Projections of the pontine nuclei to the cochlear nucleus in rats

Abstract

In the cochlear nucleus, there is a magnocellular core of neurons whose axons form the ascending auditory pathways. Surrounding this core is a thin shell of microneurons called the granule cell domain (GCD). The GCD receives auditory and nonauditory inputs and projects in turn to the dorsal cochlear nucleus, thus appearing to serve as a central locus for integrating polysensory information and descending feedback. Nevertheless, the source of many of these inputs and the nature of the synaptic connections are relatively unknown. We used the retrograde tracer Fast Blue to demonstrate that a major projection arises from the contralateral pontine nuclei (PN) to the GCD. The projecting cells are more densely located in the ventral and rostral parts of the PN. They also are clustered into a lateral and a medial group. Injections of anterograde tracers into the PN labeled mossy fibers in the contralateral GCD. The terminals are confined to those parts of the GCD immediately surrounding the ventral cochlear nucleus. There is no PN projection to the dorsal cochlear nucleus. These endings have the form of bouton and mossy fiber endings as revealed by light and electron microscopy. The PN represent a key station between the cerebral and cerebellar cortices, so the pontocochlear nucleus projection emerges as a significant source of highly processed information that is introduced into the early stages of the auditory pathway. The cerebropontocerebellar pathway may impart coordination and timing cues to the motor system. In an analogous way, perhaps the cerebropontocochlear nucleus projection endows the auditory system with a timing mechanism for extracting temporal information.

Cross-Modal Interactions of Auditory and Somatic Inputs in the Brainstem and Midbrain and Their Imbalance in Tinnitus and Deafness

“…In addition to somatosensory connections, neurons in the pontine nuclei (Ohlrogge et al, 2001) and vestibular system project to the CN (Burian et al, 1989; Kevetter & Perachio, 1989; Gstoettner et al, 1991). …”

Projections of the lateral reticular nucleus to the cochlear nucleus in rats

“…The variation could also be due in part to differences in tracer chemistry and intracellular transport. A comparison among these dyes likewise resulted in fewer fast blue-labeled cell bodies in the pontine, cuneate, and spinal trigeminal nuclei, although it is known that these nuclei give rise to robust projections to the CN (Haenggeli et al, 2005;Ohlrogge et al, 2001;Weinburg and Rustioni, 1987;Wright and Ryugo, 1996;Zhou and Shore, 2004).…”

“…Information about head and pinna position is hypothesized to assist orientation to a sound source in three-dimensional space (Oertel and Young, 2004), because sound spectra are modified by head-and pinna-related transfer functions (Musicant et al, 1990;Rice et al, 1992). The pontine nuclei send sensorimotor projections to the CN, whose function may be to coordinate the tracking of moving sounds (Babalian, 2005;Ohlrogge et al, 2001). The target of these nonauditory projections is the granule cell domain (GCD), a superficial shell region composed primarily of granule cells whose axons terminate in the dorsal cochlear nucleus (DCN) (Mugnaini et al, 1980b).…”

“…Many of the inputs to the GCD terminate in the form of mossy fiber endings (Haenggeli et al, 2005;McDonald and Rasmussen, 1971;Mugnaini et al, 1980a;Ohlrogge et al, 2001;Wright and Ryugo, 1996). CN mossy fibers were named for their structural similarity to large endings in the cerebellum.…”

“…For such information, we injected biotinylated dextran amine (BDA) into the LRN to examine the anterogradely labeled fibers and endings. Cell bodies labeled by fast blue in the cuneate, spinal trigeminal, and pontine nuclei served as positive retrograde controls (Haenggeli et al, 2005;Ohlrogge et al, 2001;Wright and Ryugo, 1996), and mossy fibers (B) illustrating the GCD of the CN in the rat. Granule cells were retrogradely labeled by placing an extracellular injection of diamidino yellow in the DCN.…”