Recovery of acetylcholine release and choline acetyltransferase activity after freezing-induced degeneration of rat soleus muscle

In order to study the effect of synaptic contact on the amounts of choline acetyltransferase (ChAT) and acetylcholine (ACh) in the nerve terminals and on their ability to release ACh, a freeze-thaw procedure was developed as a means to induce long lasting degeneration of rat soleus muscle. It was found that 4 days after the freeze thaw procedure the preparation did not contract upon direct electric stimulation and the level of creatine kinase (CK) was below detection. The preparation contained about 15% of the ChAT activity and 15% of the ACh content of the controls. The ACh release evoked by 50 mM KCl was 25% of controls, but it was, when expressed as a fraction of the ACh content, about twice as high as that in control muscles. At day 12, the preparation still did not contract and the level of CK was less than 5% of controls. The ChAT activity and the ACh content were 40% and 20% of controls, respectively. However, no release of ACh could be evoked by 50 mM KCl. At days 28 and 58 the preparation contracted upon stimulation of the nerve; the CK activity had recovered to about 20% and the ACh content to 40%, while the ChAT activity did not increase above 40%. The KCl-evoked ACh release had recovered to 20-30% of controls. The results indicate that freezing destroyed muscle cells and most intramuscular nerve branches. Subsequent regeneration of muscle fibres was slow, probably because freezing had killed many satellite cells in the muscle. Because the ChAT activity at day 12 had recovered when CK was almost absent and the preparation failed to contract, we conclude that there was expression of ChAT activity in 'nerve terminals' which do not make contact with regenerated muscle cells, although little if any ACh was released from these sites.     

Changes in stiffness induced by hindlimb suspension in rat soleus muscle

Soleus muscle atrophy was induced by hind-limb suspension of rats for 3 weeks with the intention of inducing a relative increase in the percentage of fast-twitch fibres and assessing modifications in muscle stiffness. A method of dual controlled releases was used to obtain tension/extension curves and force/velocity relationships characterizing the mechanical behaviour of the soleus. Fibre typing was achieved by myofibrillar adenosine 5'-triphosphatase staining. Results showed that hindlimb suspension decreased the percentage of slow-twitch fibres (-31%) to the profit of fast-twitch fibres (+370%) and intermediate fibres (+255%). This led to an increase in maximal shortening velocity. Tension/extension curves indicated a decrease in soleus stiffness after 3 weeks of unloading. Changes in elastic properties are interpreted in terms of modifications occurring in the active part and the passive part of the so-called series elastic component. These changes also suggest that the parameters derived from a twitch are inappropriate to account for modifications in speed-related properties of muscle.     

Myosin and troponin changes in rat soleus muscle after hindlimb suspension

We examined the myosin heavy-chain (MHC), troponin T (TnT), and troponin I (TnI) isoform composition in the rat soleus muscle after 21 days of hindlimb suspension using electrophoretic and immunoblotting analysis with specific monoclonal antibodies. The suspended soleus showed a shift in the MHC isoform distribution with a marked increase (from 1.0 to 33%) in the relative amount of type IIa and IIx MHC and a corresponding decrease in type I MHC. However, type IIb MHC, which represents a major component in fast-twitch muscles, was not detected in suspended soleus muscles. TnT and TnI isoform composition was also changed with the appearance of fast-type TnI and TnT bands. However, a high-mobility TnT band, which represents a major component in fast-twitch muscles, was not expressed in suspended soleus. These isoform transitions may be related to the increased maximal velocity of shortening and higher calcium sensitivity previously reported in the rat soleus after hindlimb suspension.     

