Changes in reciprocal ia inhibition during voluntary contraction in man

Abstract

Reciprocal Ia inhibition from ankle flexors to extensors was studied during voluntary tonic isometric dorsiflexion and plantar flexion in five normal subjects. The Ia inhibition was examined as the short-latency suppression of the soleus H-reflexes by stimulation of the low-threshold afferents in the common peroneal nerve (Mizuno et al. 1971). At rest, weak Ia inhibition was demonstrated in four subjects out of five, the maximal amount being 14.1 +/- 5.0% suppression of the control H-reflex. The absolute amount of inhibition, which was calculated by subtracting the mean size of the conditioned H-reflex from that of the control H-reflex and expressed as a percentage of the maximal M-response, increased during ankle dorsiflexion, and decreased or disappeared during plantar flexion in parallel with the amount of contraction. The neural mechanisms for facilitation of the Ia inhibitory pathway during dorsiflexion were considered to support the hypothesis of "alpha-gamma-linkage in reciprocal inhibition", i.e. combined facilitatory effects on the Ia inhibitory interneuron from the supraspinal centers directly and indirectly via the gamma motoneuron--Ia afferent route. The mechanism for inhibition of the pathway during plantar flexion was considered to be inhibition of the Ia interneuron of the flexor side by Ia interneuron of antagonist extensors. A quantitative aspect of activity in the reciprocal Ia inhibitory pathway on the performance of voluntary movement is revealed in this study.

Reciprocal Ia inhibition between ankle flexors and extensors in man.

“…2 at rest in our subjects is thus much larger than in previously published material (Tanaka, 1974; Pierrot-Deseilligny, Morin, Bergego & Tankov, 1981;Shindo et al 1984). …”

“…A possible explanation for the absence of an increase in reciprocal inhibition (which has previously been reported: Tanaka, 1974;Shindo et al 1984) subjects, but altogether seventeen subjects out of the twenty had an increased inhibition during the dynamic dorsiflexion. The mean increase in reciprocal inhibition during dynamic dorsiflexion as compared with rest for the twenty subjects was 9-0 %.…”

“…The amount of reciprocal Ia inhibition (and thus indirectly the excitability of the interneurones which mediate it) has been estimated from the depression of a test H reflex following a conditioning group I volley in the nerve from the antagonists. By this method, reciprocal inhibition between ankle flexors and extensors has been studied (mainly inhibition of soleus motoneurones from the peroneal nerve; Mizuno, Tanaka & Yanagisawa, 1971;Tanaka, 1974; Shindo, Harayama, Kondo, Yanagisawa & Tanaka, 1984;Iles, 1986) and between wrist flexors and extensors (mainly inhibition of wrist flexors from wrist extensors; Baldissera, Campadelli & Cavallari, 1983; Day, Marsden, Obeso & Rothwell, 1984;Cavallari, Fournier, Katz, Pierrot-Deseilligny & Shindo, 1984). In most of the human studies, cited above, changes in transmission of reciprocal inhibition were studied during voluntary contraction.…”

Locomotor training improves reciprocal and nonreciprocal inhibitory control of soleus motoneurons in human spinal cord injury

“…The linear relationship between the conditioned soleus H-reflex and soleus background activity suggests that reflex actions of MG group I afferents on soleus alpha motoneurons follow the soleus background excitability pattern. However, because Ib inhibition is not affected by triceps surae contraction (Pierrot-Deseilligny et al 1982), and reciprocal inhibition is not abolished following soleus muscle voluntary contraction (Yang and Whelan 1993), although it is modulated during ankle movement (Shindo et al 1984), net changes of soleus motoneuron excitability and duration of hyperpolarization cannot account solely for the observed changes.…”

Anodal transcranial direct current stimulation of the motor cortex induces opposite modulation of reciprocal inhibition in wrist extensor and flexor

“…Lundberg (1970) proposed that these connections from the brain to corresponding ␣-motoneurons and Ia interneurons were also used in parallel during voluntary movement in order to achieve a coordinated contraction and relaxation of the antagonist muscles. Consistent with animal data, it has been shown in humans that pathways mediating reciprocal inhibition in flexor and extensor motoneurons are disynaptic, and that motoneurons and inhibitory interneurons have received similar segmental and descending control (Cavallari et al 1984;Cowan et al 1986;Day et al 1984;Rothwell et al 1984;Shindo et al 1984). At the level of the elbow and ankle, extensor and flexor muscles operate as real antagonists, so interneurons relaying reciprocal inhibition to flexor and extensor motoneurons are identified as Ia inhibitory interneurons.…”