Significant Increase In Electromyographic Activity Research Articles

Analysis of the effect of combined rehabilitation training and transcutaneous vagus nerve electrical stimulation on promoting central nervous system remodeling in stroke patients.

To explore the effect of combined rehabilitation training and transcutaneous vagus nerve electrical stimulation (t-VNS) on promoting central nervous system remodeling and neurological function recovery in stroke patients. A total of 124S patients admitted to our hospital from January to December 2023 were included in this study. The therapeutic effects were evaluated using the Modified Barthel Index (MBI) and the simplified Fugl-Meyer Assessment Scale (sFMA) to measure patients' activities of daily living and motor function recovery. Additionally, neurophysiological assessments, including electromyography (EMG) and motor evoked potentials (MEPs), were conducted to evaluate changes in neuromuscular and central nervous system function. Changes in neural activity in the frontal lobe and motor cortex were assessed through transcutaneous vagus nerve stimulation and electroencephalography. Moreover, all adverse events were recorded. After treatment, patients in the t-VNS combined with rehabilitation training group showed significant improvements in sFMA and MBI scores compared to the pure rehabilitation training group (P<0.05). In terms of neurophysiology, patients in the combined treatment group exhibited significant increases in electromyographic activity and MEPs (P<0.05). EEG results indicated enhanced neuroplasticity of the frontal lobe and motor cortex with t-VNS treatment. The incidence of skin stimulation and ear pain in the combined treatment group was significantly higher than that in the pure rehabilitation training group. Combined rehabilitation training and transcutaneous vagus nerve electrical stimulation have significant effects on neurological function recovery and central nervous system remodeling in stroke patients, effectively improving patients' motor function and activities of daily living.

Neuromuscular Control During Stair Descent and Artificial Tibial Translation After Acute ACL Rupture.

Background:Anterior cruciate ligament (ACL) rupture has direct effect on passive and active knee stability and, specifically, stretch-reflex excitability.Purpose/Hypothesis:The purpose of this study was to investigate neuromuscular activity in patients with an acute ACL deficit (ACL-D group) compared with a matched control group with an intact ACL (ACL-I group) during stair descent and artificially induced anterior tibial translation. It was hypothesized that neuromuscular control would be impaired in the ACL-D group.Study Design:Cross-sectional study; Level of evidence, 3.Methods:Surface electromyographic (EMG) activity of the vastus medialis (VM), vastus lateralis (VL), biceps femoris (BF), and semitendinosus (ST) muscles was recorded bilaterally in 15 patients with ACL-D (mean, 13.8 days [range, 7-21 days] since injury) and 15 controls with ACL-I during stair descent and artificially induced anterior tibial translation. The movements of stair descent were divided into preactivity, weight acceptance, and push-off phases. Reflex activity during anterior tibial translation was split into preactivity and short, medium, and late latency responses. Walking on a treadmill was used for submaximal EMG normalization. Kruskal-Wallis test and post hoc analyses with Dunn-Bonferroni correction were used to compare normalized root mean square values for each muscle, limb, movement, and reflex phase between the ACL-D and ACL-I groups.Results:During the preactivity phase of stair descent, the hamstrings of the involved leg of the ACL-D group showed 33% to 51% less activity compared with the matched leg and contralateral leg of the ACL-I group (P < .05). During the weight acceptance and push-off phases, the VL revealed a significant reduction (approximately 40%) in the involved leg of the ACL-D group compared with the ACL-I group. At short latency, the BF and ST of the involved leg of the ACL-D group showed a significant increase in EMG activity compared with the uninvolved leg of the ACL-I group, by a factor of 2.2 to 4.6.Conclusion:In the acute phase after an ACL rupture, neuromuscular alterations were found mainly in the hamstrings of both limbs during stair descent and reflex activity. The potential role of prehabilitation needs to be further studied.

The Influence of Motoric Maneuvers on Cervical Vestibular Evoked Myogenic Potentials (cVEMPs).

