Effects of Calcitonin-Gene-Related-Peptide on Auditory Nerve Activity.

Calcitonin-gene-related peptide (CGRP) is a lateral olivocochlear (LOC) efferent neurotransmitter. Depression of sound-driven auditory brainstem response amplitude in CGRP-null mice suggests the potential for endogenous CGRP release to upregulate spontaneous and/or sound-driven auditory nerve (AN) activity. We chronically infused CGRP into the guinea pig cochlea and evaluated changes in AN activity as well as outer hair cell (OHC) function. The amplitude of both round window noise (a measure of ensemble spontaneous activity) and the synchronous whole-nerve response to sound (compound action potential, CAP) were enhanced. Lack of change in both onset adaptation and steady state amplitude of sound-evoked distortion product otoacoustic emission (DPOAE) responses indicated CGRP had no effect on OHCs, suggesting the origin of the observed changes was neural. Combined with results from the CGRP-null mice, these results appear to confirm that endogenous CGRP enhances auditory nerve activity when released by the LOC neurons. However, infusion of the CGRP receptor antagonist CGRP (8-37) did not reliably influence spontaneous or sound-driven AN activity, or OHC function, results that contrast with the decreased ABR amplitude measured in CGRP-null mice.

Disruption of lateral olivocochlear neurons with a dopaminergic neurotoxin depresses spontaneous auditory nerve activity.

Neurons of the lateral olivocochlear (LOC) system project from the auditory brainstem to the cochlea, where they synapse on radial dendrites of auditory nerve fibers. Selective LOC disruption depresses sound-evoked auditory nerve activity in the guinea pig, but enhances it in the mouse. Here, LOC disruption depressed spontaneous auditory nerve activity in the guinea pig. Recordings from single auditory nerve fibers revealed a significantly reduced proportion of fibers with the highest spontaneous firing rates (SRs) and an increased proportion of neurons with lower SRs. Ensemble activity, estimated using round window noise, also decreased after LOC disruption. Decreased spontaneous activity after LOC disruption may be a consequence of reduced tonic release of excitatory transmitters from the LOC terminals in guinea pigs.

Dynorphin release by the lateral olivocochlear efferents may inhibit auditory nerve activity: a cochlear drug delivery study.

Dynorphin (dyn) is suggested to excite the auditory nerve (AN) when released by the lateral olivocochlear (LOC) efferents. However, previous studies evaluated either intravenously delivered dyn-like agents, raising the potential for systemic (central) effects, or agent concentrations unlikely to be achieved via endogenous cochlear release. This study tested the hypothesis that biologically relevant increases in dyn levels in the cochlea achieved via diffusion of the drug of (-)pentazocine across the round window membrane enhances AN firing. In general, amplitude of the cochlear whole-nerve action potential (CAP) was depressed following drug application. These results suggest that dyn released by the LOC neurons would likely act as an inhibitory transmitter substance in the LOC system; neurotransmission is one of the LOC system's vast unknowns.

Acoustic experience alters the aged auditory system.

OBJECTIVES: Presbyacusis, one of the most common ailments of the elderly, is often treated with hearing aids, which serve to reintroduce some or all of those sounds lost to peripheral hearing loss. However, little is known about the underlying changes to the ear and brain as a result of such experience with sound late in life. The present study attempts to model this process by rearing aged CBA mice in an augmented acoustic environment (AAE). DESIGN: Aged (22-23 months) male (n = 12) and female (n = 9) CBA/CaJ mice were reared in either 6 weeks of low-level (70 dB SPL) broadband noise stimulation (AAE) or normal vivarium conditions. Changes as a function of the treatment were measured for behavior, auditory brainstem response thresholds, hair cell cochleograms, and gamma aminobutyric acid neurochemistry in the key central auditory structures of the inferior colliculus and primary auditory cortex. RESULTS: The AAE-exposed group was associated with sex-specific changes in cochlear pathology, auditory brainstem response thresholds, and gamma aminobutyric acid neurochemistry. Males exhibited significantly better thresholds and reduced hair cell loss (relative to controls) whereas females exhibited the opposite effect. AAE was associated with increased glutamic acid decarboxylase (GAD67) levels in the inferior colliculus of both male and female mice. However, in primary auditory cortex AAE exposure was associated with increased GAD67 labeling in females and decreased GAD67 in males. CONCLUSIONS: These findings suggest that exposing aged mice to a low-level AAE alters both peripheral and central properties of the auditory system and these changes partially interact with sex or the degree of hearing loss before AAE. Although direct application of these findings to hearing aid use or auditory training in aged humans would be premature, the results do begin to provide direct evidence for the underlying changes that might be occurring as a result of hearing aid use late in life. These results suggest the aged brain retains significantly anatomical, electrophysiological, and neurochemical plasticity.

