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GFP transgene was expressed in the lining cells of the perilymphatic space. Lentivirus vectors are safe and cause only minimal inflammatory reaction. Transgene products can be delivered into the perilymph by utilizing lentivirus vectors.To analyze the efficiency and safety of lentiviral vectors HOX-GFP and WOX-GFP in intracochlear gene transfer.Lentivirus vectors were tested for their transduction efficiency in vivo in CD-1 mice. Half of the animals were pretreated with kanamycin. Lentivirus vector or saline (1 microl) was injected into the inner ear. All the animals were sacrificed 14 days after the surgery and the cochleae and selected organs were analyzed immunohistochemically.HOX-GFP and WOX-GFP expression was restricted to the lining cells of the scala tympani and scala vestibuli. No GFP expression was seen in the organ of Corti or the spiral ganglion. Aminoglycoside treatment had no effect on the expression of these vectors. The distant spread of lentivirus vectors was minimal; only the liver of one animal showed some GFP expression. Inflammatory reaction caused by these vectors was mild. Few inflammatory cells were found in the perilymphatic space of the cochlea and in the vestibular organ.

This study was designed to determine if hearing status monitoring during intravenous infusion of EA reduces individual variability and to evaluate the correlation between EA dose and Bwt.Twenty-five cats with the mean age of 24 ± 3.7 weeks (range = 20.6-28.3) and a mean weight of 3.21 ± 0.84 kg (range = 1.9-5.1) were administered a subcutaneous injection of KM (300 mg/kg) followed by an intravenous infusion of EA (1 mg/min). Click-evoked auditory brainstem responses (ABRs) were recorded to monitor hearing during the infusion. When ABR thresholds exceeded a 90 dB sound pressure level, the infusion of EA was terminated. Histopathology forapex, middle, and base sections of the cochlea were examined after 6 months.The dose of EA was optimized for deafening through simultaneous ABR measurements. Bwt was positively correlated with EA dose (mg) (p 0.001, R(2) = 0.548), which was different from a study previously reported. Cochlear histopathology assessments revealed an absence of organ of Corti in the majority of cochleae.Co-administration of kanamycin (KM) and ethacrynic acid (EA) was an easy and effective method for deafening procedures in adult animals. Body weight (Bwt) was positively correlated with EA dose (mg) and an optimal EA dose can be calculated.

When newly hatched chicks were injected with kanamycin on 8 successive days, the hair cells were destroyed completely in the area 0.4 to 0.8 mm from the proximal end of the basilar papilla. At this time, and 1 and 7 days following the completion of 10 days of injections, the nerve fibres in the basilar papilla of chicks show no sign of injury. On the first day following 10 days kanamycin administration the regenerated hair cells obtained not only afferent innervation, but also efferent innervation. At 15 days following drug cessation, afferent innervation of the regenerated hair cells was already similar to the controls, and the thresholds measured at this time were significantly better than those at 1 and 7 days. The chalice efferent terminals did not appear until the 60th day of drug cessation. Efferent innervation of the regenerated hair cells also approached maturity at this time. Compared with the half month after the completion of drug injection, the hearing of birds had no evident increase. It was obvious that afferent innervation of the regenerated hair cells was related more to the recovery of hearing than efferent innervation. The regenerated hair cells beginning reinnervation early and maturing were important factors influencing the recovery of the birds' hearing function after kanamycin ototoxicity.

rAAV-NT4-ADNF-9 could ameliorate the damage to auditory function and repair previous impairment of cochlear hair cell loss induced by kanamycin.To investigate the therapeutic effect of ADNF-9 on cochlear hair cells using the recombinant adeno-associated virus (AAV) carrying fusion gene NT4-ADNF-9 and the kanamycin-deafened guinea pig model.Forty white guinea pigs with normal auricle reflex and normal auditory brainstem responses (ABRs) were randomly divided into four groups. Kanamycin was administered to the animals in groups A, B, and C to establish the deafened guinea pig model. rAAV-NT4-ADNF-9, vector only, and artificial perilymph were then delivered to the cochlear tissue of animals in groups A, B, and C, respectively, through the round window membrane. Animals in group D did not receive any treatment and acted as normal controls. The hearing thresholds on the surgery side were recorded before and after the transfection treatment. Fourteen days after treatment, cochleae were removed for paraffin slide preparation and cochlear surface preparation. A phase contrast microscope was used to observe the protective effect of ADNF-9 on hair cells.Significant reduction of the ABR threshold was observed after rAAV-NT4-ADNF-9 treatment (p0.05). After 14 days of treatment, the ABR threshold was also significantly different between the rAAV-NT4-ADNF-9-infected group and the non-infected group. Moreover, phase contrast microscopy showed significantly less hair cell damage or hair cell loss in the group treated with rAAV-NT4-ADNF-9 than in the groups treated with vector only or artificial perilymph (p0.05).

