Convergence of spinal trigeminal and cochlear nucleus projections in the inferior colliculus of the guinea pig

Abstract

In addition to ascending auditory inputs, the external cortex of the inferior colliculus (ICX) receives prominent somatosensory inputs. To elucidate the extent of interaction between auditory and somatosensory representations at the level of IC, we explored the dual projections from the cochlear nucleus (CN) and the spinal trigeminal nucleus (Sp5) to the inferior colliculus (IC) in the guinea pig, using both retrograde and anterograde tracing techniques. Injections of retrograde tracers into ICX resulted in cell-labeling primarily in the contralateral DCN and pars interpolaris and caudalis of Sp5. Labeled cells in DCN were either fusiform or multipolar cells, whereas those in Sp5 varied in size and shape. Injections of anterograde tracers into either CN or Sp5 resulted in terminal labeling in ICX primarily on the contralateral side. Most projection fibers from Sp5 terminated in a laminar pattern from ventromedial to dorsolateral within the ventrolateral ICX, the ventral border of IC, and the ventromedial edge of IC (collectively termed "the ventrolateral border region of IC," ICXV). Less dense anterograde labeling was observed in lateral and rostral ICX. Injecting different tracers into both Sp5 and CN confirmed the overlapping areas of convergent projections from Sp5 and CN in IC: The most intense dual labeling was seen in the ICXV, and less intense dual labeling was also observed in the rostral part of ICX. This convergence of projection fibers from CN and Sp5 provides an anatomical substrate for multimodal integration in the IC.

Cross-Sensory Modulation of Primary Sensory Cortex Is Developmentally Regulated by Early Sensory Experience

“…What is the best explanation for such facilitation in an early response period dominated primarily by thalamocortical inputs? There is ample evidence that subcortical auditory structures such as the dorsal cochlear nucleus (DCN) (Zhou and Shore, 2004;Haenggeli et al, 2005;Shore, 2005;Shore et al, 2008), the inferior colliculus (IC) (Jain and Shore, 2006;Zhou and Shore, 2006), and the medial division of the thalamic medial geniculate nucleus (mMGN) (Poggio and Mountcastle, 1960;Blum et al, 1979;Nicolelis et al, 1991) all receive significant somatosensory inputs and show multisensory responses. Thus, these structures, in turn, may influence subcortical somatosensory structures such as the trigeminal nucleus (TN) and the thalamic ventral posterior medial nucleus (VPM).…”

Bimodal stimulus timing-dependent plasticity in primary auditory cortex is altered after noise exposure with and without tinnitus

“…To mark the electrode tracks, the recording and stimulating electrodes were dipped in Fluorogold (2%) before being inserted into the brain. After being immersed in 4% paraformaldehyde for 48 h followed by immersion in a 20% sucrose solution (Zhou and Shore 2006), the brain was cryosectioned at 40 m, placed on slides, and examined under epifluorescence.…”

Synaptic Inputs to Granule Cells of the Dorsal Cochlear Nucleus

“…Such integration may play a role in the suppression of predicted body-generated sounds (Shore 2005;Zhou and Shore 2006) or orientation of the head or ears to a sound source (Kanold and Young 2001;May 2000;Sutherland et al 1998;Young and Davis 2002). Given the potential importance of this nonauditory pathway, it is surprising that very little is known about the physiology of synaptic inputs to granule cells.…”