A Conditioned Behavioral Paradigm for Assessing Onset and Lasting Tinnitus in Rats

Numerous behavioral paradigms have been developed to assess tinnitus-like behavior in animals. Nevertheless, they are often limited by prolonged training requirements, as well as an inability to simultaneously assess onset and lasting tinnitus behavior, tinnitus pitch or duration, or tinnitus presence without grouping data from multiple animals or testing sessions. To enhance behavioral testing of tinnitus, we developed a conditioned licking suppression paradigm to determine the pitch(s) of both onset and lasting tinnitus-like behavior within individual animals. Rats learned to lick water during broadband or narrowband noises, and to suppress licking to avoid footshocks during silence. After noise exposure, rats significantly increased licking during silent trials, suggesting onset tinnitus-like behavior. Lasting tinnitus-behavior, however, was exhibited in about half of noise-exposed rats through 7 weeks post-exposure tested. Licking activity during narrowband sound trials remained unchanged following noise exposure, while ABR hearing thresholds fully recovered and were comparable between tinnitus⁽⁺⁾ and tinnitus^(-) rats. To assess another tinnitus inducer, rats were injected with sodium salicylate. They demonstrated high pitch tinnitus-like behavior, but later recovered by 5 days post-injection. Further control studies showed that 1): sham noise-exposed rats tested with footshock did not exhibit tinnitus-like behavior, and 2): noise-exposed or sham rats tested without footshocks showed no fundamental changes in behavior compared to those tested with shocks. Together, these results demonstrate that this paradigm can efficiently test the development of noise- and salicylate-induced tinnitus behavior. The ability to assess tinnitus individually, over time, and without averaging data enables us to realistically address tinnitus in a clinically relevant way. Thus, we believe that this optimized behavioral paradigm will facilitate investigations into the mechanisms of tinnitus and development of effective treatments.

[The state of lipid peroxidation and antioxidant protection system in parietal cells under experimental chronic atrophic gastritis development]

The lipid peroxidation state and the system functioning of antioxidant protection in parietal cells under rat chronic atrophic gastritis development was investigated. It was detected that the compensatory increase of superoxide dismutase and catalase activity did not affect the lipoperoxidation process and this resulted in accumulation of toxic TBA reactive substances and diene conjugates during the whole stages of the experimental pathology development. It was shown that the reserved power of the glutathione antioxidant system is sufficient to provide adoptable response in the acute period of the disease owing to increasing intracellular found of the reduced glutathione, but it is insufficient to prevent its decreasing in parietal cells in case of the chronic atrophic gastritis development. Our findings suggest that glutathione system is involved in processes of gastric atrophy. The obtained results testify about considerable system dysfunctions of lipid peroxidation and the antioxidant protection in processes of the rat experimental atrophic gastritis development.

Sodium salicylate reduces inhibitory postsynaptic currents in neurons of rat auditory cortex

Sodium salicylate (SS) is a medicine for anti-inflammation and for chronic pain relief with a side effect of tinnitus. To understand the cellular mechanisms of tinnitus induced by SS in the central auditory system, we examined effects of SS on evoked and miniature inhibitory postsynaptic currents (eIPSCs and mIPSCs) recorded from layer II/III pyramidal neurons of rat auditory cortex in a brain slice preparation with whole-cell patch-clamp techniques. Both eIPSCs and mIPSCs recorded from the auditory cortex could be completely blocked by bicuculline, a selective GABA(A) receptor antagonist. SS did not change the input resistance of neurons but was found to reversibly depress eIPSCs in a concentration-dependent manner. SS reduced eIPSCs to 82.3% of the control level at 0.5 mM (n=7) and to 60.9% at 1.4 mM (n=12). In addition, SS at 1.4 mM significantly reduced the amplitude of mIPSCs from 24.12+/-1.44 pA to 19.92+/-1.31 pA and reduced the frequency of mIPSCs from 1.34+/-0.23 Hz to 0.89+/-0.13 Hz (n=6). Our results demonstrate that SS attenuates inhibitory postsynaptic currents in the auditory cortex, suggesting that the alteration of inhibitory neural circuits may be one of the cellular mechanisms for tinnitus induced by SS in the central auditory region.

