Cupular movement and nerve impulse response in the isolated semicircular canal

Otolith Analyses Highlight Morpho-Functional Differences of Three Species of Mullet (Mugilidae) from Transitional Water

Otoliths are used in taxonomy and ichthyology as they can provide a wide range of information about specimens. They are an essential tool to monitor the most sensitive species for a sustainable exploitation level. Despite the increasing use of sagittae in research, their inter- and intra-specific variability and eco-functionality are still poorly explored. This paper aims to investigate the inter- and intra-specific variability of Mugilidae sagittae using morphological and morphometrical analysis, as well as scanning electron microscopy and shape analysis. The sagittae of 74 specimens belonging to three different Mugilidae species, collected from a coastal lagoon, were analyzed to give an accurate description of their morphology, morphometry, shape and crystalline habits. The results highlighted the intra- and inter-specific variability of sagittae, showing morphometrical differences among species and slight differences between left and right sagittae in C. labrosus individuals. Moreover, SEM images showed a peculiar crystal organization, with several different crystal habits and polymorphs. This study provides an accurate description of sagittae in the studied species, deepening the knowledge on inter- and intra-specific variations and crystal habits and providing data which will be useful for future studies on otoliths. With this data, it will be possible to improve conservation and exploitation sustainability in sensitive habitats.

Computing simulated endolymphatic flow thermodynamics during the caloric test using normal and hydropic duct models

CONCLUSION

The obtained simulations support the underlying hypothesis that the hydrostatic caloric drive is dissipated by local convective flow in a hydropic duct.

OBJECTIVE

To develop a computerized model to simulate and predict the internal fluid thermodynamic behavior within both normal and hydropic horizontal ducts.

METHODS

This study used a computational fluid dynamics software to simulate the effects of cooling and warming of two geometrical models representing normal and hydropic ducts of one semicircular horizontal canal during 120 s.

RESULTS

Temperature maps, vorticity, and velocity fields were successfully obtained to characterize the endolymphatic flow during the caloric test in the developed models. In the normal semicircular canal, a well-defined endolymphatic linear flow was obtained, this flow has an opposite direction depending only on the cooling or warming condition of the simulation. For the hydropic model a non-effective endolymphatic flow was predicted; in this model the velocity and vorticity fields show a non-linear flow, with some vortices formed inside the hydropic duct.

Cupula displacement, hair bundle deflection, and physiological responses in the transparent semicircular canal of young eel

The transparent labyrinth of young eels (Anguilla anguilla L.) was used in toto for studying the configuration of cupula displacement, deflection of the hair bundle, and correlated changes in transepithelial voltage (delta TEV) and nerve activity (delta NA) in the semicircular canal. Microcapillaries were introduced into the canal through holes produced by a microthermocauter. Mechanical stimulation was applied either by injection of fluid into the ampulla or by electromagnetically displacing ferrofluid as a piston within the canal. Motion of individual kinocilia, stained cupulae or the ferrofluid piston was analysed by double-exposed microphotographs, photodiodes, or a video-system. The three-dimensional cupula displacement configuration was found to be piston- to diaphragm-like. Hair bundles at different sites on the crista exhibit differences in amplitude and time course of deflection. The transfer factor between shifts of the canal fluid and the tips of the kinocilia is 0.4-0.6. Displacements in opposite directions induce delta TEV and delta NA of opposite sign. Various tests confirmed delta TEV to reflect receptor potential responses. Nerve activity adapts to a tonic response with a time constant of 6.4 s. No similar adaptation occurred in delta TEV. Stimulus-response curves of TEV- and NA-responses are similar and sigmoid in shape with saturation at ciliary deflections of roughly +6 degrees and -3 degrees.

Semicircular canals: measurement of endolymphatic and cupular displacements at threshold

The left horizontal semicircular canal of the leopard frog (Rana pipiens) was exposed and the entire intact nerve was draped over a platinum-iridium hook for recording action potentials (a.p.'s). The preparation was then rotated sinusoidally in the horizontal plane at 0.3 Hz with varying angular displacements. The arm of the canal was then transected, and a fine micropipette ligated in place in one end of the arm. Artificial endolymph was pumped into and out of the canal at the same frequency, while the amplitude of the displacement was varied from sub-threshold to supra-threshold values as determined from the resulting a.p. train. By comparing the two a.p. trains, it was determined that the movement of endolymph in the canals was 5.3 x 10(-8) cm3/deg/s, and that the threshold displacement of the midpoint of the cupula was 7.6 x 10(-5) cm (0.76 micrometers).

Discharge properties of afferent fibres of the goldfish semicircular canal with high frequency stimulation

The horizontal semicircular canals of goldfish were sinusoidally stimulated 0.07 and 63 Hz (about 3 decades). Single afferent fibre recordings showed sinusoidal modulation of discharges. Above 4 Hz the discharges became phase-locked to the stimulus. With increasing frequency the number of spikes per period decreased so that finally only one spike per period remained. At 63 Hz a stimulus of as little as 0.005 degrees was sufficient to drive the units to far above their spontaneous activity. As cupular deflection is less than the angle of body movement, the cupular deflection threshold for modulation of afferent discharges must be much less than 0.005 degrees. Transfer functions of afferent activity were determined. The simple pendulum model does not fit the data. Additional introduction of a third time constant and the low pass properties of the receptor cell membrane, the synaptic delay and the leaky integrator of the post synaptic afferent terminal improve the fit.