Intracochlear injection of pseudorabies virus labels descending auditory and monoaminerg projections to olivocochlear cells in guinea pig

Abstract

Pseudorabies virus was used to label transneuronally descending auditory projections following intracochlear injections. At different time points after injection, virus-infected cells were detected immunohistochemically in the central nervous system. Initially (25 h), virus was transported retrogradely to olivocochlear cells in the pons. At 32-72 h after injection, labelling occurred in higher order auditory brainstem nuclei as well as in the locus coeruleus and pontine dorsal raphe. At 90-108 h, virus-infected neurons were found bilaterally in the medial geniculate body and in layer V of the auditory cortex. Viral transneuronal labelling in the auditory cortex after intracochlear application confirms the existence of a continuous descending chain of neurons from the auditory cortex to the cochlea, via the medial and lateral olivocochlear systems. The transneuronal labelling of the locus coeruleus and pontine dorsal raphe suggests that noradrenergic and serotonergic inputs may substantially influence the activity of olivocochlear cells, and thus the cochlea.

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

“…We also examine whether the two types of IC neurons, cells with disc-shaped dendritic fields and cells of stellate shape, are transneuronally labeled. Finally, we confirm the numerous types of "non-auditory" transneuronally labeled neurons reported by Horvath et al (2003). It is not clear how these inputs participate in the OC reflex to sound, and information here may help us better understand the role of OC neurons in the greater realm that includes auditory and non-auditory processes.…”

“…Additional variability in PRV labeling could be explained by injection-to-injection variation in where PRV most densely accumulates along the cochlear spiral, since most MOC neurons terminate in the base and middle portions whereas the LOC neurons terminate more evenly (Guinan et al 1984). Variability in the MOC/LOC ratio was not pointed out by Horvath et al (2003), although that study did not give counts for MOC neurons. They labeled more LOC neurons than the present study (560-650 vs. 0-255) and they made larger injections of PRV (50 vs. 5-30 μl).…”

“…It then crosses to nerve terminals synapsing on the cells and in turn transports back to the cell bodies providing those inputs, which are remote from the injection site and not obscured by it. Transneuronal labeling has been used to study the OC pathways in the pioneering work of Horvath et al (2003). After injections of PRV-Bartha into the cochlea, labeling was first observed in the OC neurons and, at later times, within neurons in other locations.…”

“…After injections of PRV-Bartha into the cochlea, labeling was first observed in the OC neurons and, at later times, within neurons in other locations. Transneuronally labeled neurons were found in the CN, IC, auditory cortex, and in centers not typically associated with the auditory pathway such as the subcoerulean nucleus and pontine dorsal raphe (Horvath et al 2003). PRV-Bartha is ideal for OC labeling because it is transported exclusively in the retrograde direction (O'Donnell et al 1997;Card et al 1998), thus avoiding a complication of anterograde labeling of auditory nerve projections to the CN (Horvath et al 2003).…”

“…The CN is particularly interesting because it plays a critically important intermediate stage in the MOC reflex pathway (Liberman and Guinan 1998;de Venecia et al 2005). CN transneuronal labeling is found in multipolar cells (Horvath et al 2003), but the labeled subtype within this heterogeneous class (reviewed by Doucet and Ryugo 2006) was not identified. Recent work using conventional tracers suggests that one class, planar multipolar cells, projects to MOC neurons (Darrow et al 2012), and we examine here whether they and other subtypes are transneuronally labeled.…”