Effects in feline gastrocnemius-soleus motoneurones induced by muscle fatigue

Abstract

Responses of gastrocnemius-soleus (G-S) motoneurones to stretches of the homonymous muscles were recorded intracellularly in decerebrate cats before, during and after fatiguing stimulation (FST) of G-S muscles. Ventral roots (VR) L7 and S1 were cut, and FST was applied to VR S1, a single FST session including 4 to 5 repetitions of 12-s periods of regular 40 s(-1) stimulation. Muscle stretches consisted of several phases of slow sinusoidal shortening-lengthening cycles and intermediate constant lengths. The maximal stretch of the muscles was 8.8 mm above the rest length. Effects of FST on excitatory postsynaptic potentials (EPSPs) and spikes evoked by the muscle stretches were studied in 12 motoneurones from ten experiments. Stretch-evoked EPSPs and firing were predominantly suppressed after FST, with the exception of a post-contraction increase of the first EPSP after FST, which was most likely due to after-effects in the activity of muscle spindle afferents. The post-fatigue suppression of EPSPs and spike activity was followed by restoration within 60-100 s. Additional bouts of FST augmented the intensity of post-fatigue suppression of EPSPs, with the spike activity sometimes disappearing completely. FST itself elicited EPSPs at latencies suggesting activation of muscle spindle group Ia afferents via stimulation of beta-fibres. The suppression of the stretch-evoked responses most likely resulted from fatigue-evoked activity of group III and IV muscle afferents. Presynaptic inhibition could be one of the mechanisms involved, but homosynaptic depression in the FST-activated group Ia afferents may also have contributed.

Subthreshold activation of spinal motoneurones in the stretch reflex: experimental data and modeling

“…In earlier studies (Kouchtir et al 1995;Perrier et al 2000;Brizzi et al 2002;Kostyukov et al 2005) the stretch-or contraction-evoked PSPs in the spinal motoneurones were analyzed mostly qualitatively, in this study we attempted to develop quantitative approaches that could provide additional information about the naturally evoked EPSPs and their summation at the motoneuronal membrane. Slow muscle stretch evokes a great number of "miniature" EPSPs (Burke 1967); summation of the potentials leads to a steady-state membrane depolarization.…”

“…The main results in this field are connected with analysis of both the spike activity during artificial depolarization of the cell's membrane and the postsynaptic effects evoked by stimulation of different neural structures. Intrasomatic record from motoneurones during their natural synaptic activation presents a more difficult experimental task, although some progress in this direction is associated with recent studies with microelectrode recording from the spinal motoneurones during muscle contractions or stretches of the muscles that they innervate (Brizzi et al 2002;Kostyukov et al 2005). Controlled muscle stretches allow to model different patterns of natural activation of the motoneurones and to explore summation of a great number of EPSPs.…”

“…Natural activation of motoneurones during stretch reflex can provide a useful experimental model to study summation of a great number of postsynaptic potentials arising at different places at the cell's membrane. It is known that precise repeatability of the muscle stretches in decerebrate preparation provides stable patterns of the muscle afferent firing and, as a result, these repeated stretches can evoke highly reproducible temporal changes of the MP in spinal motoneurones (Kostyukov et al 2005). Using this experimental paradigm, it is possible to distinguish separate EPSPs of different amplitude in subthreshold range of the stretch-evoked depolarization of the cell's membrane.…”

Modulation of homosynaptic depression during voluntary contraction and muscle fatigue with different test reflex size

“…Many previous studies showed that supraspinal and spinal neural mechanisms account for the development of muscle fatigue 16,22,[24][25][26][27][28][29][30] . Decreases in descending inputs, Ia inputs from muscle spindles, and inhibitory inputs from group III and IV fibers to the MN *Correspondence: komiyama@faculty.chiba-u.jp during muscular fatigue have been proposed as potential mechanisms responsible for reducing MN excitability 22,[26][27][28]31) .…”

Lead Poisoning of Waterfowl as Indicators of Water Pollution by Heavy Metals

“…For this purpose, an academic community places greater emphasis on issues dealing with the personality traits of the cerebral processes guaranteeing the manipulation movements (MM) motorial programming. Various aspects of the abovementioned problem were studied in the area of neurophysiology of motor activities (Vasilenko, 2013;Kostykov et al, 2005; Horkovenko 2006; Kurhanskyy, Hryhal, 2010;Morenko et al, 2013;Morenko, 2014).…”