficient to establish a limit on concentration of these ingredients, or to identify the minimum pH of formulations containing these ingredients, such that no skin irritation would occur, but it was recognized that it is possible to formulate cosmetic products in a way such that significant irritation would not be likely, and it was concluded that the cosmetics industry should formulate products containing these ingredients so as to be nonirritating. Although simultaneous use of several products containing Salicylic Acid could produce exposures greater than would be seen with use of baby aspirin (an exposure generally considered to not present a reproductive or developmental toxicity risk), it was not considered likely that consumers would simultaneously use multiple cosmetic products containing Salicylic Acid. Based on the available information, the Cosmetic Ingredient Review Expert Panel reached the conclusion that these ingredients are safe as used when formulated to avoid skin irritation and when formulated to avoid increasing the skin's sun sensitivity, or, when increased sun sensitivity would be expected, directions for use include the daily use of sun protection.

Erythromycin-Induced Ototoxicity: Case Report

Objective:

To report a case of erythromycin-induced ototoxicity and to discuss the occurrence of this event.

Case Summary:

A 26-year-old woman was admitted to the medical intensive care unit with a two-day history of progressive shortness of breath, high-grade fever, cough, and pleuritic chest pain. Arterial blood gases on room air showed severe hypoxemia, and a chest X-ray revealed right lower-lobe infiltrates. Provisional diagnosis was atypical pneumonia, for which erythromycin lactobionate 1 g q6h iv was administered. All other chronic medications were maintained at the same dosage and frequency. All laboratory work remained stable. After 36 hours, the patient developed sensorineural hearing loss. Erythromycin was stopped immediately. After 24 hours, there was subjective improvement of hearing, with complete return to pretreatment levels in 72 hours.

Discussion:

A review of the literature showed only 40 reported cases of reversible ototoxicity, mainly with high dosages of erythromycin (4 g/d).

Conclusions:

High-dose erythromycin therapy can cause reversible sensorineural hearing impairment. Treatment with erythromycin 4 g/d should be reserved for immunosuppressed patients with Legionnaires' disease and patients with Legionella endocarditis. Patients should have a baseline audiogram and regular monitoring for subjective evidence of sensorineural hearing loss, and the drug should be discontinued if ototoxicity is suspected.

Too much of a good thing: long-term treatment with salicylate strengthens outer hair cell function but impairs auditory neural activity

Aspirin has been extensively used in clinical settings. Its side effects on auditory function, including hearing loss and tinnitus, are considered as temporary. A recent promising finding is that chronic treatment with high-dose salicylate (the active ingredient of aspirin) for several weeks enhances expression of the outer hair cell (OHC) motor protein (prestin), resulting in strengthened OHC electromotility and enhanced distortion product otoacoustic emissions (DPOAE). To follow up on these observations, we carried out two studies, one planned study of age-related hearing loss restoration and a second unrelated study of salicylate-induced tinnitus. Rats of different strains and ages were injected with salicylate at a dose of 200 mg/kg/day for 5 days per week for 3 weeks or at higher dose levels (250-350 mg/kg/day) for 4 days per week for 2 weeks. Unexpectedly, while an enhanced or sustained DPOAE was seen, permanent reductions in the amplitude of the cochlear compound action potential (CAP) and the auditory brainstem response (ABR) were often observed after the chronic salicylate treatment. The mechanisms underlying these unexpected, permanent salicylate-induced reductions in neural activity are discussed.

Salicylate ototoxicity and its implications for cochlear microphonic potential generation

Salicylic acid causes a reversible sensori-neural hearing loss. Its ototoxicity is probably related to its effect on prestin, the motor protein of the outer hair cells. In order to gain further insight into the mechanism and implications of its ototoxicity, auditory nerve brainstem evoked responses, compound action potentials of the auditory nerve, distortion product otoacoustic emissions, and cochlear microphonic potentials (CM) and vestibular evoked potentials were recorded before and after systemic salicylate administration. These responses were depressed, except for the CM and the vestibular evoked potential. This result and additional considerations provide evidence that the extracellularly recorded CM does not represent the summation of intracellular outer hair cell receptor potentials. It is possible that the CM reflects an early stage of mechano-electrical transduction by the outer hair cells, before the activation of the cochlear amplifier and the later stages of transduction.

