Electrophysiology of Ctenophore Smooth Muscle.

Unlike in the Cnidaria, where muscle cells are coupled together into an epithelium, ctenophore muscles are single, elongated, intramesogleal structures resembling vertebrate smooth muscle. Under voltage-clamp, these fibers can be separated into different classes with different sets of membrane ion channels. The ion channel makeup is related to the muscle's anatomical position and specific function. For example, Beroe ovata radial fibers, which are responsible for maintaining the rigidity of the body wall, generate sequences of brief action potentials whereas longitudinal fibers, which are concerned with mouth opening and body flexions, often produce single longer duration action potentials.Beroe muscle contractions depend on the influx of Ca2+. During an action potential the inward current is carried by Ca2+, and the increase in intracellular Ca2+ concentration generated can be monitored in FLUO-3-loaded cells. Confocal microscopy in line scan mode shows that the Ca2+ spreads from the outer membrane into the core of the fiber and is cleared from there relatively slowly. The rise in intracellular Ca2+ is linked to an increase in a Ca2+-activated K+ conductance (KCa), which can also be elicited by iontophoretic Ca2+ injection. Near the cell membrane, Ca2+ clearance monitored using FLUO3, matches the decline in the KCa conductance. For light loads, Ca2+ is cleared rapidly, but this fast system is insufficient when Ca2+ influx is maintained. Action potential frequency may be regulated by the slowly developing KCa conductance.

D-methionine administered as late as 36 hours post-noise exposure rescues from permanent threshold shift and dose-dependently increases serum antioxidant levels.

OBJECTIVE: To elucidate D-methionine's (D-met) dose and time rescue parameters from steady-state or impulse noise-induced permanent threshold shift (PTS) and determine D-met rescue's influence on serum and cochlear antioxidant levels. DESIGN: Five D-met doses at 0, 50, 100, or 200 mg/kg/dose administered starting at 1, 24, or 36 hours post steady-state or impulse noise exposure. Auditory brainstem responses at baseline and 21 days post-noise measured PTS. Serum (superoxide dismutase [SOD], catalase [CAT],, glutathione reductaseand glutathione peroxidase [GPx]) and cochlear (Glutathione [GSH] and glutathione disulphide [GSSG]) antioxidant levels measured physiological impact. STUDY SAMPLE: Chinchillas (10/study group; 6-8/confirmatory groups). RESULTS: D-met significantly reduced PTS for impulse noise (100 mg [2, 6, 14 and 20 kHz]; 200 mg [2, 14 and 20 kHz]) and steady-state noise (all dosing groups, time parameters and tested frequencies). PTS reduction did not significantly vary by rescue time. D-met significantly increased serum SOD (100 and 200 mg for 24 hour rescue) and GPx (50 mg/kg at 24 hour rescue) at 21 days post-noise. Cochlear GSH and GSSG levels were unaffected relative to control. CONCLUSION: D-met rescues from steady-state and impulse noise-induced PTS even when administered up to 36 hours post-noise and dose-dependently influences serum antioxidant levels even 21 days post-noise. D-met's broad and effective dose/time window renders it a promising antioxidant rescue agent.

Phylogenetics of swimming behaviour in Medusozoa: the role of giant axons and their possible evolutionary origin.