To predict the possible benefit of a cochlear implant to a patient, the clinician requires a reliable objective method to monitor the presence of surviving fibres in the 8th nerve. The subjective promontory test and the evaluation of electrically evoked brainstem potentials are not adequate. An electrical stimulus artefact interferes badly with the potential recorded, but with electrical sinusoidal stimulation this stimulus artefact can be suppressed. The highly synchronous excitation of the auditory nerve fibres results in compound action potentials that can be recorded from the round window. The present animal experiments show that the method proposed is effective. Clinical tests are suggested.

Blood circulation in the cochlear lateral wall after exposure to a non-physiological level of sound (120-125 dB SPL, 3 h) was investigated immunohistologically. Kanamycin (KM), which was expected to function as a tracer of blood flow, was administered to guinea pigs 5 min to 21 h after sound termination. At 5-30 min, KM was scarce in the capillaries of the stria vascularis (CSVs), whereas abundant KM was present in the spiral ligament vessels. These findings differed markedly from those in non-sound-exposed animals. After the initial period, KM gradually did enter into the CSVs, but its pattern of existence there differed from the normal pattern. These observations suggest that acoustic trauma causes blood stagnation in the strial capillaries, leading to strial dysfunction.

Transplacental distribution of kanamycin (KM) to 35-60 day embryonal or fetal inner ear of the guinea pig following maternal treatment was investigated by an immunohistological technique. KM, administered at any stage of pregnancy, migrated through the placenta and entered into the cochlea. The drug pathway to the organ of Corti seemed to consist of two routes: the spiral vessels and the capillaries of the spiral limbus. However, at an early stage of pregnancy, KM was detected only slightly in the area corresponding to the stria vascularis, probably due to immaturation of strial capillaries.

Vestibular function testing was performed regularly on patients who were administered streptomycin, kanamycin, or enviomycin, and vestibular damage was detected at an early stage, and quantitatively. We investigated the point in time at which the therapy should be discontinued. Subjects consisted of 204 cases of tuberculosis treated with streptomycin, kanamycin, enviomycin. They were admitted to the hospital between December 1984 and August 1989. Twenty-eight cases of vestibular dysfunction due to streptomycin, kanamycin, and enviomycin could easily be detected at an early stage by performing Meyer zum Gottesberge's head-shaking test for the evaluation of jumbling, together with Romberg's test and the stepping test. All cases who had vestibular dysfunction completely recovered because of early detection. In addition, 7 cases recovered afterwards from temporary vestibular damage shown only in Meyer zum Gottesberge's head-shaking test (abnormality of vestibulo-ocular reflex was only detected and vestibulo-spinal reflex remained intact), despite continuation of streptomycin injection. When the results of the head-shaking test are less than 50% and when a sway and/or rotation in the stepping test occurs, the injections should be discontinued.

Conclusion. Mitochondrial dysfunction in the cochlea potentiates the ototoxicity of aminoglycosides. Objective. This study examined whether mitochondrial dysfunction in the cochlea affects the ototoxicity of aminoglycosides. Materials and methods. Nineteen guinea pigs were treated with the mitochondrial toxin 3-nitropropionic acid (3-NP), kanamycin, both agents, or normal saline as control. After 14 days, hair cell loss and auditory brainstem response (ABR) were assessed. Results. The administration of 400 mg/kg of kanamycin caused neither hair cell loss nor ABR threshold shift. Administration of 3-NP caused mild ABR threshold shift without significant hair cell loss. Administration of 3-NP and kanamycin caused ABR threshold shift and significant hair cell loss.

