TY - JOUR
T1 - Endbulbs of held and spherical bushy cells in cats
T2 - Morphological correlates with physiological properties
AU - Sento, Seishiro
AU - Ryugo, David K.
PY - 1989/2/22
Y1 - 1989/2/22
N2 - Single auditory nerve fibers of type I spiral ganglion cells in cats were electrophysiologically characterized by recording with micropipettes inserted into the axon and then labeled by intracellular injections of horseradish peroxidase (HRP) through the same pipettes. This method for staining and studying single neurons allowed us to describe structure‐function relationships for labeled endbulbs of Held and the somata of their postsynaptic spherical bushy cells. The silhouette areas of terminal endbulbs and the corresponding somata of spherical bushy cells were determined by planimetry from drawings made with a light microscope and drawing tube. On the presynaptic side, endbulb area is related to fiber characteristic frequency (CF, the frequency to which a fiber is most sensitive) such that the largest endbulbs arise from fibers having CFs between 1 and 4 kHz; smaller endbulbs can arise from fibers of any CF. Endbulb area is not correlated with fiber spontaneous discharge rate (SR). Dividing the endbulb's silhouette area by its silhouette perimeter, however, yields a “form factor” that is a reliable indicator of fiber SR: Endbulbs from fibers of low‐medium SR (≤18 spikes/second) have form factor values less than 0.52, whereas endbulbs of high SR fibers (>18 spikes/second) have values greater than 0.52. This form factor should therefore be predictive of SR groupings in auditory fibers for which physiological data are not available. On the postsynaptic side, the somata of spherical bushy cells receiving endbulbs from low‐medium SR fibers are on average smaller than those receiving endbulbs from high SR fibers. In contrast, the nuclei of the spherical bushy cells are the same size regardless of presynaptic fiber SR. Some of the effects of low‐medium SR fibers on their postsynaptic targets, when compared to those of high SR fibers, appear to be mimicked by effects of experimentally induced deprivation.
AB - Single auditory nerve fibers of type I spiral ganglion cells in cats were electrophysiologically characterized by recording with micropipettes inserted into the axon and then labeled by intracellular injections of horseradish peroxidase (HRP) through the same pipettes. This method for staining and studying single neurons allowed us to describe structure‐function relationships for labeled endbulbs of Held and the somata of their postsynaptic spherical bushy cells. The silhouette areas of terminal endbulbs and the corresponding somata of spherical bushy cells were determined by planimetry from drawings made with a light microscope and drawing tube. On the presynaptic side, endbulb area is related to fiber characteristic frequency (CF, the frequency to which a fiber is most sensitive) such that the largest endbulbs arise from fibers having CFs between 1 and 4 kHz; smaller endbulbs can arise from fibers of any CF. Endbulb area is not correlated with fiber spontaneous discharge rate (SR). Dividing the endbulb's silhouette area by its silhouette perimeter, however, yields a “form factor” that is a reliable indicator of fiber SR: Endbulbs from fibers of low‐medium SR (≤18 spikes/second) have form factor values less than 0.52, whereas endbulbs of high SR fibers (>18 spikes/second) have values greater than 0.52. This form factor should therefore be predictive of SR groupings in auditory fibers for which physiological data are not available. On the postsynaptic side, the somata of spherical bushy cells receiving endbulbs from low‐medium SR fibers are on average smaller than those receiving endbulbs from high SR fibers. In contrast, the nuclei of the spherical bushy cells are the same size regardless of presynaptic fiber SR. Some of the effects of low‐medium SR fibers on their postsynaptic targets, when compared to those of high SR fibers, appear to be mimicked by effects of experimentally induced deprivation.
KW - auditory nerve
KW - cochlear nucleus
KW - hearing
KW - horseradish peroxidase
KW - primary afferents
KW - spontaneous activity
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U2 - 10.1002/cne.902800406
DO - 10.1002/cne.902800406
M3 - Article
C2 - 2708566
AN - SCOPUS:0024538838
SN - 0021-9967
VL - 280
SP - 553
EP - 562
JO - Journal of Comparative Neurology
JF - Journal of Comparative Neurology
IS - 4
ER -