Parallel auditory pathways: Projection patterns of the different neuronal populations in the dorsal and ventral cochlear nuclei
ABSTRACT The cochlear nuclear complex gives rise to widespread projections to nuclei throughout the brainstem. The projections arise from separate, well-defined populations of cells. None of the cell populations in the cochlear nucleus projects to all brainstem targets, and none of the targets receives inputs from all cell types. The projections of nine distinguishable cell types in the cochlear nucleus-seven in the ventral cochlear nucleus and two in the dorsal cochlear nucleus-are described in this review. Globular bushy cells and two types of spherical bushy cells project to nuclei in the superior olivary complex that play roles in sound localization based on binaural cues. Octopus cells convey precisely timed information to nuclei in the superior olivary complex and lateral lemniscus that, in turn, send inhibitory input to the inferior colliculus. Cochlear root neurons send widespread projections to areas of the reticular formation involved in startle reflexes and autonomic functions. Type I multipolar cells may encode complex features of natural stimuli and send excitatory projections directly to the inferior colliculus. Type II multipolar cells send inhibitory projections to the contralateral cochlear nuclei. Fusiform cells in the dorsal cochlear nucleus appear to be important for the localization of sounds based on spectral cues and send direct excitatory projections to the inferior colliculus. Giant cells in the dorsal cochlear nucleus also project directly to the inferior colliculus; some of them may convey inhibitory inputs to the contralateral cochlear nucleus as well.
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- "The CNC distributes the incoming auditory information to distinct ascending pathways in the brainstem (Fig. 3). Major projections of the DCN innervate the contralateral nuclei of the LL and the IC (Cant and Benson 2003). The VCN projects mainly into the region of the ipsilateral and contralateral SOC. "
ABSTRACT: A defining feature of the mammalian auditory system is the extensive processing of sound information in numerous ultrafast and temporally precise circuits in the hindbrain. By exploiting the experimental advantages of mouse genetics, recent years have witnessed an impressive advance in our understanding of developmental mechanisms involved in the formation and refinement of these circuits. Here, we will summarize the progress made in four major fields: the dissection of the rhombomeric origins of auditory hindbrain nuclei; the molecular repertoire involved in circuit formation such as Hox transcription factors and the Eph-ephrin signaling system; the timeline of functional circuit assembly; and the critical role of spontaneous activity for circuit refinement. In total, this information provides a solid framework for further exploration of the factors shaping auditory hindbrain circuits and their specializations. A comprehensive understanding of the developmental pathways and instructive factors will also offer important clues to the causes and consequences of hearing-loss related disorders, which represent the most common sensory impairment in humans.Cell and Tissue Research 01/2015; 361(1). DOI:10.1007/s00441-014-2110-7 · 3.33 Impact Factor
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- "The third layer, the deep or polymorphic layer, has an assortment of cell types. Deep to the DCN are the fibers of the dorsal acoustic stria (das), comprised of the axons of the DCN projection neurons as well as other fibers from multiple brain regions projecting to the DCN (Barnes et al., 1943; Gacek, 1973; Adams and Warr, 1976; Masterton and Granger, 1988; Cant and Benson, 2003; Smith et al., 2005). "
ABSTRACT: The dorsal cochlear nucleus (DCN) is a brainstem structure that receives input from the auditory nerve. Many studies in a diversity of species have shown that the DCN has a laminar organization and identifiable neuron types with predictable synaptic relations to each other. In contrast, studies on the human DCN have found a less distinct laminar organization and fewer cell types, although there has been disagreement among studies in how to characterize laminar organization and which of the cell types identified in other animals are also present in humans. We have reexamined DCN organization in the human using immunohistochemistry to analyze the expression of several proteins that have been useful in delineating the neurochemical organization of other brainstem structures in humans: nonphosphorylated neurofilament protein (NPNFP), nitric oxide synthase (nNOS), and three calcium-binding proteins. The results for humans suggest a laminar organization with only two layers, and the presence of large projection neurons that are enriched in NPNFP. We did not observe evidence in humans of the inhibitory interneurons that have been described in the cat and rodent DCN. To compare humans and other animals directly we used immunohistochemistry to examine the DCN in the macaque monkey, the cat, and three rodents. We found similarities between macaque monkey and human in the expression of NPNFP and nNOS, and unexpected differences among species in the patterns of expression of the calcium-binding proteins. Anat Rec, 2014. © 2014 Wiley Periodicals, Inc.The Anatomical Record Advances in Integrative Anatomy and Evolutionary Biology 10/2014; 297(10). DOI:10.1002/ar.23000 · 1.53 Impact Factor
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- "This result verifies the tonotopic-specific distribution through the cell body and dendrites of CRNs and suggests that both CRNs and DCN neurons receive similar acoustic information. DCN projects to the IC (Beyerl, 1978; Oliver and Shneiderman, 1991; Oliver et al., 1999; Cant and Benson, 2003), which is known to participate in the modulation of the ASR (Leitner and Cohen, 1985; Fendt et al., 2001; Yeomans et al., 2006; Gómez-Nieto et al., 2008a, 2013). It is, therefore, likely that DCN might provide acoustic information to ASR modulation pathways rather than being necessary for the initiation and elicitation of the ASR. "
ABSTRACT: The acoustic startle reflex (ASR) is a survival mechanism of alarm, which rapidly alerts the organism to a sudden loud auditory stimulus. In rats, the primary ASR circuit encompasses three serially connected structures: cochlear root neurons (CRNs), neurons in the caudal pontine reticular nucleus (PnC), and motoneurons in the medulla and spinal cord. It is well established that both CRNs and PnC neurons receive short-latency auditory inputs to mediate the ASR. Here, we investigated the anatomical origin and functional role of these inputs using a multidisciplinary approach that combines morphological, electrophysiological and behavioural techniques. Anterograde tracer injections into the cochlea suggest that CRNs somata and dendrites receive inputs depending, respectively, on their basal or apical cochlear origin. Confocal colocalization experiments demonstrated that these cochlear inputs are immunopositive for the vesicular glutamate transporter 1. Using extracellular recordings in vivo followed by subsequent tracer injections, we investigated the response of PnC neurons after contra-, ipsi-, and bilateral acoustic stimulation and identified the source of their auditory afferents. Our results showed that the binaural firing rate of PnC neurons was higher than the monaural, exhibiting higher spike discharges with contralateral than ipsilateral acoustic stimulations. Our histological analysis confirmed the CRNs as the principal source of short-latency acoustic inputs, and indicated that other areas of the cochlear nucleus complex are not likely to innervate PnC. Behaviourally, we observed a strong reduction of ASR amplitude in monaural earplugged rats that corresponds with the binaural summation process shown in our electrophysiological findings. Our study contributes to understand better the role of neuronal mechanisms in auditory alerting behaviours and provides strong evidence that the CRNs-PnC pathway mediates fast neurotransmission and binaural summation of theFrontiers in Neuroscience 07/2014; DOI:10.3389/fnins.2014.00216 · 3.70 Impact Factor