Age-related GABAA receptor changes in rat auditory cortex.

Auditory cortex (AI) shows age-related decreases in pre-synaptic markers for gamma-aminobutyric acid (GABA) and degraded AI neuronal response properties. Previous studies find age-related increases in spontaneous and driven activity, decreased spectral and directional sensitivity, and impaired novelty detection. The present study examined expression of GABA(A) receptor (GABA(A)R) subunit message, protein, and quantitative GABA(A)R binding in young, middle-aged, and aged rat AI, with comparisons with adjoining parietal cortex. Significant loss of GABA(A)R α(1) subunit message across AI layers was observed in middle-aged and aged rats and α(1) subunit protein levels declined in layers II and III. Age-related increases in GABA(A)R α(3) subunit message and protein levels were observed in certain AI layers. GABA(A)R subunits, including ß(1), ß(2), γ(1), γ(2s), and γ(2L), primarily, but not exclusively, showed age-related declines at the message and protein levels. The ability of GABA to modulate [(3)H]t-butylbicycloorthobenzoate binding in the chloride channel showed age-related decreases in peak binding and changes in desensitization kinetics. Collectively, age-related changes in GABA(A)R subunit composition would alter the magnitude and temporal properties of inhibitory synaptic transmission and could underpin observed age-related functional changes seen in the elderly.

Metabolic effects of intra-abdominal fat in GHRKO mice.

Mice with targeted deletion of the growth hormone receptor (GHRKO mice) are growth hormone (GH) resistant, small, obese, hypoinsulinemic, highly insulin sensitive and remarkably long-lived. To elucidate the unexpected coexistence of adiposity with improved insulin sensitivity and extended longevity, we examined effects of surgical removal of visceral (epididymal and perinephric) fat on metabolic traits related to insulin signaling and longevity. Comparison of results obtained in GHRKO mice and in normal animals from the same strain revealed disparate effects of visceral fat removal (VFR) on insulin and glucose tolerance, adiponectin levels, accumulation of ectopic fat, phosphorylation of insulin signaling intermediates, body temperature, and respiratory quotient (RQ). Overall, VFR produced the expected improvements in insulin sensitivity and reduced body temperature and RQ in normal mice and had opposite effects in GHRKO mice. Some of the examined parameters were altered by VFR in opposite directions in GHRKO and normal mice, and others were affected in only one genotype or exhibited significant genotype × treatment interactions. Functional differences between visceral fat of GHRKO and normal mice were confirmed by measurements of adipokine secretion, lipolysis, and expression of genes related to fat metabolism. We conclude that in the absence of GH signaling, the secretory activity of visceral fat is profoundly altered and unexpectedly promotes enhanced insulin sensitivity. The apparent beneficial effects of visceral fat in GHRKO mice may also explain why reducing adiposity by calorie restriction fails to improve insulin signaling or further extend longevity in these animals.

Lack of association of a spontaneous mutation of the Chrm2 gene with behavioral and physiologic phenotypic differences in inbred mice.

The nucleotide substitution C797T in the Chrm2 gene causes substitution of leucine for proline at position 266 (P266L) of the CHRM2 protein. Because Chrm2 codes for the type 2 muscarinic receptor, this mutation could influence physiologic and behavioral phenotypes of mice. Chrm2 mRNA was not differentially expressed in 2 brain regions with high cholinergic innervation in a mouse strain that does (BALB/cByJ) or does not (C57BL/6J) have the mutation. In addition, strains of mice with and without the C797T point mutation in Chrm2 did not differ significantly in muscarinic binding properties. Variation across strains was detected in terms of acoustic startle, prepulse inhibition, and the physiologic effects of the muscarinic agonist oxotremorine. However, interstrain differences in these measures did not correlate with the presence of the mutation. Although we were unable to associate a measurable phenotype with the Chrm2 mutation, assessment of the mutation on other genetic backgrounds or in the context of other traits might reveal differential effects. Therefore, despite our negative findings, evaluation of characteristics that involve muscarinic function should be undertaken with caution when comparing mice with different alleles of the Chrm2 gene.

