A comparison of the protective effects of systemic administration of a pro-glutathione drug and a Src-PTK inhibitor against noise-induced hearing loss

Both the antioxidant, n-l-acetyl cysteine (L-NAC) and the Src inhibitor, KX1-004, have been used to protect the cochlea from hazardous noise. To date, KX1-004 has only been used locally on the round window. In the current study, the two drugs were administered systemically. LNAC was delivered intraperitoneally at a dose of 325 mg/kg while KX1-004 was administered subcutaneously at a dose of 50 mg/kg. The noise exposure consisted of a 4 kHz octave band of noise at 100 dB SPL for 6 hours/day for 4 days. The drugs were administered once each day, 30 minutes prior to the onset of the noise exposure. The animals' hearing was estimated using the evoked response records from surgically-implanted chronic electrodes in the inferior colliculi. Animals treated with LNAC and KX1-004 had from 10 to 20 dB less temporary threshold shift at day 1 and an average 10 dB less permanent threshold shift by day 21 when compared to control saline treated animals. There were no significant side effects (i.e.: appetite loss, weight loss, lethargy, etc.) related to either of the drug treatments. KX1-004 produced at least as much protection as L-NAC, but at a significantly lower concentration.

Effects of d-methamphetamine on auditory and visual reaction times and detection thresholds in the baboon

Baboons were trained in both auditory and visual reaction time procedures to release a response lever in the presence of low-intensity stimuli. By varying the stimulus intensity from trial to trial, functions relating reaction time (elapsed time from stimulus onset to lever release) to stimulus intensity were established, and detection thresholds were measured. The effects of acute, IM injections of d-methamphetamine (0.001-1.0 mg/kg) were examined on these psychophysical performance baselines. Reaction times for acoustic stimuli generally were faster for higher drug doses, whereas reaction times for visual stimuli either lengthened or shortened, depending on both drug dose and individual differences among animals. Auditory thresholds were unaffected at all drug doses studied, whereas visual thresholds were generally elevated at doses of 0.1 mg/kg and above.

Effect over time of allopurinol on noise-induced hearing loss in guinea pigs

Temporary threshold shift (TTS) and permanent threshold shift (PTS) may follow prolonged noise exposure. Several reports suggest that noise-induced damage to the cochlea may be related to the activity of reactive oxygen species (ROS). Drugs that scavenge or block ROS formation also protect the cochlea. Guinea pigs, treated with allopurinol, were exposed to white noise (120 dB SPL) or impulse noise (114 dB SPL) for 2 and 5 h. The protective effect of allopurinol was confirmed, but, at these levels of sound, it was present only after noise exposure up to 2 h. This study also offers evidence suggesting that allopurinol does not influence the establishment of PTS.

Electrophysiologic assessment of low-frequency hearing: sedation effects

Sixteen normal-hearing adults were tested in both awake and sedated states for several evoked responses to low-frequency stimuli. Responses obtained by cross-correlation function, middle latency responses, and the 40-Hz response proved most sensitive; all had mean thresholds of less than 20 dB normal hearing level for the awake-alert state, but 40-Hz and middle latency response mean thresholds were shifted about 10 dB under sedation. The cross-correlation method seems to offer promise for pediatric auditory assessment.

Nephrotoxicity and ototoxicity of aztreonam versus aminoglycoside therapy in seriously ill nonneutropenic patients

A randomized double-blind clinical trial was done of aztreonam versus aminoglycoside therapy for the empiric treatment of seriously ill nonneutropenic patients suspected of aerobic gram-negative bacterial infection. Each patient was treated for greater than or equal to 72 h with the study drug. Nephrotoxicity, defined by greater than or equal to 50% increase in baseline serum creatinine, occurred in 12 (15%) of 92 patients receiving aminoglycoside therapy and 1 (1%) of 92 patients receiving aztreonam (P less than .004). More severe nephrotoxicity, defined by greater than or equal to 100% increase in baseline serum creatinine, occurred in 6 (6.5%) of 92 patients receiving aminoglycoside therapy and in 1 of 92 receiving aztreonam (P less than .11). Patients with an elevated baseline total bilirubin level were most likely to develop nephrotoxicity. Auditory toxicity occurred in 2 (7%) of 28 evaluatable patients receiving aminoglycoside therapy and in 1 (3%) of 33 receiving aztreonam (P less than .58). One patient, who received aminoglycoside, developed vestibular toxicity. In nonneutropenic patients believed to be at increased risk for renal dysfunction, aztreonam is a less toxic alternative to aminoglycoside therapy for treatment of suspected aerobic gram-negative infection.