Auditory sensori-neural alterations induced by salicylate

Early after the development of aspirin, almost 150 years ago, its auditory toxicity has been associated with high doses employed in the treatment of chronic inflammatory diseases. Tinnitus, loss of absolute acoustic sensitivity and alterations of perceived sounds are the three auditory alterations described by human subjects after ingestion of large doses of salicylate. They develop over the initials days of treatment but may then level off, fluctuate or decrease, and are reversible within a few days of cessation of treatment. They may also occur within hours of ingestion of an extremely large dose. Individual subjects vary notably as to their susceptibility to salicylate-induced auditory toxicity. Tinnitus may be the first subjective symptom, and is often described as a continuous high pitch sound of mild loudness. The hearing loss is slight to moderate, bilaterally symmetrical and affects all frequencies with often a predominance at the high frequencies. Alterations of perceived sounds include broadening of frequency filtering, alterations in temporal detection, deterioration of speech understanding and hypersensitivity to noise. Behavioral conditioning of animals provides evidence for mild and reversible hearing loss and tinnitus, similar to those observed in humans. Anatomical examinations revealed significant alterations only at outer hair cell lateral membrane. Electrophysiological investigations showed no change in endocochlear resting potential, and small changes in the compound sensory potentials, cochlear microphonic and summating potential, at low acoustic levels. Measures of cochlear mechanical responses to sounds indicated a clear loss of absolute sensitivity and an associated broadening of frequency filtering, both of a magnitude similar to audiometric alterations in humans, but at extremely high salicylate levels. Otoacoustic emissions demonstrated changes in the mechano-sensory functioning of the cochlea in the form of decrease of spontaneous emissions and reduced nonlinearities. In vitro measures of isolated outer hair cells showed reduction of their fast motile responses which are thought to be at the origin of cochlear absolute sensitivity and associated fine filtering. Acoustically evoked neural responses from the eighth nerve to the auditory cortex showed reversible and mild losses of absolute sensitivity and associated broadening of frequency filtering. There is no evidence of a direct alteration of cochlear efferent innervation. Evidence was obtained for decreases in cochlear blood supply under control of autonomous innervation. Spontaneous neural activity of the auditory nerve revealed increases in firings and/or in underlying temporal synchronies. Similar effects were found at the inferior colliculus, mostly at the external nucleus, and at the cortex, mostly at the anterior and less at the secondary auditory cortex but not at the primary auditory cortex. These changes in spontaneous activity might underlie tinnitus as they affect mostly neural elements coding high frequencies, can occur without a loss of sensitivity, are dose dependent, develop progressively, and are reversible. Biochemical cochlear alterations are poorly known. Modifications of oxydative phosphorylation does not seem to occur, involvement of inhibition of prostaglandin synthesis appears controversial but could underlie changes in blood supply. Other biochemical alterations certainly also occur at outer hair cells and at afferent nerve fibers but remain unknown.

Effects of salicylates on evoked otoacoustic emissions and remote masking in humans

The aim of this study was to evaluate, in young volunteer subjects, the effects of salicylates on evoked otoacoustic emissions (EOAEs), which presumably reflect an active mechanical process in the cochlea due to outer hair cell (OHC) activity, and on remote masking (RM), which has been proposed as a useful tool in the study of the non-linear cochlear distortion products generated by high-frequency maskers. Data from the present research are consistent with the literature showing a reversible effect of salicylate leading to elevated hearing thresholds and reduced EOAE amplitudes. From the point of view of new findings, the results demonstrate a reversible effect of salicylates on RM magnitude, which decreases as serum salicylate concentration increases. As described previously by other authors, salicylate selectivity inhibits OHC motility and, in consequence, reduces the amplitude of the motion of the basilar membrane. According to these data it is very likely that the observed reduction in RM magnitude after salicylate administration is also the result of the decreased ability of the OHCs to contract and of the reduced basilar membrane motion. The results are consistent with the conclusion that the OHC system function plays a role in producing RM.

Frequency selectivity on aspirin-induced hearing loss in rats with auditory stimulus-induced conditioned suppression

The conditioned suppression technique was employed to examine the acute effects of aspirin on auditory function in rats. Lever pressing behavior for water reinforcement was suppressed in the presence of an auditory stimulus that had been previously paired with electric shocks. A single intravenous injection of aspirin at a dose of 225 mg/kg caused an erroneous lever pressing response in the broad sound intensities of 2 kHz tone stimulus during the conditioned stimulus period. A statistically significant increase in the threshold for 2 kHz was found 1 to 72 hr after dosing but not for 4, 8 and 10 kHz. These results suggest that the hearing for low sound frequency in rats is vulnerable to the effects of aspirin. This paradigm in rats may be useful to further assess the different outer hair cells along the cochlear duct and provide an additional evidence for the aspirin ototoxicity research.

