Tonic Electromyographic Activity Research Articles

音刺激を用いた前庭誘発節電位検査 温度刺激検査のＣＰ％との関連

Loud click or tone burst sound can activate vestibular receptor and evoke reflex changes in tonic electromyographic activity within the stenocleidomastoid muscles. This reflex is assumed to originate in the saccule, the afferent pathways being the inferior vestibular nerve, and the efferent pathways the vestibulospinal tract. Averaging these muscular responses allows vestibular evoked myogenic potentials (VEMP) to be obtained. The earliest response ipsilateral to a loud click, p13n23, is dependent upon vestibular activation, specifically saccular afferents. These new techniques are beginning to be applied clinically in the patient of vestibular neuritis, Meniere’ s disease, acoustic neuromas, Tullio phe nomenon, etc. VEMP recording will provide both a straightforward non-invasive exploration of each vestibule indepen dently and an attractive method by which to explore otolithic receptors and vestibulospinal pathways.

Effect of acute and chronic administration of 1,2,3,4-tetrahydroisoquinoline on muscle tone, metabolism of dopamine in the striatum and tyrosine hydroxylase immunocytochemistry in the substantia nigra, in rats

The effects of acute and chronic administration of 1,2,3,4-tetrahydroisoquinoline, an endogenous substance suspected of producing parkinsonism in humans, on the muscle tone and metabolism of dopamine in the striatum, and on the number of tyrosine hydroxylase-immunoreactive cells in the substantia nigra were investigated in rats. Muscle tone was examined using a combined mechanomyographic and electromyographic method which measured simultaneously the muscle resistance of the rat's hind foot to passive extension and flexion in the ankle joint and electromyographic activity of the antagonistic muscles of that joint: gastrocnemius and tibialis anterior. 1,2,3,4-Tetrahydroisoquinoline administered at doses of 50 and 100 mg/kg intraperitoneally for 19 days increased muscle resistance 1 h after the first injection (acute treatment), 1 h after the last injection (chronic treatment) and three days after compound withdrawal. Rigidity observed on the third day of 1,2,3,4-tetrahydroisoquinoline withdrawal was accompanied by an increased tonic (resting) electromyographic activity of the gastrocnemius and tibialis anterior muscles. At the same time, a significant reduction in the number of tyrosine hydroxylase-immunoreactive neurons in the substantia nigra and a decrease in the dopamine level in the striatum were also found. A declining number of tyrosine hydroxylase-immunoreactive neurons in the whole substantia nigra showed a significant negative correlation with the enhanced muscle resistance, as well as with the tonic electromyographic activity recorded at rest, i.e. before the start of movements, from the gastrocnemius and tibialis anterior muscles. Our results suggest that 1,2,3,4-tetrahydroisoquinoline may be one of the endogenous substances involved in the progress of Parkinson's disease.

Efficacy of pramipexole, a new dopamine receptor agonist, to relieve the parkinsonian-like muscle rigidity in rats

The aim of the present study was to assess the efficacy of pramipexole (2-amino-4,5,6,7-tetrahydro-6-propyl-amino-benzthiazole-dihydrochloride), a new dopamine D 2/D 3 receptor agonist, to attenuate parkinsonian-like muscle rigidity in rats. Muscle tone was examined using a combined mechano- and electromyographic (EMG) method, which simultaneously measured the muscle resistance of a rat's hindlimb to passive extension and flexion at the ankle joint, and the EMG acitivity of the antagonistic muscles of that joint: gastrocnemius and tibialis anterior. Muscle rigidity was produced by reserpine (5 mg/kg) injected in combination with α-methyl-p-tyrosine (250 mg/kg) or by haloperidol (0.5 mg/kg). Pramipexole in doses of 0.5–5 mg/kg antagonized both reserpine+α-methyl- p-tyrosine- and haloperidol-induced muscle rigidity. Pramipexole also reduced reserpine-enhanced tonic and reflex EMG activities in the gastrocnemius muscle. The present results suggest that stimulation of the postsynaptic dopamine receptor may be chiefly responsible for the antiparkinsonian action of pramipexole. The ability of pramipexole to diminish the parkinsonian-like muscle rigidity seems to indicate a therapeutic value of this compound in the treatment of Parkinson's disease.

