Multisensory activation of ventral cochlear nucleus D‐stellate cells modulates dorsal cochlear nucleus principal cell spatial coding

Abstract

In the cochlear nucleus (CN), the first central site for coding sound location, numerous multisensory projections and their modulatory effects have been reported. However, multisensory influences on sound location processing in the CN remain unknown. The principal output neurons of the dorsal CN, fusiform cells, encode spatial information through frequency-selective responses to direction-dependent spectral features. Here, single-unit recordings from the guinea pig CN revealed transient alterations by somatosensory and vestibular stimulation in fusiform cell spatial coding. Changes in fusiform cell spectral sensitivity correlated with multisensory modulation of ventral CN D-stellate cell responses, which provide direct, wideband inhibition to fusiform cells. These results suggest that multisensory inputs contribute to spatial coding in DCN fusiform cells via an inhibitory interneuron, the D-stellate cell. This early multisensory integration circuit likely confers important consequences on perceptual organization downstream.

Ventral cochlear nucleus bushy cells encode hyperacusis in guinea pigs

“…There are several possible mechanisms by which bushy cells could become more excitable after noise exposure, resulting in hyperacusis-like firing. Bushy cells in rodent and mammalian species receive somatosensory input on their dendrites which can modulate firing sensitivity 36 , 44 . Following noise-exposure, the anterior VCN receives increased glutamatergic input from non-auditory structures 36 .…”

“…These findings suggest that there could instead be a fusiform-cell contribution to tinnitus in animals with bushy-cells showing elevated HI. A reduction in wideband-inhibition from D-stellate neurons could likewise reduce inhibition of the fusiform cell 31 , 44 , potentially linking hyperacusis arising from bushy cells in the VCN with tinnitus arising from fusiform cells in the DCN. Future studies should perform concurrent bushy-cell and fusiform-cell recordings in the same animals, along with behavioral measures of tinnitus and hyperacusis.…”

“…A craniotomy and duratomy were performed to expose the cerebellum for electrode insertion. The AVCN was accessed using previously established stereotaxic co-ordinates 44 , 74 .…”

Audiotactile interactions in the mouse cochlear nucleus

“…Projections to the cochlear nucleus also arise from the spinal trigeminal nucleus 10 – 14 that conveys touch sensation from the face. Projections from these regions form mossy fibre inputs that synapse onto granule cells in the cochlear nucleus granule-cell domain, as well as onto dendrites of ventral cochlear nucleus (VCN) bushy cells 15 and D-stellate cells 16 . The D-stellate cells inhibit fusiform cells in dorsal cochlear nucleus (DCN) 17 – 19 .…”

“…The parallel fibre axons of granule cells in turn provide excitatory synaptic input to DCN cartwheel and fusiform cells. The presence of somatosensory inputs to a primary auditory nucleus such as the cochlear nucleus is intriguing in the context of the role of the pinnae and neck in generating sound localization cues 16 , as well as the suppression of self-generated signals 20 . Correct interpretation of this information requires integration of auditory signals with somatosensory and proprioceptive signals conveying information about head and pinna position.…”