Movement-related skin strain associated with goal-oriented lip actions

 It is generally accepted that sensory input contributes to the generation of natural movements. In most motor systems, muscle spindles, tendon organs, joint receptors, and cutaneous mechanoreceptors may provide proprioceptive information. However, the perioral area of the human face lacks muscle spindles, tendon organs, and joint receptors and is therefore a model system for the study of cutaneous afferent contributions to proprioception. This investigation examined a series of skin strains associated with lower-lip movements in human subjects to determine if such strains, which serve as stimuli for cutaneous mechanoreceptors, may underlie proprioception in the face. The results suggested that strains associated with lower-lip movements were of sufficient magnitude to elicit cutaneous mechanoreceptor discharge, as shown in recent human microneurographic studies. Further, the magnitude of multiple strains was predictive of lower-lip movement endpoints. These results highlight the potential importance of cutaneous mechanoreceptors as putative proprioceptors. Received: 16 February 1998 / Accepted: 26 May 1998     

The role of the fusimotor system with respect to the contribution of the diaphragm and the intercostal muscles to the respiratory tidal volume

Summary The efferent electrical activity in the phrenic nerve can be quantified in such a way that it gives a good correlation to tidal volume. After administration of the drug benzoctamine this relationship changes: more phrenic nerve activity is needed for the same tidal volume. No changes were found in the neuro-muscular transmission from the phrenic nerve to the diaphragm. There was no alteration in dynamic compliance of the lungs or in airway resistance. The afferent phrenic nerve activity from proprioceptors in the diaphragm did not change. It seems unlikely that respiratory neurons in the brainstem were affected since the sensitivity of the respiratory system to CO₂ did not change.It is known that the tonic fusimotoneuron activity is suppressed at a supraspinal level by benzoctamine. Since intercostal muscles have muscle spindles and the diaphragm hardly has any, the intercostal muscle activity will be affected more than diaphragmatic activity by benzoctamine. This could actually be shown by quantifying the electromyogram of inspiratory external intercostal muscles.The tidal volume regulation is controlled by the vagal feedback loop. In order to reach a certain tidal volume after administration of benzoctamine, the contribution of the diaphragm has to increase because the activity of the intercostal muscles is diminished.     

Respiratory muscle contractile inactivity induced by mechanical ventilation in piglets leads to leaky ryanodine receptors and diaphragm weakness

Respiratory muscle contractile inactivity during mechanical ventilation (MV) induces diaphragm muscle weakness, a condition referred to as ventilator-induced diaphragmatic dysfunction (VIDD). Although VIDD pathophysiological mechanisms are still not fully understood, it has been recently suggested that remodeling of the sarcoplasmic reticulum (SR) calcium release channel/ryanodine receptors (RyR1) in the diaphragm is a proximal mechanism of VIDD. Here, we used piglets, a large animal model of VIDD that is more relevant to human pathophysiology, to determine whether RyR1 alterations are observed in the presence of diaphragm weakness. In piglets, diaphragm weakness induced by 72 h of respiratory muscle unloading was associated with SR RyR1 remodeling and abnormal resting SR Ca²⁺ leak in the diaphragm. Specifically, following controlled mechanical ventilation, diaphragm contractile function was reduced. Moreover, RyR1 macromolecular complexes were more oxidized, S-nitrosylated and phosphorylated at Ser-2844 and depleted of the stabilizing subunit calstabin1 compared with controls on adaptive support ventilation that maintains diaphragmatic contractile activity. Our study strongly supports the hypothesis that RyR1 is a potential therapeutic target in VIDD and the interest of using small molecule drugs to prevent RyR1-mediated SR Ca²⁺ leak induced by respiratory muscle unloading in patients who require controlled mechanical ventilation.     

