Specialized features of the outer hair cell shapes in the cochlear fovea of bats.

In this study, we examined the specialized features of the outer hair cells (OHCs) and the stereocilium bundles of the bat cochlear fovea. Bat cochlea hair cells were observed by scanning and transmission electron microscopy, and the auditory brainstem response thresholds were assessed. The stereocilia bundles of the OHCs were extremely short. The OHC bodies were flask-shaped and cambiform or ball-shape in the cochlear fovea. Digitations in the Deiters cells had exaggerated lengths, and cup formation of the Deiters cell, housed at the bottom of the OHC in the base of the cell, showed a specialized shape. Our results provide the first evidence that different shapes of the OHCs in the cochlea fovea are related to the high-frequency function of auditory response. Echolocating bats have cochlear morphologies that differ from those of non-echolocating animals. Bat cochlear foveae are specialized for analyzing the Doppler-shifted echoes of the first-harmonics of the CF2 component; these are overrepresented in the frequency range around the dominant harmonic of the echolocation calls of bats. However, the OHCs of the bat cochlear fovea have not been fully characterized.

Persistência do efeito otoprotetor: qual a duração da otoproteção à amicacina? / Persistence of the otoprotective effect: how long does otoprotection against amikacin lasts?

Há comprovação de que o fenômeno de resistência ocorre quando a dose não lesiva da amicacina protege as células ciliadas contra a ototoxicidade da própria amicacina. OBJETIVO: O objetivo deste trabalho é verificar se o fenômeno de resistência é temporalmente persistente. MÉTODO: Estudo experimental com 14 cobaias albinas (Cavia porcellus) divididas em três grupos. Avaliação da função auditiva por emissões otoacústicas por produto de distorção (EOAPD): na pré-exposição à amicacina, no 15º dia de aplicação da dose não lesiva, no final da aplicação da dose lesiva e antes da decapitação. RESULTADOS: O Grupo A (controle) apresentou função auditiva e padrão histológico normais. No Grupo B (amicacina 20mg/kg/dia intramuscular por 30 dias e dose lesiva (400 mg/kg/dia) por 12 dias) e no Grupo C (mesmo esquema do grupo B, porém mantidos por 60 dias e sacrificados), as OEA-PD confirmaram função auditiva normal no período pré-exposição e manutenção do padrão após dose não lesiva, porém, houve perda importante da função auditiva após término do período de aplicação da dose lesiva. CONCLUSÃO: Não houve manutenção do fenômeno da autodefesa estendida por um período de 30 a 60 dias após a aplicação de doses lesivas de amicacina.

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.

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.

Spontaneous reversibility of damage to outer hair cells after sodium salicylate induced ototoxicity.

BACKGROUND: High sodium salicylate doses can cause reversible hearing loss and tinnitus, possibly due to reduced outer hair cell electromotility. Sodium salicylate is known to alter outer hair cell structure and function. This study determined the reversibility and cochlear recovery time after administration of an ototoxic sodium salicylate dose to guinea pigs with normal cochlear function. STUDY DESIGN: Prospective experimental investigation. METHODS: All animals received a single 500 mg sodium salicylate dose, but with different durations of action. Function was evaluated before drug administration and immediately before sacrifice. Cochleae were processed and viewed using scanning electron microscopy. RESULTS: Changes in outer hair cell function were observed to be present 2 hours after drug administration, with recovery of normal anatomy beginning after 24 hours. Subsequently, derangement and distortion of cilia reduced, with effects predominantly in row three. At 168 hours, cilia were near-normal but with mild distortions which interfered with normal cochlear physiology. CONCLUSIONS: Ciliary changes persisted for up to 168 hours after ototoxic sodium salicylate administration.

Experimental morphological and functional study of gentamicin cochleotoxicity using the regular dose given to neonates.

BACKGROUND: gentamicin is an antibiotic that acts in Gram-negative bacilli infections, having as a side effect ototoxicity. Ototoxicity is an iatrogenic disturb provoked by drugs that modify the internal ear, affecting the cochlear and/or vestibular system and causing alterations in two important functions: equilibrium and audition. The main pediatric groups that receive aminoglicosides antibiotics are newborns who present serious infections in Neonate intensive care units. AIM: to verify the occurrence of external ciliary cells (ECC) caused by gentamicin with single dose schemas of 4 mg/kg/day and 2,5mg/kg/day every 12 hours, through a morphological - scanning electronic microscopy (SEM) and functional - distortion product otoacoustic emissions (DPOAE) experimental study. METHOD: 26 albino guinea pigs were evaluated through DPOAE pre and post gentamicin treatment. The guinea pigs were sacrificed in the programmed time after the intramuscular administration of the drugs for anatomic analysis using MEV. RESULTS: the evaluation of the functional state of the ECC indicated preservation of the DPOAE in all of the guinea pigs. The SEM results, after being photographed were analyzed in terms of the number of the ECC in the cochlear basal turn in a specific photographic field. CONCLUSION: lesions or alterations in the functioning of the ECC of albino guinea-pigs after the use of 4 mg/Kg/day and 2,5mg/Kg/day every 12 hours for a period 10 and 14 days were not observed.