Salicylate blocks L-type calcium channels in rat inferior colliculus neurons

To investigate the effects of the tinnitus inducer sodium salicylate on L-type voltage-gated calcium channels, we studied freshly dissociated inferior colliculus neurons of rats by the whole-cell voltage clamp method. Salicylate's blocking of L-type calcium channels was concentration dependent, and the IC(50) value of salicylate was estimated to be 1.99 mM. An amount of 1 mM salicylate significantly shifted the steady-state inactivation curve of L-type calcium channels about 9 mV in the hyperpolarizing direction and significantly delayed calcium channel recovery. Our results suggest that salicylate's blocking of L-type calcium channels may contribute to salicylate-induced tinnitus by decreasing GABA release in the inferior colliculus.

Auditory nerve fibre responses to salicylate revisited

Ototoxicity of salicylate is accompanied by a temporary hearing loss and tinnitus and has therefore been used to study tinnitus in animal models. Salicylate induced elevated central auditory activity has been interpreted as a correlate of tinnitus. Whether this elevated activity in the central auditory system is due to an increased activity in the auditory nerve is still under discussion. To explore this issue, we recorded the activity of single auditory nerve fibres in anaesthetised gerbils following systemic injection of salicylic acid. Firstly, compound action potential (CAP) thresholds were determined at 5-0 min intervals. Fifteen to 30 min after 200 mg/kg salicylic acid, threshold loss developed in the high frequency range. At 2 h CAP threshold loss reached a plateau amounting to 15-20 dB above 16 kHz, 0-5 dB below 2 kHz. An almost immediate start of threshold loss was observed after 400 mg/kg salicylic acid. A plateau of threshold loss was reached after 1.5 h with values of 25 dB in the high, 5-10 dB in the low frequency range. Secondly, responses of single auditory nerve fibres were studied after administration of 200 mg/kg salicylic acid. Frequency tuning curves and rate intensity (RI) functions at characteristic frequency (CF) were measured. Two hours and more after application, single fibre thresholds were elevated by about 20 dB at all CFs. Sharpness of tuning was reduced. Mean spontaneous rate was significantly reduced at CFs below 5 kHz (mean: 44 vs 28 AP/s). At CFs above 5 kHz mean spontaneous rate remained unchanged. In RI functions no change in maximum discharge rate was observed. The altered response properties can be interpreted by the known effects of salicylate on the prestin mediated active process of the outer hair cells. The elevated activity in the central auditory system after salicylate intoxication thus cannot be caused by cochlear nerve hyperactivity.

Intraperitoneal administration of salicylate dose-dependently prevents stress-induced ulcer formation in rats

Stress has an important role in the induction of gastroduodenal injury. It was reported that oxygen free radicals played a role in the pathogenesis of this injury. Although some other antioxidant compounds and calcium channel blockers were examined in ulcer models, salicylate has not been tested for its gastroprotective effect in ulcer models by now. In the present study, intraperitoneal administration of 10, 25 and 50 mg/kg of salicylate dose-dependently prevented ulcer formation in obligatory immobilization model in rats. This protective effect of salicylate was found more potent than that of ranitidine for all doses tested. As expected, peroral (by gavage) administration of salicylate at 50 mg/kg exacerbated the ulcer score, in comparison with the control.

Effects of nimodipine on salicylate ototoxicity

The purpose of this study was to examine the effects of nimodipine on salicylate ototoxicity in guinea pigs. The compound action potential (CAP) was recorded at the round window, and the cochlear blood flow (CBF) was measured simultaneously from the lateral wall of the basal turn of the cochlea by laser Doppler flowmetry. After administration of salicylate (100 mg/kg), the CAP thresholds were significantly elevated, by 5 to 20 dB (p < .05), and the CBF was significantly decreased (p < .05). After administration of nimodipine (2 mg/kg), the CAP thresholds were unchanged, but the CBF had increased significantly (p < .05), while systemic blood pressure had decreased significantly (p < .05). Simultaneous administration of both salicylate (100 mg/kg) and nimodipine (2 mg/kg) resulted in significant elevation of the CAP thresholds (p < .05), while the CBF did not decrease. These results suggest that nimodipine prevents the decrease in CBF induced by salicylate, but that nimodipine does not prevent the deterioration in the CAP.