Short-term local application of kanamycin by the microcatheter method can control the region and severity of drug effect on the cochlea by changing the concentration and administration time.To investigate the effect of short-term round window administration of kanamycin by the microcatheter method on cochlear stereociliary bundle loss in a guinea pig model.Two concentrations and two time periods were used for drug administration to the inner ear. In groups of six animals, a total dose of 172.5 mg/ml or 345 mg/ml of kanamycin was instilled at the rate of 0.1 ml/h into the round window niche over either a 1 h or 2 h period by the microcatheter method. One group of six animals received a saline infusion as a control. The animals were sacrificed after 4 days and stereociliary bundle loss was observed by SEM. Functional changes were evaluated by auditory brainstem response.With regard to the severity of the damage, higher drug concentrations were associated with more severe effects. The severity of damage was the same when the same total dose was used; however, it was found that when the dose was administered over a longer period, the damage region was wider. The functional changes also corresponded with the morphological changes.

An antimicrobial agent, kanamycin, has been shown to produce as an untoward effect, ototoxicity. The purpose of this study was to investigate differential effects of kanamycin ototoxicity as a function of Rx timing with regard to circadian rhythms. Four groups of comparable weight Sprague-Dawley rats received a daily subcutaneous dosage of 225 mg/kg kanamycin sulfate with each receiving the antibiotic at a different time: 8 AM (8A), 2 PM (2P), 8 PM (8P), and 2 AM (2A). The rats were housed in separate cages, in a room on a light-dark (12:12) illumination cycle with light between 6 AM and 6 PM. Hearing loss was assessed with the auditory brainstem response (ABR) using pure tone stimuli at 8, 16, 24, and 32 kHz. ABR measures were obtained before dosing began and 2, 4, and 6 weeks after the initial dosing. Kanamycin produced a hearing loss which reflected the total dosage given to each group. Significant differences in physiologic thresholds were observed for both timing of the daily dosage (p less than 0.05), and the 2, 4 and 6 week testings (p less than 0.001). After 2 weeks, the 8A group showed an average hearing loss of 11.5 dB at 32 kHz, with the other timed treatment groups exhibiting minimal effects (3.0-6.5 dB). For the 8A group at this frequency, the loss progressed at 4 (19.5 dB) and 6 (22.5 dB) weeks. The 2P group after 4 weeks exhibited similar losses as the 8A group for this frequency, with the loss at 6 weeks being even greater (34.0 dB). The 8P and 2A groups exhibited only slight losses over all frequencies.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

The developing ear is sensitive to chemical and physical changes in its environment. Over the last ten years, many experimental studies have shown that the young ear is more susceptible to noise exposure and to the ototoxic effects of certain drugs. Other factors such as thyroid deficiency, viral infections and hyperbilirubinemia are recognized causes of hearing loss in the human infant and are beginning to be studied experimentally. These experiments are important for determining sensitive (“critical”) periods during which the young ear is more susceptible to environmental factors and may lead to a better understanding of the causes of deafness in children.

The ototoxic interaction between the aminoglycoside antibiotics (streptomycin, kanamycin, etc.) and the loop-inhibiting diuretics (ethacrynic acid, furosemide and bumetanide) has been well documented. This interaction causes extensive destruction of the hair cells of the cochlea. Brummett et al. (1974) demonstrated that this interaction did not occur with the non-loop-inhibiting diuretics and kanamycin. The present study was undertaken to determine if antibiotics other than the aminoglycosides could produce the ototoxic interaction when combined with a loop-inhibiting diuretic. Three antibiotics-viomycin, capreomycin, and polymyxin B- when given with ethacrynic acid were found to produce cochlear hair cell damage that was similar to that produced by aminoglycoside antibiotics administered with ethacrynic acid. Therefore, the interaction appears to be specific to the loop-inhibiting diuretics but not specific for the aminoglycoside antibiotics.

