Effects of Hypodynamia-Hypokinesia on the Muscle Spindle Discharges of Rat Soleus Muscle

1 Laboratoire de Plasticité Neuromusculaire, EA 1032, IFR 118, Bât. SN4, Université des Sciences et Technologies de Lille 1, F-59655 Villeneuve d'Ascq Cedex; and 2 Faculté des Sciences du Sport et de l'Education Physique, Laboratoire Commandes Motrices et Analyse du Mouvement, Université B...

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Published in:Journal of neurophysiology 2003-06, Vol.89 (6), p.3000-3007
Main Authors: De-Doncker, Laurent, Picquet, Florence, Petit, Julien, Falempin, Maurice
Format: Article
Language:English
Subjects:
Animals
Hypokinesia
Laminectomy
Male
Muscle Spindles - physiology
Muscle, Skeletal - physiology
Nerve Fibers - physiology
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Rats
Rats, Wistar
Space life sciences
Spinal Nerve Roots - physiology
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Summary:1 Laboratoire de Plasticité Neuromusculaire, EA 1032, IFR 118, Bât. SN4, Université des Sciences et Technologies de Lille 1, F-59655 Villeneuve d'Ascq Cedex; and 2 Faculté des Sciences du Sport et de l'Education Physique, Laboratoire Commandes Motrices et Analyse du Mouvement, Université Bordeaux 2, Domaine Universitaire, F-33607 Pessac Cedex, France Submitted 1 October 2002; accepted in final form 2 February 2003 The aim of this study was to determine whether Ia and II fiber discharges of soleus muscle spindles were modified after a 14-day period of hypodynamia (absence of weight bearing) and hypokinesia (reduction of motor activity). Fifty-one and 38 afferent fibers were studied, respectively, in control and hypodynamia-hypokinesia (HH) groups. Under deep anesthesia (pentobarbital, 30 mg/kg), a L 3 –L 6 laminectomy was performed. Unitary potentials from the L 5 dorsal root were recorded in response to ramp-and-hold stretches applied at two stretch amplitudes (3 and 4 mm) and four stretch velocities (6, 10, 15, and 30 mm/s) and to sinusoidal stretches applied at four stretch amplitudes (0.12, 0.25, 0.5, and 1 mm) and six stretch frequencies (0.5, 1, 2, 3, 6, and 10 Hz). In both animal groups, the Ia fibers showed higher dynamic index values, smaller linear range, and higher vibration sensitivity than the II fibers. They also exhibited a pause in their discharges during the stretch release contrary to II fibers, which displayed no pause in their responses. After HH, our results showed that for both fiber types all parameters measured under ramp-and-hold stretches (except the static sensitivity) were significantly increased and under sinusoidal stretches, the vibration sensitivity increased, and the response amplitude only increased at 0.12-mm stretch amplitude. The linear range of Ia afferents was limited to 0.12 mm, whereas it was unchanged for the II fibers. After HH, the stretches could be better transmitted to the muscle spindles, probably resulting from changes in passive mechanical properties of the soleus. Address for reprint requests: L. De-Doncker, Laboratoire de Plasticité Neuromusculaire, Bât. SN4, Université des Sciences et Technologies de Lille 1, F-59655 Villeneuve d'Ascq Cedex, France (E-mail: neuromus{at}univ-lille.fr ).
ISSN:0022-3077
1522-1598
DOI:10.1152/jn.00875.2002