Processing of broadband stimuli across A1 layers in young and aged rats.

Presbycusis can be considered a slow age-related peripheral and central deterioration of auditory function which manifests itself as deficits in speech comprehension, especially in noisy environments. The present study examined neural correlates of a simple broadband noise stimulus in primary auditory cortex (A1) of young and aged Fischer-Brown Norway (FBN) rats. Age-related changes in unit responses to broadband noise bursts and spontaneous activity were simultaneously recorded across A1 layers using a single shank, 16-channel electrode. Noise bursts were presented contralateral to the left A1 at 80 dB SPL. Aged A1 units displayed increased spontaneous (29%), peak (24%), and steady state response rates (38%) than did young A1 units. This was true across all A1 layers, although age-related differences were significantly greater for layers I-III (43% vs 18%) than lower layers. There was a significant age-related difference in the depth and duration of post-onset suppression between young and aged upper layer A1 units. The present functional differences across layers were consistent with studies showing greatest losses of gamma-aminobutyric acid (GABA) markers in superficial layers of A1 and with anatomic studies showing highest levels of inhibitory neurons located in superficial cortical layers. The present findings were also consistent with aging studies suggesting loss of functional inhibition in other cortical sensory systems.

Sleep, activity, temperature and arousal responses of mice deficient for muscarinic receptor M2 or M4.

AIMS: The type 2 muscarinic receptor (M2R) differs from the other G-protein-coupled muscarinic receptor (type 4, or M4R) in tissue distribution and physiologic effects. We studied the impact of these receptors on sleep and arousal by using M2R and M4R knock-out (KO) mice. MAIN METHODS: M2R and M4R KO and genetically intact mice were compared in terms of normal patterns of sleep, responses to sleep loss, infectious challenge and acoustic startle, and acoustic prepulse inhibition of startle (PPI). KEY FINDINGS: Under basal conditions, M2R and M4R KO mice do not differ from the background strain or each other in the amount or diurnal pattern of sleep, locomotor activity, and body temperature. After enforced sleep loss, M2R KO mice, in contrast to the other two strains, show no rebound in slow-wave sleep (SWS) time, although their SWS is consolidated, and they show a greater rebound in time spent in REMS (rapid-eye-movement sleep) and REMS consolidation. During influenza infection, M2R KO mice, as compared with the other strains, show marked hypothermia and a less robust increase in SWS. During Candida albicans infection, M2R KO mice show a greater increase in SWS and a greater inflammatory response than do the other strains. M2R KO mice also show greater acoustic startle amplitude than does the background strain, although PPI was not different across the 3 strains over a range of stimulus intensities. SIGNIFICANCE: Taken together, these findings support different roles for M2R and M4R in the modulation of sleep and arousal during homeostatic challenge.

Early prediction of response to chemoradiotherapy for head and neck cancer: reliability of restaging with combined positron emission tomography and computed tomography.

OBJECTIVE: To assess the role of combined positron emission tomography and computed tomography (PET-CT) in predicting early treatment response at the primary site and in the neck after chemoradiotherapy (CRT) for advanced squamous cell carcinoma of the head and neck (SCCHN). DESIGN: Retrospective analysis with a median follow-up of 24 months. SETTING: Academic, tertiary referral center. PATIENTS AND INTERVENTIONS: Thirty-one patients who were treated with concomitant intra-arterial CRT underwent PET-CT 6 to 8 weeks after the completion of treatment. Patients with findings on the physical examination, CT, or PET-CT indicative of persistent disease underwent appropriate surgical intervention for pathological assessment. Patients with a complete clinical response were observed with routine follow-up physical examination for disease recurrence. No evidence of disease at least 6 months after the completion of PET-CT was considered confirmation of complete clinical response. MAIN OUTCOME MEASURES: Presence or absence of residual or recurrent disease during the follow-up period was used to calculate the sensitivity, specificity, and positive and negative predictive values of PET-CT for the primary site and the neck. RESULTS: Assessment of tumor response at the primary site with PET-CT had a sensitivity, specificity, and positive and negative predictive values of 83%, 54%, 31%, and 92%, respectively. In patients with pretreatment N1 to N3 disease, the sensitivity, specificity, and positive and negative predictive values of posttreatment PET-CT were 75%, more than 94%, more than 75%, and 94%, respectively, and the specificity and negative predictive value for patients with pretreatment N0 disease in the neck were 92% and more than 92%, respectively. CONCLUSIONS: Negative PET-CT findings accurately determine early disease response at the primary site and in the neck. False-positive findings are common at the primary site. Patients with a negative PET-CT finding after the completion of intra-arterial CRT do not require surgical intervention.