Development of mechanoreceptor numbers in embryonic chick-quail chimeras

Our experiments addressed the problem of the regulation of the number of mechanoreceptors by sensory axons and/or their peripheral target tissues. According to a previous study (Zelená et al. 1997) white leghorn chickens have more muscle spindles in the plantaris muscle (45.4+/-7.8; mean+/-SD) than the Japanese quail (35.3+/-4.8) and significantly more Herbst corpuscles in the crural region (380.0+/-85.0) than the quail (124.9+/-32.8). Embryonic chick-quail chimeras were therefore used as a model with distinct recombinations of the nerve supply and peripheral tissue for studying the developmental control of these mechanoreceptors. The chick host leg bud was replaced with a quail leg bud of equal age and vice versa on embryonic day 3, prior to the onset of innervation of the periphery. Shortly before hatching the chimeras were sacrificed and muscle spindles and Herbst corpuscles counted. Recombinations of chicken nerves with quail limb buds have shown that the richer nerve supply by chick Ia axons induced a significant increase in the number of muscle spindles in the plantaris muscles (55.5+/-13.4) of the grafted quail limb. In some instances, a similar increase in spindle numbers was also found in control legs grafted onto hosts of the same species. In the reverse type of chimera where chick embryo legs were grafted onto quail hosts, spindles developed in lower numbers (27.3+/-3.2). In that case the lower number of Ia axons in quail nerves induced a lower number of spindles in the chicken muscle. The numbers of Herbst corpuscles were, however, low in both types of chimera. Quail legs grafted onto host chick embryos contained 126.8+/-26.4 corpuscles, presumably due to a restrictive influence of the smaller crural area in the quail. Chick legs grafted onto quail hosts had only 99.6+/-34.1 crural corpuscles; the target area in chick embryo legs failed to attract more quail axons and/or to induce axonal sprouting. The developmental regulation of the number of the two types of mechanoreceptors examined in our study thus differ. While sensory axons appear to play the dominant role in the development of muscle spindles, their role seems to be restricted by hitherto unknown peripheral factors during the development of Herbst corpuscles.     

Increase of elastic fibres in muscle spindles of rats following single or repeated denervation with or without reinnervation

Summary Muscle spindles in the lower lumbrical muscles of rats were studied by transmission electron microscopy following denervation with or without reinnervation. The number and total area of elastic fibres per muscle spindle increased at 3–12 months following various experimental procedures: (1) denervation and reinnervation after a single crush lesion to the sciatic nerve; (2) reinnervation after four-fold repeated crush injuries; and (3) transection and suture of the nerve. The increased number of oxytalan and elaunin fibres, the precursors of mature elastic fibres, within these muscle spindles provided further evidence for their numerical and dimensional increase. An attachment site of elastic fibres at the spindle pole was identified at the inner cells of the outer spindle capsule. The processes of these cells embraced terminating elastic fibres tightly. Attachment of elastic fibres to intrafusal muscle fibres was less conspicuous since they were not similarly embraced but were rather indistinctly, though closely, associated with the basal lamina along longitudinal surface indentations of intrafusal muscle fibres. It is concluded from this series of experiments that muscle spindles, as dynamic mechanoreceptors, maintain their elastic properties even under pathological conditions. The increase of elastic fibres following denervation and reinnervation represents an obviously meaningful reaction that may compensate for loss of tonic properties of muscle spindles without causing stiffness.     

Morphometry and histoenzymology of the hamster tenuissimus and its muscle spindles

Muscle spindles and extrafusal fibers in the tenuissimus muscle of mature golden Syrian hamsters were studied morphologically and quantitatively using several light microscopic techniques. Muscle spindles were identified in serial-transvere frozen-sections of whole muscles stained with hematoxylin and eosin. Five tenuissimus muscles were examined from origin to insertion, and the locations of individual receptors were plotted in camera-lucida reconstructions. Spindles were found in proximity to the main neurovascular bundle in the central core of each muscle. A range of 16–20 receptors was noted per muscle. The mean muscle spindle index (the total number of spindles per gram of muscle weight) was 503 and the average spindle length was 7.5 mm. Oxidative enzyme and myosin adenosine-triphosphatase (ATPase) staining profiles were also evaluated in the intrafusal and extrafusal fibers in each muscle. Even numbers of type I and type IIA extrafusal fibers were distributed homogeneously throughout all muscle cross-sections. Histochemical staining patterns varied along the lengths of the three intrafusal fiber types. Nuclear chain fibers possessed staining properties similar to the type IIA extrafusal fibers and exhibited no regional variations. Bag₁ fibers displayed staining variability, particularly when treated for myosin ATPase under acid preincubation conditions. Some spindles were isolated under darkfield illumination and then either treated with 7-nitrobenz-2-oxa-1, 3-diazole (NBD)-phallacidin to detect filamentous actin by fluorescence microscopy, or prepared for conventional scanning electron microscopy (SEM). By fluorescence microscopy, a registered actin banding-pattern was observed in the sarcomeres of the intrafusal fibers, and variations in the intensity of banding were noted amongst different fibers. SEM revealed punctaie sensory nerve endings that adhered intimately to the surfaces of underlying intrafusal fibers in the equatorial and juxtaequatorial regions. By transmission electron microscopy (TEM) these endings appeared crescent-shaped and were enveloped by external laminae. Each profile contained numerous mitochondria and cytoskeletal organelles. The high spindle density observed in this muscle suggests that the hamster tenuissimus may function in hindlimb proprioception.     

