Biomedical subjects
Publications and source records attributed to S D Comis.
Raising the K+ concentration in scala tympani of the guinea-pig cochlea generally caused a substantial increase in the spontaneous firing rate of single auditory nerve fibres. This effect was not accompanied by any observed reduction in the threshold sensitivity of these fibres. These findings cast doubt on current theories of cochlear transduction.
Scala tympani of the guinea pig was perfused with artificial perilymph containing putative transmitter substances. Single auditory nerve fibre activity was recorded during these perfusions and the responses of these fibres were studied using computer-controlled routine. Acetylcholine significantly inhibited tone-induced responses of a large proportion of the fibres tested. Glutamate appeared to be a potent depolarising agent when applied in concentrations between 2 and 10 mM. Noradrenaline did not affect tone-induced activity, but inhibited the spontaneous activity of some fibres. The results support the view that acetylcholine is the transmitter at synapses of the olivocochlear bundle, and that glutamate may be involved in the afferent synapse. The data do not support the hypothesis that noradrenaline is the afferent transmitter.
We have described cholinergic fibres which cross the tunnel to three levels of the cells on the opposite side--from the level of the efferent network to the base of a plaque at the level of the nucleus of the first Deiters cell. These fibres are dependent upon the OCB being intact. The same is true for those fibres seen within the Hensen cell region. However, the cholinesterase-staining fine fibres travelling along the floor of the tunnel to the base of the plaque are independent of the integrity of the OCB.
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Scala tympani of the guinea pig cochlea was perfused with solutions having an increased potassium concentration. The response characteristics of single auditory nerve fibres in both normal and kanamycin-damaged cochleas were studied using computer controlled routines. The results indicate that these perfusions caused a marked increase in the spontaneous firing rate of auditory nerve fibres, without loss of threshold sensitivity. Current theories of cochlear transduction support the view that the potassium concentration difference across the reticular plate is fundamental to the sensitivity of the cochlea. The results presented here do not support this view.