Raclopride and Chlorpromazine, but not Clozapine, Increase Muscle Rigidity in the Rat: Relationship with D2 Dopamine Receptor Occupancy

The aim of the present study was to investigate the relationship between effects on muscle tone and D2 receptor occupancy of two typical antipsychotic drugs, raclopride and chlorpromazine, and the atypical drug, clozapine. Increased muscle tone (i.e., muscle rigidity), was measured as increases in tonic electromyographic (EMG) activity of the antagonistic muscles of the rat hind limb. D2 dopamine receptor occupancy was assessed in the striatum and substantia nigra, areas involved in the regulation of muscle tone. Raclopride and chlorpromazine produced dose-dependent increases in EMG activity associated with D2 occupancy of 68%–80% in the striatum and 67%–76% in the nigra. No significant increases in EMG were observed with clozapine which showed low D2 occupancy. The results are consistent with those from human studies showing extrapyramidal side effects were associated with striatal D2 occupancy of >70%.

EMG activity of the muscles of the neck and forelimbs during different forms of locomotion.

We recorded the electromyographic (EMG) activity of 7 skeletal muscles in the forequarters and 1 in the hindquarters of 6 Thoroughbred horses during overground walking, swimming in a circular pool, and walking and trotting in a water treadmill. Bipolar fine wire electrodes were inserted into the muscles and the EMG signals were recorded using a telemetric system. The splenius exhibited tonic EMG activity during swimming. The brachiocephalicus showed its highest intensity during swimming followed by the walk and trot in the water treadmill and then walking overground. The triceps brachii caput longum had a similar activity pattern to the brachiocephalicus. The brachialis showed only weak EMG activity in all 3 types of locomotion. The extensor digitorum communis had higher intensity of EMG activity in the walk in the water treadmill than in other kinds of locomotion. The flexor digitorum profundus exhibited the most intense EMG activity during swimming. These results indicated that swimming evoked strong EMG activity in the antigravity muscles in spite of reduced gravitational force. Walking in the water treadmill may require more intensified EMG activity of the forelimb than the trot in the same treadmill.

Impairment of callosal and corticospinal system function in adolescents with early-treated phenylketonuria: a transcranial magnetic stimulation study.

The transcranial activation and the conduction properties of corticospinal and callosal neurons were investigated in 12 early-treated adolescents (aged 17.3, SD 3.5 years; range 14-27 years) with phenylketonuria (PKU) by focal transcranial magnetic stimulation (fTMS) of the motor cortex. The patients had no functionally relevant motor disturbances in daily life or on clinical testing. Corticospinally mediated excitatory (response thresholds, amplitudes, central motor latencies) and inhibitory [duration of postexcitatory inhibition (PI)] effects of fTMS were investigated in contralateral hand muscles. Transcallosal inhibition (TI) (onset latency, duration, transcallosal latency) of tonic electromyographic (EMG) activity was tested in ipsilateral muscles. Peripheral motor latencies were determined for responses elicited by magnetic stimulation over cervical nerve roots. Ten normal subjects served as controls. Since in all PKU patients, central and peripheral motor latencies were normal, no neurophysiological indication of a demyelination of corticospinal or peripheral motor fibres was found. However, cortical thresholds of corticospinally mediated responses were increased (52.1, SD 11.6% versus 35.0, SD 7.4% of maximum stimulator output; P < 0.05; n = 24 hands) and their amplitudes reduced (2.9, SD 1.4 mV versus 6.1, SD 1.5 mV, P < 0.05). The duration of PI was shortened (132, SD 53 ms versus 178, SD 57 ms; P < 0.05). TI was absent in 37.5% of the investigated hands or tended to be weak. When TI was present, its onset latencies (38.0, SD 3.6 ms versus 34.7, SD 3.3 ms) and transcallosal latencies were prolonged (18.5, SD 3.8 ms versus 14.8, SD 3.2 ms), while its duration was normal. These abnormal excitatory and inhibitory effects of fTMS suggest a reduced susceptibility of cortical excitatory and inhibitory neuronal structures compatible with a loss of neurons or a rarefication of their dendrites.

