Study of synaptic transmissions on hair cells

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Hair cells of the inner ear is the transducer cell of mechanical energy. Namely, the informations of sound, balance and accelerations are transduced into the electrical signal and then transmitted to the central nervous system. From the central nervous system some feedback informations are returned to the peripheral hearing organ to inhibit the hair cell. I have aimed in this research to investigate both the afferent and efferent synapses on to the hair cell, by utilizing a slice preparation of the cochlear. However, making a good slice of the hearing organ was extremely difficult, because of the mixture of hard and soft structures. I have therefore focused on the analysis by utilizing cutout preparation of vestibular organ and on the experiments with isolated hair cells. Afferent synapse activities were recorded in the cut-out preparation of vestibular organ, and the differences of the synaptic potential appearance, probably the mechanism of synapse transmission too, were detected between bouton type and calyx type synapses. The isolated hair cells were mainly studied in the analysis of acetylcholine effects. Acetylcholine hyperpolarized the hair cell membrane by increasing intracellular Ca concentration and by activating K conductance. The transmitter released from hair cell was concluded most likely as glutamate also by utilizing the isolated hair cell preparation together with cultured neuron with high glutamate receptor sensityvity.