[Clinical and electron microscopy study of sudden deafness treatment with the 10% HES 200/0.5 and pentoxifylline combination]

The incidence of sudden hearing loss has increased. The pathogenetic mechanisms are still unknown, but viral infections and vascular phenomena with acute impairment of microvascular perfusion are thought to play a major role. Infusion of hydroxyethyl starch (HES) is used as a regimen to treat sudden hearing loss. In our clinic, anaphylactic reactions due to HES have not been observed so far. However, the use of HES is still discussed controversially due to long-term storage of HES molecules in tissue and due to high incidence of long-lasting pruritus. In a retrospective analysis of 118 patients treated with HES for sudden hearing loss, we observed pruritus starting in 64% of patients one to three weeks after therapy. This symptom with a duration between two weeks and four months was refractory to medical interventions. During therapy with HES improvement of hearing was observed in 75% of patients, in 62% improvement of hearing persisted still at the end of the observation period (7 months post infusionem). Light and electron microscopic assessment of human skin biopsies of one patient after treatment with HES showed storage of HES especially within dermal macrophages. Pathogenetically a pathway independent of histamin seems responsible for the induction of pruritus. Accordingly, classic antihistaminic drugs had no therapeutic effect in our patients. Dextran is used as an alternative to hydroxyethyl starch. In contrast to HES, the often mentioned higher incidence of severe anaphylactic reactions due to dextran has dramatically decreased with hapten inhibition (after preinjection of monovalent haptendextran Promit).(ABSTRACT TRUNCATED AT 250 WORDS)

Streptomycin treatment in Menière's disease

Streptomycin treatment in Menière's disease has traditionally been used for control of vertigo in patients with severe bilateral involvement or unilateral involvement in the only hearing ear. Guidelines for use that have worked at the Shea Clinic are presented. In addition, a special case is discussed in which this form of therapy has been used for treatment of fluctuant hearing loss in a patient with Menière's disease.

Promotion of Noise-Induced Cochlear Injury by Toluene and Ethylbenzene in the Rat

Ethylbenzene + toluene are known individually to have ototoxic potential at high exposure levels and with prolonged exposure times generally of 4-16 weeks. Both ethylbenzene + toluene are minor constituents of JP-8 jet fuel; this fuel has recently been determined to promote susceptibility to noise-induced hearing loss. Therefore, the current study evaluates the ototoxic potential of combined exposure to ethylbenzene + toluene exposure in a ratio calculated from the average found in three laboratories. Rats received ethylbenzene + toluene by inhalation and half of them were subjected simultaneously to an octave band of noise (OBN) of 93-95 dB. Another group received only the noise exposure which was designed to produce a small, but permanent auditory impairment while an unexposed control group was also included. In two separate experiments, exposures occurred either repeatedly on 5 successive days for 1 week or for 5 days on 2 successive weeks to 4000 mg/m(3) total hydrocarbons for 6 h based upon initial pilot studies. The concentration of toluene was 400 ppm and the concentration of ethylbenzene was 660 ppm. Impairments in auditory function were assessed using distortion product otoacoustic emissions and compound action potential testing. Following completion of these tests, the organs of Corti were dissected to permit evaluation of hair cell loss. The uptake and elimination of the solvents was assessed by harvesting key organs at two time points following ethylbenzene + toluene exposure from additional rats not used for auditory testing. Similarly, glutathione (GSH) levels were measured in light of suggestions that oxidative stress might result from solvent-noise exposures. Ethylbenzene + toluene exposure by itself at 4000 mg/m(3) for 6 h did not impair cochlear function or yield a loss of hair cells. However, when combined with a 93-dB OBN exposure combined solvent + noise did yield a loss in auditory function and a clear potentiation of outer hair cell death that exceeded the loss produced by noise alone. No evidence was found for a loss in total GSH in lung, liver, or brain as a consequence of ethylbenzene + toluene exposure.

