Synaptic plasticity in the medial vestibular nuclei: role of glutamate receptors and retrograde messengers in rat brainstem slices

The analysis of cellular-molecular events mediating synaptic plasticity wit hin vestibular nuclei is an attempt to explain the mechanisms underlying ve stibular plasticity phenomena. The present review is meant to illustrate th e main results, obtained in vitro, on the mechanisms underlying long-term c hanges in synaptic strength within the medial vestibular nuclei. The synapt ic plasticity phenomena taking place at the level of vestibular nuclei coul d be useful for adapting and consolidating the efficacy of vestibular neuro n responsiveness to environmental requirements, as during visuo-vestibular recalibration and vestibular compensation. Following a general introduction on the most salient features of vestibular compensation and visuo-vestibul ar adaptation, which are two plastic events involving neuronal circuitry wi thin the medial vestibular nuclei: the second and third sections describe t he results from rat brainstem slice studies, demonstrating the possibility to induce long-term potentiation and depression in the medial vestibular nu clei, following high frequency stimulation of the primary vestibular affere nts. In particular the mechanisms sustaining the induction and expression o f vestibular long-term potentiation and depression, such as the role of var ious glutamate receptors and retrograde messengers have been described. The relevant role of the interaction between the platelet-activating factor, a cting as a retrograde messenger, and the presynaptic metabotropic glutamate receptors, in determining the full expression of vestibular long-term pote ntiation is also underlined. In addition, the mechanisms involved in vestib ular long-term potentiation have been compared with those leading to long-t erm potentiation in the hippocampus to emphasize the most significant diffe rences emerging from vestibular studies. The fourth part, describes recent results demonstrating the essential role of nitric oxide, another retrograd e messenger, in the induction of a vestibular potentiation. Finally the fif th part suggests the possible functional significance of different action t imes of the two retrograde messengers and metabotropic glutamate receptors, which are involved in mediating the presynaptic mechanism sustaining vesti bular long-term potentiation. (C) 2001 Elsevier Science Ltd. All rights res erved.