[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.

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. .

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.

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.