Effects of lidocaine on salicylate-induced discharge of neurons in the inferior colliculus of the guinea pig

Using the extracellular recording method, the effects of lidocaine (a local anesthetic known to relieve tinnitus) on discharge of inferior colliculus (IC) neurons of the guinea pig were studied before and after salicylate (200 mg/kg) administration. The salicylate-induced discharge was inhibited by intravenous injection of lidocaine at a concentration (1 mg/kg) clinically used for treating tinnitus. IC neurons could be classified into two groups according to the difference in sensitivity to lidocaine: (1) weakly-sensitive neurons and (2) highly-sensitive neurons. In weakly-sensitive neurons, the duration of the lidocaine effect lasted for less than 5 min, and the inhibitory action on the discharge of neurons was greater when the latency to sound stimulus became longer. In highly-sensitive neurons, on the other hand, the activity of neurons was almost completely inhibited for longer than 30 min, irrespective of the latency to sound stimulus. The clinical relevance of these types of neurons is discussed.

A characteristic of aspirin-induced hearing loss in auditory brainstem response of conscious rats

The acute effects of aspirin on auditory functions were examined electrophysiologically in conscious rats with chronically implanted electrodes for auditory brainstem response (ABR) recording. A single intravenous injection of aspirin at a dose of 225 mg/kg caused a reduction in the amplitude of the ABR P1 wave evoked by a 2 kHz tone pip 1 and 24 hr after dosing at almost all sound intensity levels, while the P1 amplitude at 4 kHz was reduced mainly 1 hr after dosing, and the P1 amplitude at 8 kHz was not significantly affected at middle and high intensities even 1 hr after dosing. The audiogram obtained from the P1 amplitude showed a significant increase in the sound threshold 1 and 24 hr after dosing at 2 kHz, and 1 hr after dosing at 4 kHz, but not at 8 kHz. The peak latency of the P1 wave was also prolonged. Furthermore, reduction of the P2 and P4 wave amplitude and prolongation of the P1-P2 and P2-P4 interpeak latency were also observed at 2 kHz but not a 4 or 8 kHz. These results suggest that the rat auditory function for low frequency is vulnerable to the effects of aspirin. This paradigm, i.e., frequency selectivity, n rats may be useful to further assess the different outer hair cells along the cochlear duct and provide additional evidence for the mechanism(s) or site underlying aspirin ototoxicity.

The vascular component of sodium salicylate ototoxicity in the guinea pig

Drugs of the salicylate family (aspirin-like drugs) are reversibly ototoxic. Electrophysiologic and ultrastructural evidence suggests an impairment of the sensory hair cells of the cochlea following salicylate treatment. In addition, since these drugs can cause vasoconstriction, the ototoxicity of salicylates may also involve an impairment of the blood circulation in inner ear. However, a vascular hypothesis of salicylate toxicity has not received much attention. In the current study, we simultaneously measured cochlear blood flow (by laser Doppler flowmetry) and the sound-evoked potentials from the round window. Sodium salicylate caused a decrease in cochlear blood flow that appeared within 30 min following an intramuscular injection of a low dose of sodium salicylate (100 mg/kg). This sodium salicylate dose did not cause a change in auditory sensitivity. For higher doses (200 mg/kg and 300 mg/kg), both cochlear blood flow and auditory sensitivity were affected. The 300 mg/kg dose decreased blood flow by about 25% and elevated compound action potential thresholds by 10 to 25 dB for high frequencies (> or = 8 kHz). Further experiments showed that salicylate-induced threshold shifts were significantly reduced for the mid-frequencies when cochlear blood flow is increased by the vasodilating drug hydralazine (negating the flow reduction caused by salicylate). These data indicate that in addition to the direct effect of systemically administered salicylate on neurosecretory function a decreased blood flow contributes to the ototoxicity of salicylates.

