Multiple origins of cholinergic innervation of the cochlear nucleus

Abstract

Acetylcholine affects a variety of cell types in the cochlear nucleus (CN) and is likely to play a role in numerous functions. Previous work in rats suggested that the acetylcholine arises from cells in the superior olivary complex, including cells that have axonal branches that innervate both the CN and the cochlea (i.e., olivocochlear cells) as well as cells that innervate only the CN. We combined retrograde tracing with immunohistochemistry for choline acetyltransferase to identify the source of ACh in the CN of guinea pigs. The results confirm a projection from cholinergic cells in the superior olivary complex to the CN. In addition, we identified a substantial number of cholinergic cells in the pedunculopontine tegmental nucleus (PPT) and the laterodorsal tegmental nucleus (LDT) that project to the CN. On average, the PPT and LDT together contained about 26% of the cholinergic cells that project to CN, whereas the superior olivary complex contained about 74%. A small number of additional cholinergic cells were located in other areas, including the parabrachial nuclei.The results highlight a substantial cholinergic projection from the pontomesencephalic tegmentum (PPT and LDT) in addition to a larger projection from the superior olivary complex. These different sources of cholinergic projections to the CN are likely to serve different functions. Projections from the superior olivary complex are likely to serve a feedback role, and may be closely tied to olivocochlear functions. Projections from the pontomesencephalic tegmentum may play a role in such things as arousal and sensory gating. Projections from each of these areas, and perhaps even the smaller sources of cholinergic inputs, may be important in conditions such as tinnitus as well as in normal acoustic processing. Keywordsarousal; sensory gating; tinnitus; olivocochlear; pedunculopontine tegmental nucleus; laterodorsal tegmental nucleus Cholinergic innervation of the cochlear nucleus (CN) has been demonstrated by many methods, including physiology, receptor binding, enzyme assays, histochemistry and Correspondence: Brett R. Schofield, PhD, NEOUCOM, Department of Anatomy and Neurobiology, PO Box 95, Rootstown, OH 44272 USA,, bschofie@neoucom.edu; Jeffrey G. Mellott, PhD, Address: as above, jmellott@neoucom.edu; Susan D. Motts, PhD, Address: as above, smotts@neoucom.edu. Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. NIH Public Access Author ManuscriptNeuroscience. Author manuscript; available in PMC 2012 April 28. and Whitfield, 1968;Caspary et al., 1983;Osen et al., 1984;Godfrey et al., 1987Godfrey ...

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Suppression of noise-induced hyperactivity in the dorsal cochlear nucleus following application of the cholinergic agonist, carbachol

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