Connections between the cochlear nuclei in guinea pig

Department of Otolaryngology, Medical College of Ohio, Toledo, Ohio, USA
Hearing Research (Impact Factor: 2.97). 10/1992; 62(1):16-26. DOI: 10.1016/0378-5955(92)90199-W
Source: PubMed


This study provides a detailed analysis of the appearances and distributions of neurons projecting from one cochlear nucleus to the other. Injections of wheatgerm agglutinin conjugated to horseradish peroxidase were made into ventral or dorsal cochlear nucleus of the guinea pig. Retrogradely labeled cells in the opposite cochlear nucleus were examined and quantified. Three major categories of labeled cells were discerned on the basis of their soma shape: elongate, round-to-oval, and polygonal. All injections resulted in widespread labeling of cells in all of these categories, but especially round-to-oval cells, in the opposite ventral cochlear nucleus and sparse labeling in the dorsal cochlear nucleus. The results suggest that there is a significant cochlear nucleus commissural projection involving heterogeneous cell types which could have diverse functions in binaural auditory signal processing.

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    • "The longest diameter of the giant cell body ranges from 28 to 70 lm, e.g., mouse (Zhang and Oertel 1993), rat (Alibardi 1999; Malmierca 2003; Pocsai et al. 2007; Pál et al. 2009), cat (Kane et al. 1981), and primates (Heiman-Patterson and Strominger 1985). Giant cells project to the ipsi-and contralateral inferior colliculus (IC) and to the contralateral CN (e.g., Cant and Gaston 1982; Shore et al. 1992; Schofield and Cant 1996). "
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    ABSTRACT: Correct interpretation of functional data obtained from various cell types of the cochlear nucleus (CN), a structure involved in auditory information processing, necessitates reliable cell identification. Our aim was to perform a quantitative morphological characterization of giant and pyramidal cells of the rat CN and identify parameters that are suitable for their adequate classification. Neurons were labeled with biocytin, visualized with a fluorescent marker, and three-dimensionally reconstructed from confocal images. The size and shape of the soma and dendritic tree of each neuron were characterized by 17 morphometric parameters. The variables were subjected to multivariate statistical analysis to determine their importance while discriminating between giant and pyramidal cells. Our results provide a new battery of morphometric data, which could not be obtained earlier, improve the chances of correct cell identification, make modeling experiments easier and more reliable, and help us to understand both the functions of individual CN neurons and the network properties of this nucleus. In addition, we demonstrate that even partial labeling and/or incomplete reconstruction of neurons may be enough for their correct identification if selected parameters describing the cell bodies and the proximal portions of the dendritic trees are utilized. We propose that our findings have specific relevance to studies which attempt cell identification after functional experiments resulting in incomplete labeling of the investigated neurons.
    Brain Structure and Function 10/2012; 218(5). DOI:10.1007/s00429-012-0457-7 · 5.62 Impact Factor
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    • "Another potential source of contralateral excitation is the CN-commissural pathway. Although this mostly glycinergic pathway likely mediates the inhibitory contralateral responses (Needham and Paolini 2003; Shore et al. 2003), a few of the neurons constituting the CN-commissural pathway have anatomical characteristics indicative of excitatory neurotransmission (Alibardi 1998, 2000; Shore et al. 1992; Zhou et al. 2007). They also terminate in granule cell regions (Alibardi 2004; Shore and Moore 1998), increasing the likelihood of slow temporal integration, which, even in principal cells in the CN, can last 10 ms (Palmer and Winter 1996). "
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    ABSTRACT: In the normal guinea pig, contralateral sound inhibits more than a third of ventral cochlear nucleus (VCN) neurons but excites <4% of these neurons. However, unilateral conductive hearing loss (CHL) and cochlear ablation (CA) result in a major enhancement of contralateral excitation. The response properties of the contralateral excitation produced by CHL and CA are similar, suggesting similar pathways are involved for both types of hearing loss. Here we used the neurotoxin melittin to test the hypothesis that this "compensatory" contralateral excitation is mediated either by direct glutamatergic CN-commissural projections or by cholinergic neurons of the olivocochlear bundle (OCB) that send collaterals to the VCN. Unit responses were recorded from the left VCN of anesthetized, unilaterally deafened guinea pigs (CHL via ossicular disruption, or CA via mechanical destruction). Neural responses were obtained with 16-channel electrodes to enable simultaneous data collection from a large number of single- and multiunits in response to ipsi- and contralateral tone burst and noise stimuli. Lesions of each pathway had differential effects on the contralateral excitation. We conclude that contralateral excitation has a fast and a slow component. The fast excitation is likely mediated by glutamatergic neurons located in medial regions of VCN that send their commissural axons to the other CN via the dorsal/intermediate acoustic striae. The slow component is likely mediated by the OCB collateral projections to the CN. Commissural neurons that leave the CN via the trapezoid body are an additional source of fast, contralateral excitation.
    Journal of Neurophysiology 06/2009; 102(2):886-900. DOI:10.1152/jn.91003.2008 · 2.89 Impact Factor
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    • "The CN is the first site in the central auditory system where convergence of binaural information occurs. Interaction between the cochlear nuclei can take place by way of the commissural pathway (Cant and Gaston 1982; Shore et al. 1992) or by descending inputs from the superior olivary complex (SOC) and inferior colliculus (IC) (Shore et al. 1991; Spangler et al. 1987). Shore and colleagues (2003) demonstrated , in VCN of the normal hearing adult guinea pig, that contralateral sound stimulation produces inhibitory responses in approximately 30% of neurons and occasional excitatory responses. "
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    ABSTRACT: Integration of multimodal information is essential for understanding complex environments. In the auditory system, multisensory integration first occurs in the cochlear nucleus (CN), where auditory nerve and somatosensory pathways converge (Shore, 2005). A unique feature of multisensory neurons is their propensity to receive cross-modal compensation after deafening. Based on our findings that the vesicular glutamate transporters, VGLUT1 and VGLUT2, are differentially associated with auditory nerve and somatosensory inputs to the CN, respectively (Zhou et al., 2007), we examined their relative distributions after unilateral deafening. After unilateral intracochlear injections of kanamycin (1 and 2 weeks), VGLUT1 immunoreactivity (ir) in the magnocellular CN ipsilateral to the cochlear damage was significantly decreased, whereas VGLUT2-ir in regions that receive nonauditory input was significantly increased 2 weeks after deafening. The pathway-specific amplification of VGLUT2 expression in the CN suggests that, in compensatory response to deafening, the nonauditory influence on CN is significantly enhanced. One undesirable consequence of enhanced glutamatergic inputs could be the increased spontaneous rates in CN neurons that occur after hearing loss and that have been proposed as correlates of the phantom auditory sensations commonly called tinnitus.
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