Similarities were noted between the nature of inner ear damage produced by loud sounds and by aminoglycoside antibiotics. Since body temperature affects cochlear function and influences the effects of noise on the ear, a similar effect was predicted for the aminoglycoside, kanamycin. By environmentally elevating the body temperatures of preweanling mice to approximately 1 degree C above that of the normal adult, kanamycin ototoxicity was increased (an average 20.4 dB threshold elevation, vs. 9.3 dB for kanamycin injected mice reared at room temperature). Hyperthermia per se had no influence on auditory thresholds. This may be of relevance to humans with fever who are treated with aminoglycoside antibiotics.

The effects of the interaction between kanamycin (KAN) and ethacrynic acid (EA) on the ultrastructure of the guinea pig cochlea were studied 3, 4, 6, and 24 hours following administration of EA (40 mg/kg) to animals pretreated 2 h earlier with KAN (400 mg/kg). Appropriate saline (SAL) controls were included giving 4 treatments: KAN/EA, KAN/SAL, SAL/EA and SAL/SAL. The outer hair cells of the organ of Corti showed nuclear and plasma membrane changes at 3 h and were completely destroyed at 24 h. The inner hair cells were unaffected. Severe swelling was seen in the stria vascularis of both KAN/EA and SAL/EA animals at 3 h and was gone by 24 h. KAN/EA had a greater effect on the stria than had SAL/EA. These results were consistent with the time course of the effect of the drugs on the a.c. and d.c. endocochlear potentials. KAN concentrations in perilymph were unaffected by treatment with EA.

Pregnant guinea pigs were treated with Kana-mycin at three different stages of gestation (dating by method of post-partum ovulation). Twenty-nine newborn guinea pigs were tested electrophysiologically by recording the cochlear microphonic potential and the compound action potential from the round window in response to clicks and filtered clicks at 8 000 Hz. Six of the test animals showed the same electrophysiological changes as those found in adult mammals after Kanamycin intoxication. The results suggest a relationship between the oto-toxicity of Kanamycin and the onset of auditory function. Cochlear potential and compound action potential were mostly affected when intoxication was performed during the last 15 days of gestation. This study confirms the results previously published by Uziel 1979.

The dynamics of changes in the electro-cochleograms of 250 guinea-pigs exposed to industrial noise and to which kanamycin was administered while the animals were being exposed to such noise for a period of 1 to 12 weeks, inclusive, have been investigated. It was found that the PM and AP changes occurred in phases but that the dynamics of the changes differed. The peripheral adaptation was preserved but a deterioration was noted. The results confirmed by statistical methods seem to indicate that drugs with ototoxic side effects lead to an earlier development of damage to the ear by industrial noise; the damage occurs with greater rapidity if the drug is administered during exposure to such noise.

In order to elucidate the mechanism of individual variation of kanamycin ototoxicity, the possible relationship between the outer hair cell damage induced by kanamycin and the levels of kanamycin in serum or perilymph and of renal damage was investigated in rabbits. No relationship was found between the extent of the outer hair cell damage and the level of kanamycin in the serum or the renal damage. The extent of the outer hair cell damage was closely correlated to the levels of kanamycin in the perilymph. These findings suggest that the individual variations in the outer hair cell damage induced by kanamycin are more closely correlated to the individual differences in the transferability of kanamycin into inner ear than to those in the vulnerability of the outer hair cells or kidneys.

The vestibular toxicity of two aminoglycoside antibiotics, dibekacin sulfate and habekacin sulfate, and of a drug with potent antimitotic activity, cisplatin (cis-diamminedichloroplatinum) has been investigated in both rats and frogs. In rats, chronic intraperitoneal injection of a saline solution of dibekacin (50 mg/kg/day), habekacin (50 mg/kg/day), cisplatin (0.5 mg/kg/day) for 4 weeks and of cisplatin (1 mg/kg/day) for 5 weeks, produced no behavioral vestibular disorders and the righting reflex could be elicited at any time. In frogs, the spontaneous discharge was recorded from individual fibres of the ampullary nerve of the horizontal semicircular canal before and after acute administration of the drugs, dissolved in Ringer, into the perilymph of the inner ear near the horizontal ampulla. Following injection of 1 microliter of solutions containing 10 micrograms or 20 micrograms of dibekacin, 20 micrograms or 50 micrograms of habekacin, 0.5 micrograms, 2.5 micrograms or 10 micrograms of cisplatin, the spontaneous discharge decreased in a number of fibres and was sometimes completely abolished. The vestibular toxicity of the three drugs tested is discussed with respect to that of aminosides whose ototoxicity is well known.

