Pharmacology of the vestibular system

This chapter summarizes and critically evaluates the current understanding of neurotransmitter receptors operating within the peripheral and central vestibular systems. The available data suggest that the vestibular hair cell-vestibular nerve afferent synapses are mediated predominantly by an EAA transmitter (probably glutamate), acting on kainate-AMPA receptors; the contribution of NMDA receptors is uncertain. ACh may mediate the brainstem efferent-hair cell synapses; the role of GABA in the periphery is unclear. A large number of in-vitro studies support the hypothesis that an EAA (probably glutamate) mediates vestibular nerve input to the MVN, acting predominantly on kainate-AMPA receptors; again, the contribution of NMDA receptors is uncertain. Whether another neurotransmitter such as ACh mediates vestibular nerve input to the LVN remains in question. Purkinje cell inhibition of ipsilateral LVN neurones is mediated by GABA, acting on GABAA receptors. MVN neurones have both GABAA and GABAB receptors; however, the GABAA receptors on MVN type I neurones appear to mediate brain-stem commissural inhibition via ipsilateral type II neurones. Receptors for DA, NA, 5-HT, histamine and several peptides have been identified on MVN and LVN neurones; at present, the precise function of these receptors remains to be elucidated. The significance of these data for the clinical treatment of vestibular disorders is discussed.