Effects of reciprocal inhibition and whole‐body relaxation on persistent inward currents estimated by two different methods

Abstract

support-information-section).Ricardo Mesquita has completed an undergraduate degree in Sports Science (Faculdade de Motricidade Humana, Portugal), a master's degree in Biology of Physical Activity (University of Jyväskylä, Finland), and the work described herein is part of his PhD in Exercise Science (Edith Cowan University, Australia). Ricardo's PhD has focused on alpha motoneurons -nerve cells in the spinal cord that innervate muscle fibres to produce muscle contractions. With a background in human physiology and neuromuscular control, Ricardo aims to better understand human motor commands and disseminate research findings that can ultimately be used to improve muscle control in healthy and clinical populations.

Motor unit dysregulation following 15 days of unilateral lower limb immobilisation

“…Although difficult to quantify in vivo , it is possible monoamine levels decrease in response to reduced activity, yet it is unclear how this would influence the immobilised limb only. PIC amplitudes are also sensitive to inhibition (Hyngstrom et al ., 2007; Mesquita et al ., 2022), and recent RNAseq data highlight increased ligand-receptor interactions between muscle and dorsal root ganglion neurons following disuse, suggestive of an increased nociceptor sensitivity and susceptibility to pain (McFarland et al ., 2022). As such, it is possible increased inhibition occurred in the immobilised limb only and suppressed PIC amplitudes and MU FR, similar to that believed to explain decreased FR following knee joint trauma (Nuccio et al ., 2021).…”

Antagonist tendon vibration dampens estimates of persistent inward currents in motor units of the human lower limb

“…The capabilities of reciprocal Ia input to dampen the magnitude of PICs in humans, however, has not been extensively tested. Mesquita and colleagues (2022) very recently showed that electrical stimulation to the common peroneal nerve at low frequencies reduces estimates of PICs in the human gastrocnemius, but the inverse was not tested (i.e. tibial nerve stimulation effects on dorsiflexor PICs).…”

Persistent inward currents in spinal motoneurones: how can we study them in human participants?

“…The results in Mesquita et al. (2022) build upon observations in animal models showing that dendritic PICs can be markedly reduced by intraspinal inhibitory circuits. Further, results indicate that the level of neuromodulatory drive to the spinal cord, when manipulated, can alter the intrinsic properties of human motoneurones.…”

“…Larger amplitude PICs are especially problematic after spinal cord injury as inhibitory inputs are weaker and less able to attenuate PICs. Findings in Mesquita et al (2022) showing that reciprocal inhibition reduces estimates of PICs in human motoneurones provide the rationale for the development of antagonist nerve stimulation therapies to combat excessive PIC amplitudes and spasticity after spinal injury. While monoamine receptor inverse agonists such as cyproheptadine and/or γ -aminobutyric acid receptor agonists like baclofen reduce spasticity after spinal cord injury, antagonist nerve stimulation is a non-pharmacological approach to attenuate PICs and is hence unlikely to induce side effects associated with medication use.…”

“…In a recent publication in The Journal of Physiology , Mesquita et al. (2022) investigated the inhibitory and neuromodulatory control of PIC activity in healthy participants using non‐pharmacological interventions. Two methods were used to study PIC activity in human motoneurones.…”