Although neural tissues in cnidarian hydroids have a nerve net structure, some cnidarian medusae contain well-defined nerve tracts. As an example, the hydrozoan medusa Aglantha digitale has neural feeding circuits that show an alignment and condensation, which is absent in its relatives Aequorea victoria and Clytia hemisphaerica. In some cases, neural condensations take the form of fast propagating giant axons concerned with escape or evasion. Such giant axons appear to have developed from the fusion of many, much finer units. Ribosomal DNA analysis has identified the lineage leading to giant axon-based escape swimming in Aglantha and other members of the Aglaura clade of trachymedusan jellyfish. The Aglaura, along with sister subclades that include species such as Colobonema sericeum, have the distinctive ability to perform dual swimming, i.e. to swim at either high or low speeds. However, the form of dual swimming exhibited by Colobonema differs both biomechanically and physiologically from that in Aglantha and is not giant axon based. Comparisons between the genomes of such closely related species might provide a means to determine the molecular basis of giant axon formation and other neural condensations. The molecular mechanism responsible may involve 'fusogens', small molecules possibly derived from viruses, which draw membranes together prior to fusion. Identifying these fusogen-based mechanisms using genome analysis may be hindered by the many changes in anatomy and physiology that followed giant axon evolution, but the genomic signal-to-noise ratio may be improved by examining the convergent evolution of giant axons in other hydrozoa, such as the subclass Siphonophora.

D-methionine immediate and continued rescue after noise exposure does not prevent temporary threshold shift but alters cochlear and serum antioxidant levels.

OBJECTIVE: Determine if D-methionine (D-met) rescue prevents temporary threshold shift (TTS) from steady-state or impulse noise and determine D-met's impact on serum and cochlear antioxidant levels. DESIGN: D-met at 50, 100 or 200 mg/kg/doses were administered 0, 6 and 18 hours-post noise. ABRs at baseline and 24 hours post-noise measured TTS. Serum (SOD, CAT, GR, GPx) and cochlear (GSH, GSSG) antioxidant levels measured physiological influence. Three control groups, with impulse or steady-state or without noise, were saline-injected. STUDY SAMPLE: Ten Chinchillas/group. RESULTS: D-met rescue did not significantly reduce TTS or impact serum CAT, SOD, GPx or GR levels vs. noise-exposed control groups, but TTS was greater in all groups relative to no-noise controls. D-met significantly elevated CAT at 50 mg/kg vs. steady-state controls and SOD at 200 mg/kg vs. impulse noise controls. D-met significantly reduced cochlear GSH/GSSG ratios in the 100 mg/kg D-met group vs. impulse noise controls. CONCLUSIONS: While D-met rescue has reduced permanent threshold shift in previous studies, it did not reduce TTS in this study. However, D-met rescue did alter selective serum and cochlear oxidative state changes 24 hours post-noise relative to controls. Results demonstrate TTS studies do not always predict PTS protection in otoprotectant experimental designs.

Preloaded D-methionine protects from steady state and impulse noise-induced hearing loss and induces long-term cochlear and endogenous antioxidant effects.

OBJECTIVE: Determine effective preloading timepoints for D-methionine (D-met) otoprotection from steady state or impulse noise and impact on cochlear and serum antioxidant measures. DESIGN: D-met started 2.0-, 2.5-, 3.0-, or 3.5- days before steady-state or impulse noise exposure with saline controls. Auditory brainstem response (ABRs) measured from 2 to 20 kHz at baseline and 21 days post-noise. Samples were then collected for serum (SOD, CAT, GR, GPx) and cochlear (GSH, GSSG) antioxidant levels. STUDY SAMPLE: Ten Chinchillas per group. RESULTS: Preloading D-met significantly reduced ABR threshold shifts for both impulse and steady state noise exposures but with different optimal starting time points and with differences in antioxidant measures. For impulse noise exposure, the 2.0, 2.5, and 3.0 day preloading start provide significant threshold shift protection at all frequencies. Compared to the saline controls, serum GR for the 3.0 and 3.5 day preloading groups was significantly increased at 21 days with no significant increase in SOD, CAT or GPx for any impulse preloading time point. Cochlear GSH, GSSG, and GSH/GSSG ratio were not significantly different from saline controls at 21 days post noise exposure. For steady state noise exposure, significant threshold shift protection occurred at all frequencies for the 3.5, 3.0 and 2.5 day preloading start times but protection only occurred at 3 of the 6 test frequencies for the 2.0 day preloading start point. Compared to the saline controls, preloaded D-met steady-state noise groups demonstrated significantly higher serum SOD for the 2.5-3.5 day starting time points and GPx for the 2.5 day starting time but no significant increase in GR or CAT for any preloading time point. Compared to saline controls, D-met significantly increased cochlear GSH concentrations in the 2 and 2.5 day steady-state noise exposed groups but no significant differences in GSSG or the GSH/GSSG ratio were noted for any steady state noise-exposed group. CONCLUSIONS: The optimal D-met preloading starting time window is earlier for steady state (3.5-2.5 days) than impulse noise (3.0-2.0). At 21 days post impulse noise, D-met increased serum GR for 2 preloading time points but not SOD, CAT, or GpX and not cochlear GSH, GSSG or the GSH/GSSG ratio. At 21 days post steady state noise D-met increased serum SOD and GPx at select preloading time points but not CAT or GR. However D-met did increase the cochlear GSH at select preloading time points but not GSSG or the GSH/GSSG ratio.