The cervical vestibular evoked myogenic potential (cVEMP) is a vestibular response that is produced by the saccule in response to intense, often low-frequency, short-duration auditory stimuli, and is typically recorded from a contracted sternocleidomastoid (SCM) muscle. Previous research has shown that the amplitude of the cVEMP is related to the amount of SCM electromyographic (EMG) activity. The aim of this study was to determine the influence of various remote motoric maneuvers on the amplitude of the cVEMP, as well as whether they influence the level of SCM EMG activity. The cVEMP was recorded from the left SCM muscle to left ear stimulation, in response to the SCM condition, as well as three different motoric maneuvers (jaw clench, eye closure, and the Jendrassik maneuver). EMG activity was also varied between 50, 75, and 100% of maximal EMG activity. Data from 14 healthy subjects, with a mean age of 25.57 years (standard deviation = 5.93 years), was included in the present study. Mean latency and amplitude of the cVEMP were compared across the four conditions and varying magnitudes of EMG contraction. SPSS 26 was used to statistically analyze the results. cVEMP latency did not vary across condition. cVEMP amplitude decreased with decreasing EMG magnitude. SCM contraction with jaw clench produced the largest increase in cVEMP amplitude; however, this condition was not significantly different from the SCM condition alone. SCM contraction with the Jendrassik maneuver produced a cVEMP amplitude that was similar and not statistically different from SCM contraction alone, and the addition of the eye closure maneuver to SCM contraction resulted in the lowest cVEMP amplitude, which was found to be statistically different from the standard SCM condition at 100 and 75% EMG activity. The amplitude relationship across the conditions was not found to vary with changes in EMG activity; however, a significant increase in EMG amplitude was found during the 50% muscle contraction condition when subjects performed the Jendrassik maneuver in addition to the standard SCM contraction. The addition of the eye closure maneuver to SCM contraction resulted in a significant decrease in cVEMP amplitude, while the addition of the Jendrassik maneuver resulted in a significant increase in EMG activity at the lowest level of SCM activation (i.e., 50%). Additional research is necessary to determine how motoric maneuvers influence the cVEMP amplitude, and whether the results are also dependent on how SCM contraction is being produced (e.g., while supine vs. sitting).

Robust Torque Predictions From Electromyography Across Multiple Levels of Active Exoskeleton Assistance Despite Non-linear Reorganization of Locomotor Output.

Robotic exoskeletons can assist humans with walking by providing supplemental torque in proportion to the user's joint torque. Electromyographic (EMG) control algorithms can estimate a user's joint torque directly using real-time EMG recordings from the muscles that generate the torque. However, EMG signals change as a result of supplemental torque from an exoskeleton, resulting in unreliable estimates of the user's joint torque during active exoskeleton assistance. Here, we present an EMG control framework for robotic exoskeletons that provides consistent joint torque predictions across varying levels of assistance. Experiments with three healthy human participants showed that using diverse training data (from different levels of assistance) enables robust torque predictions, and that a convolutional neural network (CNN), but not a Kalman filter (KF), can capture the non-linear transformations in EMG due to exoskeleton assistance. With diverse training, the CNN could reliably predict joint torque from EMG during zero, low, medium, and high levels of exoskeleton assistance [root mean squared error (RMSE) below 0.096 N-m/kg]. In contrast, without diverse training, RMSE of the CNN ranged from 0.106 to 0.144 N-m/kg. RMSE of the KF ranged from 0.137 to 0.182 N-m/kg without diverse training, and did not improve with diverse training. When participant time is limited, training data should emphasize the highest levels of assistance first and utilize at least 35 full gait cycles for the CNN. The results presented here constitute an important step toward adaptive and robust human augmentation via robotic exoskeletons. This work also highlights the non-linear reorganization of locomotor output when using assistive exoskeletons; significant reductions in EMG activity were observed for the soleus and gastrocnemius, and a significant increase in EMG activity was observed for the erector spinae. Control algorithms that can accommodate spatiotemporal changes in muscle activity have broad implications for exoskeleton-based assistance and rehabilitation following neuromuscular injury.