Estudo experimental anatômico-funcional da cocleotoxicidade da gentamicina com doses habituais para recém-nascidos / Experimental morphological and functional study of gentamicin cochleotoxicity using the regular dose given to neonates

BACKGROUND: gentamicin is an antibiotic that acts in Gram-negative bacilli infections, having as a side effect ototoxicity. Ototoxicity is an iatrogenic disturb provoked by drugs that modify the internal ear, affecting the cochlear and/or vestibular system and causing alterations in two important functions: equilibrium and audition. The main pediatric groups that receive aminoglicosides antibiotics are newborns who present serious infections in Neonate intensive care units. AIM: to verify the occurrence of external cilliary cells (ECC) caused by gentamicin with single dose schemas of 4mg/kg/day and 2,5mg/kg/day every 12 hours, through a morphological - scanning electronic microscopy (SEM) and functional - distortion product otoacoustic emissions (DPOAE) experimental study. METHOD: 26 albino guinea pigs were evaluated through DPOAE pre and post gentamicin treatment. The guinea pigs were sacrificed in the programmed time after the intramuscular administration of the drugs for anatomic analysis using MEV. RESULTS: the evaluation of the functional state of the ECC indicated preservation of the DPOAE in all of the guinea pigs. The SEM results, after being photographed were analyzed in terms of the number of the ECC in the cochlear basal turn in a specific photographic field. CONCLUSION: lesions or alterations in the functioning of the ECC of albino guinea-pigs after the use of 4mg/Kg/day and 2,5mg/Kg/day every 12 hours for a period 10 and 14 days were not observed.

TEMA: a gentamicina é um antibiótico que atua nas infecções causadas por bacilos Gram-negativos. Seu efeito colateral mais importante é a ototoxicidade. As ototoxicoses são afecções iatrogênicas provocadas por fármacos que alteram a orelha interna, podendo afetar o sistema coclear e/ou vestibular, alterando duas funções importantes: a audição e o equilíbrio. Os principais grupos pediátricos que recebem antibióticos aminoglicosídeos são recém-nascidos com infecções graves na UTI neonatal. OBJETIVOS: verificar a ocorrência de lesão às células ciliadas externas (CCE) pela gentamicina com os esquemas de dose única de 4mg/Kg/dia e de 2,5mg/Kg/dia a cada 12 horas, por meio de um estudo anatômico por microscopia eletrônica de varredura (MEV) e estudo funcional através das emissões otoacústicas por produto de distorção (OEAPD). Forma de estudo experimental. MÉTODO: foram avaliadas 26 cobaias albinas através das EOAPD pré e pós-tratamento com gentamicina. Para a avaliação anatômica por MEV, as cobaias foram sacrificadas em tempo programado após a administração das drogas via intramuscular. RESULTADOS: a avaliação do estado funcional das CCE mostrou preservação das OEAPD em todas as cobaias. Os resultados da MEV, depois de fotografados foram analisados através da contagem do número de CCE da espira basal da cóclea em determinado campo fotográfico. CONCLUSÃO: não foram observadas lesões ou alterações no funcionamento das células ciliadas externas mediante a dosagem aplicada em cobaias albinas, de 4mg/Kg/dia (dose única) e 2,5mg/Kg/dia a cada 12 horas, utilizadas por 10 e 14 dias.

The cochlea of Tadarida brasiliensis: specialized functional organization in a generalized bat.

Tadarida brasiliensis mexicana employs a broad-band sonar system at frequencies between 80 and 20 kHz and is characterized by non-specialized hearing capabilities. The cochlear frequency map was determined with extracellular horseradish peroxidase tracing in relation to quantitative morphological data obtained with light, scanning and transmission electron microscopy. These data reveal distinct species characteristic specializations clearly separate from the patterns observed in other bats with either broad-band or narrow-band sonar systems. The basilar membrane (BM) is coiled to 2.5 turns and about 12 mm long. Its thickness and width only change within the extreme basal and apical ends. The frequency range from about 30 to 80 kHz is represented in the lower basal turn with a typically mammalian mapping coefficient of about 3 mm/octave. This region exhibits morphological features correlated with non-specialized processing of high frequencies. (1) The BM is radially segmented by thickenings of pars tecta and pars pectinata. (2) The 3 rows of outer hair cells (OHCs) have similar morphology. Between 35 and 86% distance from base, frequencies between 30 and 12 kHz are represented with a slightly expanded mapping coefficient of about 6 mm/octave. In analogy to previous work, this cochlea region is termed acoustic fovea. It includes the frequency range of maximum sensitivity and sharpest tuning (21-27 kHz) but also frequencies below the sonar signals. The fovea is characterized by several morphological specializations. (1) The BM features a continuous radial thickening mainly composed of hyaline substance. (2) There is an increased number of layers of tension fibroblasts in the spiral ligament. (3) There are morphological differences in the arrangements of stereocilia bundles among the 3 rows of OHCs. The transitions between non-specialized and specialized cochlear regions occur gradually within a distance of about 600 microns. The gradients in stereocilia length of both receptor cell types and the gradations in length of the OHC bodies match specialized aspects of the frequency map.