VESTIBULAR MICROPHONIC POTENTIALS IN PIGEONS

Electrical responses to acoustic stimuli were measured by placing thin wire electrodes in the vestibular system of a pigeon model. Responses were measured after extirpation of the cochlea and the application of tetrodotoxin to the perilymphatic space. Responses seen were comparable to those of known cochlear microphonic potentials. These findings indicate that acoustic stimuli can evoke microphonic potentials in the vestibular system of the pigeon. We also found that vibrational amplitudes of less than 1 nm were sufficient to evoke a vestibular microphonic potentia

The vestibular evoked response to linear, alternating, acceleration pulses without acoustic masking as a parameter of vestibular function

In this study, short latency vestibular evoked potentials (VsEPs) were recorded in five guinea pigs in response to alternating linear acceleration pulses with and without acoustic masking. A steel bolt was implanted in the skull and coupled to a shaker. Linear acceleration pulses (n = 400) in upward, downward or alternating directions were given, with a peak acceleration of 4g after 0.5 msec. Tests were repeated with acoustic masking, after modiolus destruction and after application of KCl in the vestibule. Stimuli of the vestibular nerve were recorded with a platinum electrode in the bony facial nerve canal in the bulla. Unilateral linear acceleration showed a shallow plateau at 0.5 msec, which disappeared with alternating acceleration impulses and after modiolus destruction. Therefore all further tests were done with alternating impulses. After a latency time of 0.8 msec a multiwave response was seen, with a first positive peak P1 at 1.16 ms. These were followed by other positive and negative peaks (N1, P2, N2, P3, N3). With the elimination of cochlear influences by using acoustic masking, P1 remained stable, while subsequent peaks were altered or eliminated. After modiolus destruction, the P1 peak remained, although with a smaller amplitude due to vestibular damage. After application of a saturated KCl solution in the vestibule all responses, including P1, disappeared, thus confirming the vestibular origin of these responses. We conclude that the onset latency of the VsEP and the peak latency and level of the first positive peak P1 in response to alternating linear acceleration pulses without acoustic masking, measured in the facial canal, are good and stable parameters of vestibular function in guinea pigs

Dissecting the frog inner ear with Gaussian noise .1. Application of high-order Wiener-kernel analysis

Wiener kernel analysis was used to characterize the auditory pathway from tympanic membrane to single primary auditory nerve fibers in the European edible frog, Rana esculenta. Nerve fiber signals were recorded in response to white Gaussian noise. By cross-correlating the noise stimulus and the nerve fiber response, we computed (1) the full second-order Wiener kernel, and (2) the diagonals of the zeroth-to fourth-order Wiener kernels. These diagonals are usually referred to as polynomial correlation functions. The measured Wiener kernels were fitted with a 'sandwich' model. A new fitting procedure was used to compute the response characteristics of(1) the first filter, (2) the static nonlinearity, and (3) the second filter, which form the functional components of the model. The first filter is a bandpass filter. In the majority of low frequency fibers, with best excitatory frequency (BEF) <800 Hz, this filter was tuned to two frequencies. This dual tuning mechanism gives rise to 'off-diagonal' components in the second-order Wiener kernel. The static nonlinearity resembles a rectifier, and is dominated by second-order (quadratic) nonlinearity. As a function of BEF, the shape of the nonlinearity changes systematically. Finally, the last filter in the model was a low pass filter. Across fibers, its cutoff frequency(f-3dB) ranged from 106 to 434 Hz. (C) 1997 Elsevier Science B.V

Sensory cell damage in two-phase endolymphatic hydrops:A morphologic evaluation of a new experimental model by low-voltage scanning techniques

Hypothesis: The aim of this study was to create a more dynamic animal model of Meniere's disease combining multiple causes, such as the role of endocrine factors and endolymphatic sac dysfunction, that may mimic the fluctuant characteristics of Meniere's disease. Background: Endolymphatic hydrops remains to be considered a pathologic substrate in the etiology of Meniere's disease. The classic guinea pig model of inducing hydrops by total destruction of the endolymphatic sac is a nonphysiologic rigid model of Meniere's disease. Methods: The authors developed the two-phase endolymphatic hydrops model by inducing hydrops by mild chronic endolymphatic sac dysfunction, in combination with increased endolymph production by aldosterone. Sensory cell damage was evaluated by low-voltage field emission scanning microscopy. Results: This study describes a wide spectrum of morphologic effects of the outer hair cells in radial gradients, in which most effects were observed in the third to second row of outer hair cells, and longitudinal gradients in which the most severe effects were observed in the apical turns. Most affected were the ears that underwent distal endolymphatic sac dissection followed by the administration of aldosterone. Damaging effects proceeded from degeneration and absence of short stereocilia of outer hair cells and even some inner hair cells in the apical turns, to stereociliary disarrangement and atrophy, followed by degeneration and absence of outer hair cells, which were replaced by supporting cells. Conclusion: The two-phase endolymphatic hydrops model seems to represent a functional model that may mimic the fluctuant characteristics of Meniere's disease and emphasizes the influence of multiple and coexisting hydrops-inducing influences