Hypothesis: Muscarinic acetylcholine receptor subtypes are expressed in the human vestibular periphery to receive efferent innervation on the type II vestibular hair cells and primary afferent dendrites.
Background: Previous immunohistochemical and electrophysiologic studies have shown that acetylcholine (ACh) is likely the primary neurotransmitter of the efferent vestibular periphery. The structural distribution of nicotinic receptors (nAChR) and muscarinic receptors (mAChR) are not well established in the human vestibular periphery.
Methods: Reverse transcription polymerase chain reaction (RT-PCR) was used to study the expression of all five mAChR subtypes in Scarpa's ganglia and the vestibular end-organs of the rat and human.
Results: The authors found m1 through m5 expression in rats, and m1, m2, and m5 expression in humans.
Conclusions: These studies show evidence that both muscarinic acetylcholine receptors are present in the human vestibular periphery in addition to the nicotinic receptors reported previously. The pharmacologic implications of these data are discussed.