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Muscle & Nerve Nov 2023Long latency reflexes (LLRs) are late responses in nerve conduction studies seen after peripheral nerve stimulation during submaximal muscle contraction. They follow a...
INTRODUCTION/AIMS
Long latency reflexes (LLRs) are late responses in nerve conduction studies seen after peripheral nerve stimulation during submaximal muscle contraction. They follow a short latency reflex, also known as the H reflex, and are thought to involve transcortical pathways, providing a measure of proximal nerve and central conduction. For this reason, they have been evaluated in several central nervous system diseases, but reference values are not widely published and are mostly based on old studies with very small numbers of participants. Therefore, in this work we aim to provide comprehensive reference values for LLR testing.
METHODS
LLRs were tested in a cohort of 100 healthy participants, testing the median nerve bilaterally.
RESULTS
Mean latencies for short latency reflex (SLR), LLR1, LLR2, and LLR3 were 27.00, 38.50, 47.60, and 67.34 milliseconds, respectively. The allowable side-to-side difference was approximately 3 to 4 milliseconds. No significant sex-related differences were seen. Height correlated moderately with the SLR latency, but only weakly with LLR1, LLR2, and LLR3.
DISCUSSION
This work provides normal LLR values for comparison with future studies in disease. The technique used may allow for improved evaluation of central nervous system or proximal peripheral nerve disorders.
Topics: Humans; Adult; Median Nerve; Reaction Time; Reflex; Muscle Contraction; Reference Values; H-Reflex; Electric Stimulation
PubMed: 37811697
DOI: 10.1002/mus.27981 -
Journal of Neurophysiology Nov 2023Spasticity is a chronic neurological complication associated with spinal cord injury (SCI), characterized by increased muscle tone and stiffness. A physiological sign of...
Spasticity is a chronic neurological complication associated with spinal cord injury (SCI), characterized by increased muscle tone and stiffness. A physiological sign of spasticity is hyperreflexia, evident by the loss of evoked rate-dependent depression (RDD) in the H-reflex. Although previous work has shown that SCI-induced astrogliosis contributes to hyperexcitability disorders, including neuropathic pain and spasticity, it is unclear how reactive astrocytes can modulate synaptic transmission within the injured spinal cord. To study astrocytes' role in post-SCI hyperreflexia, we examined glutamate transporter-1 (GLT-1) and postsynaptic density protein 95 (PSD-95) proteins in astrocytes and neurons, respectively, within the ventral horn (lamina IX) below the level of injury (spinal segment L4-5). The close juxtaposition of GLT-1 and PSD-95 markers is a molecular correlate of tripartite synapses and is thought to be a key element in the astrocyte-induced plasticity of neuronal synapses. Our study compared animals with and without SCI-induced hyperreflexia and spasticity and investigated potential synaptic abnormalities associated with astrocyte involvement. As expected, 4 wk after SCI, we observed a loss in evoked H-reflex RDD in hindlimb electromyogram recordings, i.e., hyperreflexia, in contrast to uninjured sham. Importantly, our main findings show a significant increase in the presence of GLT-1-PSD-95 tripartite synapses in the ventral spinal cord motor regions of animals exhibiting SCI-induced hyperreflexia. Taken together, our study suggests the involvement of astrocyte-neuron synaptic complexes in the plasticity-driven progression of chronic spasticity. The role of astrocytes in H-reflex hyperexcitability following SCI remains understudied. Our findings establish a relationship between GLT-1 expression, its proximity to neuronal PSD-95 in the spinal cord ventral horn, and the loss of H-reflex RDD, i.e., hyperreflexia. Our findings provide a new perspective on synaptic alterations and the development of SCI-related spasticity.
Topics: Animals; Astrocytes; Reflex, Abnormal; Spinal Cord Injuries; Spinal Cord; Motor Neurons; Synapses
PubMed: 37877184
DOI: 10.1152/jn.00234.2023 -
Journal of the Association For Research... Apr 2024One-sided vestibular disorders are common in clinical practice; however, their models have not been fully established. We investigated the effect of unilateral or...