Adenosine receptor antagonists and behavioral activation in NF-kappaB p50 subunit knockout mice.

AIMS: Our previous work revealed that mice lacking the p50 subunit of transcription factor nuclear factor kappa B (NF-kappaB) (p50 KO mice) and genetically intact F2 mice have similar locomotion under basal conditions, yet p50 KO mice show greater locomotor activation after caffeine ingestion. In this report, we test whether KO mice display altered caffeine pharmacokinetics or increased caffeine-induced DA turnover relative to F2 mice, and evaluate the impact of intraperitoneal administration of specific adenosine and DA receptor antagonists on locomotor activity. MAIN METHODS: Concentrations of DA and caffeine were measured using high performance liquid chromatography. DA turnover was measured after treatment of mice with an inhibitor of tyrosine hydroxylase. Locomotor activity was measured using telemetry. KEY FINDINGS: The data reveal that 1) caffeine concentrations in blood and brain are similar in KO and F2 mice after oral or intraperitoneal administration; 2) KO mice show greater DA turnover under basal conditions, but turnover is similar in both strains after caffeine administration; 3) the specific A2AAR antagonist SCH 58261 induces greater locomotion in KO versus F2 mice; and 4) the activating effect of SCH 58261 in KO mice is prevented by prior treatment with the D2R antagonist raclopride. SIGNIFICANCE: These findings support the conclusions that 1) A2AAR has a major impact on behavioral activation of p50 KO mice, and 2) D2R mediated neurotransmission is important to this effect.

Cochlear damage changes the distribution of vesicular glutamate transporters associated with auditory and nonauditory inputs to the cochlear nucleus.

Integration of multimodal information is essential for understanding complex environments. In the auditory system, multisensory integration first occurs in the cochlear nucleus (CN), where auditory nerve and somatosensory pathways converge (Shore, 2005). A unique feature of multisensory neurons is their propensity to receive cross-modal compensation after deafening. Based on our findings that the vesicular glutamate transporters, VGLUT1 and VGLUT2, are differentially associated with auditory nerve and somatosensory inputs to the CN, respectively (Zhou et al., 2007), we examined their relative distributions after unilateral deafening. After unilateral intracochlear injections of kanamycin (1 and 2 weeks), VGLUT1 immunoreactivity (ir) in the magnocellular CN ipsilateral to the cochlear damage was significantly decreased, whereas VGLUT2-ir in regions that receive nonauditory input was significantly increased 2 weeks after deafening. The pathway-specific amplification of VGLUT2 expression in the CN suggests that, in compensatory response to deafening, the nonauditory influence on CN is significantly enhanced. One undesirable consequence of enhanced glutamatergic inputs could be the increased spontaneous rates in CN neurons that occur after hearing loss and that have been proposed as correlates of the phantom auditory sensations commonly called tinnitus.

Insulin sensitivity as a key mediator of growth hormone actions on longevity.

Reduced insulin sensitivity and glucose intolerance have been long suspected of having important involvement in aging. Here we report that in studies of calorie restriction (CR) effects in mutant (Prop1(df) and growth hormone receptor knockout [GHRKO]) and normal mice, insulin sensitivity was strongly associated with longevity. Of particular interest was enhancement of the already increased insulin sensitivity in CR df/df mice in which longevity was also further extended and the lack of changes in insulin sensitivity in calorically restricted GHRKO mice in which there was no further increase in average life span. We suggest that enhanced insulin sensitivity, in conjunction with reduced insulin levels, may represent an important (although almost certainly not exclusive) mechanism of increased longevity in hypopituitary, growth hormone (GH)-resistant, and calorie-restricted animals. We also report that the effects of GH treatment on insulin sensitivity may be limited to the period of GH administration.

Risks of allergy vial contamination: comparison of mixing in-office versus under ventilation hood.

