Monosynaptic reflex

Piezo2 transmembrane excitatory mechanosensitive ion channels were identified as the principal mechanotransduction channels for proprioception. Recently, it was postulated that Piezo2 channels could be acutely microdamaged on an autologous basis at proprioceptive Type Ia terminals in a cognitive demand-induced acute stress response time window when unaccustomed or strenuous eccentric contractions are executed. One consequence of this proposed transient Piezo2 microinjury could be a VGLUT1/Ia synaptic disconnection on motoneurons, as we can learn from platinum-analogue chemotherapy...

BACKGROUND: Sometimes it is necessary to use sedatives or even general anaesthetics to examine animals with spinal cord injuries. These drugs may affect spinal reflexes, alter the outcome of neurological examinations, and make it difficult to diagnose location of the lesion. OBJECTIVES: The aim of this study was to evaluate the effects of five pre-anaesthetic and anaesthetic agents commonly used in clinics on spinal reflexes in dogs. METHODS: Ten native adult dogs were participated in three groups...

Sensory input converging on the spinal cord contributes to the control of movement. Although sensory pathways reorganize following spinal cord injury (SCI), the extent to which sensory input from Ia afferents is regulated during voluntary contraction after the injury remains largely unknown. To address this question, the soleus H-reflex and conditioning of the H-reflex by stimulating homonymous [depression of the soleus H-reflex evoked by common peroneal nerve (CPN) stimulation, D1 inhibition] and heteronymous (d), [monosynaptic Ia facilitation of the soleus H-reflex evoked by femoral nerve stimulation (FN facilitation)] nerves were tested at rest, and during tonic voluntary contraction in humans with and without chronic incomplete SCI...

The projection pattern of low-threshold afferents from the extensor carpi radialis (ECR) to motoneurons supplying intrinsic hand muscles was investigated using the post-stimulus time-histogram (PSTH) and electromyogram-averaging (EMG-A) methods. Electrical conditioning stimulation was applied to the radial nerve branch innervating the ECR. In the PSTH study, changes in the firing probability of single motor units following the stimulation were examined. An early and significant peak (facilitation) was induced in the motoneurons innervating the muscles, but the facilitation was induced infrequently...

Wrist position is known to affect the grip strength. We focused on the spinal reflex arc, which would support the movement, and investigated the effects of low-threshold afferents from the extensor carpi radialis (ECR) on the excitability of the flexor digitorum superficialis (FDS) motoneurons using the post-stimulus time-histogram (PSTH) and electromyogram-averaging (EMG-A) methods. Electrical conditioning stimulation of an intensity below the motor threshold was applied to the radial nerve branch innervating the ECR...

Spontaneous interneuron activity plays a critical role in developing neuronal networks. Discharges conducted antidromically along the dorsal root (DR) precede those from the ventral root's (VR) motoneurons. This work studied whether spinal interneurons project axons into the neonate's dorsal roots. Experiments were carried out in postnatal Swiss-Webster mice. We utilized a staining technique and found that interneurons in the spinal cord's dorsal horn send axons through the dorsal roots. In vitro electrophysiological recordings showed antidromic action potentials (dorsal root reflex; DRR) produced by depolarizing the primary afferent terminals...

This chapter summarizes the main neurophysiological characteristics of tonic immobility (TI), in many susceptible species of mammals and birds. During TI, cortical EEG shows high voltage slow waves whose amount is affected by events preceding TI induction and is positively correlated with TI duration. The pattern of hippocampal activity helps to predict TI onset and TI termination. Both polysynaptic flexor and monosynaptic heteronymous reflexes are depressed independently from the EEG activity. Brain metabolism, signaled by glycogen mobilization and glucose utilization, indicates a reduced neuronal activity during TI...

OBJECTIVE: The role of ipsilateral motor cortex efferent pathways in the transmission of voluntary command to spinal motor nuclei remains controversial in humans. In healthy subjects, their implication in cortical control is hidden by predominant role of crossed corticospinal tract. However, evidence from electrophysiological and imaging studies suggest that ipsilateral tracts may contribute to functional recovery after unilateral brain damage. This randomized-sham control study aims to explore to what extent ipsilateral tracts from the undamaged hemisphere may strengthen corticospinal control onto spinal motor networks following stroke...

Whole-body vibration (WBV) is often applied as an alternative method for strength training or to prevent muscle force decrease. Previous studies indicated that WBV induced: 1) changes in the contractile parameters predominantly of fast motor units, 2) higher motoneuron excitability, and 3) higher motoneuron firing rates at lower stimulus intensities compared with the control. In this study, we evaluated the influence of WBV on Ia monosynaptic input from muscle spindles because the tonic vibration reflex is responsible for the enhancement of muscle activity observed after WBV...

The time series of the H-wave amplitude in soleus muscle (SOL) shows fractal (long-range) correlation, which is attributed to input from supraspinal centers. However, whether such long-range power-law correlated input also contributes to the synergistic muscles remains unclear. The purpose of this study was therefore to examine the correlation in the fractal components of H-wave amplitude fluctuations between the synergistic muscles used for plantar flexion, i.e., the medial head of the gastrocnemius muscle (MG) and SOL...