In order to investigate to what extent an immature inner ear is injured by external causes, the effect of Kanamycin on an immature cochlea was studied in mice by using scanning and transmission electron microscopes. Our results showed that immature cochleae are more highly susceptible to injury than mature cochleae, especially when the Nuel's space and the Corti tunnel open. It is suggested that in humans, during the stage corresponding to the above period, that is, in about the third gestational month, the inner ear is highly susceptible to injury by external causes.

The mechanism of ultrasonic perception was investigated electrocochleographically in guinea pigs (1) to compare AP responses in normal animals with those in kanamycin-poisoned animals with a damaged outer hair cell system; (2) and to analyse the masking property of continuous ultrasonic sound upon the AP evoked by burst stimuli within the auditory field. The study revealed several facts indicating the breakdown of cochlear sharp frequency analysis in the transduction of ultrasonic sound. We concluded that the sound perception in the ultrasonic region could be performed by the inner hair cell system without any enhancement or modulation of the outer hair cell system, which was regarded as an important process in a recent model of cochlear micromechanics.

Scala tympani of the guinea pig cochlea was perfused with solutions having an increased potassium concentration. The response characteristics of single auditory nerve fibres in both normal and kanamycin-damaged cochleas were studied using computer controlled routines. The results indicate that these perfusions caused a marked increase in the spontaneous firing rate of auditory nerve fibres, without loss of threshold sensitivity. Current theories of cochlear transduction support the view that the potassium concentration difference across the reticular plate is fundamental to the sensitivity of the cochlea. The results presented here do not support this view.

Clinical experience has demonstrated that intravenously administered local anaesthetics have a mitigating effect on severe tinnitus. In an attempt to gain some insight into the mechanism of this effect, autoradiography of the inner ear of young pigmented rats was performed after intravenous injection of 14C-lidocaine. Some accumulation of lidocaine was found in the modiolus, but almost none in the stria vascularis. A large accumulation was observed in other melanincontaining tissues, such as the hair follicles and uvea. The in vitro accumulation of 14C-labelled lidocaine adsorbed on melanin granules was low (12%) as compared with that of other drugs, such as kanamycin (89%) and chloroquine (85%). These autoradiographic results indicate that lidocaine has an effect upon the inner ear, in addition to its previously demonstrated effect on the CNS.

Adaptation of VIII nerve compound action potentials in response to trains of broad frequency spectrum clicks and high frequency filtered clicks is studied at various intensities in normal guinea pig under normal conditions, while masking with white noise and under pathological conditions after ototoxic antibiotic treatment. The results are discussed with respect to the clinical electro-cochleographic adaptation studies in man and the so-called two populations of receptors and nerve fibres in the cochlea.

Masked and absolute behavioral auditory thresholds were measured in kanamycin-treated C3H mice with a significant damage or loss of outer hair cells (OHCs) near the cochlear base, and in 17--24-month-old NMRI mice with a significant loss of OHCs and inner hair cells (IHCs) in the basal region and of OHCs near the apex. A loss of IHCs is correlated with an increase in absolute thresholds. A moderate damage or loss of OHCs in a cochlear region had no effect on absolute thresholds but correlated with a decrease and other changes of characteristics of masked thresholds in the respective frequency regions. OH C-damage makes masking by continuous white broad-band noise less efficient. It is concluded that masking and critical bands depend on the function of OHCs, which must be assumed to influence intracochlearly the activity of IHCs in processing the information to the brain.