Two swimming modes in Trachymedusae; bell kinematics and the role of giant axons.

Although members of the Rhopalonematidae family (Cnidaria, Hydrozoa, Trachymedusae) are known to exhibit unusually powerful jet swimming in addition to their more normal slow swimming behaviour, for the most part, reports are rare and anecdotal. Many species are found globally at depths of 600-2000 m, and so observation and collection depend on using remotely operated submersible vehicles. With a combination of in situ video footage and laboratory measurements, we have quantified kinematic aspects of this dual swimming motion and its electrophysiology. The species included are from two Rhopalonematidae clades; they are Colobonema sericeum, Pantachogon haeckeli, Crossota millsae and two species of Benthocodon. Comparison is made with Aglantha digitale, a species from a third Rhopalonematidae clade brought to the surface by natural water movement. We find that although all Rhopalonematidae appear to have two swimming modes, there are marked differences in their neural anatomy, kinematics and physiology. Giant motor axons, known to conduct impulses during fast swimming in A. digitale, are absent from C. sericeum and P. haeckeli. Slow swimming is also different; in C. sericeum and its relatives it is driven by contractions restricted to the base of the bell, whereas in A. digitale it is driven by contractions in the mid-bell region. These behavioural differences are related to the position of the different clades on a ribosomal DNA-based phylogenetic tree. This finding allows us to pinpoint the phylogenetic branch point leading to the appearance of giant motor axons and escape swimming. They place the remarkable dual swimming behaviour of members of the Rhopalonematidae family into an evolutionary context.

Structure and function of the nervous system in nectophores of the siphonophore Nanomia bijuga.

Although the bell-shaped nectophores of the siphonophore Nanomia bijuga are clearly specialized for locomotion, their complex neuroanatomy described here testifies to multiple subsidiary functions. These include secretion, by the extensively innervated 'flask cells' located around the bell margin, and protection, by the numerous nematocytes that line the nectophore's exposed ridges. The main nerve complex consists of a nerve ring at the base of the bell, an adjacent column-shaped matrix plus two associated nerve projections. At the top of the nectophore the upper nerve tract appears to have a sensory role; on the lower surface a second nerve tract provides a motor input connecting the nectophore with the rest of the colony via a cluster of nerve cells at the stem. N. bijuga is capable of both forward and backward jet-propelled swimming. During backwards swimming the water jet is redirected by the contraction of the Claus' muscle system, part of the muscular velum that fringes the bell aperture. Contractions can be elicited by electrical stimulation of the nectophore surface, even when both upper and lower nerve tracts have been destroyed. Epithelial impulses elicited there, generate slow potentials and action potentials in the velum musculature. Slow potentials arise at different sites around the bell margin and give rise to action potentials in contracting Claus' muscle fibres. A synaptic rather than an electrotonic model more readily accounts for the time course of the slow potentials. During backward swimming, isometrically contracting muscle fibres in the endoderm provide the Claus' fibres with an immobile base.

D-methionine (D-met) significantly reduces kanamycin-induced ototoxicity in pigmented guinea pigs.

