The Final Stage of Cholinergic Differentiation Occurs Below Inner Hair Cells During Development of the Rodent Cochlea

Abstract

To gain further insights into the cholinergic differentiation of presynaptic efferent terminals in the inner ear, we investigated the expression of the highaffinity 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 õ73 kDa protein and a glycosylated õ45 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 growthassociated 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.

Muscarinic Acetylcholine Receptors and M-Currents Underlie Efferent-Mediated Slow Excitation in Calyx-Bearing Vestibular Afferents

“…3F, left). That atropine concentrations as low as 0.3 M significantly blocked efferent-mediated slow excitation without affecting efferent-mediated fast excitation further supported a role for mAChRs while again excluding ␣4␣6␤2*nAChRs and ␣9*nAChRs (Fuchs and Murrow, 1992;Guth et al, 1994;Verbitsky et al, 2000).…”

“…However, we cannot completely dismiss ERG channels as they colocalize and can form functional, macromolecular complexes with KCNQ (Hurley et al, 2006;Ren et al, 2010;Guo et al, 2011;Lysakowski et al, 2011;Abriel et al, 2015) and could contribute to efferent-mediated slow excitation.…”

Alternative Splicing of the CaV1.3 Channel IQ Domain, a Molecular Switch for Ca2+-Dependent Inactivation within Auditory Hair Cells

“…Second, weak CDI could help prolong Ca 2ϩ entry that would sustain activity-dependent transcription underlying outer hair cell development (Platzer et al, 2000;Brandt et al, 2003;Glueckert et al, 2003). During the development of hearing, cochlear hair cells undergo major changes in potassium (Kros et al, 1998;Marcotti et al, 2003) and calcium channel expression (Beutner and Moser, 2001;Michna et al, 2003), as well as dramatic rearrangement of efferent and afferent innervation (Liberman and Simmons, 1985;Sobkowicz et al, 1986Sobkowicz et al, , 2004Simmons and Liberman, 1988a,b;Simmons et al, 1992Simmons et al, , 1996Simmons, 1994Simmons, , 2002Fuchs et al, 2003;Bergeron et al, 2005). Hence, the early presence of Ca V 1.3 IQ⌬ channels, as well as the loss of OHCs shortly after the onset of hearing in Ca V 1.3 knock-out mice (Platzer et al, 2000), cohere with a contribution of these channels to activity-dependent gene expression underlying development.…”

Distribution of the Na,K-ATPase α Subunit in the Rat Spiral Ganglion and Organ of Corti

“…Lateral olivocochlear efferent fibers make axodendritic synapses onto the unmyelinated terminals of type I afferent fibers close to where they contact the IHCs (Bergeron et al 2005). To test whether NKAα3 immunoreactivity detected in the IHC region may also be due to expression of NKAα3 in lateral efferent fibers, we performed double labeling experiments with a monoclonal anti-NKAα3 and a polyclonal antisynapsin.…”