Single soleus muscle fiber function after hindlimb unweighting in adult and aged rats

This investigation compared how hindlimb unweighting (HU) affected the contractile function of single soleus muscle fibers from 12- and 30-mo-old Fischer 344 Brown Norway F1 Hybrid rats. After 1 wk of HU, functional properties of single permeabilized fibers were studied, and, subsequently, the fiber type was established by myosin heavy chain (MHC) analysis. After HU, the relative mass of soleus declined by 12 and 19% and the relative mass of the gastrocnemius declined by 15 and 13% in 12- and 30-mo-old animals, respectively. In 12-mo-old animals, the peak active force (5.0 +/- 0.2 x10(-4) vs. 3.8 +/- 0.2 x10(-4) N) and the peak specific tension (92 +/- 4 vs. 78 +/- 3 kN/m2) were significantly reduced in the MHC type I fibers by 24 and 15%, respectively. In 30-mo-old animals, the peak active force declined by 40% (4.7 +/- 0.2 x10(-4) vs. 2.8 +/- 0. 3 x10(-4) N) and the peak specific tension declined by 30% (79 +/- 5 vs. 55 +/- 4 kN/m2). The maximal unloaded shortening velocity of the MHC type I fibers increased in 12-mo-old animals (from 1.65 +/- 0.12 to 2.59 +/- 0.26 fiber lengths/s) and in 30-mo-old animals (from 0.90 +/- 0. 09 to 1.50 +/- 0.10 fiber lengths/s) after HU. Collectively, these data suggest that the effects of HU on single soleus skeletal muscle fiber function occur in both age groups; however, the single MHC type I fibers from the older animals show greater changes than do single MHC type I fibers from younger animals.     

Distribution of myosin heavy chain isoforms in non-weight-bearing rat soleus muscle fibers

The effects of 14 days of spaceflight (SF) or hindlimb suspension (HS) (Cosmos 2044) on myosin heavy chain (MHC) isoform content of the rat soleus muscle and single muscle fibers were determined. On the basis of electrophoretic analyses, there was a de novo synthesis of type IIx MHC but no change in either type I or IIa MHC isoform proportions after either SF or HS compared with controls. The percentage of fibers containing only type I MHC decreased by 26 and 23%, and the percentage of fibers with multiple MHCs increased from 6% in controls to 32% in HS and 34% in SF rats. Type IIx MHC was always found in combination with another MHC or combination of MHCs; i.e., no fibers contained type IIx MHC exclusively. These data suggest that the expression of the normal complement of MHC isoforms in the adult rat soleus muscle is dependent, in part, on normal weight bearing and that the absence of weight bearing induces a shift toward type IIx MHC protein expression in the preexisting type I and IIa fibers of the soleus.     

Experimental muscle pain does not cause long-lasting increases in resting electromyographic activity

The mutual links between muscle pain and resting electromyographic (EMG) activity are still controversial. This study described effects of experimental muscle pain on resting EMG activity in a jaw-closing muscle and a leg muscle. Pain was induced by injections of hypertonic saline into the muscles in 10 subjects. Injections of isotonic saline served as a control. The pain intensity was scored on visual analog scales (VAS) and surface and intramuscular wire EMGs were obtained from the resting muscles before, during, and after saline injections. EMG activity was analyzed in 30-s intervals and demonstrated, in both muscles, significant increases 30-60 s after injection of hypertonic saline, but not after injection of isotonic saline. In contrast to the transient increase in EMG activity, the pain sensation lasted up to 600 s after injection of hypertonic saline. It was concluded that acute muscle pain is unable to maintain longer-lasting resting muscle hyperactivity.     

Heat production and chemical change during isometric contraction of rat soleus muscle

1. Methods are described whereby the soleus muscle of the rat may be used for the investigation of initial processes in the absence of oxidative recovery. 2. The anaerobic conditions employed had no effect on the concentration of phosphocreatine in resting muscle or the mechanical response during contraction. 3. Muscles were stimulated tetanically for 10 s at 17-18 degrees C. Measurements were made of the heat production and metabolic changes that occurred during a 13 s period following the first stimulus. 4. There was no detectable change in the concentration of ATP. Neither was there detectable activity of adenylate kinase or adenylate deaminase. The changes in the concentration of glycolytic intermediaries were undetectable or very small. 5. The change in the concentration of phosphocreatine was large and amounted to -127 +/- 11-4 mumol/mmol Ct (mean and S.E. of the mean, negative sign indicates break-down, Ct = free creatine + phosphocreatine) which is equivalent to about -2-13 mumol/g wet weight of muscle. The heat production was 6549 +/- 408 mJ/mmol Ct (mean and S.E. of mean) which is equivalent to about 110 mJ/g. 6. About 30% of the observed energy output is unaccounted for by measured metabolic changes. 7. The ratio of heat production (corrected for small amounts of glycolytic activity) to phosphocreatine hydrolysis was -49-7 +/- 5-6 kJ/mol (mean and S.E. of mean), in agreement with previous results using comparable contractions of frog muscle, but different from the enthalpy change associated with phosphocreatine hydrolysis under in vivo conditions (-34 kJ/mol). 8. The results support the notion that the discrepancy between energy output and metabolism is an indication of an unidentified process of substantial energetic significance that is common to a number of species.     

