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At least 1,243 records · Page 69Linked to original sources
PubMed2005

Electrical coupling and release of K+ from endothelial cells co-mediate ACh-induced smooth muscle hyperpolarization in guinea-pig inner ear artery.

The physiological basis of ACh-elicited hyperpolarization in guinea-pig in vitro cochlear spiral modiolar artery (SMA) was investigated by intracellular recording combined with dye labelling of recorded cells and immunocytochemistry. We found the following. (1) The ACh-hyperpolarization was prominent only in cells that had a low resting potential (less negative than -60 mV). ACh-hyperpolarization was reversibly blocked by 4-DAMP, charybdotoxin or BAPTA-AM, but not by N(omega)-nitro-L-arginine methyl ester, glipizide, indomethacin or 17-octadecynoic acid. (2) Ba(2)(+) (100 microm) and ouabain (1 microm) each attenuated ACh-hyperpolarization by approximately 30% in smooth muscle cells (SMCs) but had only slight or no inhibition in endothelial cells (ECs). A combination of Ba(2)(+) and 18beta-glycyrrhetinic acid near completely blocked the ACh-hyperpolarization in SMCs. (3) High K(+) (10 mm) induced a smaller hyperpolarization in ECs than in SMCs, with an amplitude ratio of 0.49 : 1. Ba(2)(+) blocked the K(+)-induced hyperpolarization by approximately 85% in both cell types, whereas ouabain inhibited K(+)-hyperpolarization differently in SMCs (19%) and ECs (35%) and increased input resistance. 18beta-Glycyrrhetinic acid blocked the high K(+)-hyperpolarization in ECs only. (4) Weak myoendothelial dye coupling was detected by confocal microscopy in cells recorded with a propidium iodide-containing electrode for longer than 30 min. A sparse plexus of choline acetyltransferase-immunoreactive (ChAT) fibres was observed around the SMA and its up-stream arteries. (5) Evoked excitatory junction potentials (EJP) were partially blocked by 4-DAMP in half of the cells tested. We conclude that ACh-induced hyperpolarization originates from ECs via activation of Ca(2)(+)-activated potassium channels, and is independent of the release of NO, cyclo-oxygenase or cytochrome P450 products. ACh-induced hyperpolarization in smooth muscle cells involves two mechanisms: (a) electrical spread of the hyperpolarization from the endothelium, and (b) activation of inward rectifier K(+) channels (K(ir)) and Na(+)-K(+) pump current by elevated interstitial K(+) released from the endothelial cells, these being responsible for about 60% and 40% of the hyperpolarization, respectively. The role ratio of K(ir) and pump current activation is at 8 : 1 or less.

Acetylcholine↗
PubMed1986

Phase effects in masking related to dispersion in the inner ear.

Phase effects in masking experiments using multitone maskers are usually associated with strong variations in the masker envelope. In this article, psychoacoustic experiments with such maskers that lead to phase-dependent threshold variations of up to 20 dB, although the phase transformation leaves the envelope unchanged, are described. However, after filtering the maskers with a realistic basilar membrane model, the envelopes are different owing to the models phase-dispersive properties. Comparison of model outputs with the experimental results reveals a strong correlation between the two for a wide range of parameters, provided one makes the additional assumption that the ear has a minimum integration time of a few milliseconds.

Auditory Threshold↗
PubMed1994

Wiener kernel analysis of inner ear function in the American bullfrog.

The response of 17 primary auditory nerve fibers in the American bullfrog (Rana catesbeiana) to acoustic noise stimulation of the tympanic membrane was recorded. For each fiber, the first- and second-order Wiener kernels, k1 (tau 1) and k2 (tau 1, tau 2), were computed by cross correlation of the stimulus and the response. The kernels revealed amplitude and phase characteristics of auditory filters of both phase-locking and non-phase-locking fibers. Wiener kernels of high- and midfrequency fibers (best frequency, BF > 500 Hz), implied a simple sandwich model, consisting of a cascade of a linear bandpass filter, a static nonlinearity, a linear low-pass filter, and a spike generator. The bandpass filter was at least of order 7, and had a linear phase response, for both the high- and the midfrequency fibers. Averaged across fibers, filter order 2, and cutoff frequency 451 Hz for the second filter in the model was observed. The responses of low-frequency fibers (BF < 500 Hz) could not be fit with the sandwich model, because the Fourier transform K2 (f1,f2) of the second-order Wiener kernel showed significant components at off-diagonal frequencies f1 not equal to +/- f2. The presence of these off-diagonal components shows that, in addition to the phase and gain characteristics of auditory filters, the Wiener kernel analysis reveals nonlinear two-tone interactions.

Acoustic Stimulation↗
PubMed1996

Effects of low-frequency underwater sound on hair cells of the inner ear and lateral line of the teleost fish Astronotus ocellatus.

Fish (Astronotus ocellatus, the oscar) were subject to pure tones in order to determine the effects of sound at levels typical of man-made sources on the sensory epithelia of the ear and the lateral line. Sounds varied in frequency (60 or 300 Hz), duty cycle (20% or continuous), and intensity (100, 140, or 180 dB re: 1 muPa). Fish were allowed to survive for 1 or 4 days posttreatment. Tissue was then evaluated using scanning electron microscopy to assess the presence or absence of ciliary bundles on the sensory hair cells on each of the otic endorgans and the lateral line. The only damage that was observed was in four of five fish stimulated with 300-Hz continuous tones at 180 dB re: 1 muPa and allowed to survive for 4 days. Damage was limited to small regions of the striola of the utricle and lagena. There was no damage in any other endorgan, and the size and location of the damage varied between specimens. No damage was observed in fish that had been allowed to survive for 1 day poststimulation, suggesting that damage may develop slowly after exposure.

Acoustic Stimulation↗
PubMed1976

Ultrastructure of the auditory regions in the inner ear of the lake whitefish.

Hair cell polarization patterns were investigated on the sensory macule of the sacculus and lagena of the lake whitefish. The saccular hair cells are divided into four groups, with all of the cells within a group having the same orientation. Saccular orientations are anterior, posterior, dorsal, and ventral with respect to the axis of the animal. Two groups, one dorsal and one ventral, are found on the lagena. The saccular orientations are significantly different from those in tetrapods. Since this organ appears to have different functions in fish and tetrapods it is likely that the orientation patterns in fish are adapted to some aspect of audition--perhaps directional localization of sound.

Animals↗
PubMed1986

Detection of pseudorabies virus DNA in the inner ear of intranasally infected BALB/c mice with nucleic acid hybridization in situ.

Evidence for the pathogenicity of pseudorabies virus for the auditory and vestibular organs of experimentally infected mice is presented. We demonstrate viral genomes in cells of the peripheral sensory organs, the nerve structures, and the affected areas of the brain in single sections from an entire cranium of an adult mouse. The data were obtained by an in situ hybridization technique adapted for use with fixed, plastic-embedded materials. In contrast to conventional methods which use frozen sections, we were able to analyze cartilaginous and bony materials with high resolution.

Animals↗