Gentamicin conditioning confers auditory protection against noise trauma.

Auditory conditioning consists of the pre-exposure to low levels of a potential harmful agent to protect against a subsequent harmful presentation. The agent that was first tested was noise. This paradigm was more recently successfully tested with other agents. Nonetheless, the vast majority of the studies utilize the same agent to condition and to cause the trauma. The aim of this study was to verify whether conditioning with an agent different from the agent used to cause the trauma can also be effective. Thus, the following groups were organized: group Cont, which is the noise trauma control group, was exposed to 110-dB broadband noise centered at 4 kHz for 72 h; group Gent, which is the gentamicin conditioning control group, was administered 30 mg/kg of gentamicin daily for 30 consecutive days; and group Expt was conditioned with gentamicin similarly to group Gent and then subjected to a noise trauma similarly to group Cont. The animals were functionally and morphologically evaluated through the measurement of the auditory brainstem response and scanning electron microscopy, respectively. The following variables were investigated: outer hair cell injury and auditory threshold shift. The group that was conditioned with the drug exhibited significantly less outer hair cell damage, 10.8 and 22.9%, respectively (p = 0.0146), although did not maintain the proper functioning of the auditory system. We, therefore, conclude that conditioning with a different agent from that used to cause the trauma is effective, which suggests that both agents that were used promote similar mechanisms of self-protection.

Ciliary ultrastructure in patients with chronic rhinosinusitis and primary ciliary dyskinesia.

The Cilia represent one of the main mechanisms contributing to the clearance of microorganisms and particles from the respiratory epithelium. Primary ciliary dyskinesia (PCD) is a genetically determined disorder characterized by irreversible systemic dysmotility of the cilia. Secondary ciliary dyskinesia (SCD) differs from primary defects on the reversible ultrastructural alterations that can occur after any insult to a previously normal mucosa. Hence, this study aimed to describe and compare the main ultrastructural ciliary features in PCD and SCD through transmission electron microscopy. The most frequent PCD abnormalities were missing or short dynein arms, missing central microtubules, and displacement of one of the nine peripheral doublets. The most common changes found in SCD were compound cilia and peripheral microtubule alterations associated with modifications of the respiratory epithelium. PCD presented a higher percentage of altered cilia (>30 %) when compared to SCD (5 %), demonstrating that SCD is more limited in area than PCD. Whereas in PCD the changes in the dynein arms and in the central microtubules are fundamental for diagnostic confirmation, the diagnosis of SCD usually involves compound cilia and disarrangements in peripheral microtubules.

Effects of hyperbaric oxygen treatment on auditory hair cells after acute noise damage.

Acute acoustic trauma (AAT) is a sudden sensorineural hearing loss caused by exposure of the hearing organ to acoustic overstimulation, typically an intense sound impulse, hyperbaric oxygen therapy (HOT), which favors repair of the microcirculation, can be potentially used to treat it. Hence, this study aimed to assess the effects of HOT on guinea pigs exposed to acoustic trauma. Fifteen guinea pigs were exposed to noise in the 4-kHz range with intensity of 110 dB sound level pressure for 72 h. They were assessed by brainstem auditory evoked potential (BAEP) and by distortion product otoacoustic emission (DPOAE) before and after exposure and after HOT at 2.0 absolute atmospheres for 1 h. The cochleae were then analyzed using scanning electron microscopy (SEM). There was a statistically significant difference in the signal-to-noise ratio of the DPOAE amplitudes for the 1- to 4-kHz frequencies and the SEM findings revealed damaged outer hair cells (OHC) after exposure to noise, with recovery after HOT (p = 0.0159), which did not occur on thresholds and amplitudes to BAEP (p = 0.1593). The electrophysiological BAEP data did not demonstrate effectiveness of HOT against AAT damage. However, there was improvement of the anatomical pattern of damage detected by SEM, with a significant reduction of the number of injured cochlear OHC and their functionality detected by DPOAE.