OBJECTIVE: Test D-methionine (D-met) as an otoprotectant from kanamycin-induced ototoxicity and determine the lowest maximally protective D-met dose. DESIGN: Auditory brainstem responses (ABR) were measured at 4, 8, 14, and 20 kHz at baseline and two, four, and six weeks after kanamycin and D-met administration initiation. ABR threshold shifts assessed auditory function. Following six-week ABR testing, animals were decapitated and cochleae collected for outer hair cell (OHC) quantification. STUDY SAMPLE: Eight groups of 10 male pigmented guinea pigs were administered a subcutaneous kanamycin (250 mg/kg/dose) injection once per day and an intraperitoneal D-met injection (0 (saline), 120, 180, 240, 300, 360, 420, or 480 mg/kg/day) twice per day for 23 days. RESULTS: Significant ABR threshold shift reductions and increased OHC counts (p ≤ 0.01) were measured at multiple D-met-dosed groups starting at two-week ABR assessments. A 300 mg/kg/day optimal otoprotective D-met dose provided 34-41 dB ABR threshold shift reductions and OHC protection. Lesser, but significant, D-met otoprotection was measured at lower and higher D-met doses. CONCLUSIONS: D-met significantly reduced ABR threshold shifts and increased OHC percentages compared to kanamycin-treated controls. Results may be clinically significant particularly for multidrug-resistant tuberculosis patients who frequently suffer from kanamycin-induced hearing loss in developing countries.

d-Methionine reduces tobramycin-induced ototoxicity without antimicrobial interference in animal models.

BACKGROUND: Tobramycin is a critical cystic fibrosis treatment however it causes ototoxicity. This study tested d-methionine protection from tobramycin-induced ototoxicity and potential antimicrobial interference. METHODS: Auditory brainstem responses (ABRs) and outer hair cell (OHC) quantifications measured protection in guinea pigs treated with tobramycin and a range of d-methionine doses. In vitro antimicrobial interference studies tested inhibition and post antibiotic effect assays. In vivo antimicrobial interference studies tested normal and neutropenic Escherichia coli murine survival and intraperitoneal lavage bacterial counts. RESULTS: d-Methionine conferred significant ABR threshold shift reductions. OHC protection was less robust but significant at 20kHz in the 420mg/kg/day group. In vitro studies did not detect d-methionine-induced antimicrobial interference. In vivo studies did not detect d-methionine-induced interference in normal or neutropenic mice. CONCLUSIONS: d-Methionine protects from tobramycin-induced ototoxicity without antimicrobial interference. The study results suggest d-met as a potential otoprotectant from clinical tobramycin use in cystic fibrosis patients.

Electrogenesis in the lower Metazoa and implications for neuronal integration.

Electrogenic communication appears to have evolved independently in a variety of animal and plant lineages. Considered here are metazoan cells as disparate as the loose three-dimensional parenchyma of glass sponges, the two-dimensional epithelial sheets of hydrozoan jellyfish and the egg cell membranes of the ctenophore Beroe ovata, all of which are capable of generating electrical impulses. Neuronal electrogenesis may have evolved independently in ctenophores and cnidarians but the dearth of electrophysiological data relating to ctenophore nerves means that our attention is focused on the Cnidaria, whose nervous systems have been the subject of extensive study. The aim here is to show how their active and passive neuronal properties interact to give integrated behaviour. Neuronal electrogenesis, goes beyond simply relaying 'states of excitement' and utilizes the equivalent of a set of basic electrical 'apps' to integrate incoming sensory information with internally generated pacemaker activity. A small number of membrane-based processes make up these analogue applications. Passive components include the decremental spread of current determined by cellular anatomy; active components include ion channels specified by their selectivity and voltage dependence. A recurring theme is the role of inactivating potassium channels in regulating performance. Although different aspects of cnidarian behaviour are controlled by separate neuronal systems, integrated responses and coordinated movements depend on interactions between them. Integrative interactions discussed here include those between feeding and swimming, between tentacle contraction and swimming and between slow and fast swimming in the hydrozoan jellyfish Aglantha digitale.