Trimethyltin disrupts auditory function and cochlear morphology in pigmented rats

Trimethyltin (TMT) produces auditory deficits, presumably of cochlear origin, in rats. The present study identified pathological changes in the cochlea following treatment with TMT and correlated them with auditory threshold changes. Thresholds were determined by reflex-modulation audiometry, before and after treatment with TMT or with saline vehicle. Animals were then perfused and their cochleas embedded for examination as block-surface preparations or radial sections. In the first week following treatment, all TMT-treated rats showed threshold shifts of 40 to 60 dB at 40 kHz, and smaller threshold shifts (10-25 dB) at 2.5 and 10 kHz. At 3 weeks they showed threshold shifts similar to those identified one week following treatment, but with some recovery at 10 kHz. At 10 weeks, one animal showed complete recovery and three showed recovery of function at 10 but not at 40 kHz. TMT-treated animals showed losses of outer hair cells (OHC) in the basal turn of the cochlea as early as 48 hours following exposure. Comparable OHC pathology was seen at 9 days, along with some losses of inner hair cells. More extensive pathology occurred at longer survival times including the loss of type 1 spiral ganglion cells. The loss of auditory sensitivity at high frequencies was closely related to the loss of outer hair cells in the basal turn of the cochlea.

The effect of gentamicin and furosemide given in combination on cochlear potentials in the guinea pig

Single doses of gentamicin and furosemide given in combination result in a rapid and profound loss of cochlear function. In this study, measurement of three gross cochlear potentials (cochlear microphonics, compound action potentials and the endocochlear potential) were carried out in order to determine the ototoxic sites of action of the drugs given in combination. The rapidity and severity of the cochlear deficit is dose dependent and with the doses employed in this study (80 mg/kg gentamicin i.v. 80 mg/kg furosemide i.v.), complete loss of cochlear function is seen after about 72 hours. Twenty-four hours after i.v. administration of the drugs, significant increases in compound action potential thresholds between 6 and 32 kHz were seen. In contrast, over this frequency range the generation of cochlear microphonics in response to stimulus levels of 70 dB SPL appeared to be unaffected. The endocochlear potential remained unaffected at 24 and 72 hours after administration. These findings are taken as evidence that the primary site of ototoxic action of the two drugs in combination may be at the level of the inner hair cells and/or the afferent synapse.

Hair cell regeneration after local application of gentamicin at the round window of the cochlea in the pigeon

Hair cells in the basilar papilla of birds have the capacity to regenerate after injury. Methods commonly used to induce cochlear damage are systemic application of ototoxic substances such as aminoglycoside antibiotics or loud sound. Both methods have disadvantages. The systemic application of antibiotics results in damage restricted to the basal 50% of the papilla and has severe side effects on the kidneys. Loud sound damages only small parts of the papilla and is restricted to the short hair cells. The present study was undertaken to determine the effect of local aminoglycoside application on the physiology and morphology of the avian basilar papilla. Collagen sponges loaded with gentamicin were placed at the round window of the cochlea in adult pigeons. The time course of hearing thresholds was determined from auditory brain stem responses elicited with pure tone bursts within a frequency range of 0.35-5.565 kHz. The condition of the basilar papilla was determined from scanning electron micrographs. Five days after application of the collagen sponges loaded with gentamicin severe hearing loss, except for the lowest frequency tested, was observed. Only at the apical 20% of the basilar papilla hair cells were left intact, all other hair cells were missing or damaged. At all frequencies there was little functional recovery until day 13 after implantation. At frequencies above 1 kHz functional recovery occurred at a rate of up to 4 dB/day until day 21, beyond that day recovery continued at a rate below 1 dB/day until day 48 at the 5.6 kHz. Below 1 kHz recovery occurred up to day 22, the recovery rate was below 2 dB/day. A residual hearing loss of about 15-25 dB remained at all frequencies, except for the lowest frequency tested. At day 20 new hair cells were seen on the basilar papilla. At day 48 the hair cells appeared to have recovered fully, except for the orientation of the hair cell bundles. The advantage of the local application of the aminoglycoside drug over systemic application is that it damages almost all hair cells in the basilar papilla and it has no toxic side effects. The damage is more extensive than with systemic application.