One-sided vestibular disorders are common in clinical practice; however, their models have not been fully established. We investigated the effect of unilateral or bilateral deficits in the vestibular organs on the vestibulo-ocular reflex (VOR) and optokinetic reflex (OKR) of zebrafish using in-house equipment. For physical dislodgement of the otoliths in the utricles of zebrafish larvae, one or both utricles were separated from the surrounding tissue using glass capillaries. The video data from VOR and OKR tests with the larvae was collected and processed using digital signal processing techniques such as fast Fourier transform and low-pass filters. The results showed that unilateral and bilateral damage to the vestibular system significantly reduced VOR and OKR. In contrast, no significant difference was observed between unilateral and bilateral damage. This study confirmed that VOR and OKR were significantly reduced in zebrafish with unilateral and bilateral vestibular damage. Follow-up studies on unilateral vestibular disorders can be conducted using this tool.
Topics: Animals; Reflex, Vestibulo-Ocular; Zebrafish; Vestibule, Labyrinth; Vestibular Diseases
PubMed: 38361011
DOI: 10.1007/s10162-024-00936-3 -
The Journal of Neuroscience : the... Jan 2024Spasticity is a hyperexcitability disorder that adversely impacts functional recovery and rehabilitative efforts after spinal cord injury (SCI). The loss of evoked...
Spasticity is a hyperexcitability disorder that adversely impacts functional recovery and rehabilitative efforts after spinal cord injury (SCI). The loss of evoked rate-dependent depression (RDD) of the monosynaptic H-reflex is indicative of hyperreflexia, a physiological sign of spasticity. Given the intimate relationship between astrocytes and neurons, that is, the tripartite synapse, we hypothesized that astrocytes might have a significant role in post-injury hyperreflexia and plasticity of neighboring neuronal synaptic dendritic spines. Here, we investigated the effect of selective Rac1KO in astrocytes (i.e., adult male and female mice, transgenic cre-flox system) on SCI-induced spasticity. Three weeks after a mild contusion SCI, control Rac1 animals displayed a loss of H-reflex RDD, that is, hyperreflexia. In contrast, transgenic animals with astrocytic Rac1KO demonstrated near-normal H-reflex RDD similar to pre-injury levels. Reduced hyperreflexia in astrocytic Rac1KO animals was accompanied by a loss of thin-shaped dendritic spine density on α-motor neurons in the ventral horn. In SCI-Rac1 animals, as expected, we observed the development of dendritic spine dysgenesis on α-motor neurons associated with spasticity. As compared with WT animals, SCI animals with astrocytic Rac1KO expressed increased levels of the glial-specific glutamate transporter, glutamate transporter-1 in the ventral spinal cord, potentially enhancing glutamate clearance from the synaptic cleft and reducing hyperreflexia in astrocytic Rac1KO animals. Taken together, our findings show for the first time that Rac1 activity in astrocytes can contribute to hyperreflexia underlying spasticity following SCI. These results reveal an opportunity to target cell-specific molecular regulators of H-reflex excitability to manage spasticity after SCI. Spinal cord injury leads to stretch reflex hyperexcitability, which underlies the clinical symptom of spasticity. This study shows for the first time that astrocytic Rac1 contributes to the development of hyperreflexia after SCI. Specifically, astrocytic Rac1KO reduced SCI-related H-reflex hyperexcitability, decreased dendritic spine dysgenesis on α-motor neurons, and elevated the expression of the astrocytic glutamate transporter-1 (GLT-1). Overall, this study supports a distinct role for astrocytic Rac1 signaling within the spinal reflex circuit and the development of SCI-related spasticity.
Topics: Mice; Male; Female; Animals; Reflex, Abnormal; Astrocytes; Spinal Cord Injuries; Motor Neurons; Spinal Cord; Animals, Genetically Modified; H-Reflex; Amino Acid Transport System X-AG
PubMed: 37963762
DOI: 10.1523/JNEUROSCI.1670-22.2023 -
World Neurosurgery Mar 2024Spasticity is a form of muscle hypertonia secondary to various diseases, including traumatic brain injury, spinal cord injury, cerebral palsy, and multiple sclerosis.... (Review)
Review
OBJECTIVE
Spasticity is a form of muscle hypertonia secondary to various diseases, including traumatic brain injury, spinal cord injury, cerebral palsy, and multiple sclerosis. Medical treatments are available; however, these often result in insufficient clinical response. This review evaluates the role of epidural spinal cord stimulation (SCS) in the treatment of spasticity and associated functional outcomes.
