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Spasticity is a disabling complication of spinal cord injury or stroke. Spasticity is deﬁned as a symptom of the upper motor neuron syndrome characterized by an exaggeration of the stretch reﬂex secondary to hyperexcitability of spinal reﬂexes. In this condition, the muscles are stiﬀ or rigid, which interfere with walking, movement or speech.
The H wave amplitude is attenuated by repeated activations at frequencies higher than 0.2 Hz, with a maximum reduction at 5 Hz in intact rats. The RDD is progressively reduced in individuals with SCI, and this effect is a reliable correlate of the development of the spasticity.
When the tibial nerve is stimulated in acutely injured rats, a little reflex is evoked in the FDB muscle EMG recordings, regardless of the stimulation current intensity. In contrast, stimulation of the tibial nerve in chronic spinal rats produced more long-lasting muscle contractions. This effect is a reliable correlate of the development of the spasticity.
The mean relative amplitudes of the H-reflex were significantly reduced (Kruskal-Wallis, Dunn's post-test) in baclofen-injected SCI rats (n=10) compared with vehicle-injected SCI rats (n=10). After a single I.V. administration, baclofen has an onset of action of 6 min, a maximum effect of 46 min (P < 0.05 at 1 Hz, P < 0.01 at 2 – 5 Hz) and a duration of action of at least 86 min.
Doctor Fréderic Brocard - Team Leader, Neuroscience Institute of la Timone (Marseille - France). Frédéric runs a team which explores the plasticity of rhythmic motor networks both during development and in pathological conditions. He is a scientific consultant for NSrepair and reviews our studies.