Steroid-responsive cochlear dysfunction in the MRL/lpr autoimmune mouse

Corticosteroids historically have been used to treat autoimmune sensorineural hearing loss, although little is known of how steroids restore normal inner ear function. Therefore, to identify a potential model for this field of research, this study examined the effects of prednisolone on auditory brain stem response thresholds in the MRL/lpr mouse model of autoimmune sensorineural hearing loss. Mice treated with prednisolone after auditory threshold elevations demonstrated significant improvement and stabilization of thresholds compared with untreated controls. MRL/lpr mice treated with steroids before the onset of autoimmune disease and cochlear dysfunction demonstrated decreased serum immune complexes, higher survival rates, and lower auditory thresholds compared with untreated controls. These positive results suggest the autoimmune mouse may be useful for studies of steroid-responsive mechanisms of the cochlea in autoimmune sensorineural hearing loss, as well as any hearing disorder in which steroid therapy is currently used.

Round window pH manipulation alters the ototoxicity of systemic cisplatin

The effect of manipulation of pH on the ototoxicity of systemic cisplatin was studied in Wistar rats. After control auditory brainstem responses (ABR) were performed, the auditory bullae were opened and acidic (pH 6.0), neutral (pH 7.4) or basic (pH 9.0) phosphate-buffered saline (PBS) was applied to fill the round window niche (RWN). After 30 min, 13 mg/kg cisplatin solution or saline was administered intraperitoneally. After 3 days, follow-up ABRs were performed and cochleae were processed for morphological analysis. Animals that received basic PBS on the RWN and cisplatin intraperitoneally had significantly smaller ABR threshold shifts compared to rats pretreated with neutral pH buffer (P<0.05). Animals that received acidic PBS on the RWN and systemic cisplatin showed significantly greater ABR threshold shifts compared to those pretreated with neutral pH buffer (P<0.05). No significant threshold changes were observed in animals that received buffer of any pH on the RWN, followed by saline intraperitoneally. Semiquantitative analysis of hair cell survival confirmed a protective effect by basic PBS against cisplatin and a synergistic effect by acidic PBS on cisplatin ototoxicity (P<0.05). It appears that changes in cochlear pH can modulate the ototoxic effects of systemically applied cisplatin.

Potentiation of kanamycin ototoxicity by a history of noise exposure

Chinchillas were exposed to a noise band (1,414 to 5,656 Hz, 100-dB sound pressure level [SPL] for one hour) and treated with kanamycin (150 mg/kg a day until hearings loss was noted at 6.0 kHz) either separately, simultaneously, or sequentially. Simultaneous noise and kanamycin resulted in interactive potentiation of threshold shift and cochlear pathologic condition. Kanamycin treatment two months after noise exposure produced similar potentiation. No interaction was seen when noise exposure occurred one month after kanamycin treatment.

Effects of nimodipine on noise-induced hearing loss

The effects of nimodipine, a calcium channel blocker, on noise-induced hearing loss were examined in gerbils. Animals were implanted subcutaneously with a timed-release pellet containing either nimodipine (approximately 10 mg/kg/day) or placebo and exposed to either 102 or 107 dBA noise. Serum levels were tested in two subjects and were in the range known to protect humans from cerebral artery vasospasm and ischemia-related neurologic deficits. Nimodipine and control groups had similar amounts of noise-induced (a) permanent threshold shift; (b) reductions in distortion product otoacoustic emissions; (c) reductions in tuning and suppression of the compound action potential; and (d) loss of outer hair cells. The results suggest that nimodipine, at a dose which results in clinically relevant serum levels, does not provide protection from the effects of moderately intense noise exposures.

