Melatonin inhibits rat medial vestibular nucleus neuron activity in vitro.

The present study evaluated the effects of melatonin on the discharge rate of tonically active medial vestibular nucleus (MVN) neurons in an in vitro slice preparation of the rat dorsal brainstem. The results demonstrated that, when melatonin was applied to the slice for a period of 7-10 min, a decrease in MVN neuron firing rate was observed in 21/58 (36%) of the cells sampled. The inhibitory effects of melatonin were present in synaptic uncoupling condition and were mimicked by 2-iodomelatonin, a non-selective agonist with high affinity for melatonin membrane receptor subtypes (MT(1), MT(2), MT(3)). The MT(2) receptor antagonists luzindole and 4-phenyl-2-propionamidotetraline and the MT(3) receptor antagonist prazosin did not, however, antagonise the inhibitory effects of melatonin, indicating that melatonin may act on MVN neurons through an MT(1) receptor-mediated mechanism.