Severity of Sleep Bruxism and its Implications for the Stomatognathic System in Healthy Subjects

BACKGROUND: Sleep bruxism (SB) changes the functionality patterns of the stomatognathic system. However, its severity can be an aggravating factor in the function of this complex system.&#x0D; AIM: The purpose of the study was to investigate the stomatognathic system of healthy subjects with different severity of SB, as determined by BiteStrip.&#x0D; METHODS: Thirty-four subjects were divided into two groups: Mild SB (n = 15) and severe SB (n = 19). Electromyograph was used to evaluate the electromyographic activity of the right masseter (RM), left masseter (LM), right temporal (RT), and left temporal (LT) muscles at mandibular rest, right and left laterality, protrusion, and maximum voluntary contraction. Molar bite force was measured by the dynamometer. The data were tabulated and submitted for statistical analysis (p &lt; 0.05).&#x0D; RESULTS: Molar bite force was significantly lower in the severe SB group. There was a significant increase in electromyographic activity in the severe SB group for the mandibular rest tasks (RM, RT, and LT), protrusion (RM, LM, RT, and LT), and right and left laterality in the temporalis muscles. There was a significant decrease in electromyographic activity in the severe SB group in maximum voluntary contraction for the masseter and temporalis muscles.&#x0D; CONCLUSION: Subjects with severe SB demonstrated greater functional impairment of the stomatognathic system, mainly affecting the electromyographic activity and molar bite force.

Comparison of device-supported sensorimotor training and splint intervention for myofascial temporomandibular disorder pain patients.

This study was to compare the short-term therapeutic efficacy of device-supported sensorimotor training with that of standard splint therapy for patients with myofascial temporomandibular disorder (TMD) pain over a treatment period of 3months. We tested the hypothesis that both types of intervention are equally effective for pain reduction. In addition, the electromyographic (EMG) activity of the temporal and masseter muscles was recorded under conditions of force-controlled submaximum and maximum biting in intercuspation. Of consecutive patients seeking treatment for non-odontogenic oro-facial pain, 45 patients with myofascial TMD pain (graded chronic pain status, GCPS, I and II) were randomly assigned to 2 treatment groups (sensorimotor training and conventional splint treatment). Patients were evaluated 4 times (initial examination, 2, 6 and 12weeks later) by use of the Research Diagnostic Criteria for Temporomandibular Disorders (RDC/TMD). Electromyographic activity was recorded at the initial session and after 3months. Ease-of-use of the treatment options was also evaluated. Significant (P<.0001) pain reduction (sensorimotor training 53%, splint therapy 40%) was achieved for both groups, with no significant differences (P>.05) between the groups. Force-controlled sub-maximum normalized electromyographic activity was significantly different between T0 and T3 for group A (sensorimotor training, P < .05) but was not significantly different for group B (splint, P > .05). For normalized maximum-biting EMG activity in intercuspation, however, a significant increase in EMG activity was observed for group A for the masseter and temporal muscles (P < .001) and for group B for the masseter muscle only (P < .001). Moreover, sensorimotor training was significantly (P<.05) less easy to use than the splint. The results of this study confirm the pain-reducing effect of sensorimotor training for patients with myofascial TMD pain (GCPS I and II). This innovative active treatment might be a promising option for TMD pain patients.

Masticatory efficiency and muscular activity in removable partial dental prostheses with different cusp angles

Statement of problemThe loss of posterior teeth has a negative effect on the masticatory efficiency and activity of mastication muscles. How these muscles are affected by partial removable dental prostheses (PRDPs) with different cusp angles is unknown. PurposeThe purpose of this clinical study was to evaluate the influence of different cusp angles, with anatomic (33 degrees), semianatomic (20 degrees), and nonanatomic teeth (0 degree), on the masticatory efficiency and muscular activity of participants receiving mandibular bilateral distal PRDPs. Material and methodsFifteen participants consented to the evaluation of masticatory efficiency and electromyographic (EMG) activity with a PRDP with a unified bilateral design. The cusp angles of the artificial teeth were randomly changed from anatomic (33 degrees), semianatomic (20 degrees), and nonanatomic teeth (0 degree). Masticatory efficiency was evaluated by recording 5 parameters, including number of strokes, and time of mastication while the EMG activities of the masseter and temporalis muscles, measured using surface electromyography. The data were analyzed with 1-way ANOVA and the Tukey multiple post hoc test with statistical software (α=.05). ResultsWith regard to masticatory efficiency, PRDPs with anatomic and semianatomic teeth exhibited higher masticatory efficiency than those with nonanatomic teeth, whereas no significant differences were found between PRDPs with anatomic and semianatomic teeth. With respect to EMG activity, the least EMG activity was observed in PRDPs with anatomic teeth, whereas the highest activity was observed with nonanatomic teeth. No significant differences were found between the effect of PRDPs with anatomic and semianatomic teeth on masseter activity. ConclusionsChanging the cusp angle from 33 to 20 degrees in PRDPs did not influence the masticatory efficiency or the EMG activity of the masseters. However, it did lead to increased EMG activities of the temporalis muscle. PRDPs with nonanatomic teeth were associated with a significant decrease in masticatory efficiency accompanied by a significant increase in EMG activity.

