title: Depression of Renshaw recurrent inhibition by activation of corticospinal fibres in human upper and lower limb.
abstract: 1. This study tested whether the recurrent inhibition of soleus and wrist flexor motoneurones could be modified by transcranial magnetic stimulation in human subjects. 2. Magnetic stimulation was given through a circular coil centred at the vertex. The intensity of the magnetic stimulus was subthreshold for evoking a motor response in the active soleus and wrist flexor muscles. The recurrent inhibition brought about by a conditioning H1 reflex discharge was estimated by a test H' reflex. The modifications of the recurrent inhibition after cortical stimulation were distinguished from the motoneuronal changes by comparing H' to a reference H reflex. 3. In the soleus motoneurones, the reference H reflex was inhibited at a minimum conditioning-test interval of -2 ms (H reflex stimulus before magnetic stimulation). In contrast, the H' reflex was facilitated at minimum conditioning-test intervals of +1 ms. In the wrist flexor motoneurones, both H' and reference H reflexes were facilitated. However, at lower cortical stimulus intensities, only the H' reflex was facilitated at minimum conditioning-test intervals of +1 ms. 4. In both motoneurone pools, H' facilitation started 3-4 ms later than the earliest changes in the reference H reflex. Also, the threshold of H' facilitation was lower than that of reference H reflex. 5. It is concluded that facilitation of the H' reflex is produced by corticospinal inhibition of Renshaw cells via a short interneuronal chain in both the upper and lower limb.
authors.affiliation: Laboratorio di Neurofisiologia, Università degli Studi di Siena, Italy.
authors.forename: R
authors.initials: R
authors.lastname: Mazzocchio
authors.forename: A
authors.initials: A
authors.lastname: Rossi
authors.forename: J C
authors.initials: JC
authors.lastname: Rothwell
mesh_terms: D000328:Adult; D001132:Arm / Q000294:innervation / Q000502:physiology*; D002540:Cerebral Cortex / Q000166:cytology / Q000502:physiology*; D004574:Electromagnetic Fields; D004594:Electrophysiology; D006181:H-Reflex / Q000502:physiology; D006801:Humans; D009046:Motor Neurons / Q000502:physiology*; D018482:Muscle, Skeletal / Q000294:innervation / Q000502:physiology; D009412:Nerve Fibers / Q000502:physiology*