Influence of upper airway pressure oscillations on soft palate muscle electromyographic activity

Snoring is characterized by high-frequency (30-50 Hz) pressure oscillations (HFPO) in the upper airway (UA). The soft palate is a major oscillating structure during snoring, and soft palate muscle (SPM) activity is an important determinant of velopharyngeal patency. Consequently, we examined the effect of artificial HFPO applied to the UA on the integrated electromyographic (EMG) activity of the SPMs in 11 supine mouth-closed anesthetized (pentobarbital sodium/chloralose) dogs breathing spontaneously via a tracheostomy. The EMGs of the palatinus (Pal; n = 11), levator veli palatini (LP; n = 9), and tensor veli palatini (TP; n = 8) were monitored with intramuscular fine-wire electrodes. Peak inspiratory and peak expiratory EMG activity was measured in arbitrary units (au) as the mean of five consecutive breaths. HFPO [+/- 4.5 +/- 0.4 (SE) cmH2O; 30 Hz] applied at the laryngeal end of the isolated UA increased peak inspiratory EMG from 3.3 +/- 2.0 to 8.4 +/- 1.7 au (P < 0.05) for Pal and from 2.0 +/- 1.1 to 7.3 +/- 2.7 au (P < 0.05) for LP. For the TP, increases were evident in four dogs, but mean values for the group did not change (5.8 +/- 2.4 to 11.0 +/- 4.1 au, P = 0.5). The peak expiratory EMG did not change for any SPM (all P > 0.3). Thus HFPO applied to the UA augments inspiratory SPM activity. Reflex augmentation of SPM activity by HFPO may serve to dilate the retropalatal airway and/or stiffen the soft palate during inspiration in an attempt to stabilize UA geometry during snoring.     

Vestibular-evoked electromyographic responses in soleus: a comparison between click and galvanic stimulation

The aim of this study was to demonstrate, if possible, vestibulospinal reflex responses in soleus using a stimulus known to be capable of exciting vestibular afferents, namely 100-dB (NHL) clicks. We were able to show short-latency electromyographic (EMG) responses after clicks in five of eight normal subjects, and then we compared these responses with those after transmastoid galvanic stimulation (12 normal subjects). Stimulation of the side towards which the head was rotated (i.e. the side facing backwards) with either clicks or the cathode (anode applied to the opposite side) gave an initial excitatory response in soleus, while click or cathodal stimulation of the opposite side (i.e. the side facing forwards) gave an initial inhibitory response. Onset latencies and modulation with changes in postural task were identical for both click- and galvanic-evoked responses. In addition, there was a significant correlation between the amplitudes of the responses in soleus after click and galvanic stimulation (R2=0.72). These similarities suggest that the earliest reflex responses in soleus after clicks and galvanic stimulation may be mediated by a common central pathway. In contrast, there was no correlation between the amplitudes of responses evoked by 100-dB clicks in soleus and those evoked by the same stimulus in the sternocleidomastoid. We conclude that vestibular activation by clicks can evoke reflex responses in lower-limb muscles and these responses have similar characteristics to the earliest responses evoked by galvanic vestibular stimulation.     

