The extracellular matrix (ECM) is found in the central nervous system (CNS) in aggregated form either around the perikaryon and dendrites as the perineuronal net (PNN) or at the node of Ranvier and it is dispersed in the neuropil as well. In the PNN the backbone of the ECM assembly is the hyaluronan (HA) which is linked to cell membrane receptors, and with the various chondroitin sulfate proteoglycans (CSPGs), tenascin-R (TN-R) and link proteins. There is growing evidence that the ECM plays an important role in the modification of signaling processes and the functional activity of the neurons thereby, it is involved in the neural plasticity. Our work observes whether the establishment of the vestibular neuronal circuits is associated with a peculiar organization of the ECM. The aim of our work is to map the distribution of major ECM molecules, the HA, TN-R and CSPGs such as the brevican (Br) and versican (Ve) with histochemical and immunohistochemical methods in the superior (SVN), medial (MVN), lateral (LVN) and descending (DVN) vestibular nuclei, in the eye moving cranial nerve nuclei, red nucleus, prepositus hypoglossi and inferior olive of the rat. In the vestibular nuclear complex, each staining showed positive reaction in the PNN of the SVN, MVN and LVN, whereas the DVN was devoid of PNN. The staining of neuropil displayed versatile staining pattern in the individual vestibular nuclei both in the occurrence and intensity of reactions. In the eye moving cranial nerve nuclei, the PNN was recognizable and the cytoplasm of neurons showed intense positive Br reaction in the oculomotor nucleus. In the red nucleus, the parvocellular (PC) and magnocellular (MC) parts showed different staining pattern. The PNN was recognizable with each reactions in both regions, while the cytoplasm of neurons showed intense Br labeling only in the PC part. In case of the Ve reaction the staining of the neuropil of the MC region was very strong. In the prepositus hypoglossi, the PNNs were weakly stained or they were not distinguished from the intensive TN-R and Br reaction of the neuropil. In the inferior olive, the PNN was not recognizable, the neuropil stained intensively for the TN-R and Br. Wherever the Ve reaction was positive in the neuropil or white matter, the staining showed punctuated appearance. Our results indicate that the heterogeneous distribution of ECM in the structures of the vestibular neuronal circuits may be related to their different functions in the gaze and posture control and to the restoration of impaired function during the vestibular compensation.

This work was supported by OTKA K 67641, MTA-TKI 255 and DE OEC Bridging Fund.