Recent Findings on Efferent Synapses
In addition to sending information to the brain, the inner ear is subject to feedback regulation from the brain. Neurons in the superior olivary complex of the brainstem send axons out to the cochlea where they release the neurotransmitter acetylcholine to inhibit mechanosensory hair cells. By recording from individual hair cells during this inhibitory process, we have shown that their acetylcholine receptors are related to the nicotinic receptors found in skeletal muscle, but with quite unusual pharmacology.
Surprisingly, while acetylcholine excites skeletal muscle via its nicotinic receptors, hair cells are inhibited by theirs. Calcium ions play a central role in nicotinic inhibition, serving as a second messenger to activate potassium channels that hyperpolarize the hair cell. The molecular mechanisms underlying these native inhibitory processes may provide candidate approaches for therapeutic intervention.
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