Vestibular organs constitute the main sensory system for gravitational information. Itwas therefore of interest to examine how altered gravity conditions affect labyrinthinefunction. The properties of junctional transmission were studied at the posterior canal in frogs exposed to microgravity conditions for four hours. Microgravity was simulated by rotating the anesthetised frog in a “random positioningmachine” which continually and randomly modified the orientation of the animal inspace (centre of rotation at the midpoint of the line joining the otic membranes. As thesemicircular canals are stimulated by this procedure, the effect of altered gravitycondition were isolated by comparing treated preparations (microgravity, mG) withcontrol (Ct), anesthetised frogs, and with anesthetised frogs exposed to randomrotations with similar angular acceleration intensity but constant orientation withrespect to the gravitational axis (normogravity, nG). Electrophysiological experiments were performed in the isolated labyrinth, extracted from the animals after the treatment and mounted on a turn-table. Junctional activity was measured by recording quantal events (mEPSPs) and spikes at the first afferentneuron close to the junction, at rest and during rotational stimulation. No significant differences were observed between anesthetised and Ct frogs. Marked, significant decrease was detected in the frequency of mEPSP discharge inmG-treated frogs vs. Ct or nG (mean decrease by about 50%, mG vs. Ct, n = 25;p<0.01, K-S test). Correspondent effects were observed on spike discharge: 57% ofmG-treated frogs displayed no spikes, vs. 23-31% of Ct or nG frogs (p<0.01, Chi-squared); among the firing units the average number of spikes discharged during onecycle of sinusoidal rotation at 0.1 Hz was 34.7 in mG frogs vs. 76.6 in controls (n =33; p<0.01, K-S test). Marked morphological signs of cellular suffering were observed in the sensoryepithelium. All effects of microgravity were reversible in few days.
Exposure to reduced gravity decreases junctional transmission at the frog labyrinth
RUBBINI, Gemma;MARTINI, Marta;CANELLA, Rita;LEPARULO, Alessandro;ROSSI, Marialisa
2008
Abstract
Vestibular organs constitute the main sensory system for gravitational information. Itwas therefore of interest to examine how altered gravity conditions affect labyrinthinefunction. The properties of junctional transmission were studied at the posterior canal in frogs exposed to microgravity conditions for four hours. Microgravity was simulated by rotating the anesthetised frog in a “random positioningmachine” which continually and randomly modified the orientation of the animal inspace (centre of rotation at the midpoint of the line joining the otic membranes. As thesemicircular canals are stimulated by this procedure, the effect of altered gravitycondition were isolated by comparing treated preparations (microgravity, mG) withcontrol (Ct), anesthetised frogs, and with anesthetised frogs exposed to randomrotations with similar angular acceleration intensity but constant orientation withrespect to the gravitational axis (normogravity, nG). Electrophysiological experiments were performed in the isolated labyrinth, extracted from the animals after the treatment and mounted on a turn-table. Junctional activity was measured by recording quantal events (mEPSPs) and spikes at the first afferentneuron close to the junction, at rest and during rotational stimulation. No significant differences were observed between anesthetised and Ct frogs. Marked, significant decrease was detected in the frequency of mEPSP discharge inmG-treated frogs vs. Ct or nG (mean decrease by about 50%, mG vs. Ct, n = 25;p<0.01, K-S test). Correspondent effects were observed on spike discharge: 57% ofmG-treated frogs displayed no spikes, vs. 23-31% of Ct or nG frogs (p<0.01, Chi-squared); among the firing units the average number of spikes discharged during onecycle of sinusoidal rotation at 0.1 Hz was 34.7 in mG frogs vs. 76.6 in controls (n =33; p<0.01, K-S test). Marked morphological signs of cellular suffering were observed in the sensoryepithelium. All effects of microgravity were reversible in few days.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
