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Conclusion. Since aquaporin-6 (Aqp6) protein was located in the membrane of intracellular vesicles of the stria vascularis, endolymphatic sac, and vestibule, Aqp6 might be involved in some distinct physiological function of acid-base metabolism and water balance in endolymphatic fluid homeostasis. However, its lack of expression on the plasma membrane indicates that Aqp6 does not have a direct role in water flux via the plasma membrane. Objective. To evaluate the expression and immunolocalization of Aqp6 in the rat inner ear. Materials and methods. Wistar rats were used. Aqp6 mRNA expression in the rat inner ear was investigated in the vestibulum as well as in the cochlea and endolymphatic sac using the reverse transcription-polymerase chain reaction (RT-PCR) method, and detailed immunolocalization of Aqp6 in the rat inner ear was investigated using immunohistochemical methods including immunofluorescence microscopy and immunoelectron microscopy. Results. We obtained novel data showing that not just Aqp6 mRNA but also Aqp6 protein is expressed in the cochlea, endolymphatic sac, and vestibule. Immunoelectron microscopic studies revealed that the immunolabelled gold was diffusely seen in the intracellular area of the stria vascularis, endolymphatic sac, and vestibule, but never in the plasma membranes. [ABSTRACT FROM AUTHOR]

Changes in ambient pressure can elicit the vertigo and bodily disequilibrium known clinically as alternobaric vertigo. Our previous studies showed that changes in middle ear pressure altered the activity of the primary vestibular neuron, and the finding suggests that the pressure-induced vestibular response causes alternobaric vertigo. To investigate the roles played by the round window (RW) and the oval window (OW) in the vestibular response induced by pressure, we measured the change in perilymphatic pressure and the firing rates of primary vestibular neurons after the application of positive or negative pressure to the middle ear. We found an increase in the pressure-induced vestibular response in the group with a closed OW, and a decrease in the group with a closed RW. Measurements showed that the amplitude of the change in perilymphatic pressure in the group with a closed OW did not differ from that in the control group, whereas the amplitude of the perilymphatic pressure change in the group with a closed RW was significantly reduced. A discrepancy between the number of neurons responding and the amplitude of the perilymphatic pressure change in the closed OW group suggests that the vestibular response induced by the change in middle ear pressure was not related solely to the magnitude of the pressure change in the inner ear, but also involved the oval and round windows. [ABSTRACT FROM AUTHOR]

Shows the effect of experimental endolymphatic hydrops and histamine on plasma vasopressin level in the guinea pig. Role of vasopressin or antidiuretic hormone in body organs; Characteristics of guinea pigs used in experiment; Determination of vasopressin control plasma level through blood samples; Analysis of results of experiment.