Projection of the marginal shell of the anteroventral cochlear nucleus to olivocochlear neurons in the cat

Abstract

The marginal shell of the anteroventral cochlear nucleus is anatomically and physiologically different from its central core. Previous studies suggest that neurons in the marginal shell are well suited to encode the intensity of acoustic stimuli. To investigate the projections of the marginal shell, a focal injection (<100 nl) of a mixture of biotinylated dextran amine (BDA) and 3H‐leucine was made into the marginal shell of the cat combined with injection of cholera toxin subunit‐B (CTB) into the cochleas. Following a 7‐day survival, the cats were perfused. Axons and swellings labeled with BDA and olivocochlear neurons labeled with CTB were immunocytochemically stained black and brown, respectively. 3H‐leucine labels were visualized by autoradiography. Labeled neural structures were examined via light microscopy. We found that swellings labeled with BDA, sometimes doubly labeled with BDA and 3H‐leucine, were in close apposition with dendrites and/or somata of olivocochlear neurons identified with CTB labeling. Double labeling with BDA and 3H‐leucine signifies that the label was anterogradely transported. The results support the conclusion that the anteroventral cochlear nucleus projects to medial olivocochlear neurons bilaterally and to lateral olivocochlear neurons ipsilaterally. Furthermore, the results are consistent with the interpretation that the marginal shell provides a source of the above‐mentioned projections. Together with information in the literature, the present anatomical results support a hypothesis that the marginal shell provides information about stimulus intensity as a part of a reflex (or feedback gain control) system comprising the cochlea, cochlear neurons, cochlear nucleus, medial olivocochlear neurons, and cochlear outer hair cells. J. Comp. Neurol. 420:127–138, 2000. © 2000 Wiley‐Liss, Inc.

Commissural Neurons in the Rat Ventral Cochlear Nucleus

“…The small cell cap is emerging as a nexus of auditory brainstem regulatory pathways. Neurons that reside there are components of circuits that control the middle ear reflex (Billig et al 2007) and cochlear output (Ye et al 2000). The small cell cap is the preferred target of the collateral projections of medial olivocochlear neurons (Liberman and Brown 1986;Brown et al 1988;Benson et al 1996), whose principal role is to modulate cochlear gain via their innervation of outer hair cells.…”

Medial olivocochlear reflex interneurons are located in the posteroventral cochlear nucleus: A kainic acid lesion study in guinea pigs

“…In contrast, projections from PVCN to MOC neurons have been suggested by fiber degeneration studies (Warr, 1969) and further clarified by tracer experiments (Thompson and Thompson, 1991). Other tracer studies have shown that neurons in the AVCN marginal shell also project to MOC neurons (Ye et al, 2000). Physiological studies are necessary to determine the respective roles of these different pathways in the MOC reflex circuitry and to determine whether other CN areas may also be involved.…”

“…Facilitation may have been missed, though, because our contralateral effect is small and variable. Such facilitation may be generated by a very different reflex pathway, possibly from the marginal shell of AVCN (Ye et al, 2000). Schematic of medial olivocochlear (MOC) reflex pathways that can affect cochlear responses from the ipsilateral (right) ear.…”

“…1, black arrows) begins with auditory nerve projections to the ipsilateral cochlear nucleus (CN; Fekete et al, 1984) and ends with projections from MOC cells in the contralateral superior olivary complex that cross the midline to reach ipsilateral outer hair cells. The interneurons connecting these afferent and efferent limbs are incompletely characterized, although direct projections from the CN to terminals on or near MOC somata have been demonstrated (Warr, 1969;Robertson and Winter, 1988;Thompson and Thompson, 1991;Ye et al, 2000). For the Contra MOC reflex pathway (Fig.…”

Identification of Inputs to Olivocochlear Neurons Using Transneuronal Labeling with Pseudorabies Virus (PRV)

“…Reflexive inputs from the cochlear nucleus (CN) drive the MOC neuron's response to sound (Warr 1969;Thompson et al 1991;Liberman and Guinan 1998;Ye et al 2000;Brown et al 2003). LOC neurons also receive CN inputs but their sound-evoked responses have not been determined.…”