Neck muscle activity after unilateral labyrinthectomy in the alert guinea pig.

In the guinea pig, lateral deviation of the head is a cardinal symptom of the vestibular syndrome caused by unilateral labyrinthectomy. In the course of recovery from this syndrome (vestibular compensation), lateral deviation of the head disappears completely in 2-3 days. Because this symptom is known to be due to the lesion of the horizontal semicircular canal system, and since obliquus capitis inferior (OCI) muscle is activated predominantly by yaw rotation (horizontal vestibulocollic reflex), we hypothesized that changes in the activity of this muscle could be at least in part responsible for the lateral head deviation caused by unilateral labyrinthectomy. In order to test this hypothesis, electromyographic (EMG) activities of the right and left OCI muscles, as well as eye movements, were recorded in 12 head-fixed alert guinea pigs at various times after left surgical labyrinthectomy (performed with the animals under halothane anesthesia). After the operation, a decrease in tonic EMG activity was observed in the right (contralateral to the lesion) OCI muscle while an increase in tonic EMG activity was detected in the left (ipsilateral) OCI muscle. In addition, phasic changes in EMG activity associated with ocular nystagmic beats occurred in the OCI muscles. These phasic changes were in the opposite direction to those of the tonic changes. There were bursts of activity in the right OCI and pauses in the left OCI. From measurements of rectified averaged EMG activities which took into account both parts (tonic and phasic) of the phenomenon, it was concluded that the labyrinthectomy-induced asymmetry between the activities of the left and right OCI muscles was high enough and lasted long enough to be an important mechanism in the lateral deviation of the head caused by unilateral labyrinthectomy.

The effects of an irreversible dopamine receptor antagonist, N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ), on the regulation of muscle tone in the rat: the role of the substantia nigra

Recent evidence has questioned the view that the increased muscle tone of Parkinson's disease results solely from reduced release of dopamine in the striatum, by emphasising the important role of the substantia nigra. The aim of the current study was to compare the effects on muscle tone of inactivating D 1 and D 2 dopamine receptors throughout the brain with those seen following their inactivation only in the substantia nigra. Inactivation of dopamine receptors by N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline injected either intraperitoneally, or bilaterally into the substantia nigra, resulted in similar increases in muscle tone, measured as changes in tonic electromyographic (EMG) activity. The magnitude and onset of EMG increases was related to the level of dopamine receptor inactivation. The results are consistent with the hypothesis that nigral dopamine mechanisms play a key role in the maintenance of muscle tone.

Evidence of a preprogrammed deactivation of the hamstring muscles for triggering rapid changes of posture in humans

Normal subjects were asked to make rapid flexions of the legs from a stationary initial standing posture in a self-paced mode. Because this movement implicates a rapid change in posture, questions were asked about the type of central command which must include the rupture of the erect posture and the accomplishment of the goal directed movement. Movements of the different segments of the body were recorded and analyzed using the optoelectronic ELITE system. Electromyographic (EMG) activities of 8 muscles of the lower limb on one side were recorded, rectified and integrated. The time relationships of the different EMG signals (activation or deactivation) were analyzed with respect to selected kinetic measures of the related segments of the body. In the majority of the subjects, before the movement onset, EMG events included a specific deactivation of the tonic EMG activity of the semimembranous (SM) and semitendinous (ST) muscles (time onset relative to the onset of the legs flexion: −196.9±96.4 ms and −180.5±89.7 ms, respectively). A second event was a phasic activation of the tibialis anterior (TA) muscle (time onset: −60.5±117.6 ms). Conjugate cross-correlation analysis of these EMG signals demonstrated the existence of a common coordinated strategy between the deactivation of the hamstring and the TA activation. Even though a small horizontal displacement of the head was recorded prior to leg movement, it occurred too late to induce deactivation of the hamstring muscles. These results demonstrate that for rapid legs flexion, where the gravity forces are the main source of joint angle acceleration, the deactivation of the SM and ST muscles acts in conjunction with the phasic activation of the TA. The preprogrammed deactivation of the SM and ST muscles represents the early phase of the central command to switch from the standing to the squatting posture.