Short term modulation of trunk neuromuscular responses following spinal manipulation: a control group study

BackgroundLow back pain (LBP) is one of the most frequent musculoskeletal conditions in industrialized countries and its economic impact is important. Spinal manipulation therapy (SMT) is believed to be a valid approach in the treatment of both acute and chronic LBP. It has also been shown that SMT can modulate the electromyographic (EMG) activity of the paraspinal muscle. The purpose of this study was to investigate, in a group of patients with low back pain, the persistence of changes observed in trunk neuromuscular responses after a spinal manipulation (SMT).MethodsSixty adult participants with LBP performed a block of 5 flexion-extension movements. Participants in the experimental group (n=30) received lumbar SMT whereas participants in the control group (n=30) were positioned similarly for the treatment but did not receive SMT. Blocks of flexion-extension movements were repeated immediately after the manipulation as well as 5 and 30 minutes after SMT (or control position). EMG activity of paraspinal muscles was recorded at L2 and L5 level and kinematic data were collected to evaluate the lumbo-pelvic kinematics. Pain intensity was noted after each block. Normalized EMG, pain intensity and lumbo-pelvic kinematics were compared across experimental conditions.ResultsParticipants from the control group showed a significant increase in EMG activity during the last block (30 min) of flexion-extension trials in both flexion and full-flexion phases at L2. Increase in VAS scores was also observed in the last 2 blocks (5 min and 30 min) in the control group. No significant group x time interaction was seen at L5. No significant difference was observed in the lumbo-pelvic kinematics.ConclusionChanges in trunk neuromuscular control following HVLA spinal manipulation may reduce sensitization or muscle fatigue effects related to repetitive movement. Future studies should investigate short term changes in neuromuscular components, tissue properties and clinical outcomes.

Analysis of electromyographic activity of ankle muscles on stable and unstable surfaces with eyes open and closed

Proprioceptive exercises are performed on a daily basis in physiotherapy with the use of different unstable platforms in order to improve joint stability using the mechanical and sensory properties of ligaments, joint capsule and integrated activity of the muscles surrounding the joint. Changes in the myoelectrical characteristics of the muscles during activity can be identified using surface electromyography (EMG), which provides important information on the behavior of muscles submitted to different types of load. The aim of the present study was to analyze the electromyographic activity of the tibialis anterior, tibialis posterior, peroneus longus, gastrocnemius lateralis and gastrocnemius medialis on stable and unstable surfaces with eyes open and closed. Twenty-five active, healthy, male and female individuals were submitted to an anthropometric evaluation and a protocol involving warm up and the electromyographic assessment of muscle activity on different surfaces. The order of the data collection was chosen randomly by lots [on stable ground or unstable platforms (trampoline, balance platform, proprioceptive disk and proprioceptive board) with eyes open and on a trampoline, balance platform and stable ground with eyes closed]. The individuals remained balanced on these surfaces for 15s with the knee at 30° flexion in order to provide greater instability. There was a significant increase (p<0.05) in muscle activity on the unstable surfaces, with the exception of the trampoline, which did not achieve statistically significant differences in relation to the stable ground. The tibialis anterior and peroneus longus exhibited the greatest electromyographic activity on all surfaces. The proprioceptive tests performed with eyes closed exhibited significantly greater electromyographic activity than with eyes open. Proprioceptive exercises on unstable surfaces generated a significant increase in electromyographic activity, especially with eyes closed, and are therefore a valuable resource in the sensory-motor rehabilitation of the ankle.