Neurophysiologic mechanisms of tinnitus

Research over the past decade has provided new insights into the neural mechanisms likely to produce the false percepts of sound associated with tinnitus. These insights have emerged mainly as a result of electrophysiologic studies, examining changes in brain activity, and behavioral studies, examining changes in perception, in animals that have been treated with well-known tinnitus inducers such as salicylates, quinine, and intense sound. The available evidence, based on electrophysiologic studies, suggests that tinnitus is associated with disturbances in spontaneous neural activity in the auditory system. These abnormalities include increases in spontaneous activity (hyperactivity), changes in the timing of neural discharges (i.e., the temporal firing properties of neurons), and an increase in bursting activity of neurons. Parallel studies using behavioral testing methods have demonstrated that agents, which produce these neural changes, also cause tinnitus in animals. This article reviews the literature concerned with both behavioral evidence for tinnitus in animal models and the associated changes that occur at peripheral and central levels of the auditory system.

[Effects of salicylate on electrically evoked otoacoustic emissions in the guinea pig]

Clinically, salicylates have been known to have a ototoxic side effect of reversible hearing loss and to reduce the voltage-dependent length change (electromotility) in experiments on isolated outer hair cells (OHC). In order to clarify how the reduction of OHC electromotility due to salicylates contributes to cochlear dysfunction in vivo, we observed compound action potentials (CAP) threshold as well as the outputs of the electrically evoked otoacoustic emissions (EEOAE) before and after intravenous administration of 500 mg/kg sodium salicylate in a guinea pig model. A silver ball electrode placed on the round window membrane of the animal was used for both recording of the CAP and stimulation to elicit the EEOAE. The CAP threshold to tone bursts with frequencies from 2 to 10 kHz elevated by 13 to 22 dB, and outputs of the EEOAE decreased approximately 4 dB for 5 kHz stimulation, and 12 dB for 8 kHz after salicylate administration. These results suggested that systemically administered salicylate also reduced the electromotility of the OHC, and caused the hearing impairment in vivo.

Repair of rat gastric mucosa: effect of 16,16-dimethyl prostaglandin E2

Prostaglandins protect the gastric mucosa against a variety of injurious agents and may accelerate the recovery of the gastric mucosa following damage. In previous studies prostaglandins were given prior to the injurious agent, so it was not possible to distinguish their potential effects on accelerating repair or reducing initial damage. We have investigated the effect of 16,16-dimethyl prostaglandin E2 (dmPGE2) on the repair of the gastric mucosa after injury induced by several injurious agents. dmPGE2 was given orally 15 min prior to aspirin or sodium salicylate, or 30 min after aspirin, sodium salicylate, or ethanol. dmPGE2 delivered prior to injury reduced the aspirin-induced fall in mucosal potential difference (PD), but had no effect on that induced by sodium salicylate. dmPGE2 administered after ASA injury significantly increased recovery of PD (P < 0.05), but did not alter the rate of recovery of PD with other damaging agents. Histological damage was decreased in rats treated with dmPGE2 after aspirin compared to aspirin-only-treated rats (P < 0.02). Exogenous dmPGE2 protects and restores gastric mucosal integrity after aspirin damage but has no effect on the repair of sodium salicylate and ethanol injured mucosa, suggesting that repair of the gastric mucosa after aspirin damage is enhanced by dmPGE2 due to its ability to prevent ongoing damage, rather than directly enhancing repair processes.

Effect of corticosteroid treatment on salicylate ototoxicity

Our previous studies showed that salicylate ototoxicity is associated with decreased levels of prostaglandins (PGs) and elevated levels of leukotrienes (LTs) in the perilymph. The purpose of this study was to determine whether or not pretreatment with corticosteroid, which suppresses both PGs and LTs in arachidonic acid metabolism, prevents salicylate ototoxicity. Salicylate ototoxicity was induced in chinchillas with or without treatment with dexamethasone. Hearing thresholds were measured by auditory brain stem response, and perilymph samples were assayed by high-performance liquid chromatography. Dexamethasone pretreatment, given by either systemic or local round window membrane application, partially prevented salicylate-induced hearing loss. Prevention of salicylate ototoxicity by dexamethasone seems to be correlated with increased PG levels and decreased LT levels in the perilymph. This is another piece of evidence that salicylate ototoxicity may be mediated by abnormal arachidonic acid metabolism in the inner ear.