The muscle spindles in slow and twitch skeletal muscle of the lizard

1. Responses from stretch receptors, identified as muscle spindles, were recorded in filaments of the nerve supplying a twitch muscle, semimembranosus, and a slow muscle, semitendinosus in the lizard Tiliqua.2. While recording afferent discharges in one filament of the motor nerve, several adjacent filaments were each in turn stimulated repetitively until one was encountered which on stimulation produced a powerful increase in spindle firing. Such an effect of the motor stimulus was interpreted as resulting from intrafusal contraction. Any interference with spindle firing patterns from extrafusal contraction produced by the motor stimulation was removed by differentially blocking the contraction with the drug curare.3. Discharge patterns of spindles in response to a slow stretch of the muscle were compared with the response to the same stretch, but during repetitive stimulation of the motor nerve filament which produced an intrafusal contraction.4. At the initial length, the firing rate of spindles in the twitch muscle was greatly increased by the motor tetanus. There was little further increase in the response during and following stretch of the muscle.5. While the spindles in the slow muscle were only moderately excited by the motor tetanus at the initial length of the muscle, a large increase was recorded during the dynamic component of the stretch. At the new length, the steady-state firing continued at a rate well above that for the initial length.6. The effect of the motor tetanus on the response to stretch of muscle spindles in the slow muscle could be mimicked by adding succinyl choline (5 mug/ml.) to the perfusion solution. Spindles in the twitch muscle did not show a sustained sensitivity to the drug.7. It is suggested that while the different effects of motor stimulation on the responses to stretch of spindles in slow and twitch muscle can be explained by propositions based on the sliding filament theory of contraction, the sustained elevation, at the new length, of firing frequencies of spindles in slow muscle might require an additional explanation.     

Morphometry and histoenzymology of the hamster tenuissimus and its muscle spindles.

Muscle spindles and extrafusal fibers in the tenuissimus muscle of mature golden Syrian hamsters were studied morphologically and quantitatively using several light microscopic techniques. Muscle spindles were identified in serial-transverse frozen-sections of whole muscles stained with hematoxylin and eosin. Five tenuissimus muscles were examined from origin to insertion, and the locations of individual receptors were plotted in camera-lucida reconstructions. Spindles were found in proximity to the main neurovascular bundle in the central core of each muscle. A range of 16-20 receptors was noted per muscle. The mean muscle spindle index (the total number of spindles per gram of muscle weight) was 503 and the average spindle length was 7.5 mm. Oxidative enzyme and myosin adenosine-triphosphatase (ATPase) staining profiles were also evaluated in the intrafusal and extrafusal fibers in each muscle. Even numbers of type I and type IIA extrafusal fibers were distributed homogeneously throughout all muscle cross-sections. Histochemical staining patterns varied along the lengths of the three intrafusal fiber types. Nuclear chain fibers possessed staining properties similar to the type IIA extrafusal fibers and exhibited no regional variations. Bag1 fibers displayed staining variability, particularly when treated for myosin ATPase under acid preincubation conditions. Some spindles were isolated under darkfield illumination and then either treated with 7-nitrobenz-2-oxa-1,3-diazole (NBD)-phallacidin to detect filamentous actin by fluorescence microscopy, or prepared for conventional scanning electron microscopy (SEM). By fluorescence microscopy, a registered actin banding-pattern was observed in the sarcomeres of the intrafusal fibers, and variations in the intensity of banding were noted amongst different fibers. SEM revealed punctate sensory nerve endings that adhered intimately to the surfaces of underlying intrafusal fibers in the equatorial and juxtaequatorial regions. By transmission electron microscopy (TEM) these endings appeared crescent-shaped and were enveloped by external laminae. Each profile contained numerous mitochondria and cytoskeletal organelles. The high spindle density observed in this muscle suggests that the hamster tenuissimus may function in hindlimb proprioception.     