Increases in muscle activity produced by vibration of the thigh muscles during locomotion in chronic human spinal cord injury

The purpose of this study was to determine whether the muscle vibration applied to the quadriceps has potential for augmenting muscle activity during gait in spinal cord injured (SCI) individuals. The effects of muscle vibration on muscle activity during robotic-assisted walking were measured in 11 subjects with spinal cord injury (SCI) that could tolerate weight-supported walking, along with five neurologically intact individuals. Electromyographic (EMG) recordings were made from the tibialis anterior (TA), medial gastrocnemius (MG), rectus femoris (RF), vastus lateralis (VL), and medial hamstrings (MH) during gait. Vibration was applied to the anterior mid-thigh using a custom vibrator oscillating at 80 Hz. Five vibratory conditions were tested per session including vibration applied during: (1) swing phase, (2) stance phase, (3) stance-swing transitions, (4) swing-stance transitions, and (5) throughout the entire gait cycle. During all vibration conditions, a significant increase in EMG activity was observed across both SCI and control groups in the RF, VL, and MH of the ipsilateral leg. In the SCI subjects, the VL demonstrated a shift toward more appropriate muscle timing when vibration was applied during stance phase and transition to stance of the gait cycle. These observations suggest that the sensory feedback from quadriceps vibration caused increased muscle excitation that resulted in phase-dependent changes in the timing of muscle activation during gait.

Regional brain activation in conscious, nonrestrained rats in response to noxious visceral stimulation

Preclinical drug development for visceral pain has largely relied on quantifying pseudoaffective responses to colorectal distension (CRD) in restrained rodents. However, the predictive value of changes in simple reflex responses in rodents for the complex human pain experience is not known. Male rats were implanted with venous cannulas and with telemetry transmitters for abdominal electromyographic (EMG) recordings. [ 14C]-iodoantipyrine was injected during noxious CRD (60 mmHg) in the awake, nonrestrained animal. Regional cerebral blood flow (rCBF)-related tissue radioactivity was quantified by autoradiography and analyzed in the three-dimensionally reconstructed brain by statistical parametric mapping. 60-mmHg CRD, compared with controls (0 mmHg) evoked significant increases in EMG activity (267 ± 24% vs. 103 ± 8%), as well as in behavioral pain score (77 ± 6% vs. 3 ± 3%). CRD elicited significant increases in rCBF as expected in sensory (insula, somatosensory cortex), and limbic and paralimbic regions (including anterior cingulate cortex and amygdala). Significant decreases in rCBF were seen in the thalamus, parabrachial nucleus, periaqueductal gray, hypothalamus and pons. Correlations of rCBF with EMG and with behavioral pain score were noted in the cingulate, insula, lateral amygdala, dorsal striatum, somatosensory and motor regions. Our findings support the validity of measurements of cerebral perfusion during CRD in the freely moving rat as a model of functional brain changes in human visceral pain. However, not all regions demonstrating significant group differences correlated with EMG or behavioral measures. This suggests that functional brain imaging captures more extensive responses of the central nervous system to noxious visceral distension than those identified by traditional measures.

Electromyographic evaluation of masseter and anterior temporalis muscles in rest position of edentulous patients with temporomandibular disorders, before and after using complete dentures with sliding plates

This study was performed with the purpose of investigating electromyographic (EMG) activity of the anterior temporalis and masseter muscles in edentulous individuals with temporomandibular disorder (TMD), before and after using sliding plates on complete dentures in the mandibular rest position. Edentulous patients may present TMD, which is characterised by pain in temporomandibular joints, masticatory and neck muscles, uncoordinated and limited mandible movements, joint sounds and an altered occlusal relationship. It is imperative to offer treatment in order to re-establish stomatognathic system structures before submitting the individual to any definitive restorative treatment. The patients were edentulous for at least 10 years. EMG recordings were made before the insertion of the dentures (0 months) and also after using the sliding plates at the fourth month, 9th month and 12th month, using computerised electromyography K6-I/ EMG Light Channel Surface. EMG evaluations of the muscles were performed under the following clinical conditions: rest position with dentures (R1), rest position without dentures (R2), rest position with dentures post-activity (chewing) (R3), rest position without dentures post-activity (chewing) (R4). All patients obtained remission of muscular fatigue and reduced pain in stomatognathic system structures. Temporalis muscle showed significant increase in EMG activity compared with initial values (p < 0.01). Masseter muscles showed significantly lower mean values (p < 0.01) compared with initial values. The sliding plates allowed the process of neuromuscular deprogramming, contributing to muscular balance of the masticatory system, and are therefore indicated to be used before the fabrication of definitive complete dentures in patients with TMD.

