Effects of surgical lesions on choline acetyltransferase activity in the cat cochlea (original) (raw)
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Journal of Histochemistry & Cytochemistry, 1981
Within the cochlear nucleus of the rat, as well as some nearby regions, quantitative histochemical mapping procedures were used to construct maps of the distributions of choline acetyltransferase and acetylcholinesterase activities. The results were in some ways consistent with results previously reported for cat, e.g., very low activities of both enzymes were found in the auditory nerve root, and also in the vestibular nerve root, except where acetylcholinesterase-positive centrifugal fibers are located, very high activities were found in the facial nerve system. In many ways, however, the results for the rat cochlear nucleus contrasted with those for the cat. Notably, choline acetyltransferase activities in some regions of the rat coch-'Supported by the National Institutes of Health through Research Grant NS 08000 and a National Institutes of Health Postdoctoral Fellowship to D.A.G.
ACTA HISTOCHEMICA ET CYTOCHEMICA, 2013
We previously discovered a splice variant of choline acetyltransferase (ChAT) mRNA, and designated the variant protein pChAT because of its preferential expression in peripheral neuronal structures. In this study, we examined the immunohistochemical localization of pChAT in rat cochlea and compared the distribution pattern to those of common ChAT (cChAT) and acetylcholinesterase. Some neuronal cell bodies and fibers in the spiral ganglia showed immunoreactivity for pChAT, predominantly the small spiral ganglion cells, indicating outer hair cell type II neurons. In contrast, cChAT-and acetylcholinesterase-positive structures were localized to fibers and not apparent in ganglion cells. After ablation of the cochlear nuclei, many pChAT-positive cochlear nerve fibers became clearly visible, whereas fibers immunopositive for cChAT and acetylcholine esterase disappeared. These results suggested that pChAT and cChAT are localized in different systems of the rat cochlea; pChAT in the afferent and cChAT in the efferent structures.
Hearing Research, 1987
Using a microdissection and quantitative microassay approach, choline acetyltransferase activities were mapped in the cochlear nuclei of rats having either transection of the trapezoid body or destruction of the superior olivary complex on one side in the brain stem. Lateral trapezoid body transection resulted in dramatic loss of choline acetyltransferase activity in all parts of the ipsilateral cochlear nucleus, while more medial transection had little effect. Destruction of the superior olivary complex resulted in dramatic loss of choline acetyltransferase activity in the ipsilateral co&ear nucleus, and detectable loss also contralaterally. The results suggest that most of the centrifugal chohnergic projections to the rat eochiear nucleus derive from or traverse the vicinity of the superior ohvary complex bilaterally and enter the cochlear nucleus ventrally from the region of the trapezoid body.
Cholinergic Responses in Developing Outer Hair Cells of the Rat Cochlea
European Journal of Neuroscience, 1996
Acetylcholine-evoked currents were investigated using the conventional whole-cell patch-clamp recording technique in developing outer hair cells (OHCs). The cells were isolated from the rat cochlea at different stages of postnatal development ranging from day 4 (P4) to P30. Acetylcholine-evoked currents could be recorded at P6 and P8. At this developmental stage, the majority of OHCs displayed inward nicotinic-like currents near the resting membrane potential. These cholinergic currents zeroed near 0 mV, as expected for a non-selective cation current, and could be reversibly blocked by d-tubocurarine. At P12 and adult stage, the cholinergic response of OHCs switched to an outward current reversing near EK and displaying a bell shape peaking between-40 and-30 mV. This change in polarity of the acetylcholine response during postnatal development might be explained by progressive functional coupling between acetylcholine ionotropic receptors permeable to Ca2+ and nearby Ca2+-activated K+ channels at the synaptic pole of OHCs. The cells were obtained essentially as previously described (Lenoir et al., 1995). Temporal bones, excised from animals under deep anaesthesia (mixture of ketamine and xylazine), were rapidly immersed in HBSS (1.25 mM CaC12(2H20), 5.55 mM glucose, 0.81 mM MgS04, 0.44 mM KH2PO4, 136.9 mM NaCl, 0.34 mM Correspondence to: Didier Dulon, as above
Journal of the Association for Research in Otolaryngology, 2006
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.
Journal of Neurophysiology, 2007
A novel effect of cochlear efferents: in vivo response enhancement does not require ␣9 cholinergic receptors. Outer hair cells in the mammalian cochlea receive a cholinergic efferent innervation that constitutes the effector arm of a sound-evoked negative feedback loop. The well-studied suppressive effects of acetylcholine (ACh) release from efferent terminals are mediated by ␣9/␣10 ACh receptors and are potently blocked by strychnine. Here, we report a novel, efferent-mediated enhancement of cochlear sound-evoked neural responses and otoacoustic emissions in mice. In controls, a slow enhancement of response amplitude to supranormal levels appears after recovery from the classic suppressive effects seen during a 70-s epoch of efferent shocks. The magnitude of post-shock enhancement can be as great as 10 dB and tends to be greater for high-frequency acoustic stimuli. Systemic strychnine at 10 mg/kg eliminates efferentinduced suppression, revealing a purely enhancing effect of efferent shocks, which peaks within 5 s after efferent-stimulation onset, maintains a constant level through the stimulation epoch, and slowly decays back to baseline with a time constant of ϳ100 s. In mice with targeted deletion of the ␣9 ACh receptor subunit, efferent-evoked effects resemble those in wild types with strychnine blockade, further showing that this novel efferent effect is fundamentally different from all cholinergic effects previously reported. Altschuler RA, Parakkal MH, Rubio JA, Hoffman DW, Fex J. Enkephalinlike immunoreactivity in the guinea pig organ of corti: ultrastructural and lesion studies. Hear Res 16: 17-31, 1984. Bao J, Lei D, Du Y, Ohlemiller KK, Beaudet AL, Role LW. Requirement of nicotinic acetylcholine receptor subunit beta2 in the maintenance of spiral ganglion neurons during aging. J Neurosci 25: 3041-3045, 2005. Batta TJ, Panyi G, Szucs A, Sziklai I. Regulation of the lateral wall stiffness by acetylcholine and GABA in the outer hair cells of the guinea pig. Eur J Neurosci 20: 3364 -3370, 2004. Bobbin RP, Konishi T. Action of cholinergic and anticholinergic drugs at the crossed olivocochlear bundle-hair cell junction. Acta Otolaryngol 77: 56 -65, 1974. Cooper NP, Guinan JJ Jr. Separate mechanical processes underlie fast and slow effects of medial olivocochlear efferent activity. J Physiol 548: 307-312, 2003. Counter SA, Borg E, Engstrom B. Acoustic middle ear reflexes in laboratory animals using clinical equipment: technical considerations. Audiology 28: 135-143, 1989. Dallos P, He DZ, Lin X, Sziklai I, Mehta S, Evans BN. Acetylcholine, outer hair cell electromotility, and the cochlear amplifier.