The following hypothesis is presented: A dysfunction of the hair cell cilia, either in the form of ciliary pathology or as a temporary loss of ciliary stiffness, both of which are documented, ought to lead to a partial decoupling of the involved hair cells from the tectorial membrane. Consequently, 1) energy transmission should be attenuated (= hearing loss), 2) the noise level at the hair cell input should be increased (= tinnitus) and, owing to the concomitant center-clipping of the signal waveform, 3) the input/output function should become steeper (= recruitment) and 4) the formant structure of speech should be largely destroyed (= relatively poor speech discrimination). The above signs and symptoms are characteristic of a number of acute cochlear disorders and would thus find a common explanation.

The effects of neomycin, kanamycin and dihydrostreptomycin on the cochlear microphonic, the action potential of the auditory nerve and the endocochlear potential were studied in guinea pigs in which these drugs were locally administered by perfusion. These drugs suppressed the cochlear responses markedly when applied to the endolymph but were less effective when applied to the perilymph. The mechanisms of action of antibiotics on the hair cells of the organ of Corti are discussed.

Several species undergo age-dependent changes in susceptibility to noise-induced and drug-induced hearing loss. In this experiment 18-day-old mice were given 200 mg/kg kanamycin plus varying doses of bumetanide (20, 30 or 40 mg/kg). Thresholds of the scalp-recorded compound action potential of the auditory nerve indicated that diuretic doses of 30 and 40 mg/kg produced significant loss of hearing sensitivity. Thirty-eight-day-old mice were then treated with 200 mg/kg kanamycin plus 40 mg/kg bumetanide and demonstrated no loss of hearing sensitivity. These results confirm the existence of age-dependent changes in susceptibility to ototoxic hearing loss in mice. Furthermore, the treatment, consisting of two injections on the same day, offers promise as a means of defining the critical period of susceptibility in greater detail than has been possible with aminoglycosides alone.

Ultrastructural study of ototoxicity is well documented with two points of interest: organ of Corti for aminoglycosides and stria vascularis for loop diuretics. As a previous study suggested initial lesions of stria vascularis, an attempt of comparison and of chronological study was made between the organ of Corti and stria vascularis lesions by kanamycin intoxication. The method was devised by J. M. ARAN, with electrophysiological control. We failed to find in the stria vascularis a radial or longitudinal pattern of lesions. We could not discern a chronological injury between the organ of Corti and stria vascularis because both were damaged even in the less deafened animals. Nevertheless, two facts were clarified: (i) hair cell lesions are lysosomial as for the kidney lesions, while stria vascularis lesions are mitochondrial, (ii) melanine granulations play a part in drug metabolism (increased number, secretory aspect) and deserve further study.

In a previous report, kanamycin (400 mg/kg/d) seemed to increase the number of melanine granulations in intermediate cells of the stria vascularis, especially in the second and third turns. To precise these data, melanine was studied in those turns by ultrastructural morphometry in a control group with 12 animals. We observed a large intra-individual and inter-individual variation before intoxication. Thus, the meaning of melanine modifications by kanamycin must be carefully evaluated.

The morphological changes after kanamycin intoxication of the inner ear, including both the cochlea and the vestibule, were quantitatively analysed by the surface preparation technique after succinic dehydrogenase staining. 75 guinea pigs were used. The outer hair cells in the basal coil and the inner hair cells in the upper coils of the cochlea were the most severely damaged, but many unusual modes of damage were also revealed. For example, the initial hair cell damage in the cochlea appeared in the upper hair cells. The clearly observed vestibular damage contradicts the general belief that kanamycin is not so toxic to the vestibular hair cells. The utricular macula and the lateral crista were most severely damaged. The delayed ototoxicity of kanamycin was observed for the first time in the vestibular hair cells.

The administration of the aminoglycoside antibiotics often gives rise to sensori-neural hearing loss. in a study undertaken to explore the progression of hearing loss caused by these drugs, guinea pigs were administered with kanamycin, a representative member of this family of antibiotics, and subsequently were investigated for the presence or absence of hearing loss and its progressive-ness during and after the period of medication in terms of audiogenic brain stem response (BSR). Further, in an attempt to investigate the relationship between the function and morphology of a KM-damaged inner ear, light microscopic as well as scanning and transmission electron microscopic examinations were made of the cochleas excised from the treated animals. the results are summarized as follows(1) Four distinct wave forms, i.e., P1, P2, P3 and P4, were seen in BSR tracings from normal guinea pigs.(2) a comparative study was made of BSR amplitude as an index of hearing. in the group receiving KM in consecutive daily dos...