Observational study on the benefit of a nutritional supplement, supporting immune function and energy metabolism, on chronic fatigue associated with the SARS-CoV-2 post-infection progress.

BACKGROUND & AIMS: Recent studies have verified that the SARS-CoV-2 infection (from December 2019 has affected 123 million people throughout the world and more than 3 million people in Italy), can have medium-term and long-term effects, collectively referred to as "post-Covid syndrome" or "long-Covid" characterized by chronic fatigue, followed by muscle weakness, dyspnea and headache. Chronic fatigue or chronic tiredness is a persistent symptom both in patients who have experienced a severe infection and in those who have experienced a mild form of infection. Studies conducted on both patients discharged from hospital and patients managed at home showed that there was no association between the severity of the Coronavirus disease (Covid-19) and the subsequent chronic fatigue symptom. The aim of this study was to evaluate the ability of a nutritional supplement based on vitamins, minerals, amino acids and plant extracts (Apportal®) intake, to ameliorate the general health status in particular the chronic fatigue symptom in subjects after SARS-CoV-2 negativity. METHODS: Participants were advised to take one sachet daily of Apportal® for 28 consecutive days. At the beginning (T0), after 14 days (T1) and after 28 days (T2) of supplementation, general fatigue, mental fatigue and Quality of Life indexes were evaluated through specific questionnaires. The assessment of quality of life and health status were measured through the EuroQoL-5D questionnaire, chronic fatigue using the FACIT-Fatigue questionnaire and mental fatigue using the modified Chalder questionnaire. RESULTS: 201 subjects were enrolled for the study; results showed a significant improvement in all indexes analyzed after 14 and 28 days of supplementation. The main significant improvement was observed after the first 14 days and it was further confirmed at 28 days as well. The RTE (Relative Treatment Effect) trend about quality of life, health status, FACIT-Fatigue and mental fatigue in the three questionnaires was statistically significant (Wald Statistic, p < 0.0001). The data of FACIT-questionnaire showed an improvement of at least 1 unit in 76.62% of subjects after 14 days and in 90.05% of subjects after 28 days. An improvement of 10-unit was found in about one third of subjects after 14 days and in half of the subjects after 28 days. CONCLUSIONS: This study shows that Apportal® can reduce chronic fatigue and improve quality of life and health status in subjects after SARS-CoV-2 negativity due to the synergistic effect of its components.

Otoprotection Mechanisms Against Oxidative Stress Caused by Cisplatin.

Introduction Cisplatin damages the auditory system and is related to the generation of free radicals. Glutathione peroxidase is an endogenous free radicals remover. Objective To investigate the mechanisms involved in otoprotection by N-acetylcysteine through the expression of glutathione peroxidase in outer hair cells from rats treated with cisplatin. Methods Male Wistar rats were intraperitoneally injected with cisplatin (8 mg/Kg) and/or received oral administration by gavage of N-acetylcysteine (300 mg/Kg) for 3 consecutive days. On the 4 th day, the animals were euthanized and beheaded. The tympanic bullae were removed and prepared for scanning electron microscopy and immunofluorescence. Results Among the groups exposed to ototoxic doses of cisplatin, there was an increase in glutathione peroxidase immunostaining in two groups, the one exposed to cisplatin alone, and the group exposed to both cisplatin and N-acetylcysteine. Conclusion The expression of glutathione peroxidase in the outer hair cells of rats exposed to cisplatin showed the synthesis of this enzyme under cellular toxicity conditions.

Understanding the anatomy of ears from guinea pigs and rats and its use in basic otologic research.