D-methionine pre-loading reduces both noise-induced permanent threshold shift and outer hair cell loss in the chinchilla.

OBJECTIVE: This study tested multiple dosing epochs of pre-loaded D-methionine (D-met) for otoprotection from noise-induced hearing loss (NIHL). DESIGN: Auditory brainstem response (ABR) thresholds were measured at baseline, 1 day, and 21 days following a 6-hour 105 dB sound pressure level (SPL) octave band noise (OBN) exposure. Outer hair cell (OHC) counts were measured after day 21 sacrifice. STUDY SAMPLE: Three groups of five Chinchillas laniger each were given a 2-day regimen comprising five doses of D-met (200 mg/kg/dose) intraperitoneally (IP) starting 2, 2.5, or 3 days prior to noise exposure. A control group (n = 5) received five doses of equivalent volume saline IP starting 2.5 days prior to noise exposure. RESULTS: ABR threshold shifts from baseline to day-21 post-noise exposure were reduced in all D-met groups versus controls, reaching significance (p < 0.05) in the 3-day group. D-met groups showed reduced OHC loss relative to controls at day-21 post-noise exposure, reaching significance (p < 0.05) at all frequency regions in the 3-day group and at the 2, 4, and 8 kHz frequency regions in the 2.5-day group. CONCLUSIONS: D-met administration in advance of noise-exposure, without further administration, significantly protects from noise-induced ABR threshold shift and OHC loss.

A contribution to the history of the proton channel.

The low numbers of hydrogen ions in physiological solutions encouraged the assumption that H(+) currents flowing through conductive pathways would be so small as to be unmeasurable even if theoretically possible. Evidence for an H(+)-based action potential in the luminescent dinoflagellate Noctiluca and for an H(+)-conducting channel created by the secretions of the bacterium Bacillus brevis, did little to alter this perception. The clear demonstration of H(+) conduction in molluscan neurons might have provided the breakthrough but the new pathway was without an easily demonstrable function, and escaped general attention. Indeed the extreme measures that must be taken to successfully isolate H(+) currents meant that it was some years before proton channels were identified in mammalian cells. However, with the general availability of patch-clamp techniques and evidence for an important role in mammalian neutrophils, the stage was set for a series of structure/function studies with the potential to make the proton channel the best understood channel of all. In addition, widespread genomic searches have established that proton channels play important roles in processes ranging from fertilization of the human ovum to the progression of breast cancer. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

D-methionine (D-met) significantly rescues noise-induced hearing loss: timing studies.

We have previously reported rescue from noise-induced auditory brainstem response (ABR) threshold shifts with d-methionine (d-met) administration 1 h after noise exposure. The present study investigated further d-met rescue intervals at 3, 5 and 7 h post-noise exposure. Chinchillas laniger were exposed to a 6 h 105 dB sound pressure level (dB SPL) octave band noise (OBN) and then administered d-met i.p. starting 3, 5, or 7 h after noise exposure; controls received saline i.p. immediately after noise exposure. ABR assessments were performed at baseline and on post-exposure days 1 and 21. Outer hair cell (OHC) loss was measured in cochleae obtained at sacrifice 21 days post-exposure. Administration of d-met starting at any of the delay times of 3-7 h post-noise exposure significantly reduced day 21 ABR threshold shift at 2 and 4 kHz and OHC loss at all hair cell regions measured (2, 4, 6 and 8 kHz). ABR threshold shifts in the control group at 6 and 8 kHz were only 8 and 11 dB respectively allowing little opportunity to observe protection at those 2 frequencies.

Nerves in the endodermal canals of hydromedusae and their role in swimming inhibition.