Sodium salicylate sensitivity in an asthmatic patient with aspirin sensitivity

Non-acetylated salicylates have been recommended for use as alternatives to nonsteroidal anti-inflammatory drugs (NSAIDs) in aspirin and/or tartrazine-sensitive patients. We experienced a case of an aspirin-sensitive asthmatic patient who developed a broncho-obstructive reaction after taking 100 mg of sodium salicylate. The result of this study suggests that sodium salicylate may cross-react with aspirin in aspirin-and tartrazine-sensitive patients.

Acute respiratory failure following pharmacologically induced hyperventilation: an experimental animal study

The pulmonary effects of hyperventilation following infusion of sodium salicylate into the cisterna magna was studied in 16 spontaneously breathing adult sheep. We found a fall in PaO2, a decrease in the static compliance of the respiratory system, abnormal chest roentgenographic films, and grossly abnormal lungs following 3.5 to 13 h of hyperventilation. A control group of 15 sheep (10 sheep similarly injected with sodium salicylate, but then sedated and paralyzed and ventilated at normal tidal volume and respiratory rate on a mechanical ventilator, and 5 sheep infused with saline alone and breathing spontaneously) showed no pulmonary or arterial blood gas abnormalities. We conclude that prolonged hyperventilation under the conditions of this experiment precipitated events that resulted in acute lung injury.

[Alcohol-drug interaction in rat embryogenesis: the effect of separate and combined action of sodium salicylate and ethanol]

A combined administration of sodium salicylate and ethanol to female rats in threshold embryotoxic doses on the 9th, 10th, 12th and 13th days of pregnancy results in a sharp increase of embryolethal and teratogenic effects. The embryotoxic effect of sodium salicylate and ethanol at their combined injection exceeds the summational embryotoxic effect at the separate action of the preparations. The spectrum of malformations after their combined effect does not differ from that induced with sodium salicylate.

Should corneas from donors receiving a high dose of salicylate be used as grafts: an animal experimentation

Rabbits were injected intravenously with a single dose of sodium salicylate (350 mg kg-1) in order to study the following in vivo: (i) the distribution of the drug in the various eye tissues and fluids, particularly the cornea and aqueous humour, and (ii) transfer of the drug from corneal grafts obtained from donors receiving sodium salicylate to the eye tissues of the recipient. In additional experiments, the in vitro effects of sodium salicylate on the growth and protein synthesis of corneal cells grown in tissue culture were also studied. In vivo experiments showed that the periods during which we observed the highest concentration of salicylate in the serum and in the eye tissues were within 30 min and 2 hr respectively following the injection. These experiments also showed that salicylate was transferred from the treated donor via corneal graft to the recipient's eye tissues where it could still be detected 48 hr after the operation. In vitro experiments showed that a 50% inhibition of cell growth was obtained at a concentration of about 1000 micrograms salicylate ml-1 while protein synthesis was decreased by 50% at a concentration of about 200 micrograms ml-1. A consideration of our data from the in vivo and in vitro experiments together suggests that ingestion by the donor of high concentrations of salicylate may have the potentiality of subjecting the corneal endothelial cells to cytotoxic concentrations of the drug thus jeopardizing the success rate of corneal graft operations.

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

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

Salicylate ototoxicity in the chinchilla: a behavioral and electron microscope study

Normal audiograms were obtained from a group of behaviorally conditioned chinchillas. Following this the animals were injected with sodium salicylate. Temporary hearing losses were measured 1 1/2 hours after treatment. Animals were anesthetized and blood samples taken to determine salicylate levels. The animals were then decapitated and the temporal bones were examined by SEM and TEM. No morphological correlate was seen for temporary hearing losses which were generally in the neighborhood of 30-40 dB.