OBJECTIVE: Compare the risk of bacterial contamination of allergy immunotherapy vials prepared in-office versus those mixed under a ventilation hood. STUDY DESIGN: Prospective single-blinded study. SETTING: Tertiary otolaryngology outpatient clinic. RESULTS: Five hundred thirty-seven vials were prepared and cultured for aerobes and anaerobes over an 11-month period. Three hundred twenty vials were arbitrarily assigned to in-office preparation and 217 to under-hood preparation. A total of two positive cultures occurred in vials prepared in-office and one from under-hood preparation. Follow-up cultures of these three vials were all negative. No patients receiving injections had signs or symptoms of skin or systemic infections from the injections. CONCLUSION: Our results suggest that the risk of bacterial contamination in immunotherapy vials in both groups is rare.

Quantitative assessment of laryngeal muscle morphology after recurrent laryngeal nerve injury: right vs. left differences.

OBJECTIVES/HYPOTHESIS: Reports of laryngeal response to denervation are inconsistent. Some document atrophy and fibrosis in denervated laryngeal muscles, whereas others indicate resistance to atrophy. Spontaneous reinnervation has also been documented. The goal of this study was to clarify the effects of nerve injury and reinnervation on thyroarytenoid (TA) and posterior cricoarytenoid (PCA) muscles. STUDY DESIGN: Laboratory experiment. METHODS: TA and PCA muscles of cats were harvested 5 to 6 months after transecting right or left recurrent laryngeal nerve (RLN). Images of muscle cross-sections were acquired and studied using an image analysis workstation. Cross-sectional areas as well as total cross-sectional area of randomly selected muscle fibers were recorded. RESULTS: TA reinnervation was robust on both sides, but there was less reinnervation of the PCA muscle after left-sided RLN lesion than after right-sided injury. CONCLUSIONS: Differences in reinnervation after RLN injury could contribute to the higher clinical incidence of left- vs. right-sided laryngeal paralysis.

The safety of multi-dose vials in allergy immunotherapy.

OBJECTIVE: To prospectively evaluate the risks of vial contamination after routine clinical use of multiple-dose vials for immunotherapy. STUDY DESIGN: Prospective observational study of immunotherapy vial cultures from June 2007 to January 2008. SETTING: Tertiary care outpatient otolaryngology clinic. RESULTS: Over an 8-month period, 136 consecutive vials were cultured for aerobic and anaerobic bacteria at the 3-month expiration date after regular use in an outpatient allergy clinic and dispensation of multiple doses of injection immunotherapy from each vial. All vials had negative cultures. CONCLUSION: Immunotherapy vials are at low risk to undergo contamination in routine use. Important factors include aseptic technique, bacteriostatic agents, and expiration dating.

Study of tracheal dyskinesia impact on the cardiac hemodynamics.

BACKGROUND: Tracheal dyskinesia (TD) was recently recognized as a possible mechanism for acute pulmonary edema (Elamin and Firdose, J Bronchol 2004;11:118-21; Khan and Elamin Eur Respir J 2005;26:319). This study was designed to evaluate possible impact of TD on cardiac hemodynamics. METHODS: Patients were prospectively assigned to either study "A" or control "B" groups (TD >50% or <50%, respectively) diagnosed by bronchoscopy or dynamic chest computed tomography. The cardiac hemodynamics was assisted by impedance cardiography (BioZ; CardioDynamics, San Diego, CA) at rest and during coughing. The latter was repeated after 5 minutes of rest. RESULTS: Thirteen patients were assigned to group A and 14 to group B. There was higher incidence of hypertension, diabetes mellitus, and history of congestive heart failure in group A compared with group B. The percentage of TD was 85% +/- 10.0% versus 25% +/- 2.5%, in the A and B groups, respectively (P < 0.05). Stroke volume index (normal = 35-65 mL/beat/body surface area) was significantly reduced in group A 29.68 [95% confidence interval (CI), 25.557-33.818] compared with group B 38.321 (95% CI, 35.199-41.444; P < 0.05). In addition, the velocity index (representative of aortic blood velocity) was 32.188 (95% CI, 20.841-43.534, P < 0.049) in group A compared with 46.786 (95% CI, 38.209-55.363) in group B, and the left ventricular ejection time measured in milliseconds was 265.813 (95% CI, 246.065-285.560 in group A, P < 0.004) compared with 303.821(95% CI, 288.894-318.749) in group B. CONCLUSION: This prospective study demonstrated the importance of recognizing TD as a pathologic entity and the need to consider TD in the workup of acute pulmonary edema especially if other tests were unrevealing.

Inhibitory neurotransmission, plasticity and aging in the mammalian central auditory system.

