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The Journal of Neuroscience, July 15, 1999, 19(14):6058-6067
Loss of Distal Axons and Sensory Merkel Cells and Features
Indicative of Muscle Denervation in Hindlimbs of P0-Deficient Mice
Regula
Frei1, 3,
Sandra
Mötzing1,
Ilka
Kinkelin2,
Melitta
Schachner4,
Martin
Koltzenburg1, and
Rudolf
Martini1, 3
Departments of 1 Neurology and
2 Dermatology, University of Würzburg, D-97080
Würzburg, Germany, 3 Department of Neurobiology,
Swiss Federal Institute of Technology, CH-8093 Zürich,
Switzerland, and 4 Zentrum für Molekulare
Neurobiologie, University of Hamburg, D-20246 Hamburg, Germany
Mice lacking the major Schwann cell myelin component P0 show a
severe dysmyelination with pathological features reminiscent of the
Déjérine-Sottas syndrome in humans. Previous morphological and electrophysiological studies on these mice did not only demonstrate a compromised myelination and myelin maintenance, but were suggestive of an impairment of axons as well. Here, we studied the axonal pathology in P0-deficient mice by quantitative electron microscopy. In
addition, we investigated epidermal receptor end organs by immunocytochemistry and muscle pathology by histochemistry.
In proximal sections of facial and femoral nerves, axon calibers were
significantly reduced, whereas the number of myelin-competent axons was
not diminished in 5- and 17-month-old P0-deficient mice. However, in
distal branches of the femoral and sciatic nerve (digital nerves
innervating the skin of the first toe) the numbers of myelin-competent axons were reduced by 70% in 6-month-old P0-deficient mice.
Immunolabeling of foot pads revealed a corresponding loss of Merkel
cells by 75%, suggesting that survival of these cells is dependent on
the presence or maintenance of their innervating myelinated axons. In
addition, quadriceps and gastrocnemius muscles showed pathological features indicative of denervation and axonal sprouting. These findings
demonstrate that loss of an important myelin component can initiate
degenerative mechanisms not only in the Schwann cell but also in the
distal portions of myelinated axons, leading to the degeneration of
specialized receptor end organs and impairment of muscle innervation.
Key words:
hereditary neuropathies; animal models; axonopathy; axonal degeneration; Schwann cell; myelin
Copyright © 1999 Society for Neuroscience 0270-6474/99/19146058-10$05.00/0
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