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PubMed1977

[Participation of vertical semicircular canals in the vestibulo-oculomotor response to the horizontal rotation test].

The horizontal rotatory test was shown to elicit in rabbits a complex three-plane vestibular oculomotor response with rotatory nystagmus (RN) in sagittal plane. The leftward accelerating rotation caused the clockwise RN of the right eye; during decelerating rotation the RN was directed counterclockwise. Its frequency may differ from that of the horizontal nystagmus. The cupulo-endolymphatic displacements seem to occur not only in the horizontal canal, i.e. in the plane of rotation, but also in the vertical canals as a result of a hypothetical hydrodynamic interaction between the canals. The displacements in the anterior and the horizontal canals of the labyrinth were analogous, whereas that in the posterior canal was of the opposite direction. That suggests that the utriculofugal displacements in the horizontal and the anterior canals are accompanied by an utriculofugal displacement in the posterior canal, and vice versa.

Animals↗
PubMed1976

Inhibitory interaction between the vestibulo-ocular reflexes arising from semicircular canals of rabbits.

In anesthetized albino rabbits, electric pulse stimulation was applied to ampullary branches of the vestibular nerve. Reflex discharges evoked from a canal in an extraocular muscle were depressed very effectively by conditioning stimulation at a certain other canal. The present systematic survey revealed that this reflex depression occurred specifically in 3 combinations of conditioning and testing canals; 1. anterior and posterior canals of the same side; 2. anterior and posterior canals of the opposite sides; and 3. horizontal canals of the two sides. Occurrence of postsynaptic inhibition in oculomotor neurons, on the other hand, was indicated by appearance of slow muscle potentials in extraocular muscles. It was confirmed that this motoneuronal inhibition did not contribute to the reflex depression in the above combination (1). Even in combinations (2) and (3), the accompanying motoneuronal inhibition was eliminated by adjusting intensities of canal stimuli or by severing its pathway in the medulla, or it was discriminated from the reflex depression by their different latencies and time courses. Hence, it was concluded that the reflex depression was attributable, at least largely, to non-motoneuronal inhibition, presumably postsynaptic inhibition at relay neurons for vestibulo-ocular reflexes. Slow muscle potentials evoked from a canal were also used as testing responses, but their depression could not be detected after conditioning at other canals.

Animals↗