STEPS TOWARD RECOVERY OF FUNCTION AFTER HEMILABYRINTHECTOMY IN FROGS

Removal of the labyrinthine organs on one side results in a number of severe postural and dynamic reflex deficits, Over time some of these b ehavioral deficits normalize again, At a chronic stage the brain of fr ogs exhibits a number of changes in vestibular and propriospinal circu its on the operated side that were studied in vitro, The onset of chan ges in the vestibular nuclear complex was delayed, became evident only after head posture had recovered by more than 50%, and was independen t of the presence or absence of a degeneration of vestibular nerve aff erent fibers, The time course of changes measured in the isolated spin al cord paralleled the time course of normalization of head and body p osture. Results obtained after selective lesions of individual labyrin thine nerve branches show that unilateral inactivation of utricular af ferent inputs is a necessary and sufficient condition to provoke postu ral deficits and propriospinal changes similar to those after the remo val of all labyrinthine organs, The presence of multiple synaptic chan ges at distributed anatomic sites over different periods of time sugge sts that different parts of the central nervous system are involved in the normalization of different manifestations of the vestibular lesio n syndrome.