Frog muscle spindles with unbranched myelinated afferent axons: the response to stretch and the length of the first myelinated segment.

1. Twenty-five muscle spindles innervated by unbranched myelinated axons in the capsule were isolated from sartorius muscle in young frogs (2-2--9-5 g in weight, 28-47 mm in rostro-caudal length). 2. The lengths and the diameters of the first myelinated segments varied from 30 to 170 mum and from 9 to 20 mum respectively. There was no relationship between the lengths and the diameters. 3. Dynamic and static components were analysed from discharge rates of the muscle spindles during ramp-and-hold stretches of 0-8 mm from different initial lengths. The values of the dynamic components to a certain stretch stimulation increased with shortening in the length of the first myelinated segment. The values of the static components were independent in length. 4. The amplitudes of action potentials recorded from the spindle terminal decreased during the dynamic phase of the stretch. The ratio of amplitude decrease at the end of the dynamic phase versus the initial length depended upon the length of the first myelinated segment. 5. These results suggest that the discharges during stretch may arise at the first node, though the spontaneous discharges may be generated at the terminal.     

Physiological properties of muscle spindles in dorsal neck muscles of the cat.

1. Single-fiber recording was used to examine the properties of 107 spindle endings in cat biventer cervicis (BC) and complexus (CM) muscles. Responses of receptors were examined following muscle contraction and ramp and hold stretch. Twenty-two endings in splenius (SP) were also examined, but their responses could not be quantitated because the anatomy of SP prevented the application of appropriate stretches. 2. Conduction velocitites of spindle afferents ranged from 13 to 90 m/s. Endings with primary response patterns usually had faster conduction velocities than secondary endings, but there was overlap in the conduction velocity ranges of the two subgroups. 3. Most neck spindle afferents could be classified as either primary or secondary by a constellation of physiological criteria including dynamic response pattern, dynamic index, and variability of resting discharge frequency. However, 22 of 107 endings from BC and CM had responses with characteristics intermediate between primary and secondary responses. The possible sources of these characteristics are discussed. 4. Despite the similarity in properties between spindles of different neck muscles, the length sensitivities of CM spindles were high compared to those of BC spindles. CM spindles showed length-related modulation of firing frequency over a more restricted range of initial muscle lengths than did BC spindles. 5. Eight Golgi tendon organs (GTO) were identified by their characteristics responses. Conduction velocities obtained for five GTO afferent nerves ranged from 50 to 67 m/s. Recordings were also made from receptros in deep muscles surrounding the vertebrae. These receptors had properties characteristic of muscle spindles.     

Effect of pentoxifylline on diaphragmatic contractility in septic rats

We investigated the effects of pentoxifylline (PTX) on endotoxin-induced diaphragmatic dysfunction in vitro. Seventy-two rats were divided into 3 groups: a group in which endotoxin (20 mg/kg) was injected intraperitoneally (endotoxin-group), a group in which PTX (100 mg/kg) was injected intraperitoneally 30 min before injection of endotoxin (endotoxin-PTX group), and a group in which only saline was given (sham group). Left hemidiaphragms were removed 4 h after injection of endotoxin. We evaluated the diaphragmatic contractility by twitch characteristics and force-frequency curves in vitro. We measured serum TNF-alpha concentrations, diaphragm malondialdehyde (MDA) levels (an index of oxygen-derived free radical-mediated lipid peroxidation), and diaphragm cAMP concentrations. Diaphragmatic force generation capacity was signifi cantly reduced after injection of endotoxin. Serum TNF-alpha concentrations and diaphragmatic MDA levels were significantly elevated after injection of endotoxin. PTX administration significantly improved diaphragmatic contractility and prevented the elevation in TNF-alpha concentrations and MDA levels after injection of endotoxin. There were no significant changes in the diaphragm cAMP concentrations among the 3 groups. These results demonstrated that PTX administration prevented endotoxin-induced diaphragmatic dysfunction without changing diaphragm muscle cAMP concentrations. The protective effects of PTX against endotoxininduced diaphragmatic contractile deterioration might be caused by attenuating TNF-alpha-mediated oxygen-derived free radical production.     