Peripheral NMDA receptor modulation of jaw muscle electromyographic activity induced by capsaicin injection into the temporomandibular joint of rats

We have previously documented that peripheral N-methyl- d-aspartate (NMDA) receptor mechanisms are involved in nociceptive reflex increases in jaw muscle activity to injection of mustard oil or glutamate into the rat temporomandibular joint (TMJ). The aim of the present study was to determine whether peripheral NMDA receptor mechanisms are also involved in the nociceptive reflex responses in the jaw muscles evoked by injection of the inflammatory irritant and algesic chemical capsaicin into the TMJ. The effects of peripheral injection of NMDA receptor antagonists, MK-801 and APV, on the increases in electromyographic (EMG) activities of digastric and masseter muscles reflexly evoked by capsaicin injection into the TMJ were tested in halothane-anesthetized male rats. The capsaicin injection following pre-injection of vehicle evoked significant increases in EMG activity in both digastric and masseter muscles whereas pre-injection of MK-801 or APV into the TMJ resulted in a significant concentration-related reduction in the magnitude of capsaicin-evoked digastric and masseter EMG activity (ANOVA-on-ranks, P < 0.05). This finding indicates that capsaicin-evoked digastric and masseter EMG activity can be attenuated by pre-injection into the TMJ of NMDA receptor antagonists, and that the activation of peripheral NMDA receptors may be important in the mechanisms whereby capsaicin evokes nociceptive trigeminal responses.

Pelvic Floor Muscle Behavior During Valsalva Leak Point Pressure Measurement in Males and Females Affected by Stress Urinary Incontinence

We evaluated pelvic floor muscle (PFM) behavior during Valsalva leak point pressure (VLPP) measurement in males and females affected by stress urinary incontinence and investigated whether VLPP results are influenced by PFM contraction. A total of 25 females and 14 males underwent surface electromyographic (EMG) recording of PFM activity while performing VLPP. We investigated 2 conditions, VLPP during spontaneous strain (test A), and with simultaneous relaxation of the pelvic floor (test B). We analyzed average EMG activity (microV) at rest and during VLPP in tests A and B, the increasing EMG activity during tests A and B (the difference between average EMG activity during tests A and B and at rest), and the mean duration (seconds) of EMG activity during tests A and B. We detected a significant increase in EMG activity during tests A and B as compared to activity at rest (p <0.0001). Increasing EMG activity during test B was significantly reduced in females (p <0.05) but not in males. During test A patients reporting urinary incontinence showed a significantly lower EMG activity than that of continent patients (p <0.05). A significant reduction in maximum abdominal pressure was detected in test B compared to test A, but there was no difference in VLPP values between tests A and B. PFM activity significantly increases during VLPP measurement. Eliminating muscular contraction of the pelvic floor does not significantly alter VLPP results.

Uterine responses to exogenous oxytocin before and after pre-partum luteolysis in the cow.

The aim of this study was to test the functional status of uterine oxytocin receptors in cows in vivo around parturition. The animals received consecutive, intra-arterial injections of 800, 1,600 and 3,200 mU of oxytocin at three different stages: during late gestation (days 260-274), at 12 h and at 24 h after intramuscular injection of a prostaglandin F2alpha analogue at day 275 to induce parturition. Cows (n = 6) had been provided with myometrial electrodes and a catheter had been installed in the aorta and in a branch of the uterine vein (UV). Regular blood samples were obtained from the UV from 5 min before until 45 min after each oxytocin injection to measure plasma levels of prostaglandin F2alpha (PGF2alpha) and oxytocin. Uterine electromyographic (EMG) activity was registered continuously during each experiment. The increase of oxytocin levels in UV plasma after intra-arterial injections was dose dependent (p < 0.02). Pre- and post treatment oxytocin levels at 24 h after induction of parturition were significantly increased (p = 0.0313). Both during late pregnancy and at 12 h after induction of parturition, oxytocin caused a significant increase in EMG activity (p = 0.022). After the 3,200 mU dose the increase was significantly higher than with the other 2 doses (p = 0.004). After each dose, EMG activity returned to baseline levels within some 15 min. At 24 h after induction of parturition, the pre-treatment level of EMG activity had increased. Doses of 800 mU and 1,600 mU of oxytocin produced a significant (p = 0.022) increment of EMG activity, which was of the same magnitude as during the preceding stages; after 3,200 mU of oxytocin the response was significantly higher than before (p = 0.008). No significant increases of PGF2alpha levels in UV plasma could be measured after oxytocin injections at any of the three stages. It is concluded that the myometrium of the pregnant cow responds in vivo to physiological doses of oxytocin. At 24 h after induction of parturition, when luteolysis has occurred and a parturient pattern of parturient myometrial activity has already started to develop, the response is enhanced. Physiological doses of oxytocin did not evoke a spurt release of PGF2alpha in uterine venous blood during the peripartal period.