UNLABELLED: The use of animal samples is important in otologic research and understanding the anatomy of their ears help make proper use of them in research projects. AIM: to study guinea pig's and rat's ears under light microscopy(LM) and scanning electron microscopy(SEM) and understand their anatomical advantages in basic otologic research. MATERIALS AND METHODS: The temporal bones, tympanic bullas and cochleas from three albino guinea pigs and rats were photographed and analyzed under LM and SEM. RESULTS: Rats aren't as simple to handle as guinea pigs, and often present with otitis media. Rats have a fragile junction of the tympanic bulla, two and half turns in the cochlea, and their tympanic membranes do not seal off the entire external auditory canal. Guinea pigs have full bullas, their incus and malleus are fused and they have three and half cochlear turns. Under SEM, guinea pigs and rats have Tectori Membrane, Raissner's Membrane and the Organ of Corti. Only guinea pigs have Hensen's Cells. CONCLUSION: Guinea pigs were considered easy to handle for microdissection purposes because of the size and robustness of their temporal bones, and for surgical experiments involving the stapes, the oval window and the tympanic membrane. Under SEM there are similarities guinea pigs and rats, and both can be used in inner ear studies.

Ototoxicity and otoprotection in the inner ear of guinea pigs using gentamicin and amikacin: ultrastructural and functional aspects.

UNLABELLED: Ototoxicity is still a challenge to medicine. The discovery of self-protecting endogenous mechanisms of the outer hair cells associated with their functional and ultra-structural assessment methods has opened new horizons in the understanding and controlling of these mechanisms. AIM: this paper aimed at establishing whether or not underdoses of gentamicin could protect the inner ear against the harmful effects of amikacin, based on these protection mechanisms and determine if the otoacoustic emission amplitudes could be associated with the level of hair cell integrity. MATERIALS AND METHODS: Experimental study. We used 31 guinea pigs. They were injected with saline solution, gentamicin and amikacin, alone and in combinations -intramuscular injections - during 12, 30 and 42 days. The otoacoustic emissions were recorded in the beginning and at the end of the experiment, comparing it with the cochlear integrity study carried out by electron microscopy. RESULTS: gentamicin underdoses did not protect the inner ear against amikacin toxicity; the reduction in otoacoustic emissions was strongly associated with an increase in hair cell lesions. CONCLUSION: these findings help understand inner ear otoprotection and ototoxicity. Establishing the correlation between the emissions amplitude an cell integrity plays an important role in the follow up of hair cell damage, with possible monitoring of ototoxicity caused by drugs in humans.

Clinical and ultrastructural study after partial inferior turbinectomy.

UNLABELLED: We report clinical and histological results obtained after partial inferior turbinectomy (PIT), surgery indicated for the treatment of chronic nasal obstruction. METHODS: Twenty patients were divided into two groups submitted to PIT plus septoplasty and PIT alone. The patients were reassessed clinically and histologically by means of a biopsy of the regenerated areas in the inferior turbinates at two different times after PIT, i.e., after 8 to 12 months (group A) and after two years (group B). RESULTS: The clinical results proved to be satisfactory for the relief of nasal obstruction in group A and unsatisfactory in group B. However, better histological results with better recovery and epithelial differentiation of the regenerated mucosa of the inferior turbinates after PIT were observed in group B. CONCLUSION: Surgery proved to be effective on a short-term but not on a long-term basis, and histological recovery did not accompany improvement of clinical signs and symptoms.

[Amifostine otoprotection to cisplatin ototoxicity: a guinea pig study using otoacoustic emission distortion products (DPOEA) and scanning electron microscopy]. / Otoproteção da amifostina aos efeitos ototóxicos da cisplatina: estudo em cobaias albinas por emissões otoacústicas produtos de distorção e microscopia eletrônica de varredura.

UNLABELLED: Cisplatin is an antineoplastic drug for cancer treatment in children and adults. The side effects of cisplatin ototoxicity are significant: irreversible bilateral hearing damage to high frequencies (4 kHz - 8 kHz). Reports recognize some drugs that are associated with cisplatin to obtain an otoprotector effect. The ototoxicity mechanisms of cisplatin are related to injury of hair cell oxidation mechanism, especially of outer hair cells. AIM: Using otoacoustic emissions distortion products (DPOEA) and scanning electron microscopy we intended to verify the action of amifostine, a radioprotective drug that has well known antioxidant characteristics and otoprotector effects to cisplatin injury. STUDY DESIGN: Experimental. MATERIAL AND METHODS: We used an experimental guinea pig model. The study was performed as follows: group 1: 6 animals, 12 ears, cisplatin 8.0 mg/Kg/day (IP), 3 days. Group 2: 6 animals, 12 ears, amifostine 100 mg/Kg/day (IP) and after 90 minutes, cisplatin 8.0 mg/Kg/day (IP), 3 days and group 3: 3 animals, 6 ears, amifostine 100 mg/Kg/day (IP), 3 days. RESULTS: DPOEA were present before and after treatment in groups 2 and 3. The normal cilium architecture of outer hair cells was supported in all cochlear turns in groups 2 and 3. We concluded that amifostine has a potential otoprotector effect against cisplatin ototoxicity and could be used in clinical trials.

