Influence of visual experience on developmental shift from long-term depression to long-term potentiation in the rat medial vestibular nuclei

The influence of visual experience deprivation on changes in synaptic plasticity during postnatal development was studied in the ventral part of the rat medial vestibular nuclei (vMVN). We analysed the differences in the occurrence, expressed as a percentage, of long-term depression (LTD) and long-term potentiation (LTP) induced by high frequency stimulation (HFS) of the primary vestibular afferents in rats reared in the light (LR) and those in the dark (DR). In LR rats, HFS only induced LTD in the early stages of development, but the occurrence of LTD progressively decreased to zero before their eyes opened, while that of UP enhanced from zero to about 50%. Once the rats' eyes had opened, LTD was no longer inducible while UP occurrence gradually reached the normal adult value (70%). In DR rats, a similar shift from LTD to UP was observed before their eyes opened, showing only a slightly slower LTD decay and UP growth, and the LTD annulment was delayed by I day. By contrast, the time courses of LTD and UP development in DR and LR rats showed remarkable differences following eye opening. In fact, LTD occurrence increased to about 50% in a short period of time and remained high until the adult stage. In addition, the occurrence of UP slowly decreased to less than 20%. The effect of light-deprivation was reversible, since the exposure of DR rats to light, 5 days after eye opening, caused a sudden disappearance of LTD and a partial recover of UP occurrence. In addition, we observed that a week of light deprivation in LR adult rats did not affect the normal adult UP occurrence. These results provide evidence that in a critical period of development visual input plays a crucial role in shaping synaptic plasticity of the vMVN, and suggest that the visual guided shift from LTD to UP during development may be necessary to refine and consolidate vestibular circuitry.