Projections of the second cervical dorsal root ganglion to the cochlear nucleus in rats

Abstract

Physiological, anatomical, and clinical data have demonstrated interactions between somatosensory and auditory brainstem structures. Spinal nerve projections influence auditory responses, although the nature of the pathway(s) is not known. To address this issue, we injected biotinylated dextran amine into the cochlear nucleus or dorsal root ganglion (DRG) at the second cervical segment (C2). Cochlear nucleus injections retrogradely labeled small ganglion cells in C2 DRG. C2 DRG injections produced anterograde labeling in the external cuneate nucleus, cuneate nucleus, nucleus X, central cervical nucleus, dorsal horn of upper cervical spinal segments, and cochlear nucleus. The terminal field in the cochlear nucleus was concentrated in the subpeduncular corner and lamina of the granule cell domain, where endings of various size and shapes appeared. Examination under an electron microscope revealed that the C2 DRG terminals contained numerous round synaptic vesicles and formed asymmetric synapses, implying depolarizing influences on the target cell. Labeled endings synapsed with the stalk of the primary dendrite of unipolar brush cells, distal dendrites of presumptive granule cells, and endings containing pleomorphic synaptic vesicles. These primary somatosensory projections contribute to circuits that are hypothesized to mediate integrative functions of hearing.

Cervical Spine Dysfunctions in Patients With Chronic Subjective Tinnitus

“…The existence of CST is supported by several animal studies, which have found connections between the cervical somatosensory system and the cochlear nuclei (CN) (3,4). Cervical somatosensory information is conveyed by afferent fibers, the cell bodies of which are located in the dorsal root ganglia or the trigeminal ganglion, to the brain.…”

“…Within the group of patients suffering from chronic subjective nonpulsatile tinnitus, a subgroup can be defined where the tinnitus is related to the somatosensory system of the cervical spine (2). This type of tinnitus is named cervicogenic somatic tinnitus (CST).The existence of CST is supported by several animal studies, which have found connections between the cervical somatosensory system and the cochlear nuclei (CN) (3,4). Cervical somatosensory information is conveyed by afferent fibers, the cell bodies of which are located in the dorsal root ganglia or the trigeminal ganglion, to the brain.…”

Listening to another sense: somatosensory integration in the auditory system

“…1). Specific sensory projection neurons to the CN originate in the trigeminal ganglion and the spinal trigeminal nucleus (Sp5) (Haenggeli, et al, 2005, Shore, et al, 2000, Zhou and Shore, 2004), dorsal root ganglion and dorsal column nuclei (Itoh, et al, 1987, Zeng, et al, 2011, Zhan, et al, 2006, Zhou and Shore, 2004), saccule and vestibular nucleus (Barker, et al, 2012, Bukowska, 2002, Burian and Gstoettner, 1988). Most of the projections from non-auditory sensory ganglia and brainstem nuclei terminate in the CN granule cell domain (GCD), but some of them end in magnocellular CN regions (Gomez-Nieto and Rubio, 2011).…”

Cochlear Damage Changes the Distribution of Vesicular Glutamate Transporters Associated with Auditory and Nonauditory Inputs to the Cochlear Nucleus

“…VGLUT1 expression is intense in the core region of VCN and deep DCN where ANFs terminate on principal projection neurons, while VGLUT2 expression is stronger in the granule cell domain (GCD), which receives most of the non-auditory inputs to the CN (Haenggeli et al, 2005; Ohlrogge et al, 2001; Wright and Ryugo, 1996; Zhan et al, 2006; Zhan and Ryugo, 2007; Zhou et al, 2007; Zhou and Shore, 2004; 2006b). Furthermore, terminal endings originating in the spinal trigeminal nucleus (Sp5), cuneate nucleus and lateral reticular nucleus co-label with VGLUT2 and not VGLUT1 (Cui and Shore, 2008; Zhou et al, 2007).…”