Control of epiglottic position in dogs: role of negative upper airway pressure

We investigated the influence of negative upper airway pressure (NUAP) on hyoepiglotticus and genioglossus muscle electromyographic (EMG) activity in anaesthetised (sodium pentobarbitone/chloralose) dogs breathing via a tracheostomy. Changes in pressure were not transmitted through the entire upper airway, thus confirming airway occlusion during NUAP. When NUAP was applied at the larynx, peak inspiratory and tonic EMG activity of the genioglossus and HE both increased significantly ( p < 0.05) and reached a plateau at NUAP of −10 to −20 cmH 2O. Nasal NUAP at any level failed to influence either genioglossus or HE EMG activity. Following bilateral section of the internal branches of the superior laryngeal nerves (SLNin), resting levels of HE and genioglossus EMG activity decreased to virtually zero. Moreover, NUAP applied at the larynx now failed to recruit EMG activity for either muscle. These findings suggest active control of epiglottic position in dogs during NUAP.

Restoration of extensor excitability in the acute spinal cat by the 5-HT2 agonist DOI

1. The decerebrate cat preparation with an intact spinal cord is characterized by a high degree of excitability in extensor motoneuron pools, which is eliminated by acute spinalization. Subtype-specific agonists for serotonin (5-HT) were investigated in terms of their effectiveness in restoring the extensor excitability following spinalization. 2. Our hypothesis was that 5-HT2 receptors have the primary role in enhancement of extensor reflex excitability, whereas 5-HT1A and 5-HT1B/D receptors are relatively unimportant. Reflex excitability was assessed from the tonic levels of force and electromyographic (EMG) output from the ankle extensors medial gastrocnemius (MG) and soleus (SOL), and from the reflex forces in both these muscles generated by ramp-and-hold stretches of MG. 3. Before spinal transection, MG and SOL usually exhibited a small amount of tonic background EMG activity and force output. Ramp-and-hold stretch of MG generated a large-amplitude reflex response. Spinal transection at the level of T10 virtually abolished tonic background activity in both extensors and greatly attenuated the MG stretch reflex. Ventral topical application of the selective 5-HT2A/2C agonist (+-)-1-(2,5-dimethoxy-4-iodophenyl)-2-amino-propane hydrochloride (DOI) restored the amplitude of the MG stretch reflex in a dose-dependent fashion. However, a considerable portion of the DOI-mediated restoration of MG stretch reflex force was due to elevation of tonic background force levels above previous intact cord levels. 4. The DOI-induced increase in extensor tonic background excitability and facilitation of MG stretch reflex were reversed by ventral topical administration of the selective 5-HT2 antagonist ketanserin. No increase in extensor excitability was observed in spinalized preparations after administration of either the 5-HT1A agonist (+-)-8-hydroxy-dipropylaminotetralin hydrobromide or the 5-HT1B/1D agonist 7-trifluoromethyl-4-(4 methyl-1-piperazinyl)-pyrrolo[1,2- a]quinoxaline maleate. These data strongly suggest that the DOI-induced facilitation of extensor stretch reflex and tonic activity in spinalized preparations is mediated through an action on spinal 5-HT2 receptors. 5. One important difference between the actions of DOI in spinalized versus intact states was that the DOI-induced tonic and reflex forces in the spinalized state were subject to irregular oscillations. In contrast, DOI did not noticeably affect the smoothness of reflex force generation in the intact state. This discrepancy was probably due to the effects of clasp knife inhibition from muscular free nerve endings, which have potent reflex actions in the spinalized but not intact states. Thus DOI elevated excitability levels but did not alter the effects of spinalization on stretch reflex patterns.

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.

