Modification of synaptic input following unilateral labyrinthectomy

Abstract

UNILATERAL vestibular nerve transection is followed by postural and locomotor disturbances that disappear to a large extent with time after the lesion¹. This compensation requires a central readjustment of the tonic and phasic output from the remaining vestibular apparatus to the motor nuclei involved in the control of limb and head muscles. To study the mechanisms of this type of motor learning at the single neurone level, we have used the frog (Rana temporaria), because in this species the time course of the postural compensation following hemilabyrinthectomy has been thoroughly studied². Furthermore, the synaptic circuitry and functional organisation of the peripheral and central vestibular systems are well known for this species³. Since the vestibular nuclei are the first integrative structures in which bilateral vestibular and other sensory inputs converge, and since their output influences motor systems directly or indirectly, we began to look for plastic changes in second order vestibular neurones. Many of these neurones are monosynaptically excited from the ipsilateral⁴ and disynaptically through commissural fibres from the contralateral⁵ labyrinth.