Aging and acoustic trauma may result in partial peripheral deafferentation in the central auditory pathway of the mammalian brain. In accord with homeostatic plasticity, loss of sensory input results in a change in pre- and postsynaptic GABAergic and glycinergic inhibitory neurotransmission. As seen in development, age-related changes may be activity dependent. Age-related presynaptic changes in the cochlear nucleus include reduced glycine levels, while in the auditory midbrain and cortex, GABA synthesis and release are altered. Presumably, in response to age-related decreases in presynaptic release of inhibitory neurotransmitters, there are age-related postsynaptic subunit changes in the composition of the glycine (GlyR) and GABA(A) (GABA(A)R) receptors. Age-related changes in the subunit makeup of inhibitory pentameric receptor constructs result in altered pharmacological and physiological responses consistent with a net down-regulation of functional inhibition. Age-related functional changes associated with glycine neurotransmission in dorsal cochlear nucleus (DCN) include altered intensity and temporal coding by DCN projection neurons. Loss of synaptic inhibition in the superior olivary complex (SOC) and the inferior colliculus (IC) likely affect the ability of aged animals to localize sounds in their natural environment. Age-related postsynaptic GABA(A)R changes in IC and primary auditory cortex (A1) involve changes in the subunit makeup of GABA(A)Rs. In turn, these changes cause age-related changes in the pharmacology and response properties of neurons in IC and A1 circuits, which collectively may affect temporal processing and response reliability. Findings of age-related inhibitory changes within mammalian auditory circuits are similar to age and deafferentation plasticity changes observed in other sensory systems. Although few studies have examined sensory aging in the wild, these age-related changes would likely compromise an animal's ability to avoid predation or to be a successful predator in their natural environment.

Expression of striatal adenosine and dopamine receptors in mice deficient in the p50 subunit of NF-kappaB.

The striatal dopamine D2 receptor (D2R) and adenosine A2A receptor (A2AAR) exhibit mutually antagonistic effects through physical interactions and by differential modulation of post-receptor signaling pathways. The expression of the A2AAR and the D2R is differentially regulated by nuclear factor-kappaB (NF-kappaB). In this report, we determined the role of NF-kappaB in regulation of these receptors by comparing mice deficient in the NF-kappaB p50 subunit (p50 KO) with genetically intact B6129PF2/J (F2) mice. Quantification of adenosine receptor (AR) subtypes in mouse striatum by real time PCR, immunocytochemistry and radioligand binding assays showed more A2AAR but less A1AR in p50 KO mice as compared with F2 mice. Striata from p50 KO mice also had less D2R mRNA and [(3)H]-methylspiperone binding than did striata from F2 mice. G(alphaolf) and G(alphas) proteins, which are transducers of A2AAR signals, were also present at a higher level in striata from the p50 KO versus F2 mice. In contrast, the G(alphai1) protein, which transduces signals from the A1AR and D2R, was significantly reduced in striata from p50 KO mice. Behaviorally, p50 KO mice exhibited increased locomotor activity relative to that of F2 mice after caffeine ingestion. These data are consistent with a role for the NF-kappaB in the regulation of A1AR, A2AAR, D2R and possibly their coupling G proteins in the striatum. Dysregulation of these receptors in the striata of p50 KO mice might sensitize these animals to locomotor stimulatory action of caffeine.

Free radical scavengers vitamins A, C, and E plus magnesium reduce noise trauma.

Free radical formation in the cochlea plays a key role in the development of noise-induced hearing loss (NIHL). The amount, distribution, and time course of free radical formation have been defined, including a clinically significant formation of both reactive oxygen species and reactive nitrogen species 7-10 days after noise exposure. Reduction in cochlear blood flow as a result of free radical formation has also been described. Here we report that the antioxidant agents vitamins A, C, and E act in synergy with magnesium to effectively prevent noise-induced trauma. Neither the antioxidant agents nor the magnesium reliably reduced NIHL or sensory cell death with the doses we used when these agents were delivered alone. In combination, however, they were highly effective in reducing both hearing loss and cell death even with treatment initiated just 1 h before noise exposure. This study supports roles for both free radical formation and noise-induced vasoconstriction in the onset and progression of NIHL. Identification of this safe and effective antioxidant intervention that attenuates NIHL provides a compelling rationale for human trials in which free radical scavengers are used to eliminate this single major cause of acquired hearing loss.