Dose-effect curves for inhibition of growth of P388/P mouse lymphoma cells by ethacrynic acid and kanamycin used alone and in combination were determined in vitro. Ethacrynic acid was 600 times more potent than kanamycin and combinations of the drugs resulted in overall additive effects. These results were compared with known dose-effect data on the ototoxicity of these drugs in vivo. Kanamycin was highly selective in its toxicity for cochlear hair cells compared to cultured cells. The dose-effect data for ethacrynic acid was coincident with that reported for functional and biochemical effects on the cochlea following perilymphatic perfusion with the drug. The potentiation observed following the ototoxic interaction the two drugs in vivo was not observed following combinations of the drugs in vitro.

In 41 guinea pigs an experiment was conducted to determine the effect of kanamycin on ears with or without blockage of the cochlear aqueduct. In 24 animals the cochlear aqueduct was blocked on one side, and after 1 to 21 days, kanamycin (300 mg/kg) was given daily and subcutaneously until the pinna reflex began to decrease. The remaining animals were used for controls: exposure of and trauma to the aperture of the cochlear aqueduct and kanamycin administration (8), blockage of the cochlear aqueduct only (3 plus 17 previous cases), and kanamycin administration to normal animals (6). The survival time of all these animals was four months. The results showed that ears with blockage of the cochlear aqueduct and kanamycin administration consistently demonstrated a more severe and extensive atrophy of the cochlear sensory cells. The lesions occurred primarily at the basal end and spread toward the apical turn, although the lesions in some specimens jumped from the basal to apical turn. The outer hair cells were more extensively affected than the inner hair cells. Proteinaceous precipitates were often found to be slightly greater in the perilymph of cochleae with blocked cochlear aqueducts. From these observations, it is concluded that the decrease in patency of the cochlear aqueduct will impair perilymph metabolism, causing the cochlear sensory cells at the basal turn to become more vulnerable to noxious substances.

The cochleo- and vestibulotoxicities of a new aminoglyco-sidic antibiotic, dibekacin, have been compared, in the guinea pig, with those of gentamicin and tobramycin. Besides an untreated control group, three groups of pigmented guinea pigs have been treated with 20 consecutive daily subcutaneous injections of one of these antibiotics respectively, with a dosage of 90 mg/kg/day (30 times the recommended human therapeutic dose which is the same for the three aminosides studied: 3 mg/kg/day). The auditory and vestibular functions in the awake animal were studied respectively by the measurement of thresholds of click-evoked responses at the auditory cortex and by the recording of eye movements (electronystagmography) during damped sinusoidal rotatory stimulation. These functions were monitored before, during and after the treatments in a few guinea pigs in each group, chronically implanted with auditory cortex and periocular electrodes. These functions were assessed only at the end of the experiments in the o...

The pathological patterns of the sensory epithelium of the crista ampullaris of a guinea pig were studied after streptomycin and kanamycin administration. The silver reaction method and succinic dehydrogenase staining were applied for the entire surfaces of all specimens. Differences in sensitivity to antibiotics were confirmed in the sensory cells of the central and the peripheral regions of the crista (Lindeman, 1969 a).

In normal guinea pigs Ethacrynic acid was shown to cause a reversible high-tone hearing loss with evidence of recruitment. There was a definite tendency to a dose-response relationship. The unchanged Preyer reflex level, in animals with even marked elevations of the hearing threshold, demonstrated the impossibility of evaluating hearing function by Preyer reflex determinations only. Kanamy-cin-treated animals demonstrated unimpaired ability to respond to Ethacrynic acid as above.

Surface preparations of the organ of Corti have been studied by phase contrast microscopy in guines pigs treated with minimal doses of kanamycin. One of the earliest changes observed is a disturbance of the orderly W-pattern of the stereocilia of the outer hair cells in the basal coil. Occasional cells also show enlarged nuclei. Gaps appear in the ranks of the outer hair cells, especially in the first row, where cells have degenerated and disappeared, leaving only the empty reticular framework. At a later stage the inner hair cells also begin to drop out. Cell counts are presented showing the distribution of the losses. The method permits a quick, direct, quantitative assessment of damage to the organ of Corti, without the delays and uncertainties of the celloidin technique.