METHODS
A systematic review of the literature was performed using the Embase, CENTRAL, and MEDLINE databases. We included studies that used epidural SCS to treat spasticity. Studies investigating functional electric stimulation, transcutaneous SCS, and animal models of spasticity were excluded. We also excluded studies that used SCS to treat other symptoms such as pain.
RESULTS
Thirty-four studies were included in the final analysis. The pooled rate of subjective improvement in spasticity was 78% (95% confidence interval, 64%-91%; I = 77%), 40% (95% confidence interval, 7%-73%; I = 88%) for increased H-reflex threshold or decreased Hoffman reflex/muscle response wave ratio, and 73% (65%-80%; I = 50%) for improved ambulation. Patients with spinal causes had better outcomes compared with patients with cerebral causes. Up to 10% of patients experienced complications including infections and hardware malfunction.
CONCLUSIONS
Our review of the literature suggests that SCS may be a safe and useful tool for the management of spasticity; however, there is significant heterogeneity among studies. The quality of studies is also low. Further studies are needed to fully evaluate the usefulness of this technology, including various stimulation paradigms across different causes of spasticity.
Topics: Animals; Humans; Spinal Cord Stimulation; Spinal Cord Injuries; Pain; Muscle Spasticity; Walking; Reflex, Abnormal; Spinal Cord
PubMed: 38181878
DOI: 10.1016/j.wneu.2023.12.158 -
Journal of Oral Rehabilitation Nov 2023Chewing and licking are primarily activated by central pattern generator (CPG) neuronal circuits in the brainstem and when activated trigger repetitive rhythmic...
BACKGROUND
Chewing and licking are primarily activated by central pattern generator (CPG) neuronal circuits in the brainstem and when activated trigger repetitive rhythmic orofacial movements such as chewing, licking and swallowing. These CPGs are reported to modulate orofacial reflex responses in functions such as chewing.
OBJECTIVE
This study explored the modulation of reflex responses in the anterior and posterior bellies (ant-Dig and post-Dig, respectively) of the digastric muscle evoked by low-intensity trigeminal stimulation in conscious rats.
METHODS
The ant-Dig and post-Dig reflexes were evoked by using low-intensity electrical stimulation applied to either the right or left inferior alveolar nerve. Peak-to-peak amplitudes and onset latencies were measured.
RESULTS
No difference was observed between threshold and onset latency for evoking ant-Dig and post-Dig reflexes, suggesting that the latter was also evoked disynaptically. The peak-to-peak amplitude of both reflexes was significantly reduced during chewing, licking and swallowing as compared to resting period and was lowest during the jaw-closing phase of chewing and licking. Onset latency was significantly largest during the jaw-closing phase. Inhibitory level was similar between the ant-Dig and post-Dig reflex responses and between the ipsilateral and contralateral sides.
CONCLUSION
These results suggest that both the ant-Dig and post-Dig reflex responses were significantly inhibited, probably due to CPG activation during feeding behaviours to maintain coordination of jaw and hyoid movements and hence ensure smooth feeding mechanics.
Topics: Animals; Rats; Jaw; Electromyography; Reflex; Mandibular Nerve; Electric Stimulation; Neck Muscles
PubMed: 37322854
DOI: 10.1111/joor.13537 -
Autonomic Neuroscience : Basic &... Dec 2023The cardiovascular response is appropriately regulated during exercise to meet the metabolic demands of the active muscles. The exercise pressor reflex is a neural... (Review)
Review
The cardiovascular response is appropriately regulated during exercise to meet the metabolic demands of the active muscles. The exercise pressor reflex is a neural feedback mechanism through thin-fiber muscle afferents activated by mechanical and metabolic stimuli in the active skeletal muscles. The mechanical component of this reflex is referred to as skeletal muscle mechanoreflex. Its initial step requires mechanotransduction mediated by mechanosensors, which convert mechanical stimuli into biological signals. Recently, various mechanosensors have been identified, and their contributions to muscle mechanoreflex have been actively investigated. Nevertheless, the mechanosensitive channels responsible for this muscular reflex remain largely unknown. This review discusses progress in our understanding of muscle mechanoreflex under healthy conditions, focusing on mechanosensitive channels.
Topics: Rats; Animals; Mechanotransduction, Cellular; Muscle Contraction; Rats, Sprague-Dawley; Reflex; Muscle, Skeletal; Blood Pressure
PubMed: 37925831
DOI: 10.1016/j.autneu.2023.103128 -
Scientific Reports Aug 2023Walking on unknown and rough terrain is challenging for (bipedal) robots, while humans naturally cope with perturbations. Therefore, human strategies serve as an...