An electromyographic study of masseter muscle activity amongst overdenture and complete denture patients

Recently, several systems of topical antibiotic administration have been investigated. Most systems use sustained release devices to obtain high levels of antibiotics in the deepened periodontal pockets. Metronidazole and tetracycline can be administered without causing systemic side-effects. All systems summarized in this article are to be used after scaling and root planing of the diseased sites to increase the effect of the mechanical treatment.     

Bilateral experimental muscle pain changes electromyographic activity of human jaw-closing muscles during mastication

The effects of bilateral experimental muscle pain on human masticatory patterns were studied. Jaw movements and electromyographic (EMG) recordings of the jaw-closing muscles were divided into multiple single masticatory cycles and analyzed on a cycle-by-cycle basis. In ten men simultaneous bilateral injections of hypertonic saline (5%) into the masseter muscles caused strong pain (mean+/-SE: 7.5+/-0.4 on a 0-10 scale), significantly reduced EMG activity of jaw-closing muscles in the agonist phase, and significantly increased EMG activity in the antagonist phase. Nine of the subjects reported a sensation of less intense mastication during pain. Injections of isotonic saline (0.9%) did not cause pain or significant changes in masticatory patterns. The influence of higher brain centers on conscious human mastication can not be discarded but the observed phase-dependent modulation could be controlled by local neural circuits and/or a central pattern generator in the brain stem which are capable of integrating bilateral nociceptive afferent activity.     

Influence of two weeks of non-weight bearing on rat soleus motoneurons and muscle fibers

OBJECTIVES: To analyse the ethical implications of informing patients about their do-not-resuscitate status (DNR). DESIGN: Questionnaire. SETTING: Nationwide, 6 months after the publication of guidelines on DNR in 1994. SUBJECTS: A 10% random sample of the members of the Swedish Cardiac Society. 104 physicians and 196 nurses. MAIN OUTCOME MEASURES: To what extent are patients, physicians and nurses involved in decisions about DNR, and how should the ethical conflict involved in informing patients about their DNR status be described and analysed? RESULTS: Of 73% responding, 84% of the physicians and 8% of the nurses had made a DNR decision. The decision was regarded as ethically right and well timed and it was discussed with 33% of the competent patients. Half of the respondents believed that DNR orders should be discussed with the competent patient. but still only one third of the patients are involved. The ethical conflict is analysed using the principles of autonomy and nonmaleficence as value premises. CONCLUSIONS: Many physicians are still reluctant to find out what the patient wants. Being ignorant they risk harming the patient. It is recommended that information about DNR status should be given incrementally and that the attitudes of the old and chronically ill in-hospital patients are studied. Do they want to be informed, and if so, how and when do they want it to be done?     

The effect of pain from orthodontic arch wire adjustment on masseter muscle electromyographic activity

Pain has been shown to have an effect on muscle activity even when it does not originate in the muscle itself or in the related joint. The effect of pain from arch wire adjustment on jaw muscle activity is unclear. This study systematically evaluated the effects of orthodontic arch wire adjustment pain on masseter electromyographic (EMG) activity and on the swallowing threshold. The EMG recordings were made on 22 subjects (ages 11 to 15) under three conditions: chewing five peanuts (10 seconds), watching TV chewing gum (15 minutes), and watching TV with no gum (15 minutes). An arch wire adjustment or placebo adjustment was then made. Subjects returned after 48 hours, and the EMG measurements were made under the same conditions. After 3 weeks, subjects received arch wire or placebo treatment in a crossover design with identical recording procedures. The EMG levels while chewing peanuts decreased in 18 of 22 subjects after treatment, compared with 9 of 22 subjects after the placebo. While watching TV with gum, the EMG levels of 20 of 22 subjects decreased after treatment, compared with 9 of 22 subjects after the placebo. The number of chewing strokes before swallowing increased significantly after treatment compared with after placebo. The results suggest that orthodontic pain on teeth tend to reduce muscle activity during function.     

