Modulation of Brachioradialis Motoneuron Excitabilities by Group I Fibers of the Median Nerve in Humans

Abstract

Group I fibers from muscle spindles and Golgi tendon organs modulate motoneuron excitabilities to coordinate smooth movements. In this study, to elucidate the effects of group I fibers of the median nerve (MN) on the excitabilities of the brachioradialis (BR), we evaluated the changes in the firing probability of a BR motor unit after electrical conditioning stimulation (CS) to MN with a post-stimulus time-histogram technique in six healthy human subjects. We tested 171 motor units: in 72 of them CS to MN at the elbow with the intensity just below the threshold of alpha motor fibers (MT) produced a facilitatory effect (facilitation), while in 43 of them it produced inhibitory one (inhibition). The facilitation and inhibition were not produced by electrical stimulation of the skin overlaying MN. The central synaptic delays of the facilitation and inhibition were on average -0.13 and 0.13 msec, respectively, longer than those of the homonymous facilitation mediated by a monosynaptic path. The thresholds of the facilitation and inhibition were less than 0.7-0.8 and 0.7-0.9 times MT, respectively. CS to MN of hand muscles produced facilitatory effects and that of the pronator teres, palmaris longus, and flexor carpi radialis inhibitory effects. The facilitatory and inhibitory effects were compatible, for latency, with the facilitation and inhibition. These findings suggest that BR motoneurons receive monosynaptic facilitation and oligosynaptic inhibition from MN in humans. Group I fibers of the hand and forearm muscles should mediate the facilitation and inhibition, respectively, to coordinate movements of the hand, forearm, and elbow. median nerve; brachioradialis; monosynaptic facilitation; oligosynaptic inhibition; humans

Administration of low-dose FK 506 accelerates histomorphometric regeneration and functional outcomes after allograft nerve repair in a rat model

“…It is the regeneration and firing of myelinated nerve fibres which innervate the muscle (McNulty and Macefield, 2005;Miyasaka et al, 2007;Koob et al, 2007) that determine the walking tracks (ASA and SFI), not the total count of axons stained with different methods (Lyons et al, 1994;Archibald et al, 1995;Steuer et al, 1999;Weber et al, 2000;Arai et al, 2000;Oktay et al, 2006). Hence, for histomorphological assessment in our study, it was feasible to use polyclonal antibodies with a high affinity for marking intact MBP only (Groome et al, 1998).…”

Prefabricated nerve conduits advance histomorphological and functional outcomes in nerve regeneration of the sciatic nerve of the rat

“…It is not the total count of axons stained with different methods 2,11,17 that determines the walking tracks (ASA and SFI), but the regeneration and firing of group I nerve fibres which innervate the muscle 21,30,31 . For histomorphological assessment it was feasible to use polyclonal antibodies with a high affinity for marking the intact myelin basic protein of group I nerve fibres 12 .…”

Histomorphological and functional impacts of postoperative motor training in rats after allograft sciatic nerve transplantation under low‐dose FK 506

“…The total count of axons stained with different methods does not determine the walking tracks (ASA and SFI), but the regeneration and firing of group I nerve fibers that innervate the muscle does. 15,22,25 Hence, for histomorphological assessment in our study it was feasible to use polyclonal antibodies with a high affinity for marking only intact myelin basic protein of group I nerve fibers. 9 By using this method, blobs that could represent residual, unphagocytosed myelin were minimized, and only healthy myelin sheaths were stained.…”