Reflex responses of gamma motoneurones to vibration of the muscle they innervate.

Abstract

SUMMARY1. High frequency vibration was applied to the tendon of the noncontracting triceps surae muscle while recording the background discharges of single y efferents from the nerves to the gastrocnemius muscles in the decerebrate cat. For isolation of y fibres only small nerve bundles were cut, leaving most of the nerve supply to the triceps intact.2. 22 % out of a total of sixty-three y efferents were tonically inhibited by vibration. The inhibition appeared between 25 and 50 #sm peak-to-peak amplitude of vibration and increased to a plateau for amplitudes of about 100 gm. The dependence of the tonic vibration reflex of a efferents on the amplitude of vibration was found to be similar. Increasing the frequency of vibration from 150 to 300 Hz increased the degree of inhibition.3. 33 % of the fusimotor neurones investigated responded to muscle vibration with an increase in discharge rate. The threshold amplitudes of this reflex ranged from 20 to 50 /m. Some features of the reflex, in particular the parallel post-vibratory facilitation found in a and y efferents, pointed to a polysynaptic pathway organized in an c-y linkage.4. All y efferents inhibited by vibration showed inhibitory responses to antidromic stimulation of the parent ventral root, and most of them were inhibited by ramp stretch of the triceps. The y motoneurones facilitated by vibration, however, were excited by muscle stretch and were less susceptible to antidromic inhibition, some lacking it completely.5. Cutting the nerves to triceps abolished the inhibitory as well as the excitatory responses of y efferents to muscle vibration. Both fusimotor reflexes were preserved after spinal section and subsequent administration of L-DOPA. 6. It is concluded that both of the fusimotor reflex effects of vibration are caused by excitation of primary spindle endings within the triceps.

Autogenetic inhibition of extensor gamma‐motoneurones revealed by electrical stimulation of group I fibres in the cat.

“…Renshaw inhibition (Ellaway, 1971;Noth, 1971), inhibitory responses evoked by stimulation of the triceps nerve or muscle vibration may be due to Renshaw inhibition, mediated via excited x-motoneurones (Fromm & Noth, 1976). Such a contribution of Renshaw inhibition to the observed autogenetic inhibition can be ruled out if antidromic ventral root stimulation fails to provoke inhibition in units inhibited by stimulation of the homonymous muscle nerve.…”

“…The Achilles tendon was tied to the extension of the moving part of an electromagnetic puller (see Fromm & Noth, 1976), which was mounted on a heavy steel board without direct connexion to the experimental table. The puller was feed-back controlled (position and velocity) using the signal from a length transducer (Hewlett-Packard, 24 D C D T) and its first derivative.…”

On the nature of the electromyographic signals recorded during vibration exercise

“…TVR derives from the stimulation of Ia-afferents when applying a sinusoidal stimulation directly to a muscle or a tendon (Bongiovanni et al 1990;Fromm 1976;Burke et al 1976). However, TVR seems also to be modulated by alterations in spindle sensitivity through γ control (Matthews 1966;Ribot-Ciscar et al 2000).…”

Fusimotor reflexes in triceps surae elicited by natural stimulation of muscle afferents from the cat ipsilateral hind limb

“…Yet Golgi tendon organs and group III and IV afferents may also have been activated. As to primary spindle afferents it is known that they may weakly excite or inhibit unclassified homonymous y-motoneurones (Ellaway & Trott, 1978;Fromm & Noth, 1976). It is also known that muscle group II fibres, most likely secondary spindle afferents, may strongly excite y-motoneurones.…”

“…The reflex pattern seemed similar to what was already known for a-motoneurones apart from the effects of I a spindle afferents. More recently most of the work concerned with reflexes to y-motoneurones has been devoted to studies of autogenetic effects of spindle primaries on y-cells using both electrical and natural stimulation in widely denervated hind limb preparations (Ellaway, 1971; Ellaway & Trott, 1978;Fromm & Noth, 1976;Trott, 1976).…”