Effect of unilateral labyrinthectomy on aggrecan expression in the vestibular nuclear complex

Unilateral labyrinthectomy (UL) results in postural deficits and disturbances in the eye movements in mammalian species. The symptoms are spontaneously restored after a shorter or longer period during the vestibular compensation, which is a favorite model of neuronal plasticity in the adult central nervous system (CNS). Recent studies have shown that the extracellular matrix (ECM) molecules have an important role in the neural plasticity however their permissive or non-permissive roles have not yet been studied in the vestibular system. In the CNS, the ECM is composed of various macromolecules such as the hyaluronan, chondroitin sulfate proteoglycans (aggrecan, brevican, versican, neurocan) and link proteins. The characteristic accumulation of ECM in the CNS is the perineuronal net (PNN) surrounding the perikaryon, proximal dendrites and the axon hillock of neurons in a mesh-like manner. In the present study the expression of aggrecan was examined in the rat brainstem following unilateral labyrinthectomy and subsequent compensation.
Under urethane anesthesia, the left middle and inner ear was approached and destruction of membranous labyrinth was completed with a surgical hook. After a period of 1, 3, 7 and 14 days of survival, immunohistochemical reaction for aggrecan was performed on the brainstem sections. In the control animals, the aggrecan showed very intense reaction in the PNN of vestibular neurons except in the caudal part of descending vestibular nucleus.
On the 1st postoperative day, the staining pattern of the PNN in the bilateral vestibular nuclei was similar to that of the control animals. At 3 days of survival no PNN was recognizable in superior vestibular nucleus, similarly at 7 days in the superior, lateral and medial vestibular nuclei showed no PNN and faint neuropil staining was detected. On the 14th postoperative day, the PNN reformed on the operated side, but the staining intensity was fainter than the unaffected side.
Our results showed that the UL is accompanied by the modification of aggrecan staining pattern in the vestibular nuclei and the time course of re-establishment of PNN is parallel to the improvement of postural deficits.