The effects of microgravity on frog semicircular canals have been studied by electrophysiological and morphological approaches. Reduced gravity (microG) was simulated by a “random positioning machine” (RPM) which continually and randomly modified the orientation in space of the anesthetized animal. As this procedure stimulates the semicircular canals, the effect of altered gravity was isolated by comparing microG-treatment with an identical rotary stimulation in the presence of normogravity (normoG). Electrophysiological experiments were performed in the isolated labyrinth, extracted from the animals after the treatment and mounted on a turntable. Junctional activity was measured by recording quantal events (mEPSPs) and spikes from the afferent fibers close to the junction, at rest and during rotational stimulation. MicroG treated animals displayed a marked decrease in the frequency of resting and evoked mEPSP discharge, versus both control and normoG (mean decrease ~50%). Spike discharge was also depressed: 57% of microG-treated frogs displayed no spikes at rest and during rotation at 0.1 Hz, vs. 23-31% of control or normoG frogs. Among the firing units, during one cycle of sinusoidal rotation at 0.1 Hz microG treated units emitted an average of 41.8 +/- 8.06 spikes, vs. 77.2 +/- 8.19 in controls. Patch-clamp analysis on dissociated hair cells revealed altered Ca2+ handling, after microG, consistent with and supportive of the specificity of microG effects. Marked morphological signs of cellular suffering were observed after microG, mainly in the central part of the sensory epithelium. Functional changes due to microgravity were reversible within a few days.
Exposure to reduced gravity impairs junctional transmission at the semicircular canal in the frog labyrinth.
ROSSI, Marialisa;RUBBINI, Gemma;MARTINI, Marta;
2010
Abstract
The effects of microgravity on frog semicircular canals have been studied by electrophysiological and morphological approaches. Reduced gravity (microG) was simulated by a “random positioning machine” (RPM) which continually and randomly modified the orientation in space of the anesthetized animal. As this procedure stimulates the semicircular canals, the effect of altered gravity was isolated by comparing microG-treatment with an identical rotary stimulation in the presence of normogravity (normoG). Electrophysiological experiments were performed in the isolated labyrinth, extracted from the animals after the treatment and mounted on a turntable. Junctional activity was measured by recording quantal events (mEPSPs) and spikes from the afferent fibers close to the junction, at rest and during rotational stimulation. MicroG treated animals displayed a marked decrease in the frequency of resting and evoked mEPSP discharge, versus both control and normoG (mean decrease ~50%). Spike discharge was also depressed: 57% of microG-treated frogs displayed no spikes at rest and during rotation at 0.1 Hz, vs. 23-31% of control or normoG frogs. Among the firing units, during one cycle of sinusoidal rotation at 0.1 Hz microG treated units emitted an average of 41.8 +/- 8.06 spikes, vs. 77.2 +/- 8.19 in controls. Patch-clamp analysis on dissociated hair cells revealed altered Ca2+ handling, after microG, consistent with and supportive of the specificity of microG effects. Marked morphological signs of cellular suffering were observed after microG, mainly in the central part of the sensory epithelium. Functional changes due to microgravity were reversible within a few days.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