Jaw electromyographic activity induced by the application of algesic chemicals to the rat tooth pulp

The aim of this study was to determine if the application of mustard oil (MO), a small-fiber excitant and inflammatory irritant, or other algesic chemicals (capsaicin, CAP, and bradykinin, BK) to the rat maxillary molar tooth pulp induces electromyographic (EMG) activity of the masseter and digastric muscles, and also to determine if endogenous opioid mechanisms may be involved in any documented EMG changes. Application of MO to the tooth pulp induced a significant increase in EMG activity of the ipsilateral masseter up to 30 min. The application of mineral oil to the pulp or MO application to the pulp-extirpated tooth did not induce any significant EMG increases. The application of CAP or BK to the pulp in contrast had much weaker effects on EMG activity of the jaw muscles. CAP produced a small but prolonged increase in masseter EMG activity, and BK induced a short-lasting increase in digastric EMG activity. The systemic administration of the opiate antagonist naloxone significantly reactivated (i.e. rekindled) the EMG response evoked by MO application to the pulp. Naloxone did not produce any such significant rekindling effect on EMG activity following CAP, BK or mineral oil application to the pulp or following MO application to the pulp-extirpated tooth. The MO, BK and especially CAP groups showed histological evidence of vasodilatation and polymorphonuclear leukocyte infiltration in the pulp tissue and a significant increase in plasma extravasation of Evans Blue dye, whereas mineral oil did not induce these changes. These findings suggest that pulp afferent inputs to the central nervous system evoked by BK, CAP and especially MO may induce enhanced jaw muscle activity. In addition, the naloxone data suggest that an opioid suppressive mechanism may be induced by the pulpal afferent inputs evoked by MO, and may serve to limit the jaw muscle activity elicited by these inputs.

Development of an animal model for neuroleptic malignant syndrome: heat-exposed rabbits with haloperidol and atropine administration exhibit increased muscle activity, hyperthermia, and high serum creatine phosphokinase level

The neuroleptic malignant syndrome (NMS) is a life-threatening complication of neuroleptic treatment. To elucidate the pathogenesis of NMS, an animal model has been developed. Experimental rabbits treated with haloperidol (1 mg/kg) by intramuscular injection, were studied for the diagnostic symptoms of increased muscle rigidity, elevated body temperature, and high serum creatine phosphokinase (CPK) level. Administration of haloperidol (1 mg/kg) and atropine (0.4 mg/kg), and exposure to high ambient temperature (35°C) induced a significant increase in electromyographic activity with muscle rigidity similar to that observed in patients with NMS. Such rabbits also showed elevated body temperature and serum CPK value. In addition to the similarity of the signs and symptoms, all parameters measured (muscle rigidity, body temperature, and serum CPK level) were normalized by dantrolene treatment. The effectiveness of dantrolene in the experimental animal partially confirms the validity of this animal model for NMS. This experimental animal model for NMS may be useful to elucidate the pathogenesis of NMS.

A new view of the role of dopamine receptors in the regulation of muscle tone.