Functional and morphological effects of styrene on the auditory system of the rat

The effect of inhaled styrene on the structure and function of the auditory organ of the male Wistar rat was studied. The animals were exposed either to 600, 300 or 100 ppm styrene (12 h/day, 5 days/week, for 4 weeks). Auditory sensitivity was tested prior to and after the exposure by auditory brain stem audiometry (ABR) at frequencies of 1.0, 2.0, 4.0 and 8.0 kHz. Inner ear morphological changes were studied by light- and electron-microscopy. Exposure to 600 ppm styrene caused a 3 dB hearing loss only at the highest test frequency (8 kHz). Quantitative morphological analysis of cochlear hair cells (cytocochleograms) showed that 600 ppm styrene caused a severe outer hair cell (OHC) loss particularly in the third OHC row of the upper basal and lower middle coil. The inner hair cells were usually intact. Exposure to lower styrene concentrations (100 and 300 ppm) caused no unequivocal functional deficit or hair cell damage. We conclude that there appears to be a concentration threshold for styrene ototoxicity in rats (between 300 and 600 ppm).

Kanamycin ototoxicity in glutamate transporter knockout mice

Glutamate-aspartate transporter (GLAST), a powerful glutamate uptake system, removes released glutamate from the synaptic cleft and facilitates the re-use of glutamate as a neurotransmitter recycling system. Aminoglycoside-induced hearing loss is mediated via a glutamate excitotoxic process. We investigated the effect of aminoglycoside ototoxicity in GLAST knockout mice using the recorded auditory brainstem response (ABR) and number of hair cells in the cochlea. Kanamycin (100 mg/mL) was injected directly into the posterior semicircular canal of mice. Before the kanamycin treatment, there was no difference in the ABR threshold average between the wild-type and knockout mice. Kanamycin injection aggravated the ABR threshold in the GLAST knockout mice compared with the wild-type mice, and the IHC degeneration was more severe in the GLAST knockout mice. These findings suggest that GLAST plays an important role in preventing the degeneration of inner hair cells in aminoglycoside ototoxicity.

Detection of tobramycin- and netilmicin-induced ototoxicity in guinea pigs with evoked action potentials

To evaluate the action potentials evoked in the cochlea in aminoglycoside-induced ototoxicity, 80 guinea pigs were given 25, 50, 75, or 100 mg of tobramycin or netilmicin/kg per day for 14 or 28 days. Ten other guinea pigs (controls) were given 200 mg of ampicillin/kg per day for 14 or 28 days. Cochlear evoked action potentials (CEAP) before and after treatment were measured, and the cochlea was examined microscopically after treatment. Comparison of initial and final values showed that the threshold of the main negative (N1) wave rose (p less than 0.00001 for dose and duration factors), the amplitude decreased (P less than 0.00001 for dose factors at sound intensities of 120 and 90 dB, P less than 0.001 at 70 dB), and the latency lengthened (P less than 0.0001 for dose factors at 120 and 90 dB). The CEAP method appeared to be more sensitive than microscopic examination of the cochlea for detection of ototoxicity induced by the lower dosages of the aminoglycosides. No significant differences were observed between the effects of tobramycin and netilmicin. In conclusion, the CEAP method appears to be a promising tool for detection of aminoglycoside-induced ototoxicity.

Hearing preservation using topical dexamethasone alone and associated with hyaluronic acid in cochlear implantation

CONCLUSION

Topical dexamethasone associated with hyaluronic acid in cochlear implant surgery demonstrated a statistically significant difference in the preservation of low-frequency thresholds when compared with topical dexamethasone alone and a control group. Topical dexamethasone alone was not superior in hearing preservation when compared to the control group.

OBJECTIVE

To compare the effects of topical dexamethasone alone and associated with hyaluronic acid intraoperatively in hearing preservation in cochlear implantation.

METHODS

Eighteen severely to profoundly hearing-impaired adult patients with measurable hearing were divided into three groups preoperatively: cochlear implantation as a control group (group 1), cochlear implantation using topical dexamethasone intraoperatively (group 2), and cochlear implantation using topical dexamethasone associated with hyaluronic acid intraoperatively (group 3). Preimplant and postimplant low-frequency pure-tone averages (PTAs) were calculated from unaided audiograms at 125, 250, and 500 Hz.

