Number and distribution of stapedius motoneurons in cats

Authors

  • Michael P. Joseph,

    Corresponding author
    1. Eaton-Peabody Laboratory of Auditory Physiology and Department of Otolaryngology, Massachusetts Eye and Ear Infirmary, Boston, Massachusetts 02114
    2. Departments of Otolaryngology, Harvard Medical School, Boston, Massachusetts 02215
    • Eaton-Peabody Laboratory, Mass. Eye and Ear Infirmary, 243 Charles Street, Boston, MA 02114.
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  • John J. Guinan Jr.,

    1. Eaton-Peabody Laboratory of Auditory Physiology and Department of Otolaryngology, Massachusetts Eye and Ear Infirmary, Boston, Massachusetts 02114
    2. Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139
    3. Department of Electrical Engineering & Computer Science, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139
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  • Barbara C. Fullerton,

    1. Eaton-Peabody Laboratory of Auditory Physiology and Department of Otolaryngology, Massachusetts Eye and Ear Infirmary, Boston, Massachusetts 02114
    2. Departments of Anatomy, Harvard Medical School, Boston, Massachusetts 02215
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  • Barbara E. Norris,

    1. Eaton-Peabody Laboratory of Auditory Physiology and Department of Otolaryngology, Massachusetts Eye and Ear Infirmary, Boston, Massachusetts 02114
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  • Nelson Y. S. Kiang

    1. Eaton-Peabody Laboratory of Auditory Physiology and Department of Otolaryngology, Massachusetts Eye and Ear Infirmary, Boston, Massachusetts 02114
    2. Departments of Otolaryngology, Harvard Medical School, Boston, Massachusetts 02215
    3. Departments of Physiology, Harvard Medical School, Boston, Massachusetts 02215
    4. Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139
    5. Department of Electrical Engineering & Computer Science, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139
    6. Whitaker College, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139
    7. Department of Psychology, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139
    8. Neurology Service, Massachusetts General Hospital, Boston, Massachusetts 02114
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Abstract

Cell bodies of stapedius motoneurons were identified by retrograde transport of horseradish peroxidase (HRP) following injections into the stapedius muscle. Large injections were made in an attempt to label all stapedius motoneurons. To control for labeling of non-stapedial neurons resulting from spread of HRP, we determined the locations of brainstem neurons labeled by HRP applied to the facial nerve, the chorda tympani nerve, the auricular branch of the vagus nerve, the tensor tympani muscle, and the cochlea. In three cats analyzed in detail, 1,133–1,178 neurons projecting to the stapedius muscle were identified. Arguments are given which suggest that in these three cats all stapedius motoneurons were labeled. The labeled stapedius neurons may all be motoneurons because they all stain positively for acetylcholinesterase and have medium–coarse Nissl bodies. Most stapedius motoneurons were located around the motor nucleus of the facial nerve. Stapedius motoneurons were also found near the descending limb of the facial-nerve root, in the peri-olivary neuropil, and in the reticular formation with the ascending fibers of the facial-nerve root.

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