Rescue of motoneurones by MK-801 innervating partially denervated rat muscles |
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Authors: | F Ty? G Vrbová |
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Institution: | Department of Anatomy and Developmental Biology, Centre for Neuroscience, UCL, Gower Street, London WC1E 6BT, UK. tyc@univ-littoral.fr |
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Abstract: | Partial denervation of the extensor digitorum longus muscle by cutting the L4 spinal nerve in 3-day-old rats causes some
of the remaining uninjured motoneurones to die. A previous study has shown that of the 12 motor units usually present in the
remaining uninjured L5 spinal nerve, a significantly smaller number of motor units to extensor digitorum longus muscle is
found in animals operated on at 3 days. This reduction can be caused by a greater sensitivity of neonatal motoneurones with
axons in a partially denervated muscle, to excitotoxic effects of glutamate. Therefore an N-methyl-D-aspartic acid (NMDA) receptor antagonist, MK-801, was injected daily for 12 days after partial denervation at 3 days. Two
months after the operation contractile properties, motor unit numbers and sizes were studied. Following MK-801 treatment,
the reduction in muscle weight and force output of the partially denervated muscle was less than that in the untreated group.
Moreover there were more motor units in MK-801 treated animals. After partial denervation only, 15% of the total number of
motor units was present whereas when the same operation was followed by treatment with MK-801, 29% remained. The mean motor
unit size in the untreated group was 69% while after treatment with MK-801 it was 152% of the control. Thus treatment with
MK-801 after partial denervation of neonatal animals rescued some of the motoneurones destined to die, and allowed expansion
of motor unit territory of most of the surviving motoneurones.
Electronic Publication |
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Keywords: | Partial denervation EDL Motor unit NMDA Excitotoxicity |
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