RESULTS

The mean changes in the low-frequency PTA comparing postoperative against preoperative thresholds were 28.03 ± 6.77 dB in group 1, 30 ± 14.53 dB in group 2, and 7.23 ± 6.12 dB in group 3. There was statistical difference when comparing group 3 with groups 1 and 2 using one-way ANOVA (p = 0.002) followed by Scheffé post hoc test.

Mice expressing constitutively active Gsalpha exhibit stimulus encoding deficits similar to those observed in schizophrenia patients

People with schizophrenia display sensory encoding deficits across a broad range of electrophysiological and behavioral measures, suggesting fundamental impairments in the ability to transduce the external environment into coherent neural representations. This inability to create basic components of complex stimuli interferes with a high fidelity representation of the world and likely contributes to cognitive deficits. The current study evaluates the effects of constitutive forebrain activation of the G(s)alpha G-protein subunit on auditory threshold and gain using acoustic brainstem responses and cortically generated N40 event-related potentials to assess the role of cyclic AMP signaling in sensory encoding. Additionally, we examine the ability of pharmacological treatments that mimic (amphetamine) or ameliorate (haloperidol) positive symptoms of schizophrenia to test the hypothesis that the encoding deficits observed in G(s)alpha transgenic mice can be normalized with treatment. We find that G(s)alpha transgenic mice have decreased amplitude of cortically generated N40 but normal acoustic brainstem response amplitude, consistent with forebrain transgene expression and a schizophrenia endophenotype. Transgenic mice also display decreased stimulus intensity response (gain) in both acoustic brainstem response and N40, indicating corticofugal influence on regions that lack transgene expression. N40 deficits in transgenic animals were ameliorated with low dose haloperidol and reversed with higher dose, suggesting dopamine D2 receptor-linked Gi activity contributes to the impairment. Consistent with this hypothesis, we recreated the G(s)alpha transgenic deficit in wild type animals using the indirect dopamine agonist amphetamine. This transgenic model of sensory encoding deficits provides a foundation for identifying biochemical contributions to sensory processing impairments associated with schizophrenia.

Effect of intratympanically administered gentamicin on hearing and tinnitus in Menière's disease

We have examined the effect of intratympanic gentamicin on hearing and tinnitus in 69 patients with intractable Menière's disease. Tinnitus was scored from 1 to 4 depending on its severity. The mean pure tone audiometry level before treatment was 57.5 dB and 1 year after treatment 63.5 dB Five subjects became deaf in the treated ear, and in 13 subjects hearing loss was > 10 dB and in 21 subjects 0 10 dB. In 25 subjects significant improvement (> 10 dB) was gained, and in 5 patients. Tinnitus was significantly reduced after treatment with gentamicin. A total of 66 patients had tinnitus before treatment and tinnitus relief was rated as good. Four percent of the subjects had no tinnitus, 30% had slight tinnitus. 27% moderate tinnitus. 18% severe and 8% handicapping tinnitus.

[Experimental studies of the protective effect of deferoxamine mesilate on cisplatin induced toxicity]