1. Clinical and experimental studies support the view that nigrostriatal dopaminergic neurons are involved in the maintenance of muscle tone. 2. The effects of inactivating dopamine receptors in the rat substantia nigra on muscle tone, assessed as tonic electromyographic (EMG) activity, was investigated. 3. Dopamine receptors were inactivated by injections of the irreversible dopamine receptor antagonist, N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ) into the pars reticulata of the substantia nigra. 4. Significant increases in EMG activity were observed from 2 to 24 h after EEDQ injection and were associated with a loss of nigral dopamine receptors. 5. Increases in EMG activity were found only when both D1 and D2 receptors were inactivated. 6. Inactivation of alpha-adrenoceptors, 5HT2c and muscarinic receptors had no effect on EMG activity. 7. Injections of apomorphine did not reduce the increased EMG activity associated with nigral dopamine receptor loss. 8. The results are consistent with the hypothesis that dopamine receptors in the substantia nigra of the rat play an important role in the regulation of muscle tone.

An electromyographic analysis of orofacial motor activities during trained tongue-protrusion and biting tasks in monkeys

This study sought to characterise the electromyographic (EMG) activity patterns of orofacialmuscles during trained tongue-protrusion and biting tasks in two awake monkeys ( Macaca fascicularis). Chronic or acute EMG electrodes were placed in the anterior digastric (DIG), genioglossus (GG), masseter (MASS), platysma (PLAT), zygomaticus major (ZYGO), orbicularis oris superior (OOS), and orbicularis oris inferior (OOI) muscles and their EMG activity as well as the force signals of the tongue-protrusion and biting tasks were recorded. A total of 327 tongue-protrusion task trials and a total of 210 biting-task trials were successfully completed in several recording sessions and the EMG patterns were generally consistent between the different sessions. For the tongue task, the mean onset time of increase in GG activity significantly ( p < 0.0001) led the mean onset time of increase in the force. The DIG, GG, and OOI (and also the OOS in one of the monkeys) showed a significant ( p < 0.0001) increase in mean EMG amplitude during the holding phase, but the GG in both monkeys had the highest mean EMG amplitude ratio (MAR), i.e. the mean EMG amplitude during the holding or dynamic phase divided by the mean EMG amplitude during the pre-trial period. A similar EMG pattern was documented for different directions of the tongue-protrusion task (right, symmetrical, and left) and changes in the levels of EMG activities occurred in GG and OOI as the direction of the tongue-protrusion task changed from left to right. The task at different forces was associated with no apparent change in MAR for the holding phase for each muscle recorded. However, during the dynamic phase, only the GG showed a significant increase in EMG activity as the forces were increased. For the biting task, the mean onset times of the MASS activity and force were not significantly different. The MASS and ZYGO muscles (and the PLAT in one of the monkeys) showed a significant increase in mean EMG amplitude during the holding phase compared with the pre-trial period, and the MASS showed the highest MAR. It was also the only muscle showing a significant increase in the EMG activity when the bite-force level was increased. These findings reveal that certain orofacial muscles are selectively recruited during the two different orofacial tasks. Based on the EMG activity pattern during different directions or force levels of the task, the data suggest that, of the muscles recorded, the principal agonist for the tongue task is the GG and that for the biting task is the MASS; the other muscles that may be active appear to serve as accessories to the task.

Power spectral analysis of electromyographic and systemic arterial pressure signals during fentanyl-induced muscular rigidity in the rat

We have measured electromyographic (EMG) and systemic arterial pressure (SAP) signals during fentanyl-induced muscular rigidity in adult male Sprague-Dawley rats anaesthetized initially with ketamine 120 mg kg-1 i.p. during controlled ventilation. Fentanyl 100 micrograms kg-1 i.v. induced significant increase in EMG activity, recorded from the sacrococcygeus dorsi lateralis muscle. Power spectral analysis revealed that this was produced by an increase in the root mean square and a decrease in the mean power frequency values of the signals, signifying recruitment and synchronous activation of motor units. Together with transient hypotension and bradycardia, power spectral analysis of the SAP signals demonstrated a reduced but maintained power density of the frequency components that represent respiratory, baroreceptor and vasomotor activities. All these effects were only demonstrated unequivocally in rats maintained by i.v. infusion of ketamine until 10 min before the administration of fentanyl. We conclude that analysis of the temporal alterations in the spectral components of the EMG and SAP signals in rats during mechanical ventilation provides a sensitive method of measuring fentanyl-induced muscular rigidity and the accompanying alterations in haemodynamic variables.