Ototoxicity associated with salicylates. A brief review

Aspirin, the prototype of the salicylates, is a ubiquitous agent. The availability of aspirin, other salicylates and nonsteroidal anti-inflammatory drugs (NSAIDs) as prescription and over-the-counter medications means there is a wealth of clinical experience with these agents. Among the documented adverse effects of aspirin is the potential for ototoxicity. Tinnitus and hearing loss, usually reversible, are associated with acute intoxication and long term administration of salicylates. A range of measured serum concentrations are reported as correlating with documented ototoxicity (19.6 to > 67 mg/dl). Most case reports are based on total serum salicylate concentrations whereas unbound serum salicylate concentrations appear to reflect more closely the risk of ototoxicity. The pathophysiology of toxicity may be related to biochemical and subsequent electrophysiological changes in the inner ear and eighth cranial nerve impulse transmission. Localised drug accumulation and vasoconstriction in auditory microvasculature may be mediated by the antiprostaglandin activity of these agents. Ototoxicity, although not life-threatening, may add to the morbidity of patients taking salicylates or NSAIDs in therapeutic and toxic doses.

Intracochlear salicylate reduces low-intensity acoustic and cochlear microphonic distortion products

Salicylate is well-known to produce reversible hearing loss and tinnitus. The site and mechanism of salicylate's ototoxic actions, however, remain unresolved. Recent experiments demonstrating primarily low-intensity effects on cochlear afferent outflow and effects on otoacoustic emissions (OAEs) suggest that salicylate acts to compromise active, energy-enhancing processes within the cochlea (i.e., the active process). We tested this hypothesis by examining the effect of salicylate on distortion product emissions. Distortion product responses to two-tone stimulation were monitored in the guinea pig before, during, and after intracochlear administration of increasing concentrations of salicylate (0.6-5 mM). These responses were recorded as acoustic signals in the ear canal spectrum (ADP), and as present in the cochlear microphonic (CM) recorded from a wire in basal turn scala vestibuli (CMDP). We also recorded the CM response to a single tone. Cochlear perfusion of salicylate resulted in a dose-responsive reduction in ADPs that was greater for low intensities of stimulation. CMDPs also demonstrated a concentration-dependent reduction at low intensities, but were increased slightly, though not significantly, by salicylate when elicited by high intensity primaries. CM was essentially unchanged by intracochlear salicylate. These results are consistent with an action of salicylate that involves the outer hair cells (OHCs) and are in harmony with the hypothesis that salicylate may selectively compromise the active process.

Salicylate ototoxicity: review and synthesis

The effects of salicylates on the auditory system are reviewed. The clinical manifestations of aspirin ototoxicity are described, including changes in the sensitivity and suprathreshold characteristics of hearing, as well as tinnitus. The results of animal experiments on salicylate ototoxicity are discussed, including behavioral, anatomic, and physiologic studies examining the mechanisms of salicylate ototoxicity. The sue of salicylates in the study of the basic mechanisms of hearing and hearing loss is also considered.

Mechanisms of salicylate ototoxicity

The ototoxic effects of salicylates, reversible hearing loss and tinnitus, are well documented. However, the pharmacological mechanisms underlying these changes in cochlear function are not well understood. The studies reported here were an investigation of the site and mechanism of salicylate ototoxicity through an examination of its effects on ionic, neural and mechanical aspects of cochlear transduction. Salicylate administration produced an intensity dependent reduction of the AP and SP, with the predominant effects occurring at low stimulus levels. In direct contrast, a significant increase was observed for corresponding CM responses, independent of stimulus intensity. Salicylates also reduced the magnitude of efferent induced shifts in the AP, CM and EP. Cochlear mechanics were altered as evidenced by the reduction in two-tone distortion products, electrically evoked emissions, and electrophonic APs. These changes in cochlear function are attributed to a salicylate mediated increase in the membrane conductance of the outer hair cells. This change in membrane permeability interferes with the reverse transduction process, effectively reducing the gain of the cochlear amplifier. Results of single unit recordings suggest parallels between salicylate intoxication and noise trauma, which are discussed with regard to potential mechanisms of tinnitus generation.