Spontaneous activity of otolith-related vestibular nuclear neurons in the decerebrate rat

The discharge properties of lateral and descending vestibular neurons responsive to constant velocity off-vertical axis rotations (OVAR) in the clockwise (CW) and counterclockwise (CCW) directions, were studied at the stationary and earth-horizontal position of decerebrate adult rats. From the coefficient of variation (CV), the spontaneous activities of OVAR-responsive neurons were classified into regular and irregular patterns. Of the neurons (n = 36) that showed symmetric and stable bidirectional response sensitivity (delta defined as CW gain over CCW gain) to OVAR (10 degrees tilt), some exhibited progressive phase shift with velocity (1.75-15 degrees/s) while others exhibited stable response phase. Most neurons of the former group (93% or 12/13) showed regular discharge pattern while only 22% (n = 5/23) of the latter group showed such a pattern. Though the phase-stable neurons showed a significantly higher average CV than the phase-shifted neurons, there was no significant difference between the mean spontaneous firing rates of these neurons. The neurons (n = 17) that showed asymmetric and variable delta to OVAR velocity can also be grouped-those that exhibited a greater gain with rotations directed towards the side of recording (I neurons) showed irregular discharge pattern while those that exhibited a greater gain with rotations directed towards the side contralateral to recording (C neurons) showed regular discharge pattern. The I and C neurons also exhibited significant difference in mean firing rates. The relationship between the response characteristics of the OVAR-responsive neurons and their spontaneous activity at the stationary and earth-horizontal position is discussed.     

Effects of long-term phasic electrical stimulation on denervated soleus muscle: guinea-pig contrasted with rat

Guinea-pig soleus muscles were denervated and electrically stimulated for periods of 43 to 66 days. Stimuli were in 1 s bursts of 40 Hz pulses, repeated every 5 min. Other guinea-pigs were denervated for 82 days without stimulation and, in a third group, the soleus muscle was necrotized and allowed to regenerate without reinnervation for 13-15 days. Isometric and isotonic recordings were made in vivo. Denervated guinea-pig muscles were embedded in epoxy resin for light and electron microscopy. Chronic stimulation of denervated guinea-pig soleus had no effects on the prolonged twitch or on reduced maximal shortening velocity, maximal rate of rise of tension and tetanic force. This contrasts with the slow-to-fast conversion produced by denervation and denervation-stimulation of rat soleus. Loss of force was much greater in rat than guinea-pig after denervation, and chronic stimulation increased force in rat to the same level as in guinea-pig after denervation (with or without stimulation). Eighty-day denervated guinea-pig soleus did not reveal those morphological signs of fibre breakdown and regeneration which are prominent in denervated rat soleus muscles. Those changes in rat resembled aneurally regenerated muscles in several aspects, especially the increased incidence of fibres with internal myo-nuclei which did not appear in guinea-pig soleus after denervation. Aneurally regenerated guinea-pig soleus became fast like aneurally regenerated rat muscle. Our data are compatible with the hypothesis that slow-to-fast transformation of denervated rat soleus is not directly brought about by chronic stimulation but by de-novo formation of fast-contracting regenerated fibres. The persistence of fibrillation in guinea-pig but not rat after denervation may account for the species difference.     

Properties of isolated adult rat muscle fibres maintained in tissue culture

1. Adult rat skeletal muscles were dissociated by collagenase treatment and trituration, and the isolated muscle fibres were maintained in vitro for 2-3 weeks. At various stages, the fibres were examined physiologically and morphologically. 2. The isolated fibres underwent some changes characteristic of muscle denervated in vivo. For instance, input resistance increased and extrajunctional acetylcholine (ACh) receptors appeared. In addition, the beginning stages of apparent muscle fibre fragmentation were observed. 3. In other respects, the cultured isolated fibres behaved differently than in vivo denervated fibres. Fibrillation developed only occasionally in vitro. The onset of ACh supersensitivity was slower (6 days) than after denervation in vivo (2-3 days). Some fibres developed localized regions of destriation, which apparently was due to loss of in-register alignment of myofibrils.     

Spontaneous thymic hemorrhage in an adult

Acute hemorrhage in a normal thymus in neonates and infants has been reported in the literature. These patients were known to have an antecedent cause or defects in coagulation. The case of an adult who developed acute hemorrhage in a normal thymus and who was known not to have any defects in coagulation, hypertension, or other underlying cause is reported.