Vibration sensitivity of cat muscle spindles at short muscle lengths

 Experiments are described in which the vibration sensitivity was tested for primary and secondary endings of soleus muscle spindles of the anaesthetised cat. The vibratory stimulus was applied longitudinally to the muscle tendon and, after locating the site of the spindle in the muscle, applied transversely to muscle fibres directly overlying the spindle. All measurements were made with the muscle slack, at 20 mm shorter than its maximum physiological length (L _m–20 mm). Spindles were separated into two groups: spontaneous spindles, which maintained background activity at this length, and silent spindles, which did not. Two forms of muscle conditioning were used: hold-long, in which the muscle was stretched by 5 mm, contracted and then returned to the test length, and hold-test, in which a conditioning contraction was given at the test length. After hold-test, most spindles responded to longitudinal vibration; after hold-long, most did not. This difference in responsiveness was attributed to the presence or absence of slack in intrafusal and extrafusal fibres, due to the muscle’s thixotropic property. When the vibration was applied transversely, at a site directly overlying the spindle, responses of silent spindles continued to show thixotropic behaviour, whereas responses of spontaneous spindles were almost independent of the form of muscle conditioning. It is proposed that the ability of spontaneous spindles to maintain background activity at short muscle lengths is due to connective tissue or elastic fibre links between the sensory ending and the spindle capsule. The vibratory stimulus, applied transversely, reaches the sensory ending via these strands which, as non-muscle tissue, do not alter their mechanical state as a result of muscle conditioning. Received: 23 March 1998 / Accepted: 4 August 1998     

Responses of primary endings of cat muscle spindles to locally applied vibration

Summary Responses of muscle spindles in the cat soleus muscle have been studied during vibration applied locally to the belly of the muscle. Bursts of vibration at 170 Hz and with a peak amplitude of 200 m were applied to a site at which local pressure initiated impulses from the spindle. The response to vibration depended on the conditioning of the muscle immediately beforehand and the placement of the vibrator. The length at which the vibration was applied was called the test length; this was typically 10 mm less than the muscle's maximum length in the body. After a fusimotor strength contraction at a length 2–5 mm longer than the test length, vibration sensitivity, measured on return to the test length, was low. If the muscle was contracted at a length 2–5 mm shorter than the test length, vibration sensitivity was high. The low vibration sensitivity following conditioning at the longer length was attributed to the development of slack in intrafusal fibres. In the presence of slack, stimulation of some static fusimotor fibres was able to restore vibration sensitivity fully. It is suggested that the vibration sensitivity of passive spindles arises largely in bag₂ intrafusal fibres.     

Activity patterns of the diaphragm during voluntary movements in awake cats

The diaphragm is an important inspiratory muscle, and is also known to participate in the postural function. However, the activity of the diaphragm during voluntary movements has not been fully investigated in awake animals. In order to investigate the diaphragmatic activity during voluntary movements such as extending or rotating their body, we analyzed the electromyogram (EMG) of the diaphragm and trunk muscles in the cat using a technique for simultaneous recordings of EMG signals and video images. Periodic respiratory discharges occurred in the left and right costal diaphragm when the cat kept still. However, once the cat moved, their periodicity and/or synchrony were sometimes buried by non-respiratory activity. Such non-periodic diaphragmatic activities during voluntary movements are considered as the combination of respiratory activity and non-respiratory activity. Most of the diaphragmatic activities started shortly after the initiation of standing-up movements and occurred after the onset of trunk muscle activities. Those activities were more active compared to the normal respiratory activity. During rotation movements, left and right diaphragmatic activities showed asymmetrical discharge patterns and higher discharges than those during the resting situation. This asymmetrical activity may be caused by taking different lengths of each side of the diaphragm and trunk muscles. During reaching movements, the diaphragmatic activity occurred prior to or with the onset of trunk muscle activities. It is likely that diaphragmatic activities during reaching movements and standing-up movements may have been controlled by some different control mechanisms of the central nervous system. This study will suggest that the diaphragmatic activity is regulated not only by the respiratory center but also by inputs from the center for voluntary movements and/or sensory reflex pathways under the awake condition.     