Drug-induced ototoxicity. Pathogenesis and prevention

Ototoxicity is a disabling adverse effect of several widely used classes of drugs, such as diuretics, anti-inflammatory agents, antineoplastic agents and aminoglycoside antibiotics. High-dose therapy with either diuretics or anti-inflammatory agents is primarily associated with acute and transient impairment of hearing or tinnitus. In contrast, long term treatment with antineoplastic agents or aminoglycoside antibiotics is typically associated with delayed and irreversible loss of hearing; lesion in the organ of Corti include the destruction of auditory sensory cells. Vestibular function can also be compromised by ototoxic drugs. Occasional cases of ototoxicity have been reported for a variety of other therapeutic compounds and environmental toxins. In addition, the simultaneous administration of multiple agents which are potentially ototoxic can lead to synergistic loss of hearing. Exposure to loud noise may also potentiate the hearing loss due to cochleotoxic drugs. Ototoxic agents can impair the sensory processing of sound at many cellular or subcellular sites. However, the molecular mechanisms of ototoxicity have not been established for most of these drugs, and structure-toxicity relationships have not been determined. It has therefore been difficult to predict the ototoxic potential of new drugs, and rational approaches to the prevention of ototoxicity are still lacking. The clinical and experimental features of ototoxicity are reviewed for several classes of drugs, with an emphasis on current knowledge of the mechanism and the possibilities for the prevention of ototoxicity for each.

Risk factors in the genesis of sensorineural hearing loss in Finnish forestry workers

A detailed analysis of risk factors for the development of sensorineural hearing loss (SNHL) was carried out in 199 forest workers. The hearing threshold of both ears at 4000 Hz was measured, and the effect of age, exposure to noise, blood pressure, presence of vibration induced white finger (VWF), tobacco smoking, plasma LDL-cholesterol concentration, and consumption of drugs were evaluated by multiple linear regression analysis. Aging was the major risk factor, followed by exposure to occupational noise and the presence of VWF. Plasma LDL-cholesterol concentration and the use of antihypertensive drugs also correlated significantly with SNHL. These main factors were able to explain about 28% of the SNHL variance. Additional factors in the analysis, including smoking, systolic and diastolic blood pressure, and consumption of salicylates did not significantly contribute to the genesis of SNHL.

Comparative actions of salicylate on the amphibian lateral line and guinea pig cochlea

1. Salicylate actions on afferent nerve activity in the Xenopus lateral line and on cochlear potentials in guinea pig were investigated. 2. In the lateral line, salicylate (0.3-2.5 mM) suppressed spontaneous activity, water motion evoked excitation and responses to L-glutamate (1-2 mM) and kainate (10-20 microM). 3. In the guinea pig, salicylate (0.6-10 mM) suppressed the compound action potential (CAP) and increased N1 latency at low but not high sound intensities. 4. In the lateral line salicylate action may involve an antagonism of the hair-cell transmitter on the afferent nerve. 5. In the cochlea salicylate may suppress the active process or cochlear amplifier.

Acute effects of noradrenalin related vasoactive agents on the ototoxicity of aspirin: an experimental study in the guinea pig

Aspirin is known to be ototoxic when administered at high doses. Its mode of action is unknown but an alteration of the vascular function has been suspected. To further document this hypothesis, acute effects of some vasoactive agents on the ototoxicity of aspirin were tested in experiments on the guinea pig using sensori-neural electrophysiological responses and morphometry of the vessels of the stria and the spiral lamina. Electrophysiological measures showed no modification of sensory responses but neural responses revealed clear changes after administration of noradrenalin related agents, limited modifications after a drug acting partly as a serotonin antagonist, and no change after a dopaminergic agent. Morphometric studies showed no modification of the strial but some effect on the spiral vessels. The results are compatible with the hypothesis of a vascular involvement in the ototoxicity of aspirin and they point toward an interaction with the noradrenergic sympathetic cochlear system in the spiral lamina.

The effects of deferoxamine mesylate and hypoxia on the cochlea

Deferoxamine mesylate (DF) is a chelating agent used for the treatment of iron overload. Recently audiological testing of patients on long-term treatment with this drug indicated the possibility of an ototoxic side effect (1). We administered DF to chinchillas with both acute and chronic regimes. Functional and histological damage to the cochlea was detected only in the acute experiment. This was assumed to come not from the direct effect of DF on the cochlea but from the hypoxia as a result of respiratory suppression due to DF toxicity. To confirm this, animals were exposed to hypoxia during the same time course as for the DF experiment. Histological and physiological consequences of this hypoxia alone revealed very similar results to that observed in the acute DF experiment. This implies that DF has little direct toxic effect on the cochlea and, more importantly that considerable attention to hypoxia should be paid when assessing the cochlear pathology of animals which have been subjected to general anesthesia for long periods.

