Koseki, T. | Search bioRxiv

bioRxiv2025

Intensity-dependent corticospinal facilitation by repetitive peripheral magnetic stimulation: Evidence for a major contribution of group I afferents

BackgroundRepetitive peripheral magnetic stimulation (PMS) is increasingly used in neurorehabilitation, yet the optimal stimulation intensity for inducing corticospinal facilitation and the underlying afferent mechanisms remain unclear. We investigated the intensity-dependent effects of repetitive PMS on corticospinal excitability and single motor unit responses, and tested group I afferent contribution. MethodsHealthy participants received repetitive PMS (25 Hz; 2-s ON/2-s OFF) over the extensor carpi radialis (ECR) in a crossover design at 0.9x motor threshold (MT), 1.2xMT, and high intensity sufficient to induce maximal wrist dorsiflexion (mean 1.8xMT). Motor-evoked potentials (MEPs) elicited by transcranial magnetic stimulation were recorded from the ECR and flexor carpi radialis (FCR) before and during the intervention (total 15 min). The lasting effects were assessed after 9 min of high-intensity PMS for 50 min. To examine group I afferent contribution, the same high-intensity protocol was applied during upper-arm ischemia after reducing the ECR H-reflex to <10% of baseline. Sensory-motor input characteristics across stimulation intensities were compared using post-stimulus time histograms of ECR single motor unit firings during weak voluntary contraction. ResultsHigh-intensity PMS significantly increased ECR MEPs after 9 min of intervention, whereas 1.2xMT of PMS required 15 min to induce a marked effect. PMS at 0.9xMT did not induce significant MEP changes. Across all intensities, the FCR MEPs remained unaltered. ECR MEPs remained markedly elevated for up to 30 min after 9 min of high-intensity PMS. In contrast, PMS delivered during ischemia produced no MEP enhancement. The motor unit analysis revealed that suprathreshold PMS elicited an early peak in firing probability--consistent with monosynaptic Ia excitation--whose amplitude increased with stimulation intensity, whereas PMS at 0.9xMT produced no discernible peak. ConclusionsRepetitive PMS above MT facilitates corticospinal excitability in an intensity-dependent manner. Facilitation was abolished during ischemia. Together with the presence of a short-latency peak in motor unit firing via a monosynaptic pathway, this finding supports a major contribution of large-diameter muscle afferents, with a substantial Ia component, to PMS-induced corticospinal facilitation.

neuroscience↗

bioRxiv2024

Identification and structural characterization of a novel acetyl xylan esterase from Aspergillus oryzae

Acetyl xylan esterase plays a crucial role in the degradation of xylan, the major plant hemicellulose, by liberating acetic acid from the backbone polysaccharides. Acetyl xylan esterase B from Aspergillus oryzae, designated AoAXEB, was biochemically and structurally investigated. The AoAXEB-encoding gene with a native signal peptide was successfully expressed in Pichia pastoris as an active extracellular protein. The purified recombinant protein had pH and temperature optima of 8.0 and 30 {degrees}C, respectively, and was stable up to 35{degrees}C. The optimal substrate for hydrolysis by purified recombinant AoAXEB among a panel of -naphthyl esters was -naphthyl acetate. Recombinant AoAXEB catalyzes the release of acetic acid from wheat arabinoxylan. The release of acetic acid from wheat arabinoxylan increases synergistically with xylanase addition. No activity was detected using the methyl esters of ferulic, p-coumaric, caffeic, or sinapic acids. The crystal structures of AoAXEB in the apo and succinate complexes were determined at resolutions of 1.75 and 1.90 [A], respectively. Although AoAXEB has been classified in the Esterase_phb family in the ESTerases and alpha/beta-Hydrolase Enzymes and Relatives (ESTHER) database, its structural features partly resemble those of ferulic acid esterase in the FaeC family. Phylogenetic analysis also indicated that AoAXEB is located between the clades of the two families. Docking analysis provided a plausible binding mode for xylotriose substrates acetylated at the 2- or 3-hydroxy position. This study expands the repertoire of side chain-degrading enzymes required for complete plant biomass degradation.

biochemistry↗