Effects of sodium salicylate and acetylsalicylic acid on intramural pH and ulceration of rabbit antral mucosa

This study examines the relationship between the pH within the middle third of antral mucosa (intramural pH [IMpH]) and the development of ulceration caused by salicylates. Luminal soldium salicylate does not significantly alter the IMpH or cause ulceration of mucosa maintained at luminal pH 7. Salicylate at pH 3.5 initially decrease IMpH (7.28 to 6.75), during which time ulceration occurs. IMpH subsequently increase, resulting in profound alkalinization (pH 7.67) associated with increased HCO3 secretion. Salicylate at pH 1 causes a sustained decrease in IMpH (6.57), which is associated with more severe ulceration. Neither sodium salicylate nor acetylsalicylic acid given intravenously affects. IMpH or causes ulceration at luminal pH 7 or 3.5. However, at pH 1 both salicylate compounds cause ulceration and subtle changes in net ion fluxes without altering IMpH. The data suggest that acidification of the midportion of the mucosa in general is not a prerequisite for the occurrence of gross damage, and the damaging effects of intravenous salicylates cannot be explained by thier metabolic actions alone. However, it appears that the metabolic effects of salicylate make the mucosa more susceptible to the deleterious effects of diffusing acid. Since intravenous sodium salicylate and acetylsalicylic acid both cause ulceration but only acetylsalicylic acid alters prostaglandin synthesis, interference with prostaglandin metabolism does not appear to be a prerequisite for the occurrence of ulceration.

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

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

Aspirin and concomitant idiosyncrasies in adult asthmatic patients

The nasal and respiratory symptoms observed after oral challenge to aspirin (ASA), tartrazine, and other nonsteroidal anti-inflammatory substances are best described as idiosyncratic reactions. A positive response to oral challenge, defined as a 20% fall in forced expiratory volume in 1 sec (FEV1) from baseline for up to 4 hr, occurred in 44 of 230 patients with ASA, 11 of 277 with tartrazine, 2 of 93 with sodium salicylate, and 2 of 69 with acetaminophen. No one had a positive response to tartrazine, sodium salicylate, or acetaminophen who was not also positive to ASA. The dose of ASA causing a positive response was less than 5 grains in 95% of the patients. Of 50 patients with a suspicious history studied in detail, 96% of those with ASA idiosyncrasy had sinusitis and 71% had nasal polyps. Methacholine challenges and random circulating and sputum eosinophils did not differentiate patients with a negative challenge from those with a positive challenge. However, patients with a positive history and positive challenge had significantly more random nasal eosinophils than those with negative aspirin challenges. The term "aspirin triad" has outlived its usefulness since ASA idiosyncrasy can exist in patients lacking certain components of the triad. ASA idiosyncrasy is unsuspected in many patients and possibly overdiagnosed in others.

A comparative study with indomethacin and combined indomethacin sodium-salicylate in rheumatoid arthritis

A double-blind cross-over clinical trial was performed to compare clinical effectiveness of indomethacin (3 x 25 mg/day) alone to that of a combination of indomethacin + sodium-salycylate (3 x 25 mg/day and 3 x 250 mg/day, respectively) in rheumatoid arthritis. It was established that enteral blood loss was significantly reduced by combined treatment as determined by Cr51 labelled erythrocytes in comparison to that after treatment with indomethacin alone. Therapeutic effect was maintained in both groups, no significant disparities were observed. Occurrence of subjective complaints was less frequent in the combined treatment group. It was concluded that the combined preparation consisting of indomethacin and sodium-salicylate has a favourable effect in rheumatoid arthritis.

Fever: effect of drug-induced antipyresis on survival

To determine whether the prevention of fever affects the survival of an animal infected with pathogenic bacteria, lizards (Dipsosaurus dorsalis) were infected with live Aeromonas hydrophila and received varying doses of sodium salicylate, an antipyretic drug. Twelve lizards received identical injections of bacteria along with a nontoxic dose of sodium salicylate; five animals increased their mean body temperature at least 0.6 degrees C and survived the week, whereas seven did not develop a fever and died within 3 days. These data indicate that in these lizards the prevention of fever by use of an antipyretic drug such as sodium salicylate increases the mortality rate from bacterial infection.