Excitability of Spinal Inhibitory Circuits in Patients with Spasticity

Abstract

The excitability of Ia inhibition and D1 inhibition after stimulation of the common peroneal nerve to the soleus motoneuron pool was investigated in 37 spastic patients at rest and onset of voluntary ankle dorsiflexion. Ia inhibition was determined as the short-latency depression of the soleus H-reflex and D1 inhibition as the long-latency depression. There was no significant difference in Ia inhibition between the paraplegic and control groups, however Ia inhibition in the hemiplegic group was significantly decreased. D1 inhibition was reduced in the paraplegic and hemiplegic groups compared with controls. Although inhibition of the soleus H-reflex appeared at the onset of voluntary dorsiflexion in control subjects, it was not observed in the patients. Although the excitability of the Ia inhibitory pathway at rest in the patients did not differ from that in control subjects, facilitation of the Ia inhibitory pathway at the onset of movement was decreased in the patients. Ia inhibition and D1 inhibition were evaluated in two paraplegic patients who were treated with local anesthesia and surgery, respectively. The excitability of both inhibitory pathways at rest was unchanged despite improvement of reciprocal movement in one patient, and was enhanced despite reduction in muscle strength in the other patient. The excitability of spinal inhibitory pathways at rest was not always reflected by motor function in spastic patients.

Stimulus Point Distribution in Deep or Superficial Peroneal Nerve for Treatment of Ankle Spasticity

“…We found that the Sol H‐reflex was suppressed by deep peroneal nerve stimulation at C‐T stimulus intervals between 1.0 and 3.0 msec. This finding was consistent with previous studies (3,5,6,11). The timing of short‐latency inhibition was comparable with disynaptic Ia inhibition.…”

Long-Term Plasticity in Reflex Excitability Induced by Five Weeks of Arm and Leg Cycling Training after Stroke

“…Modulation of Ia PSI by rhythmic activity in cervical spinal cord oscillators is an important mechanism for reflex modulation in the legs in response to arm cycling [3,22]. This mechanism appears partially preserved after stroke [34,35], although participants with stroke have difficulty in modulating the excitability of inhibitory pathways in different motor tasks [76,77,78]. However, given the involvement of the fusimotor system on excitability in the stretch reflex pathway [79,80], changes in gamma bias related to changes in supraspinal regulation could also have contributed to changes in MA SOL stretch reflex excitability.…”

D1 and D2 Inhibitions of the Soleus H-Reflex Are Differentially Modulated during Plantarflexion Force and Position Tasks

“…A malfunction in some spinal pathways responsible for controlling the excitability of the stretch reflex has been associated with the development of spasticity in conditions such as following stroke and spinal cord injury. For instance, reduced PSI of Ia terminals [ 64 – 67 ] has been reported for these patients as compared to healthy controls. As weak steady contractions of spastic muscles may be used in the early stages of rehabilitation programs designed to recover/maintain function in these patients, the results of the present study suggest that it would be preferable to use protocols relying on isometric (FTs) rather than on anisometric (PTs) contractions, so as to favor recovery of lost spinal inhibition (specifically PSI) by training contractions under higher excitability of the primary afferent depolarization interneurons mediating PSI of Ia afferents.…”