Otoprotection Mechanisms Against Oxidative Stress Caused by Cisplatin

Abstract Introduction Cisplatin damages the auditory system and is related to the generation of free radicals. Glutathione peroxidase is an endogenous free radicals remover. Objective To investigate the mechanisms involved in otoprotection by N-acetylcys- teine through the expression of glutathione peroxidase in outer hair cells from rats treated with cisplatin. Methods Male Wistar rats were intraperitoneally injected with cisplatin (8 mg/Kg) and/or received oral administration by gavage of N-acetylcysteine (300 mg/Kg) for 3 consecutive days. On the 4th day, the animals were euthanized and beheaded. The tympanic bullae were removed and prepared for scanning electron microscopy and Results Among the groups exposed to ototoxic doses of cisplatin, there was an increase in glutathione peroxidase immunostaining in two groups, the one exposed to cisplatin alone, and the group exposed to both cisplatin and N-acetylcysteine. Conclusion The expression of glutathione peroxidase in the outer hair cells of rats exposed to cisplatin showed the synthesis of this enzyme under cellular toxicity conditions.

[Lack of protection against gentamicin ototoxicity by auditory conditioning with noise]. / Falta de proteção contra a ototoxicidade da gentamicina pelo condicionamentoauditivo com ruído.

INTRODUCTION: Auditory conditioning consists of the pre-exposure to low levels of a potential harmful agent to protect against a subsequent harmful exposure. OBJECTIVE: To confirm if conditioning with an agent different from that used to cause the trauma can also be effective. METHODS: This was an experimental study with 17 guinea pigs, divided into three groups: an ototoxic control group (Cont) that received intramuscular administration of gentamicin 160 mg/kg/day for ten consecutive days, but no sound exposure; a sound control group (Sound) that was exposed to 85 dB broadband noise centered at 4 kHz, 30 min each day for ten consecutive days, but received no ototoxic medications; and an experimental group (Expt) that received sound exposure identical to the Sound group and after each noise presentation, received gentamicin similarly to Cont group. The animals were evaluated by distortion product otoacoustic emissions (DPOAEs), brainstem auditory evoked potentials (BAEPs), and scanning electron microscopy. RESULTS: The animals that were conditioned with noise did not show any protective effect compared with the ones that received only the ototoxic gentamicin administration. This lack of protection was observed functionally and morphologically. CONCLUSION: Conditioning with 85 dB broadband noises, 30 min a day for ten consecutive days does not protect against an ototoxic gentamicin administration of 160 mg/kg/day for ten consecutive days in the guinea pig.

The effects of hyperbaric oxygen therapy upon ototoxic injuries produced by amikacin in guinea pigs.

UNLABELLED: Hyperbaric oxygen therapy (HBOT) has enhanced the prevention and treatment of auditory ailments such as ototoxicity. OBJECTIVE: To study the effects of HBOT upon ototoxic injuries produced by amikacin. METHOD: This experimental study included 12 albino guinea pigs, whose auditory function was assessed through distortion product otoacoustic emissions (DPOAEs) and brainstem auditory evoked potentials (BAEPs) before and after the administration of amikacin (600 mg/kg/day) and HBOT sessions (2 ATA, 60 minutes). Morphological features were analyzed through scanning electron microscopy. Subjects were divided into four groups, as follows: group 1 - saline solution + HBOT; group 2 - amikacin for 8 days; group 3 - amikacin + seven days of rest; and group 4 - amikacin + HBOT. RESULTS: Group 1 subjects had preserved function and morphology throughout the experiment; Group 2 subjects had statistically significant levels of hair cell injury and functional impairment; Subjects on groups 3 and 4 had statistically significant functional and morphological impairment after the administration of amikacin, which were still present after the proposed procedures had been carried out. CONCLUSION: Hyperbaric oxygen therapy did not change the cochlear hair cell morphology or the electro-physiological thresholds of the guinea pigs given amikacin.