Negative potential in scala media during early anoxia was recorded in both normal and kanamycin-treated guinea pigs. In kanamycin-treated animals, in which the cochlear microphonic was remarkably depressed, decline of the dc potential was slower and its negative value smaller than in non-treated animals. After prolonged asphyxia, amplitude of postmortem cochlear microphonic was increased by an anodal current. The polarity of the negative potential could be changed by application of positive pressure to scala vestibuli, whereby the postmortem cochlear microphonic was enhanced. However, neither application of pressure nor current produced any enhancement of cochlear microphonic after the negative potential in scala media reached zero. These data indicate that the negative potential in the scala media of the asphyxiated cochlea is ascribed to depolarization of the normally polarized hair-bearing ends of the hair cells and that stria vascularis is sensitive, while the hair-bearing ends of the hair cells are i...

The spiral ganglion cell population was evaluated in 41 ears from 29 profoundly deaf patients. In 10 ears 66 to 100 per cent of the spiral ganglion cells remained, in 3 ears 33 to 66 per cent of the cells remained, and in 28 ears less than 33 per cent remained. In all of these ears there was severe atrophy of the organ of Corti. When the etiology of the deafness is known it often is possible to predict the condition of the ganglion. An excellent ganglion cell population would be expected if the deafness was due to ototoxic drugs and a severe loss of ganglion if due to bacterial labyrinthitis.

A patient with chronic pyelonephritis and uremia was treated with Kanamycin, 1 g daily for 11 days. This treatment caused grave damage to the internal ear, manifesting itself by complete deafness of both ears, as well as abolished caloric reaction of the right ear and reduced caloric reaction of the left. Subsequent histological examination of the temporal bones revealed degeneration of the neuroepithelial hair-cells everywhere in the internal ear, though chiefly in the basal part of the organ of Corti. The case demonstrates the great risk involved in the Kanamycin treatment of patients with impaired renal function. This risk must be supposed to be increased if the patient has been treated previously with streptomycin or dihydrostreptomycin.

The levels of streptomycin, kanamycin and neomycin in inner ear fluid were determined. These antibiotics penetrate into the inner ear slowly and relatively in small amounts and are eliminated more slowly than from the blood. The most slow to be eliminated is neomycin and therefore after repeated daily doses there is regularly some cumulation. In cases of the middle ear otitis concentration of antibiotics in the inner ear is multiplied.

Pregnant guinea pigs were treated with Kanamycin at three different stages of gestation (dating by method of post-partum ovulation). Twenty-nine newborn guinea pigs were tested electrophysiologically by recording the cochlear microphonic potential and the compound action potential from the round window in response to clicks and filtered clicks at 8,000 Hz. Six of the test animals showed the same electrophysiological changes as those found in adult mammals after Kanamycin intoxication. The results suggest a relationship between the ototoxicity of Kanamycin and the onset of auditory function. Cochlear potential and compound action potential were mostly affected when intoxication was performed during the last 15 days of gestation. This study confirms the results previously published by Uziel 1979.

It has previously been shown that simple compounds with multiple amine groups are ototoxic, the degree of ototoxicity depending on the number of amine groups in the molecule. The relationship between the number of amino groups and ototoxicity in aminoglycoside was studied using kanamycin A and kanamycin B, which contain 4 and 5 amino groups respectively. Forty-five pigmented guinea pigs were injected intratympanically with 0.1 ml of different concentrations of kanamycin A and kanamycin B. The animals were sacrificed 4 days after injection and the organ of Corti was studied by scanning electron microscopy. It was found that on an equimolar basis, kanamycin B (with 5 amino groups) is more cochleotoxic than kanamycin A (with 4 amino groups). The greater cochleotoxic potential of kanamycin B may be explained by the higher cationic nature of the molecule due to protonation of the amino--NH2 groups at physiological pH, resulting in a greater affinity between the drug and the cell membrane.