Dendrites of medial olivocochlear neurons in mouse

Abstract

Stains for acetylcholinesterase (AChE) and retrograde labeling with Fluorogold (FG) were used to study olivocochlear neurons and their dendritic patterns in mice. The two methods gave similar results for location and number of somata. The total number of medial olivocochlear (MOC) neurons in the ventral nucleus of the trapezoid body (VNTB) is about 170 per side. An additional dozen large olivocochlear neurons are located in the dorsal periolivary nucleus (DPO). Dendrites of all of these neurons are long and extend in all directions from the cell bodies, a pattern that contrasts with the sharp frequency tuning of their responses. For VNTB neurons, there were greater numbers of dendrites directed medially than laterally and those directed medially were longer (on average, 25-50% longer). Dendrite extensions were most pronounced for neurons located in the rostral portion of the VNTB. When each dendrite from a single neuron was represented as a vector, and all the vectors summed, the result was also skewed toward the medial direction. DPO neurons, however, had more symmetric dendrites that projected into more dorsal parts of the trapezoid body, suggesting that this small group of olivocochlear neurons has very different physiological properties. Dendrites of both types of neurons were somewhat elongated rostrally, about 20% longer than those directed caudally. These results can be interpreted as extensions of dendrites of olivocochlear neurons toward their synaptic inputs: medially to meet crossing fibers from the cochlear nucleus that are part of the MOC reflex pathway, and rostrally to meet descending inputs from higher centers. Keywords superior olive; cochlear nucleus; efferent; descending pathway; auditory reflex Dendrites represent an important site for neurons to receive synaptic input. As such, dendrite corientation and pattern can shape a neuron's response properties. For example, octopus cells of the posteroventral cochlear nucleus have long dendrites oriented perpendicular to the incoming auditory nerve fibers (Osen, 1969;Brawer et al., 1974). This orientation allows them to receive input from auditory-nerve fibers that are tuned to a range of frequencies. Octopus cells, which have an onset pattern of discharge in response to a tone burst (Rouiller and Ryugo, 1983; Rhode et al., 1983), are often tuned more broadly than their inputs (Godfrey et al., *Corresponding Author. Tel: (617) 573-3875; fax (617) . Address: Eaton-Peabody Laboratory, Massachusetts Eye & Ear Infirmary, 243 Charles St., Boston, MA 02114. Email address: Chris_Brown@meei.harvard.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 ...

Olivocochlear Neuron Central Anatomy Is Normal in α9 Knockout Mice

“…2B). MOC neurons have large somata and were located in the ventral nucleus of the trapezoid body (VNTB), as described previously by retrograde labeling studies in other strains of mice (Campbell and Henson 1988;Brown and Levine 2008) and rat (Vetter et al 1991;Vetter and Mugnaini 1992). Their distribution in all strains extends a considerable distance in the rostro-caudal direction, beginning somewhat caudal to the lateral superior olivary nucleus (LSO) and extending rostrally to the caudal part of the ventral nucleus of the lateral lemniscus.…”

“…Available data suggest that this stain is a specific marker for OC neurons in the mouse superior olivary complex because it yields essentially the same spatial distribution and number as retrograde labeling of OC neurons (Brown and Levine 2008). On this basis, we will presume that AChE staining is a marker for OC neurons in the superior olivary complex.…”

“…A few large OC neurons were located just dorso-medial to the LSO in a region identified as the dorsal periolivary nucleus (DPO). Although it is not clear that these DPO neurons are MOC neurons, they bear similarities to MOC neurons in the VNTB except that their dendrites are more symmetric about the soma (Brown and Levine 2008). The number of DPO neurons was small and again did not differ between strains (on one side of the brain the average number of DPO neurons ranged from 10.7 to 12.8, Fig.…”

“…Stains for acetylcholinesterase (AChE) were performed as described previously (Brown and Levine 2008). Mice were anesthetized with ketamine (100 mg/kg, i.p.)…”

“…OC neurons and their collateral branches were visualized using stains for acetylcholinesterase (Schuknecht and Nomura 1965;Osen 1969;Brown and Howlett 1972;Warr 1975;Martin 1981;White and Warr 1983;Osen et al 1984;Brown and Levine 2008). Available data suggest that this stain is a specific marker for OC neurons in the mouse superior olivary complex because it yields essentially the same spatial distribution and number as retrograde labeling of OC neurons (Brown and Levine 2008).…”