New multifunctional surfactants from natural phenolic acids.

Several new multifunctional molecules derived from natural sources such as amino acids and hydroxycinnamic acids were synthesized. They exhibit various activities such as emulsifying, UV-protecting, and radical scavenging, thereby conforming to the latest requirements for cosmetic ingredients. The synthesis comprises only a few steps: (i) the amino acid, the acid groups of which are protected by esterification, is coupled with ferulic or caffeic acid; (ii) the p-hydroxyl group of the cinnamic derivative reacts with dodecyl bromide in the presence of potassium carbonate (the resulting compounds are highly lipophilic and tested as water/oil (W/O) emulsifiers); (iii) these molecules, by deprotonating the acid groups of the amino acids, with successive salification, are more hydrophilic, with stronger O/W emulsifying properties. The new multifunctional surfactants might prove useful for the treatment of multiple skin conditions, including loss of cellular antioxidants, damage from free radicals, damage from UV, and others.

Persistence of the otoprotective effect: how long does otoprotection against amikacin lasts?

UNLABELLED: There is evidence that a "resistance phenomenon" occurs when a none-damaging dose of amikacin protects the hair cells from ototoxicity. Our goal is to prove that this resistance is persistent. METHOD: Experimental study - 14 albino guinea pigs (Cavia porcellus) divided into three groups. The auditory function was assessed by distortion product otoacoustic emissions (DPOAE): before exposure to amikacin, on the 15th day after the non-damaging dose was injected, at the end of the damage dose injection and prior to decapitation. RESULTS: Group A (control) presented normal hearing and histological pattern. Group B (amikacin 20mg/kg/day (IM) for 30 days and affecting dose (400 mg / kg / day) for 12 days and Group C (same protocol of Group B, but kept for 60 days and slaughtered), the DPOAE confirmed normal auditory function in the pre-exposure and maintenance of the standard-dose; however, significant loss of auditory function after the end of the damaging dose injection. CONCLUSION: The protection phenomenon did not extended for a period of 30 to 60 days after the application of damaging doses of amykacin.

Assessing the maxillary sinus mucosa of rabbits in the presence of biodegradable implants.

UNLABELLED: In an attempt to improve the quality of life of patients with vitreous humor disease, ophthalmologists began offering steroid-eluting biodegradable implants to their patients. These implants can be used as an alternative treatment for CRS and this is why this experimental study was carried out on rabbit maxillary sinuses. OBJECTIVE: This study aims to assess the histology of the mucosa of the maxillary sinuses of rabbits after the placement of a prednisolone-eluting biodegradable implant. METHOD: Eighteen rabbits were randomly divided into two groups: group 1 - subjects had drug-eluting implants placed on their left maxillary sinuses; group 2 - subjects had non-drug-eluting implants placed on their left maxillary sinuses. The right maxillary sinuses served as the controls. After seven, 14, and 28 days three rabbits in each group were randomly picked to have their tissue inflammatory response assessed. RESULTS: Levels of mucosal inflammation were not significantly different between the groups with and without drug-eluting implants and the control group, or when the groups with drug-eluting implants and non-drug-eluting implants were compared. CONCLUSION: Signs of toxicity or mucosal inflammation were not observed in the maxillary sinuses of rabbits given prednisolone-eluting implants or non-drug-eluting implants.

A functional study on gentamicin-related cochleotoxicity in its conventional dose in newborns.