N eoturris breviconis (Anthomedusae) has a nerve plexus in the walls of its endodermal canals. The plexus is distinct from the ectodermal nerve plexuses supplying the radial and circular muscles in the ectoderm and no connections have been observed between them. Stimulation of the endodermal plexus evokes electrical events recorded extracellularly as "E" potentials. These propagate through all areas where the plexus has been shown by immunohistology to exist and nowhere else. When Neoturris is ingesting food, trains of "E" potentials propagate down the radial canals to the margin and cause inhibition of swimming. This response is distinct from the inhibition of swimming associated with contractions of the radial muscles but both may play a part in feeding and involve chemoreceptors. Preliminary observations suggest that the "E" system occurs in other medusae including Aglantha digitale (Trachymedusae) where the conduction pathway was previously thought to be an excitable epithelium.

Non-neural reflexes: sponges and the origins of behaviour.

Sponges 'sneeze' without the benefit of nerves or muscles. While genomic analysis has uncovered a surprisingly complex set of molecular components in these ancient metazoans, physiological studies have revealed equally sophisticated cellular coordination.

A conductive pathway generated from fragments of the human red cell anion exchanger AE1.

Human red cell anion exchanger AE1 (band 3) is an electroneutral Cl-HCO3- exchanger with 12-14 transmembrane spans (TMs). Previous work using Xenopus oocytes has shown that two co-expressed fragments of AE1 lacking TMs 6 and 7 are capable of forming a stilbene disulphonate-sensitive (36)Cl-influx pathway, reminiscent of intact AE1. In the present study, we create a single construct, AE1Delta(6: 7), representing the intact protein lacking TMs 6 and 7. We expressed this construct in Xenopus oocytes and evaluated it employing a combination of two-electrode voltage clamp and pH-sensitive microelectrodes. We found that, whereas AE1Delta(6: 7) has some electroneutral Cl-base exchange activity, the protein also forms a novel anion-conductive pathway that is blocked by DIDS. The mutation Lys(539)Ala at the covalent DIDS-reaction site of AE1 reduced the DIDS sensitivity, demonstrating that (1) the conductive pathway is intrinsic to AE1Delta(6: 7) and (2) the conductive pathway has some commonality with the electroneutral anion-exchange pathway. The conductance has an anion-permeability sequence: NO3- approximately I- > NO2- > Br- > Cl- > SO4(2-) approximately HCO3- approximately gluconate- approximately aspartate- approximately cyclamate-. It may also have a limited permeability to Na+ and the zwitterion taurine. Although this conductive pathway is not a usual feature of intact mammalian AE1, it shares many properties with the anion-conductive pathways intrinsic to two other Cl-HCO3- exchangers, trout AE1 and mammalian SLC26A7.

Prevention of noise- and drug-induced hearing loss with D-methionine.

A number of otoprotective agents are currently being investigated. Various types of agents have been found in animal studies to protect against hearing loss induced by cisplatin, carboplatin, aminoglycosides, or noise exposure. For over a decade we have been investigating D-methionine (D-met) as an otoprotective agent. Studies in our laboratory and others around the world have documented D-met's otoprotective action, in a variety of species, against a variety of ototoxic insults including cisplatin-, carboplatin-, aminoglycoside- and noise-induced auditory threshold elevations and cochlear hair cell loss. For cisplatin-induced ototoxicity, protection of the stria vascularis has also been documented. Further D-met has an excellent safety profile. D-met may act as both a direct and indirect antioxidant. In this report, we provide the results of three experiments, expanding findings in D-met protection in three of our translational research areas: protection from platinum based chemotherapy-, aminoglycoside- and noise-induced hearing loss. These experiments demonstrate oral D-met protection against cisplatin-induced ototoxicity, D-met protection against amikacin-induced ototoxicity, and D-met rescue from permanent noise-induced hearing loss when D-met is initiated 1h after noise exposure. These studies demonstrate some of the animal experiments needed as steps to translate a protective agent from bench to bedside.

