Projections from the dorsal and ventral cochlear nuclei to the medial geniculate body

Abstract

Direct projections from the cochlear nucleus (CN) to the medial geniculate body (MG) mediate a high-speed transfer of acoustic information to the auditory thalamus. Anderson etal. (2006) used anterograde tracers to label the projection from the dorsal CN (DCN) to the MG in guinea pigs. We examined this pathway with retrograde tracers. The results confirm a pathway from the DCN, originating primarily from the deep layers. Labeled cells included a few giant cells and a larger number of small cells of unknown type. Many more labeled cells were present in the ventral CN (VCN). These cells, identifiable as multipolar (stellate) or small cells, were found throughout much of the VCN. Most of the labeled cells were located contralateral to the injection site. The CN to MG pathway bypasses the inferior colliculus (IC), where most ascending auditory information is processed. Anderson etal. (2006) hypothesized that CN-MG axons are collaterals of axons that reach the IC. We tested this hypothesis by injecting different fluorescent tracers into the MG and IC and examining the CN for double-labeled cells. After injections on the same side of the brain, double-labeled cells were found in the contralateral VCN and DCN. Most double-labeled cells were in the VCN, where they accounted for up to 37% of the cells labeled by the MG injection. We conclude that projections from the CN to the MG originate from the VCN and, less so, from the DCN. A significant proportion of the cells send a collateral projection to the IC. Presumably, the collateral projections send the same information to both the MG and the IC. The results suggest that T-stellate cells of the VCN are a major source of direct projections to the auditory thalamus.

Subcollicular projections to the auditory thalamus and collateral projections to the inferior colliculus

“…A similar collateral projection characterizes the pathway from the cochlear nucleus to the MG (Schofield et al, 2014). Collateral projections may serve multiple functions.…”

“…Moreover, many cochlear nucleus cells that project to the MG send collateral projections to the inferior colliculus (IC) (Schofield et al, 2014). We conducted three experiments to characterize projections to the MG from the superior olivary and the lateral lemniscal regions in guinea pigs.…”

Maladaptive plasticity in tinnitus — triggers, mechanisms and treatment

“…Additionally, there is an increase in excitatory neurotransmission after severe and partial cochlear damage [75, 76] and an upregulation of excitatory non-auditory projections [77]. Decreased inhibition combined with increased excitation could result in hyperactivity of CN neurons that could be transmitted through the IC, or bypass the IC [60, 78], to the MGB. At the level of the MGB, however, there is little evidence of tinnitus-related decreases in GABAergic neurotransmission [79].…”

Listening to another sense: somatosensory integration in the auditory system

“…It is analogous to ICX with broader tuning properties and reception of non-auditory inputs (Ledoux, et al, 1987, Ryugo and Weinberger, 1978). The auditory inputs to MGm are derived from ICC and ICX (Calford and Aitkin, 1983), as well as a separate, direct pathway from the DCN and CN small cell cap region that bypass IC (Anderson, et al, 2006, Malmierca, et al, 2002, Schofield, et al, 2014). Multisensory inputs to MGm – and partially MGd – include somatosensory afferents from the spinal-thalamic, dorsal column, and the trigeminal pathways (Jones and Burton, 1974, Lund and Webster, 1967a, Lund and Webster, 1967b), as well as visual afferents from SC (Linke, et al, 1999).…”