UNLABELLED: The early identification of hearing impairment allows for an intervention still in the 'critical' and ideal period of hearing and language stimulation. Pediatric ototoxicity is a very controversial topic. There have been variable percentages of ototoxicity cases in children with different aminoglycosides antibiotics. The main pediatric groups whom receive aminoglycosides are newborns with severe infections on the neonatal ICU. AIM: to check the functional aspect of the cochlear external hair cells and treatment regimens used to treat infections during the neonatal period. STUDY DESIGN: Experimental. MATERIALS AND METHODS: we studied 26 albino guinea pigs, through distortion product otoacoustic emissions, before and after the use of gentamicin. RESULTS: in all the assessments, the external hair cells functional status, studied by means of the distortion product otoacoustic emissions, proved preserved. CONCLUSION: In the present study, we did not notice changes in outer hair cell function in the albino guinea pigs treated with gentamicin in the doses of 4 mg/Kg/day and 2.5 mg/Kg/day every 12 hours for 10 and 14 days.

Macroscopic description of the external and middle ear of paca (Cuniculus paca Linnaeus, 1766) / Descrição macroscópica da orelha externa e media da paca (Cuniculus paca Linnaeus, 1766)

Paca (Cuniculus paca), one of the largest rodents of the Brazilian fauna, has inherent characteristics of its species which can conribute as a new option for animal experimantation. As there is a growing demand for suitable experimental models in audiologic and otologic surgical research, the gross anatomy and ultrastructural ear of this rodent have been analyzed and described in detail. Fifteen adult pacas from the Wild Animals Sector herd of Faculdade de Ciências Agrárias e Veterinárias, Unesp-Jaboticabal, were used in this study. After anesthesia and euthanasia, we evaluated the entire composition of the external ear, registering and ddescribing the details; the temporal region was often dissected for a better view and detailing of the tympanic bulla which was removed and opened to expose the ear structures analyzed mascroscopically and ultrastructurally. The ear pinna has a triangular and concave shape with irregular ridges and sharp apex. The external auditory canal is winding in its path to the tympanic mebrane. The tympanic bulla is is on the back-bottom of the skull. The middle ear is formed by a cavity region filled with bone and membranous structures bounded by the tympanic membrane and the oval and round windows. The tympanic membrane is flat and seals the ear canal. The anatomy of the paca ear is similar to the guinea pig and from the viewpoint of experimental model has major advantages compared with the mouse ear.

A paca (Cuniculus paca), um dos maiores roedores da fauna brasileira, possui características inerentes à sua espécie que podem contribuir como uma nova opção de animal experimental; assim, considerando-se que há crescente busca por modelos experimentais apropriados para pesquisas audiológicas e otológica cirúrgicas foram analisados e descritos em detalhes a anatomia macroscópica e ultraestrutural da orelha desse roedor. Para o estudo, utilizaram-se 15 animais adultos provenientes do plantel do Setor de Animais Silvestres da Faculdade de Ciências Agrárias e Veterinárias, Unesp-Jaboticabal, Jaboticabal/SP. Após anestesia e eutanásia, avaliou-se toda a composição da orelha externa, registrando-se e descrevendo-se os detalhes, também se dissecou a região temporal para melhor visibilização e detalhamento da bula timpânica e estas foram removidas e abertas a fim de expor as estruturas da orelha, as quais foram analisadas, macroscopicamente e ultraestruturalmente. O pavilhão auricular apresenta forma triangular e côncava com cristas irregulares e ápice pontiagudo; o conduto auditivo externo é sinuoso em seu trajeto até a membrana timpânica; a bula timpânica encontra-se na parte posterior-inferior do crânio; a orelha média é formada por uma região cavitária preenchida por estruturas ósseas e membranosas. É delimitada pela membrana timpânica e as janelas redonda e oval, sendo a membrana timpânica de forma plana e que veda todo o conduto auditivo. A anatomia da orelha da paca é semelhante à da cobaia e do ponto de vista de modelo experimental apresenta grandes vantagens em comparação com a orelha do rato.

