- Intracellularly Labeled Fusiform Cells in Dorsal Cochlear Nucleus of the Gerbil. II. Comparison of Physiology and Anatomy


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Figure 1   Summary of position measurements.

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Figure 2   Tonotopic organization of the gerbil dorsal cochlear nucleus (DCN). A: the basal dendrites of the 17 fusiform cells from this study mapped onto a single DCN. A patch has been removed from the surface of the DCN to show the interior. Dendrites are color-coded according to best frequency (BF) as shown. D, dorsal; R, rostral; L, lateral. B: scatterplots showing BF vs. relative X-position (top) and relative Z-position (bottom). Regression line for X-position given by log(BF) = 2.38x - 0.72, r = 0.62, P < 0.01. Regression line for Z-position given by log(BF) = 1.30x - 0.26, r = 0.74, P < 0.001.

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Figure 3   Comparison of frequency-place maps for the gerbil cochlea and DCN. Place-frequency data for fusiform cells obtained by projecting soma locations onto frequency axis computed in the text. Place-frequency map for the gerbil cochlea from Müller (1996)ref-arrow.gif. Place-frequency map for the cat DCN from Spirou et al. (1993)ref-arrow.gif.

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Figure 4   Fusiform cell orientation changes with rostral-caudal position. DCN is represented by a series of coronal slices. Arrows point from soma locations to renderings of fusiform cells in a sagittal view. Thick gray lines indicate the long axis of each cell. D, dorsal; C, caudal.

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Figure 5   Spontaneous activity and basal dendrite arrangement. Neurons are from the 0- to 2-kHz region and are drawn in a parasagittal view. Apical dendrites are shown in gray; basal dendrites in black. Basal dendrites of low spontaneous rate (SR) cells (top row) are oriented primarily in the caudal direction. Those of the high SR cells (bottom row) have both rostrally and caudally directed branches. This difference is quantified using the parameter ZC, which is the rostral-caudal component of the basal arbor's centroid, measured with respect to the soma. The low SR units have larger ZC values (centroids located more caudally) than the high SR units.

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Figure 6   Relationship between input resistance and arbor length. A: input resistance is highly correlated with apical dendrite length. Regression line: y = -10.5x + 48.2, r = -0.79, P < 0.001. Triangles indicate data points omitted as outliers. B: input resistance is uncorrelated with basal dendrite length. Regression line: y = 0.6x + 16.8, r = 0.08, ns.

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Figure 7   Relationship between regularity histogram shape and orientation of apical arbor. Top: slope m1 from the regularity histogram plotted vs. the orientation of the apical arbor. The orientation phiapical is the rotation about the long axis giving the narrowest arbor profile. See text for a detailed description of how these values are measured. Regression line: y = -1.1x + 21.8, r = -0.82, P < 0.01. Data points indicated by circles, triangles, and squares represent high, middle, and low m1 values, respectively. Bottom: each group corresponds to the data points above and shows the fusiform cell apical arbors after superimposing the somata. The view is looking down on top of apical arbors, so that the long axes project out of the page. R, rostral; M, medial.

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Figure 8   Physiological properties correlated with position. Relative noise index (A) and input resistance (B) are negatively correlated with position in the X-direction. Regression line for noise index: y = -1.16 × 10-3x +1.30, r = -0.53, P < 0.05. Regression line for input resistance: y = -50.0 × 10-3x + 50.7, r = -0.67, P < 0.01. C: total apical dendritic length increases with X-position. Regression line: y = 3.01 × 10-3x + 1.17, r = 0.56, P < 0.025. Triangle indicates an outlier removed from the regression analysis.

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Figure 9   Two neighboring fusiform cells from the caudal end of the DCN. Long axes are nearly horizontal in accordance with the general rostral-caudal shift in orientation. At the top, the cells are drawn in their correct relative positions. At the bottom, they are drawn separately to show individual details clearly.

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Figure 10   Inhibitory components of a type IV unit response map. Gray, inhibition from type II units that probably correspond to vertical cells. The peak of this inhibitory area is typically below the BF of the type IV unit. Lorente de Nó (1981)ref-arrow.gif observed a decrease in the height of the vertical cell layer from ventrolateral (VL) to dorsomedial (DM). If a type IV unit draws input from a spatially symmetrical band of vertical cells, the center frequency of that band will be lower than the type IV unit BF because the verticals cells are more dense in the low-frequency direction. White, inhibition from a band of wideband inhibitors, possibly stellate cells in the posteroventral cochlear nucleus (PVCN). The peak of this inhibitory band is above the type IV unit BF. The results of this study suggest that the strength of wideband inhibition increases in the dorsomedial direction. A band of wideband inhibitors distributed symetrically in space with respect to a type IV unit will be centered higher in frequency because the wideband inhibitory strength increases in that direction.


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