Nitric oxide regulates swimming in the jellyfish Aglantha digitale.

The cnidarian nervous system is considered by many to represent neuronal organization in its earliest and simplest form. Here we demonstrate, for the first time in the Cnidaria, the neuronal localization of nitric oxide synthase (NOS) in the hydromedusa Aglantha digitale (Trachylina). Expression of specific, fixative-resistant NADPH-diaphorase (NADPH-d) activity, characteristic of NOS, was observed in neurites running in the outer nerve ring at the base of the animal and in putative sensory cells in the ectoderm covering its tentacles. At both sites, diphenyleneiodonium (10(-4) M) abolished staining. Capillary electrophoresis confirmed that the NO breakdown products NO2- and NO3- were present at high levels in the tentacles, but were not detectable in NADPH-d-negative areas. The NADPH-d-reactive neurons in the tentacles send processes to regions adjacent to the inner nerve ring where swimming pacemaker cells are located. Free-moving animals and semi-intact preparations were used to test whether NO is involved in regulating the swimming program. NO (30-50 nM) and its precursor L-arginine (1 mM) stimulated swimming, and the effect was mimicked by 8-Br-cGMP (50-100 microM). The NO scavenger PTIO (10-100 microM) and a competitive inhibitor of NOS, L-nitroarginine methyl ester (L-NAME, 200 microM), significantly decreased the swimming frequency in free-moving animals, while its less-active stereoisomer D-nitroarginine methyl ester (D-NAME, 200 microM) had no such effect. 1H-[1,2,4]oxadiazolo[4,3-a]quinoxaline-1-one (ODQ, 5-20 microM), a selective inhibitor of soluble guanylyl cyclase, suppressed spontaneous swimming and prevented NO-induced activation of the swimming program. We suggest that an NO/cGMP signaling pathway modulates the rhythmic swimming associated with feeding in Aglantha, possibly by means of putative nitrergic sensory neurons in its tentacles.

Glutathione ester but not glutathione protects against cisplatin-induced ototoxicity in a rat model.

Glutathione (GSH) provides an important antioxidant and detoxification pathway. We tested to determine if direct administration of GSH or GSH ester could reduce cisplatin- (CDDP) induced ototoxicity. We tested eight groups of five rats each: a control group, a group receiving 16 mg/kg ip CDDP infused over 30 minutes, and six groups receiving either GSH or GSH ester at 500, 1000, or 1500 mg/kg intraperitoneally 30 minutes prior to 16 mg/kg CDDP. Auditory brainstem response thresholds were measured for click and tone-burst stimuli at baseline and 3 days later. Outer hair cell (OHC) loss was measured for the apical, middle and basal turns. The 500 mg/kg GSH ester reduced hearing loss and OHC loss, but protection decreased as dosage increased, suggesting possible toxicity. GSH was not significantly protective. The best GSH ester protection was less than we have previously reported with D-methionine.

Antioxidant enzyme levels inversely covary with hearing loss after amikacin treatment.

This study's purpose was to determine if a correlation exists between cochlear antioxidant activity changes and auditory function after induction of amino-glycoside (AG) ototoxicity. Two groups of five 250-350 g albino guinea pigs served as subjects. For 28 days, albino guinea pigs were administered either 200 mg/kg/day amikacin, or saline subcutaneously. Auditory brainstem response testing was performed prior to the first injection and again before sacrifice, 28 days later. Cochleae were harvested and superoxide dismutase, catalase, glutathione peroxidase, glutathione-S-transferase, glutathione reductase activities and malondialdehyde levels were measured. All antioxidant enzymes had significantly lower activity in the amikacin group (p < or = 0.05) than in the control group. The difference in cochlear antioxidant enzyme activity between groups inversely correlated significantly with the change in ABR thresholds. The greatest correlation was for the high frequencies, which are most affected by aminoglycosides. This study demonstrates that antioxidant enzyme activity and amikacin-induced hearing loss significantly covary.