An increase in glycinergic quantal amplitude and frequency during early vestibular compensation in mouse

The process of vestibular compensation includes both behavioral and neuronal recovery after unilateral loss of peripheral vestibular organs. The mechanisms that underlie this process are poorly understood. Previous research has shown the presence of both gamma-aminobutyric acid type A (GABA(A)) and glycine receptors in the medial vestibular nuclei (MVN). It has been suggested that inhibitory transmission mediated by these receptors may have a role in recovery during vestibular compensation. This study investigated changes in fast inhibitory synaptic transmission of GABA(A)ergic and glycinergic quantal events after unilateral labyrinthectomy (UL) at three different time points. Mice were anesthetized and peripheral vestibular organs were removed from one side of the head. After recovery, transverse brain stem sections (300 mum) were prepared from mice that had undergone UL either 4 hours, 2 days, or 7 days earlier. Our experiments do not show evidence for alterations in synaptic GABA(A) receptor properties in MVN neurons after UL at any time point investigated. In contrast, during early vestibular compensation (4 hours post UL) there is a significant increase in the glycinergic quantal current amplitude in contralesional MVN neurons compared with control. Our results also show an increase in the frequency of glycinergic quantal events of both ipsi- and contralesional MVN neurons during this early period. We suggest that changes in both pre- and postsynaptic glycine receptor mediated inhibitory synaptic transmission after sensory loss is an important mechanism by which neuronal discharge patterns can be modulated.