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Biomedical subjects

J M Segenhout

Publications and source records attributed to J M Segenhout.

22 records · Page 2Linked to original sources

The glycocalyx and stereociliary interconnections of the vestibular sensory epithelia of the guinea pig. A freeze-fracture, low-voltage cryo-SEM, SEM and TEM study.

In this study freeze fracture, low-voltage cryo-SEM, SEM and TEM were used to characterise the glycocalyx and stereociliary interconnections in the hair cell bundle of the vestibular sensory epithelia of the guinea pig. The glycocalyx resembles a shell-like structure separately surrounding each stereocilium and kinocilium over its entire length. The lateral interciliary connections emerge from the glycocalyx layer, forming an extensive extracellular network maintaining the stereocilia as a bundle. These connections are morphologically similar to the glycocalyx, and grossly oriented in the same direction, indicative of a role in the mechanical transduction system. The matrix material around the glycocalyx also appears to be morphologically similar to the glycocalyx, suggesting the glycocalyx to be even more important in the mechanical transduction system. The tip-links are covered with a layer, which is a continuation of the glycocalyx covering the stereocilia.

Animals↗

Endolymphatic hydrops after total dissection or cauterization of the distal portion of the endolymphatic sac.

In this study, a more subtle animal model of Menière's disease is investigated by damaging the distal portion of the endolymphatic sac by dissection or cauterization to produce mild dysfunction of endolymphatic outflow. Cauterization resulted in low degrees of hydrops without any correlation with the inflicted damage. Total dissection of the distal portion of the sac adjacent to the sigmoid sinus produced moderate to severe endolymphatic hydrops with interanimal variation. The consequences of these relatively severe effects, in relation to the mild damage of the endolymphatic sac, and the influence on damaged and undamaged parts of the endolymphatic sac will be discussed.

Animals↗

Caloric stimulation of the vestibular system of the pigeon under minimal influence of gravity.

Vestibular microphonics in response to acoustical stimulation were recorded in cochlea-deprived pigeons. Endolymph flow in the semicircular canals alters this response. A caloric stimulus was applied to the horizontal canal or the posterior vertical canal close to the ampulla. To minimize the influence of gravity, the canal being studied was positioned in the horizontal plane. Local temperature changes were generated with an electrically heated miniature copper probe, producing an approximately trapezoidal temperature profile. Because of the opposite hair cell polarization in the horizontal and the vertical ampulla, we could prove that the observed effects were of (hydro-)mechanical origin and were not caused by a direct effect of sensory epithelium temperature change. The first effect of temperature increase was an utriculopetal endolymph flow, as predicted by the 'expansion theory'.

Acoustic Stimulation↗

Bárány's theory is right, but incomplete. An experimental study in pigeons.

The horizontal semicircular canal in pigeons was thermally stimulated with a miniature Peltier-element device. Sound evoked electric responses from the vestibular organ were modulated by the caloric stimulus. Experiments were performed under minimal influence of gravity, (horizontal canals in horizontal plane), and with the pigeons head tilted forwards or backwards. On the basis of the results it was concluded that the influence of gravity can be described by Bárány's convection theory. Extra effects are, however, present and they are most probably partly of mechanical origin (fluid expansion) and partly due to a direct influence of temperature on the vestibular receptors. Further experiments are needed to investigate the origin of these extra effects in more detail.

Animals↗