Soft palate muscle activity in response to hypoxic hypercapnia

We studied the effects of increasing respiratory drive on electromyographic (EMG) soft palate muscle (SPM) activity in nine anesthetized tracheostomy-breathing dogs during hypoxic hypercapnia (HH) with a 14% O2-8% CO2-78% N2 inspired gas mixture. Moving time average EMG activity was recorded from palatinus (PAL), levator veli palatini (LP), and tensor veli palatini (TP) muscles (with bipolar fine-wire electrodes) and diaphragm (DIA; with bipolar hook electrodes). During HH, peak inspiratory DIA activity increased from 18.8 +/- 1.3 to 30.1 +/- 2.0 arbitrary units and minute ventilation increased from 6.2 +/- 0.3 to 18.3 +/- 1.8 l/min (both P < 0.001). Phasic inspiratory, expiratory, and/or tonic EMG activity was present in each SPM during room air breathing (control) and increased during HH (P < 0.05), except for phasic inspiratory PAL and phasic expiratory TP activities. Peak inspiratory LP and TP activities increased during HH to 250 and 179% of control, respectively, and peak expiratory activity increased to 187, 235, and 181% of control in PAL, LP, and TP, respectively. These findings demonstrate respiratory-related regulation of SPM activity independent of local reflex control from the upper airway. However, the combined inspiratory and expiratory phasic recruitment of these muscles differs from the inspiratory recruitment of known upper airway dilator muscles.

Atipamezole, an alpha 2 antagonist, augments opiate-induced muscle rigidity in the rat

Atipamezole is a new, highly selective alpha 2-adrenoceptor antagonist currently undergoing clinical trials as an antagonist for dexmedetomidine, a potent alpha 2 agonist with sedative and analgesic properties. It has previously been demonstrated that dexmedetomidine, acting at central alpha 2 adrenoceptors, antagonizes opiate-induced muscle rigidity. However, the role of endogenous alpha 2-adrenergic systems in opiate-induced rigidity remains to be elucidated. The present study was designed to assess the effects of atipamezole on basal muscle tone and on alfentanil-induced muscle rigidity in the rat. Muscle tone was measured using gastrocnemius electromyography (EMG). After a 15-min baseline, saline or atipamezole (0.3 or 1.0 mg/kg) was administered, and 10 min later, saline or alfentanil (50, 150, or 300 μg/kg) was injected subcutaneously. Data were collected for an additional 60 min. Atipamezole (1.0 mg/kg) pretreatment (in the absence of alfentanil) produced a small increase in tonic EMG activity when compared with saline pretreatment. After saline pretreatment, significant muscle rigidity occurred in the two highest alfentanil dose groups. Atipamezole (0.3 and 1.0 mg/kg) augmented alfentanil-induced muscle rigidity. The ability of the alpha 2 antagonist to potentiate both basal muscle tone and alfentanil-induced rigidity suggests that endogenous adrenergic activity and/or direct alpha 2-adrenoceptor interaction with opioid receptors mediate opiate-induced muscle rigidity. These findings may be of clinical as well as basic neuropharmacological interest.

Effects of sleep on the tonic drive to respiratory muscle and the threshold for rhythm generation in the dog.

1. The present study was designed to determine the effect of sleep on the tonic output to respiratory muscle and on the level of chemical respiratory stimulation required to produce rhythmic respiratory output. 2. Chronically implanted electrodes recorded expiratory (triangularis sterni) and inspiratory (diaphragm and parasternal intercostal) electromyographic (EMG) activities in three trained dogs during wakefulness and sleep. The dogs were mechanically hyperventilated via an endotracheal tube inserted into a permanent tracheostomy. During the studies, a cold block of the cervical vagus nerves was maintained to avoid the complicating effects of vagal inputs on respiratory drive and rhythm. 3. During wakefulness, steady-state hypocapnia (partial pressure of CO2, PCO2 = 30 mmHg) abolished inspiratory EMG activity, resulting in apnoea, but the expiratory muscle became tonically active. Compared to wakefulness, the level of the tonic expiratory EMG activity was decreased in non-REM (non-rapid eye movement) sleep (median decrease = 34%, P = 0.005) and was further decreased in REM sleep (median decrease = 78%, P < 0.0001). During REM sleep, the tonic expiratory EMG activity was highly variable (mean coefficient of variation = 39% compared to 7% awake, P < 0.0001) and in some periods of REM, bursts of inspiratory EMG activity and active breathing movements were observed despite the presence of hypocapnia. 4. During constant mechanical hyperventilation, progressive increases in arterial PCO2 (in hyperoxia) were produced by rebreathing. Measurement of the CO2 threshold for the onset of spontaneous breathing showed that this threshold was not different between wakefulness and non-REM sleep (mean difference = 0.1 mmHg from paired observations, 95% confidence interval for the difference = -1.0 to +1.1 mmHg, P = 0.898). 5. The results show that sleep reduces the tonic output to respiratory muscles but does not increase the CO2 threshold for the generation of rhythmic respiratory output. These observations suggest that changes in the tonic drives to the respiratory motoneurones may be a principal mechanism by which changes in sleep-wake states produce changes in respiratory output.