Renin-angiotensin system in ventilator-induced diaphragmatic dysfunction: Potential protective role of Angiotensin (1–7)

Ventilator-induced diaphragmatic dysfunction is a feared complication of mechanical ventilation that adversely affects the outcome of intensive care patients. Human and animal studies demonstrate atrophy and ultrastructural alteration of diaphragmatic muscular fibers attributable to increased oxidative stress, depression of the anabolic pathway regulated by Insulin-like growing factor 1 and increased proteolysis. The renin-angiotensin system, through its main peptide Angiotensin II, plays a major role in skeletal muscle diseases, mainly increasing oxidative stress and inducing insulin resistance, atrophy and fibrosis. Conversely, its counter-regulatory peptide Angiotensin (1–7) has a protective role in these processes. Recent data on rodent models show that renin-angiotensin system is activated after mechanical ventilation and that infusion of Angiotensin II induces diaphragmatic skeletal muscle atrophy. Given: (A) common pathways shared by ventilator-induced diaphragmatic dysfunction and skeletal muscle pathology induced by renin-angiotensin system, (B) evidences of an involvement of renin-angiotensin system in diaphragm atrophy and dysfunction, we hypothesize that renin-angiotensin system plays an important role in ventilator-induced diaphragmatic dysfunction, while Angiotensin (1–7) can have a protective effect on this pathological process.The activation of renin-angiotensin system in ventilator-induced diaphragmatic dysfunction can be demonstrated by quantification of its main components in the diaphragm of ventilated humans or animals. The infusion of Angiotensin (1–7) in an established rodent model of ventilator-induced diaphragmatic dysfunction can be used to test its potential protective role, that can be further confirmed with the infusion of Angiotensin (1–7) antagonists like A-779. Verifying this hypothesis can help in understanding the processes involved in ventilator-induced diaphragmatic dysfunction pathophysiology and open new possibilities for its prevention and treatment.     

Diaphragmatic muscle reconstruction with an aligned electrospun poly(ε-caprolactone)/collagen hybrid scaffold

Large diaphragmatic muscle defects in congenital diaphragmatic hernia (CDH) are reconstructed by prosthetic materials or autologous grafts, which are associated with high complications and reherniation. In this study we examined the feasibility of using aligned electrospun poly(ε-caprolactone) (PCL)/collagen hybrid scaffolds for diaphragmatic muscle reconstruction. The hybrid scaffolds were implanted into a central left hemi-diaphragmatic defect (approximately 70% of the diaphragmatic tissue on the left side) in rats. Radiographic and magnetic resonance imaging (MRI) analyses showed no evidence of herniation or retraction up to 6 months after implantation. Histological and immunohistochemical evaluations revealed ingrowth of muscle tissue into the scaffolds. The mechanical properties of the retrieved diaphragmatic scaffolds were similar to those of normal diaphragm at the designated time points. Our results show that the aligned electrospun hybrid scaffolds allowed muscle cell migration and tissue formation. The aligned scaffolds may provide implantable functional muscle tissues for patients with diaphragmatic muscle defects.     

The responses of secondary endings of cat soleus muscle spindles to succinyl choline

This report describes the effects of succinylcholine (SCh) on the secondary endings of cat soleus muscle spindles and attempts to explain them in terms of the action of the drug on intrafusal fibres. All but 2 of 41 secondary endings studied in detail showed a significant response to a single intravenous injection of 200 g kg^-1 SCh. This consisted of a rise in the resting rate or development of a resting discharge if the spindle had previously been silent and an increase in the response to stretch. The increases in the responses to stretch were weaker than those observed for primary endings of spindles, but were much larger than those of tendon organs, which showed very little effect with this concentration of drug. The response to SCh showed two features consistent with its action being mediated via an intrafusal muscle fibre contraction rather than a direct depolarising action on the afferent nerve ending. In the presence of SCh, secondary endings were able to maintain a discharge during muscle shortening at rates, on average, more than 5 times greater than under control conditions. Secondly, the increase in spindle discharge produced by SCh showed a length dependence similar to that for fusimotor stimulation. Further support for the action of SCh being principally via an intrafusal fibre contraction was provided by the observation that its effects were abolished by the neuromuscular blocker gallamine triethiodide. The time course of recovery of SCh responses, following their blockade by gallamine, was much slower than recovery of extrafusal tension and closely paralleled that for the recovery of fusimotor responses. In three separate experiments on the medial gastrocnemius muscle the possibility that SCh may exert an excitatory action on spindle sensory endings through the liberation of potassium ions from the muscle was tested by tetanic stimulation of the muscle. This had no detectable excitatory effect. Several observations were made on the effect of SCh on responses of cutaneous receptors. SCh did not change levels of spontaneous activity or responses to mechanical stimulation of either slowly or rapidly adapting mechanoreceptors. It was argued for both tendon organs and cutaneous receptors that if SCh had a direct action on the nerve ending at the concentrations used here, some responses of these receptors to the drug might have been expected. All of the above supports the view that secondary endings of spindles are able to respond to SCh by the development of an intrafusal fibre contracture. The question of the intrafusal fibre types involved is discussed.     