Walking on unknown and rough terrain is challenging for (bipedal) robots, while humans naturally cope with perturbations. Therefore, human strategies serve as an excellent inspiration to improve the robustness of robotic systems. Neuromusculoskeletal (NMS) models provide the necessary interface for the validation and transfer of human control strategies. Reflexes play a crucial part during normal locomotion and especially in the face of perturbations, and provide a simple, transferable, and bio-inspired control scheme. Current reflex-based NMS models are not robust to unexpected perturbations. Therefore, in this work, we propose a bio-inspired improvement of a widely used NMS walking model. In humans, different muscles show an increase in activation in anticipation of the landing at the end of the swing phase. This preactivation is not integrated in the used reflex-based walking model. We integrate this activation by adding an additional feedback loop and show that the landing is adapted and the robustness to unexpected step-down perturbations is markedly improved (from 3 to 10 cm). Scrutinizing the effect, we find that the stabilizing effect is caused by changed knee kinematics. Preactivation, therefore, acts as an accommodation strategy to cope with unexpected step-down perturbations, not requiring any detection of the perturbation. Our results indicate that such preactivation can potentially enable a bipedal system to react adequately to upcoming unexpected perturbations and is hence an effective adaptation of reflexes to cope with rough terrain. Preactivation can be ported to robots by leveraging the reflex-control scheme and improves the robustness to step-down perturbation without the need to detect the perturbation. Alternatively, the stabilizing mechanism can also be added in an anticipatory fashion by applying an additional knee torque to the contralateral knee.
Topics: Humans; Muscle, Skeletal; Walking; Locomotion; Reflex; Knee; Biomechanical Phenomena; Electromyography; Gait
PubMed: 37580375
DOI: 10.1038/s41598-023-39364-3 -
Journal of Hypertension Sep 2023Altered baroreflex function is well documented in hypertension; however, the female sex remains far less studied compared with males. We have previously demonstrated a...
BACKGROUND
Altered baroreflex function is well documented in hypertension; however, the female sex remains far less studied compared with males. We have previously demonstrated a left-sided dominance in the expression of aortic baroreflex function in male spontaneously hypertensive rats (SHRs) and normotensive rats of either sex. If lateralization in aortic baroreflex function extends to hypertensive female rats remains undetermined. This study, therefore, assessed the contribution of left and right aortic baroreceptor afferents to baroreflex modulation in female SHRs.
METHOD
Anesthetized female SHRs (total n = 9) were prepared for left, right and bilateral aortic depressor nerve (ADN) stimulation (1-40 Hz, 0.2 ms, 0.4 mA for 20 s) and measurement of reflex mean arterial pressure (MAP), heart rate (HR), mesenteric vascular resistance (MVR) and femoral vascular resistance (FVR). All rats were also matched for the diestrus phase of the estrus cycle.
RESULTS
Reflex (%) reductions in MAP, HR, MVR and FVR were comparable for both left-sided and right-sided stimulation. Bilateral stimulation evoked slightly larger ( P = 0.03) reductions in MVR compared with right-sided stimulation; however, all other reflex hemodynamic measures were similar to both left-sided and right-sided stimulation.
CONCLUSION
These data show that female SHRs, unlike male SHRs, express similar central integration of left versus right aortic baroreceptor afferent input and thus show no laterization in the aortic baroreflex during hypertension. Marginal increases in mesenteric vasodilation following bilateral activation of the aortic baroreceptor afferents drive no superior depressor responses beyond that of the unilateral stimulation. Clinically, unilateral targeting of the left or right aortic baroreceptor afferents may provide adequate reductions in blood pressure in female hypertensive patients.
Topics: Rats; Male; Female; Animals; Baroreflex; Rats, Inbred SHR; Blood Pressure; Aorta; Pressoreceptors; Hypertension; Heart Rate; Electric Stimulation
PubMed: 37382160
DOI: 10.1097/HJH.0000000000003493 -
World Journal of Pediatrics : WJP Nov 2023
Topics: Humans; Child; Baroreflex; Syncope, Vasovagal; Syncope; Tilt-Table Test
PubMed: 37014537
DOI: 10.1007/s12519-023-00693-y