Respiratory-related activity of soft palate muscles: augmentation by negative upper airway pressure.

We studied respiratory-related activity of the soft palate muscles in 10 anesthetized tracheostomized supine dogs. Moving time average (MTA) electromyographic (EMG) activity was measured in the palatinus (PAL), levator veli palatini (LP), and tensor veli palatini (TP) with bipolar fine-wire electrodes and in the diaphragm with bipolar hook electrodes. Measurements were made during tracheostomy breathing and nasal breathing with the mouth sealed (NB). During tracheostomy breathing, all soft palate muscles displayed respiratory-related phasic inspiratory and expiratory as well as tonic EMG activity. During NB, peak inspiratory EMG activity increased in PAL, LP, and TP because of an increase in both phasic inspiratory and tonic MTA activity. In contrast, phasic expiratory activity did not change. A constant negative pressure equal to peak inspiratory tracheal pressure during NB was applied to the caudal end of the isolated upper airway with the nose occluded. This was associated with soft palate muscle responses qualitatively similar to the responses during NB but accounted for only 39, 25, and 32% of the magnitude of the peak inspiratory MTA EMG responses to NB in PAL, LP, and TP, respectively. Our results demonstrate that the soft palate muscles exhibit respiratory-related activity in common with other upper airway muscles. Furthermore, such activity is augmented in each soft palate muscle during NB, and negative upper airway pressure makes a substantial contribution to the recruitment of soft palate muscle activity.

Symptomatic and essential palatal tremor. 1. Clinical, physiological and MRI analysis.

Palatal tremor (brief, rhythmic involuntary movements of the soft palate) apparently comprises two different nosological entities: essential palatal tremor (EPT) and symptomatic palatal tremor (SPT). The site of the abnormality in EPT is unknown, whereas SPT is believed to arise from a lesion of the brainstem or cerebellum (within the Guillain-Mollaret triangle). The clinical and physiological properties of these conditions were studied in four patients with EPT and six patients with SPT. Patients with EPT had normal cerebellar function, but those with SPT had clinical signs of cerebellar dysfunction. The palatal movements were consistent with activation of the tensor veli palatini muscle in EPT and of the levator veli palatini muscle in SPT. During sleep, EPT stopped, whereas SPT continued with only slight variations in the tremor rate. The cycle of palatal tremor could not be reset by stimulation of trigeminal afferents in either EPT or SPT patients, and Valsalva's manoeuvre did not consistently affect the rhythm of the tremor in either group. The palatal tremor cycle exerted remote effects on the tonic electromyographic activity of the upper and lower extremities only in patients with SPT. These effects were present only on the side of the cerebellar signs (opposite the side with the enlarged inferior olive) in patients with a unilateral syndrome. Essential palatal tremor patients had only polysynaptic brainstem reflex abnormalities, whereas SPT patients had abnormalities of monosynaptic, oligosynaptic and polysynaptic brainstem reflexes. Magnetic resonance imaging showed no evidence of structural abnormalities in EPT patients, but SPT patients had a hyperdense signal of the ventral upper medulla (the region of the inferior olive) on T2-weighted images. These observations support the hypothesis that EPT and SPT are two different diseases. In SPT, cerebellar dysfunction ipsilateral to the palatal tremor may be due, in part, to abnormal function of the contralateral hypertrophic inferior olive. The proposed basis of SPT is a disturbance of electrotonic coupling between the cells of the inferior olive induced by a lesion of the dentato-olivary pathway. Similar mechanisms could be responsible for postural tremors in general. The pathophysiological basis of EPT remains unknown.

Muscle stiffness and continuous electromyographic activity in old rats; An animal model for spasticity?

