Endothelin-1-induced Barrel Rotation: No Direct Modulation of Rat Medial Vestibular Nucleus Neurone Activity by Endothelin-1

Fourth ventricular injections of endothelin-1 (30-100 ng) induced rotation along the long axis of the body (barrel rotation) in rats. N-methyl-D-aspartate (NMDA, 1-10 μg), an excitatory amino acid, and muscimol (1-10 μg), a GABAA receptor agonist, also evoked barrel rotation. Bath application of NMDA and muscimol on the spontaneous tonic discharge of medial vestibular nucleus (MVN) neurones in rats, showed excitatory and inhibitory responses, respectively. Interestingly, endothelin-1 did not affect the spontaneous discharge rate of MVN neurones when applied either as a 60 s pulse or when the drug was continuously perfused for a period of 5 min. Reciprocal relationship between excitatory and inhibitory inputs, such as glutamate and GABA receptor agonists, for MVN neurones may be crucial in inducing barrel rotation. The results also suggest that the barrel rotation induced by endothelin-1 is mediated by its modulatory effects on indirect pathways to the vestibular nucleus.