Functional sparing of intrafusal muscle fibers in muscular dystrophies.
In a previous study, we showed that patients with muscular dystrophies (MDs) perceive passive movements, experience sensations of illusory movement induced by muscle tendon vibration, and have proprioceptive-regulated sways in response to vibratory stimulation applied to the neck and ankle muscle tendons. These findings argue for preserved proprioceptive functions of muscle spindles. However, it is unclear whether the function of intrafusal muscle fibers is spared, i.e., whether they retain their ability to contract when submitted to a fusimotor drive. To answer this question, we analyzed the effects of reinforcement maneuvers (mental computation and the Jendrassik maneuver) that are known to increase muscle spindle sensitivity via fusimotor drive in healthy subjects. Nine patients with different MDs participated in the study. Reinforcement maneuvers increased both the mean amplitude of the Achilles tendon reflex (187 +/- 52.9% of the mean control amplitude) and the sensitivity of muscle spindle afferents to imposed movements of the ankle. The same reinforcement maneuvers failed to alter the amplitude of the Hoffmann reflex in the triceps surae muscle. These results suggest that the intrafusal muscle fibers preserve their contractile abilities in slowly progressive MDs. The reasons for a differential impairment of intrafusal and extrafusal muscle fibers and the clinical implications of the present results are discussed.
Aimonetti
Jean-Marc
JM
Laboratoire de Neurobiologie Humaine, UMR 6149, Université de Provence-CNRS, Pôle 3C Case B, Centre de Saint-Charles 3, Place Victor Hugo, 13331 Marseille, France. aimon@up.univ-mrs.fr
Ribot-Ciscar
Edith
E
Rossi-Durand
Christiane
C
Attarian
Shahram
S
Pouget
Jean
J
Roll
Jean-Pierre
JP
D000125:Achilles Tendon / Q000294:innervation / Q000502:physiology; D000328:Adult; D004576:Electromyography; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009119:Muscle Contraction / Q000502:physiology; D018485:Muscle Fibers, Skeletal / Q000166:cytology / Q000502:physiology*; D009470:Muscle Spindles / Q000502:physiology*; D018482:Muscle, Skeletal / Q000166:cytology / Q000294:innervation / Q000502:physiology*; D009136:Muscular Dystrophies / Q000473:pathology* / Q000503:physiopathology*; D011434:Proprioception; D012026:Reflex, Stretch / Q000502:physiology; D014732:Vibration