A mechanomyographic response of the hind foot to passive straightening and bending, as well as an electromyographic activity of the gastrocnemius and tibialis anterior muscles were recorded in old (35–44-month-old) and young female rats. In old rats, spontaneous, tonic electromyographic activity patterns were concurrently observed in both antagonistic muscles; they were low-amplitude, dense tonic activity and continuous, high-amplitude, sparse electromyographic activity. The tonic electromyographic activity was correlated with a decline in the strength and mass of muscles, as well as with motor disturbances, including paresis of the rigidly straightened backward hind legs, dragged behind by an animal. In muscles of old rats, morphological features of a chronic denervation atrophy were found. Baclofen (10 and 15 mg/kg, i.p.) diminished the spontaneous tonic electromyographic activity and potently decreased the whole body muscle tone, whereas Madopar (50 mg/kg of l-DOPA + 12.5 mg/kg of benerazide) was ineffective. It is suggested that old rats in which the above-described pathologic alterations are observed might be a useful animal model in the search for basic etiopathological mechanisms of spasticity and similar disturbances found in humans.

Influence of stabilization occlusal splints on sternocleidomastoid and masseter electromyographic activity.

The present work was conducted in order to determine the effect of stabilization occlusal splints on electromyographic (EMG) activity of sternocleidomastoid and masseter muscles, in subjects with tenderness to palpation in these muscles. A full-arch maxillary stabilization occlusal splint was made for each of 14 subjects. Tonic EMG activity, as well as during saliva swallowing and maximal voluntary clenching, was recorded with and without a stabilization occlusal splint inserted. Similar tonic, as well as maximal voluntary clenching EMG activity, with and without the stabilization occlusal splint, was observed. During saliva swallowing, the activity in both muscles was significantly lower with the stabilization occlusal splint. This suggests that daytime use of the stabilization occlusal splint might improve tenderness to palpation in the studied muscles, since the frequency of swallowing function is higher during waking hours.

Electromyographic studies of neck muscles in the intact cat. I. Patterns of recruitment underlying posture and movement during natural behaviors.

Natural head movements in alert, unrestrained cats were studied using video-filming, videofluoroscopy and electromyographic (EMG) recording methods. In each cat, up to sixteen neck muscles or neck-muscle compartments were implanted with recording electrodes. Patterns of muscle recruitment were examined during systematically-selected behavioral epochs in which the cat held a range of stationary postures, and when it performed volitional and exploratory behaviors such as flexion-extension or turning, grooming, eating, or headshaking. Patterns of muscular activity were interpreted with reference to simultaneous video images of head and neck movements. In separate, videofluoroscopic analysis, flexion-extension movements were examined to gain insight into the underlying movements of the skull and cervical vertebrae. These and other movements were found commonly to depend upon changes in joint angles between lower as well as upper cervical joints. Stationary postures in which the neck was held vertically were consistently associated with tonic EMG activity in only two long dorsal muscles, biventer cervicis and occipitoscapularis. Less consistent activity was also present in dorsal intervertebral muscles crossing lower cervical joints. When the neck was held horizontally, the long dorsal muscles increased their EMG activity and moderate activity was also recorded in deeper intervertebral and suboccipital muscles. When flexion-extension occurred around upper cervical joints, greatest activity was recorded in rectus capitis posterior and complexus, but when it involved the lower cervical joints, large changes in EMG activity could also be detected in biventer cervicis, occipitoscapularis, and the intervertebral muscles crossing lower cervical joints. During specialized, sagittal-plane movements such as grooming, well-defined patterns of synergy could be recognized that varied according to the degree of involvement of upper and lower cervical joint-sets. Movements in the horizontal plane were associated with EMG activity in a largely different subset of neck muscles including splenius, longissimus capitis and obliquus capitis inferior. The levels of EMG activity during flexion-extension or turning movements were much lower than those observed during other more vigorous behaviors, such as head shaking. Some neck muscles, such as clavotrapezius and sternomastoideus, could only be recruited during forceful or ballistic head movements. Results showed that the patterns of muscular activation were linked not only to the speed and trajectory of the movements of the skull, but also to the kinematics of the motion occurring across different parts of the cervical column.