The senescent rat diaphragm does not exhibit age-related changes in caspase activities, DNA fragmentation, or myonuclear domain

The diaphragm muscle is essential for normal ventilation and it is chronically active throughout the lifespan. In most skeletal muscles, aging is associated with increased oxidative stress and myofiber atrophy. Since the diaphragm maintains a unique chronic contractile activity, we hypothesized that these alterations would not occur in senescent diaphragms compared to young diaphragms. In addition, we investigated whether senescence leads to altered diaphragmatic caspase activity and myonuclear domain. We harvested diaphragm muscles from 6 and 24–26?month old male Fisher 344 rats (n?=?10 per group). Measurements of protein carbonyls, caspase 2, 3, 9, and 12 activities, DNA fragmentation, myofiber cross-sectional area, and myonuclear domain of diaphragm muscles were performed. No age-related changes (p?>?0.05) in diaphragmatic protein oxidation or activities of caspase 2, 3, 9, and 12 were observed between groups. In addition, DNA fragmentation, as detected by the ligation-mediated polymerase chain reaction ladder assay, was not different (p?>?0.05) between young and senescent diaphragms. Importantly, the cross-sectional area and myonuclear domain of diaphragm myofibers from senescent animals were also not different (p?>?0.05) from young diaphragms. In conclusion, our data show that the senescent diaphragm does not atrophy or exhibit changes in select markers of the apoptotic pathway and this may be a result of the diaphragm’s unique continuous contractile activity.     

The afferent discharge pattern of atrial mechanoreceptors in the cat during sinusoidal stretch of atrial strips in situ

1. The differences in spike discharge from atrial mechanoreceptors in vivo suggest the existence of different receptor types. To test this possibility, and to see how atrial receptors compare with other mechanoreceptors, their response was studied under comparable stimulus conditions.2. Sinusoidal length changes, with frequencies from 1 to 10 Hz and amplitudes of 1.5-5.0 mm at a given static extension, were imposed in situ on strips of atrial receptor areas of cats.3. The receptor response was evaluated from functional single fibres in terms of number of spikes per stimulus period, average discharge rate, instantaneous spike frequency, and phase angle between forcing function and instantaneous frequency.4. Irrespective of the fibre type, atrial fibres appear to originate from identical mechanoreceptors which sense length at low stimulus frequency and low stimulus amplitudes, but also sense velocity in the high frequency range and with large stimulus amplitudes.5. The difference in the discharge pattern and in the functional behaviour of the atrial fibres in vivo can be explained on the basis of identical receptors.6. The difference in the temporal occurrence of the atrial burst is still open to debate, but probably is related to the site of the receptor.     

呼吸电刺激训练改善膈肌和腹肌功能治疗功能性便秘的作用

目的　观察呼吸电刺激训练对功能性便秘患者的治疗作用。 方法　纳入功能性便秘患者共46例,按随机数字表法分为治疗A组、治疗B组和对照组。A组采用呼吸电刺激和盆底生物反馈治疗联合口服乳果糖治疗,共15例;B组进行盆底生物反馈联合口服乳果糖治疗,共16例;对照组只口服乳果糖治疗,共15例。治疗前和治疗2周后,评估功能性便秘严重程度,并评估膈肌和腹肌增厚率、膈肌活动度。 结果　治疗2周后,各组患者便秘严重程度明显下降（P<0.05）,A组膈肌和腹肌增厚率、膈肌活动度较治疗前改善（P<0.05）;与B组及对照组比较,A组便秘严重程度评分明显改善（P<0.05）,膈肌和腹肌增厚率、膈肌活动度改善程度改善明显（P<0.05）。 结论　呼吸电刺激训练可增强盆底生物反馈治疗改善功能性便秘的治疗效果。