The postnatal rodent spinal cord in-vitro is a useful model to investigate early pathophysiological changes after injury. While low dose nicotine (1 µM) induces neuroprotection, how higher doses affect spinal networks is unknown. Using spinal preparations of postnatal wild-type Wistar rat and Wnt1Cre2:Rosa26Tom double-transgenic mouse, we studied the effect of nicotine (0.5-10 µM) on locomotor networks in-vitro. Nicotine 10 µM induced motoneuron depolarization, suppressed monosynaptic reflexes, and decreased fictive locomotion in rat spinal cord...

The posterior root muscle response (PRM) is a monosynaptic reflex that is evoked by single pulse transcutaneous spinal cord stimulation (tSCS). The main aim of this work was to analyse how body weight loading influences PRM reflex threshold measured from several lower limb muscles in healthy participants. PRM reflex responses were evoked with 1-ms rectangular monophasic pulses applied at an interval of 6 s via a self-adhesive electrode (9 × 5 cm) at the T11-T12 vertebral level. Surface electromyographic activity of lower limb muscles was recorded during four different conditions, one in decubitus supine (DS) and the other three involving standing at 100%, 50%, and 0% body weight loading (BW)...

The nucleus of the solitary tract (NTS) receives viscerosensory information from the vagus nerve to regulate diverse homeostatic reflex functions. The NTS projects to a wide network of other brain regions, including the paraventricular nucleus of the hypothalamus (PVN). Here we examined the synaptic characteristics of primary afferent pathways to PVN-projecting NTS neurons in rat brainstem slices.Expression of the Transient Receptor Potential Vanilloid receptor (TRPV1+) distinguishes C-fiber afferents within the solitary tract (ST) from A-fibers (TRPV1-)...

Restoring neuromuscular reflex properties in the control of a prosthetic hand may potentially approach human-level grasp functions in the prosthetic hand. Previous studies have confirmed the feasibility of real-time emulation of a monosynaptic spinal reflex loop for prosthetic control. This study continues to explore how well the biomimetic controller could enable the amputee to perform force-control tasks that required both strength and error-tolerance. The biomimetic controller was programmed on a neuromorphic chip for real-time emulation of reflex...

AIM: This study aims to simultaneously record the magnetic and electric components of the propagating muscular action potential. METHOD: A single-subject study of the monosynaptic stretch reflex of the musculus rectus femoris was performed; the magnetic field generated by the muscular activity was recorded in all three spatial directions by five optically pumped magnetometers. In addition, the electric field was recorded by four invasive fine-wire needle electrodes...

Increased use of epidural Spinal Cord Stimulation (eSCS) for the rehabilitation of spinal cord injury (SCI) has highlighted the need for a greater understanding of the properties of reflex circuits in the isolated spinal cord, particularly in response to repetitive stimulation. Here, we investigate the frequency-dependence of modulation of short- and long-latency EMG responses of lower limb muscles in patients with SCI at rest. Single stimuli could evoke short-latency responses as well as long-latency (likely polysynaptic) responses...

For normal viewing, the eyes are held open by the tonic actions of the levator palpebrae superioris (levator) muscle raising the upper eyelid. This activity is interrupted during blinks, when the eyelid sweeps down to spread the tear film or protect the cornea. We examined the circuit connecting the principal trigeminal nucleus to the levator motoneurons by use of both anterograde and retrograde tracers in macaque monkeys. Injections of anterograde tracer were made into the principal trigeminal nucleus using either a stereotaxic approach or localization following physiological characterization of trigeminal second order neurons...

The C3-C4 propriospinal system is an important pathway mediating movement in cats; it contributes to movements in primates (including humans), and may have a role in recovery after lesion. Validated clinical tests of this system would find many applications, therefore we sought to test whether non-monosynaptic homonymous facilitation of the forearm flexor H reflex is mediated solely via a C3-C4 propriospinal pathway. In one anesthetized macaque monkey, median nerve stimulation elicited an H reflex in the flexor carpi radialis (FCR)...

The trigeminal blink reflex plays an important role in protecting the corneal surface from damage and preserving visual function in an unpredictable environment. The closing phase of the human reflex, produced by activation of the orbicularis oculi (ObOc) muscles, consists of an initial, small, ipsilateral R1 component, followed by a larger, bilateral R2 component. We investigated the circuitry that underlies this reflex in macaque (Macaca fascicularis and Macaca mulatta) monkeys by the use of single and dual tracer methods...

Epidural electrical stimulation (EES) applied over the human lumbosacral spinal cord provides access to afferent fibers from virtually all lower-extremity nerves. These afferents connect to spinal networks that play a pivotal role in the control of locomotion. Studying EES-evoked responses mediated through these networks can identify some of their functional components. We here analyzed electromyographic (EMG) responses evoked by low-frequency (2-6 Hz) EES derived from eight individuals with chronic, motor complete spinal cord injury...