Cisplatin (CDDP) is an antitumor agent against several types of neoplasms. It has, however, various side effects such as nephrotoxicity and ototoxicity. Several efforts have been made to prevent these toxic side effects. On the other hand, deferoxiamine mesilate (DFO), an iron-chelating agent, has been used for iron-overloaded patients. Since the 1980s, many authors have reported DFO-associated hearing impairment. Some experimental data suggest that DFO itself was responsible for ototoxicity. In addition, it has also been recognized that DFO can act as a free radical scavenger. Experimental trials using DFO are also expected to prevent CDDP-induced toxicity because its generation mechanism is thought to be associated with free radical formation. The present study was planned to investigate whether DFO, which might be an ototoxic agent, had a protective effect against various CDDP-induced toxicities including ototoxicity. Fisher rats were used in this study and were divided into four groups: 1) Group I, a vehicle control, 2) Group II, animals receiving 100 mg of DFO per kg, 3) Group III, animals administered 0.9 mg of CDDP per kg alone and 4) Group IV, animals receiving 100 mg of DFO per kg 60 min before 0.9 mg of CDDP per kg for 10 days. First, the protective effect of DFO against CDDP-induced ototoxicity was studied. The auditory threshold was determined by using the compound action potential (CAP) from the round window membrane. CAPs were recorded on the 5th day after completion of drug administration. Then CAPs recording, cochlear sensory epithelia were observed over all the turns of the cochlea by scanning electron microscopy. There were no significant differences in CAP thresholds between Group I and IV, though the thresholds in Group III were significantly higher at 16 kHz and 20 kHz than those in Group IV. The rate of missing outer hair cells in Group IV was significantly lower than that in Group III. The results clearly demonstrated that DFO had a protective effect against CDDP-induced ototoxicity. Second, the protective effect of DFO against CDDP-induced nephrotoxicity was studied. Renal function was evaluated by measuring blood urea nitrogen (BUN) and serum creatinine (Cr) levels. Both BUN and Cr levels in Group IV were significantly lower than those in Group III. The data suggested that DFO preadministration prevented CDDP-induced nephrotoxicity. Third, the influence of DFO on the antitumor activity of CDDP was investigated in rats inoculated with squamous cell carcinoma cells (SCC-131) subcutaneously. The influence of drugs was determined by measuring the tumor growth rate. There was no difference in the tumor growth rate between Group III and IV. The result revealed that DFO had no influence on CDDP antitumor activity. In conclusion, the above results demonstrating that DFO preadministration can prevent both CDDP-induced ototoxicity and nephrotoxicity without attenuation of CDDP antitumor activity, suggest the usefulness of CDDP antitumor chemotherapy.

Effects of d-amphetamine and methylphenidate upon auditory threshold in the squirrel monkey

The effects of d-amphetamine sulfate and methylphenidate hydrochloride on auditory thresholds in ten squirrel monkeys were examined using a 4.2 kHz stimulus in a free field. The results indicated that d-amphetamine raised auditory thresholds but methylphenidate did not alter the thresholds. The elevation of sensory thresholds by d-amphetamine was in agreement with previous studies suggesting that the drug acts as a behavioral depressant in diurnal animals.

Decreased inhibition to lateral superior olive neurons in young and aged Sprague-Dawley rats

Lateral superior olive (LSO) neurons in young and aged Sprague-Dawley rats have functional properties consistent with a limited contralateral inhibition, which is markedly different from other animals. An unusually low proportion of LSO cells (36/113) exhibited contralateral inhibition (and ipsilateral excitation, IE), while over 25% of LSO units exhibited excitatory responses to contralateral stimuli. Inhibition of most IE LSO neurons was evident only when the contralateral intensity was greater than the ipsilateral intensity, resulting in a marked shift in sensitivity to interaural intensity differences (IID). The firing rate of IE neurons was also affected more by a change in intensity of ipsilateral compared to contralateral stimuli. The shift in the IID sensitivity and the relative decrease in effectiveness of contralaterally driven inhibition in Sprague-Dawley rat LSO neurons could be due to decreased inhibitory inputs from the MNTB principal cells, increased contralateral excitatory effects and/or increased ipsilateral excitatory effects. Age-related decreases in the numbers of MNTB neurons observed anatomically is not reflected in a change in LSO function. The Sprague-Dawley rat may be a useful model for the effect of reduced inhibition in the superior olivary complex on auditory behavior.

Frequency selective effects of alcohol on auditory detection and frequency discrimination thresholds

In the first of two experiments, the effects of ethyl alcohol on monaural and binaural thresholds for pure tones were measured for a range of frequencies. The results showed a frequency-specific effect in which low frequencies were more severely affected than higher ones. Also, monaural thresholds tended to be more affected by alcohol than binaural ones. The second experiment extended this exploration by measuring frequency discrimination at several different frequencies. In this case, we also obtained a frequency-dependent effect: the increase in discrimination thresholds above 1000 Hz was three times greater than that for lower frequencies. The data suggest that the choice of stimuli may influence the ability to detect changes in auditory performance after alcohol and may account in part for the differences among earlier studies. The results are consistent with the hypothesis that alcohol is acting centrally, at the level of mechanisms involved in the temporal and binaural summation of auditory signals, rather than influencing peripheral structures.