Temporary hearing loss induced by combinations of intense sounds and nonsteroidal anti-inflammatory drugs

Intense sounds were delivered to 11 subjects with normal hearing both before and during administration of standard doses of four nonsteroidal anti-inflammatory drugs. After four days of aspirin treatment (3.9 g daily), the subjects' resting hearing levels raised by about 10 dB. Administration of intense sounds that had previously been shown to produce about 12 dB of temporary hearing loss added increments of 10 to 15 dB to the aspirin-induced hearing loss. That is, the total temporary hearing loss produced by aspirin plus exposure to intense sound was about 10 to 15 dB greater than that produced by exposure to the intense sound alone. A similar effect was observed for sodium salicylate. After similar administrations of sulindac (400 mg per day) and diflunisal (750 mg per day), there was no corresponding increase in the sound-induced hearing loss. Under certain reasonable assumptions about underlying mechanisms, these findings suggest that persons taking moderate doses of aspirin or sodium salicylate may be at increased risk of noise-induced hearing loss.

Aspirin can potentiate the temporary hearing loss induced by intense sounds

Aspirin is known to produce a reversible loss of hearing that can be as great as 40 dB, depending upon the dose and the individual subject. Here we show that aspirin-induced losses exacerbate the temporary hearing loss induced by exposure to intense sound. EXPOSUREs that ordinarily produce about 14 dB of temporary threshold shift (TTS) will produce about 18-27 dB of TTS if the listener has been taking 3.9 g of aspirin for the past two days or more. A lesser dose or a shorter duration of use produces a smaller, or no, increment in temporary hearing loss. This greater TTS, and an apparent prolongation of recovery from exposure, make chronic aspirin use ill-advised for people routinely exposed to intense sounds.

EXPOSURE

2500 Hz, 10 min, varying intensity. TTS frequency: 3550 Hz. Psychophysical method: 2IFC, adaptive.

Potentiation of acoustic-trauma-induced audiogenic seizure susceptibility by salicylates in mice

Combined exposure to noise and salicylates was found to produce greater acoustic trauma induced audiogenic seizure risk than exposure to the noise alone. The result suggests that salicylates could make the mouse cochlea more vulnerable to the traumatic action of noise.

Potentiation of noise-induced audiogenic seizure risk by salicylate in mice as a function of salicylate-noise exposure interval

Audiogenic seizure risk can be induced in genetically seizure-resistant BALB/c mice by exposure to an intense noise. Results of this experiment showed that combined exposure to noise and sodium salicylate could produce a greater priming effect than exposure to the noise alone, and the greatest potentiation effect was obtained when animals were exposed to the noise 6 hr after the intake of salicylate. The findings were taken as indirect evidence suggesting that the ototoxic action of sodium salicylate could potentiate vulnerability of the mouse cochlea to noise damage.

Effects of combinations of sodium salicylate and noise on the auditory threshold

Thirty-nine monaural chinchillas were used to study the interaction between sodium salicylate and various TTS-producing noise paradigms. Five animals were included in each of the following three groups: 1) sodium salicylate (400 mg/kg) plus 2-4 kHz, 95 dB SPL noise band for one hour; 2) sodium salicylate (400 mg/kg) plus 4 kHz CF octave band noise at 80 dB SPL for 96 hours; and 3) sodium salicylate (400 mg/kg) plus 50 impulses having 50 musec A-duration and 158 dB peak SPL, presented at one per minute. The remaining 24 animals served as various controls in groups exposed to sodium salicylate or the noise paradigm alone. Thresholds were estimated before, during, and after exposure using the AER technique and cochleagrams were mapped for each cochlea 30 days after exposure. When sodium salicylate was combined with the various noise conditions, the maximum TTS values obtained from the combination studies were comparable to those obtained from the single agent producing the greatest TTS at a particular frequency. No consistent alteration in either magnitude or time course of posttreatment threshold shift was found following the combination treatments as compared to the individual agents alone. Hazard to the auditory system resulting from a combination of sodium salicylate and noise was concluded to be no greater than the hazard presented by either agent alone. This result is also substantiated in the histological results.

Cochlear damage resulting from kanamycin and furosemide

Permanent cochlear damage has been shown to occur in guinea pigs following the combined administration of kanamycin and furosemide. At the doses used, only a transient effect was measured with furosemide alone and no effect was detectable with kanamycin alone. This interaction results when a single subcutaneous dose of 400 mg/kg of kanamycin is followed in 2 hours by a single intravenous dose of furosemide. The dosage range for furosemide was 50 mg/kg for a just-detectable effect to 100 mg/kg for a very severe effect. Damage to the cochlea was ascertained by measures of the a.c. cochlear potential as well as surface preparation histology.