The role of reflex activity in the regulation of muscle tone in rats

Abstract

SUMMARYThe aim of the study was to assess the contribution of reflex activity to the regulation of muscle tone in rats. The experiment was carried out on young Wistar male and female rats. The hindfoot of a rat was flexed or extended at the ankle joint by 25 deg over 250 ms. The resistance of the foot to passive movements, as well as the electromyographic (EMG) activity in the gastrocnemius and the tibialis anterior muscles, were recorded simultaneously. During passive movements, reflex EMG activity developed simultaneously in both antagonistic muscles of the foot. Three components were distinguished: a short-latency EMG-A (within the first 0-20 ms of a movement), long-latency EMG-B (within 60-160 ms), and EMG-C (within 220-340 ms). When the amplitudes of EMG-B and EMG-C components of the gastocnemius muscle reflex response were greater than 50 ,uiV, a significant correlation was found between them and the maximum resistance of the hindfoot (MMGmaX) during flexion, whereas no such correlation was observed for the tibialis anterior muscle. No correlation was found when the amplitudes of the long-latency components of the gastrocnemius muscle were less than 50 #uV. Moreover, no correlation was observed between the EMG-A and the MMGmaX. The above results suggest that: (1) the muscle tone of the gastrocnemius muscle in rats seems to be regulated by long-latency (supraspinal) reflexes only when the level of EMG activity exceeds a critical threshold of ca 50 ,#V; (2) when the level of EMG activity is lower, a major role in the resistance of hindlimb muscles is played by some non-neuronal factors; and (3) the proposed animal model emphasizes new aspects of the reflex which may be useful in a search for basic mechanisms underlying changes in the muscle tone.

A robust role for motor cortex

“…Still, they preceded any overt behavior corrections from the animal following the perturbation, as observed in the high-speed video recordings. The onset of these evoked potentials is in the range of the long-latency stretch reflex, which has been suggested to involve a transcortical loop through the motor cortex (Phillips, 1969;Matthews et al, 1990;Capaday et al, 1991;Ossowska et al, 1996). However, the simultaneous complexity and rapidity of adaptive motor responses we observed in control animals is striking, as they appear to go beyond simple corrective responses to reach a predetermined goal and include a fast switch to entirely different investigatory or compensatory motor strategies adapted to the novel situation, similar to the behaviorally selective fast responses recently observed in mice (Miri et al, 2017).…”

L-701,324, a selective antagonist at the glycine site of the NMDA receptor, counteracts haloperidol-induced muscle rigidity in rats

“…Rats were pretreated with haloperidol (1 or 5 mg/kg IP) and injected with L-701,324 [7-chloro-4-hydroxy-3(3-phenoxy)phenylquinoline-2-(H)-one, 2.5-40 mg/kg IP] or vehicle 45 min later. The measurement commenced 15 min later and lasted 1 h. Simultaneous measurements of the muscle resistance of the rat's hind limb (MMG) and the electromyographic activity of muscles (EMG), developed in response to passive movements, were carried out as described previously (Kolasiewicz et al 1987;Wolfarth et al 1992;Lorenc-Koci et al 1996;Ossowska et al 1996a). Briefly, each rat was placed in a Metaplex cage, well ventilated and adapted to its size.…”