Analysis of the cytoprotective effect of amifostine on the irradiated inner ear of guinea pigs: an experimental study.

UNLABELLED: Radiation can cause damage to the inner ear, from a simple hearing loss all the way to profound deafness. Amifostine is a cytoprotective substance extensively used during radio-chemotherapy for malignant tumors. AIM: the objective of the present investigation was to establish the antioxidant and radioprotective effects of amifostine on the organ of Corti of albino guinea pigs irradiated in the head and neck region. MATERIALS AND METHODS: An experimental study conducted on four groups of guinea pigs were used; One group received only amifostine, one group was submitted to a single dose of 350 cGy and the other two were similarly irradiated but received amifostine doses of 100 or 200 mg/kg. All animals were slaughtered 30 days after the experiment, their bullae were removed and the damaged outer hair cells were counted. RESULT: The extent of injury was lower in the outer hair cells of the two groups treated with amifostine compared to the group that was only irradiated. There was no difference between the group treated with 100 and 200 mg/kg of amifostine. The group that received only amifostine had no cochlear damage. CONCLUSION: Amifostine is an effective cytoprotective substance in the Organ of Corti of irradiated guinea pigs.

Lack of protection against gentamicin ototoxicity by auditory conditioning with noise / Falta de proteção contra a ototoxicidade da gentamicina pelo condicionamento auditivo com ruído

INTRODUCTION: Auditory conditioning consists of the pre-exposure to low levels of a potential harmful agent to protect against a subsequent harmful presentation. OBJECTIVE: To confirm if conditioning with an agent different from the used to cause the trauma can also be effective. METHOD: Experimental study with 17 guinea pigs divided as follows: group Som: exposed to 85 dB broadband noise centered at 4 kHz, 30 minutes a day for 10 consecutive days; group Cont: intramuscular administration of gentamicin 160 mg/kg a day for 10 consecutive days; group Expt: conditioned with noise similarly to group Som and, after each noise presentation, received gentamicin similarly to group Cont. The animals were evaluated by distortion product otoacoustic emissions (DPOAEs), brainstem auditory evoked potentials (BAEPs) and scanning electron microscopy. RESULTS: The animals that were conditioned with noise did not show any protective effect compared to the ones that received only the ototoxic gentamicin administration. This lack of protection was observed functionally and morphologically. CONCLUSION: Conditioning with 85 dB broadband noise, 30 min a day for 10 consecutive days does not protect against an ototoxic gentamicin administration of 160 mg/kg a day for 10 consecutive days in the guinea pig. .

INTRODUÇÃO: O condicionamento auditivo consiste da pré-exposição de um agente lesivo em baixos níveis para proteger contra uma posterior apresentação lesiva. OBJETIVO: Confirmar se o condicionamento com um agente diferente do utilizado para causar o trauma pode ser efetivo. MÉTODO: Estudo experimental com 17 cobaias albinas divididas como a seguir- grupo Som: exposto a um ruído branco de 85 dB centrado em 4 kHz, 30 minutos por dia, por 10 dias consecutivos; grupo Cont: administração intramuscular de gentamicina 160 mg/kg por dia, por 10 dias consecutivos; grupo Expt: condicionado com ruído como o grupo Som. Após cada exposição ao ruído, recebeu gentamicina similarmente ao grupo Cont. Os animais foram avaliados por emissões otoacústicas produto de distorção (EOAPDs), potencial evocado auditivo de tronco encefálico (PEATE) e microscopia eletrônica de varredura (MEV). RESULTADOS: Os animais que foram condicionados com ruído não mostraram qualquer efeito protetor quando comparados com os que receberam apenas a gentamicina em doses ototóxicas. Esta ausência de proteção foi observada tanto funcionalmente quanto morfologicamente. CONCLUSÃO: Os autores concluíram que o condicionamento com ruído branco a 85 dB por 30 minutos, por dia por 10 dias consecutivos, não protege contra uma administração de gentamicina 160 mg/kg/dia, por 10 dias consecutivos. .