The Final Stage of Cholinergic Differentiation Occurs Below Inner Hair Cells During Development of the Rodent Cochlea |
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Authors: | Adam L Bergeron Angela Schrader Dan Yang Abdullah A Osman Dwayne D Simmons |
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Institution: | (1) Department of Otolaryngology, Washington University School of Medicine, Box 8115, 660 South Euclid Ave., St. Louis, MO 63110, USA;(2) Program in Neuroscience, Washington University School of Medicine, St. Louis, MO 63110, USA;(3) Department of Anatomy and Neurobiology, Washington University School of Medicine, St. Louis, MO 63110, USA |
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Abstract: | To gain further insights into the cholinergic differentiation of presynaptic efferent terminals in the inner ear, we investigated
the expression of the high-affinity choline transporter (ChT1) in comparison to other presynaptic and cholinergic markers.
In the adult mammalian cochlea, cholinergic axons from medial olivocochlear (OC) neurons form axosomatic synapses with outer
hair cells (OHCs), whereas axons from lateral OC neurons form axodendritic synapses on afferent fibers below inner hair cells
(IHCs). Mouse brain and cochlea homogenates reveal at least two ChT1 isoforms: a nonglycosylated ∼73 kDa protein and a glycosylated
∼45 kDa protein. In mouse brain, ChT1 is preferentially expressed by neurons in periolivary regions of the superior olive
consistent with the location of medial OC neurons. In the adult mouse cochlea, ChT1-positive terminals are located almost
exclusively below OHCs consistent with a medial OC innervation. Between postnatal day 2 (P2) and P4, ChT1-positive terminals
are below IHCs and occur after the expression of growth-associated protein 43, synapsin, and the vesicular acetylcholine transporter.
By P15, ChT1-positive terminals are mostly on OHCs. Accounting for differences in gestational age, the developmental expression
of ChT1 in the rat cochlea is similar to the mouse. However, in older rats ChT1-positive terminals are below IHCs and OHCs.
In both rat and mouse, our observations indicate that the onset of ChT1 expression occurs after efferent terminals are below
IHCs and express other presynaptic and cholinergic markers. In the mouse, but not in the rat, ChT1 may preferentially identify
medial OC neurons. |
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Keywords: | olivocochlear efferent neurons auditory inner ear mouse rat |
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