RESUMO
The zebrafish (Danio rerio) is a valuable vertebrate model for human hearing disorders because of many advantages in genetics, embryology, and in vivo visualization. In this study, we investigated auditory function of zebrafish during the first week postfertilization using microphonic potential recording. Extracellular microphonic potentials were recorded from hair cells in the inner ear of wild-type AB and transgenic Et(krt4:GFP)(sqet4) zebrafish at 3, 5, and 7 days postfertilization in response to 20, 50, 100, 200, 300, and 400-Hz acoustic stimulation. We found that microphonic threshold significantly decreased with age in zebrafish. However, there was no significant difference of microphonic responses between wild-type and transgenic zebrafish, indicating that the transgenic zebrafish have normal hearing like wild-type zebrafish. In addition, we observed that microphonic threshold did not change with the recording electrode location. Furthermore, microphonic threshold increased significantly at all tested stimulus frequencies after displacement of the saccular otolith but only increased at low frequencies after displacement of the utricular otolith, showing that the saccule rather than the utricle plays the major role in larval zebrafish hearing. These results enhance our knowledge of early development of auditory function in zebrafish and the factors affecting hearing assessment with microphonic potential recording.
Assuntos
Audição , Sáculo e Utrículo/fisiologia , Peixe-Zebra/fisiologia , Estimulação Acústica , Animais , Animais Geneticamente Modificados/crescimento & desenvolvimento , Animais Geneticamente Modificados/fisiologia , Células Ciliadas Auditivas/citologia , Células Ciliadas Auditivas/fisiologia , Larva/fisiologia , Sáculo e Utrículo/crescimento & desenvolvimento , Peixe-Zebra/crescimento & desenvolvimentoRESUMO
Hair cell ribbon synapses exhibit several distinguishing features. Structurally, a dense body, or ribbon, is anchored to the presynaptic membrane and tethers synaptic vesicles; functionally, neurotransmitter release is dominated by large EPSC events produced by seemingly synchronous multivesicular release. However, the specific role of the synaptic ribbon in promoting this form of release remains elusive. Using complete ultrastructural reconstructions and capacitance measurements of bullfrog amphibian papilla hair cells dialyzed with high concentrations of a slow Ca²âº buffer (10 mM EGTA), we found that the number of synaptic vesicles at the base of the ribbon correlated closely to those vesicles that released most rapidly and efficiently, while the rest of the ribbon-tethered vesicles correlated to a second, slower pool of vesicles. Combined with the persistence of multivesicular release in extreme Ca²âº buffering conditions (10 mM BAPTA), our data argue against the Ca²âº-dependent compound fusion of ribbon-tethered vesicles at hair cell synapses. Moreover, during hair cell depolarization, our results suggest that elevated Ca²âº levels enhance vesicle pool replenishment rates. Finally, using Ca²âº diffusion simulations, we propose that the ribbon and its vesicles define a small cytoplasmic volume where Ca²âº buffer is saturated, despite 10 mM BAPTA conditions. This local buffer saturation permits fast and large Ca²âº rises near release sites beneath the synaptic ribbon that can trigger multiquantal EPSCs. We conclude that, by restricting the available presynaptic volume, the ribbon may be creating conditions for the synchronous release of a small cohort of docked vesicles.
Assuntos
Fenômenos Biofísicos/fisiologia , Cálcio/metabolismo , Células Ciliadas Auditivas/citologia , Potenciais da Membrana/fisiologia , Sinapses/ultraestrutura , Vesículas Sinápticas/metabolismo , Éster Metílico do Ácido 3-Piridinacarboxílico, 1,4-Di-Hidro-2,6-Dimetil-5-Nitro-4-(2-(Trifluormetil)fenil)/farmacologia , Animais , Fenômenos Biofísicos/efeitos dos fármacos , Biofísica , Agonistas dos Canais de Cálcio/farmacologia , Quelantes/farmacologia , Ácido Egtázico/análogos & derivados , Ácido Egtázico/farmacologia , Capacitância Elétrica , Potenciais Pós-Sinápticos Excitadores/efeitos dos fármacos , Exocitose/efeitos dos fármacos , Feminino , Técnicas In Vitro , Masculino , Potenciais da Membrana/efeitos dos fármacos , Microscopia Eletrônica/métodos , Modelos Neurológicos , Método de Monte Carlo , Técnicas de Patch-Clamp , Rana catesbeiana , Estatística como Assunto , Sinapses/efeitos dos fármacos , Sinapses/fisiologia , Vesículas Sinápticas/efeitos dos fármacosAssuntos
DNA , Ciências Forenses , Cabelo , Laboratórios , Polícia , DNA/análise , DNA/história , Ciências Forenses/classificação , Ciências Forenses/economia , Ciências Forenses/educação , Ciências Forenses/ética , Ciências Forenses/história , Ciências Forenses/instrumentação , Ciências Forenses/métodos , Ciências Forenses/normas , Ciências Forenses/tendências , Cabelo/anatomia & histologia , Cabelo/citologia , Células Ciliadas Auditivas/anatomia & histologia , Células Ciliadas Auditivas/citologia , História do Século XIX , História do Século XX , História do Século XXI , Laboratórios/economia , Laboratórios/história , Laboratórios/normas , Laboratórios/estatística & dados numéricos , Laboratórios/provisão & distribuição , Laboratórios/tendências , Microscopia/instrumentação , Microscopia/métodos , Cidade de Nova Iorque , Polícia/normas , Polícia/tendências , Televisão/tendências , Recursos HumanosRESUMO
The radial width of three rows of cuticular plates of outer hair cells (width of the OHC triad), the distribution of inner hair cells along the organ of Corti, and postnatal maturation of the middle ear were examined in rats of the Srague-Dawley and Lewis strains aged 0-24 days and two months. The width of the OHC triad is a good indication of the course of maturation of the reticular lamina and the organ of Corti in different regions of the cochlea. The width of the OHC triad in adult rats decreases continuously from the apex toward the base, while in newborn pups the trend is just the reverse. Thus, there is a region of the cochlea in which the width of the OHC triad is the same, or changes insignificantly, from birth to adulthood. This particular region (where the process of postnatal maturation of the organ of Corti begins?) corresponds to the region of maximum density of inner hair cells and tonotopically to the region of 'best hearing'. The width of the OHC triad will reach its adult values earlier in the basal than in the apical regions. The time-course of middle ear maturation correlates well with the time-course of maturation of the reticular lamina. The parameters under study are in many respects strain-specific.