Ventrolateral medullary control of cardiovascular activity during muscle contraction

While adolescent substance use has been the focus of extensive research over the last few decades, Hispanic adolescent substance use has received only limited attention. Studies exploring predictors of Hispanic adolescent substance use have failed to adequately explore the contribution of the family on substance use. The present study examined the relative influence of family, school and peer influences, perceived student substance use, family substance use, and acculturation on a sample of Mexican-American early adolescents using structural equations modeling. The findings varied for males and females. Family functioning and family use directly influenced substance use for males. Family functioning influenced school and peer variables, however, these were unrelated to use. For females, family use and student use directly influenced substance use. Family functioning influenced family use and school and peer attachments. School and peer attachment predicted perceived student use. These findings suggest that family functioning has a primary role in Hispanic adolescent substance use.     

A technique for diagnosing the individual patterns of innervation of the trapezius muscle prior to neck dissection

Based on the techniques of regional anaesthesia, a method for simulating the effects of radical neck dissection on the innervation of the trapezius muscle by selectively and reversibly blocking the accessory nerve and its superficial cervical anastomoses, was developed and tested on 40 patients who were due to undergo radical neck dissection. Action potentials of the three portions of the muscle were recorded after this blockade as well as after radical neck dissection, and compared. It was found that the electromyograms were congruent in 92.5% of the cases. Four patterns of innervation were demonstrated, ranging from complete substitution of the resected or blocked nerves to a remaining muscle activity of less than 20% after blockade or radical neck dissection.     

Visuo-motor adaptation: evidence for a distributed amplitude control system

We investigated the constraints for visuo-motor adaptation in human pointing movements. Subjects pointed at sequentially presented visual targets while visual feedback about their finger position was either absent (pre- and post-period), or was manipulated such as to require a gradual reduction of response amplitude (per-period). We found that response amplitudes were smaller during the post- than during the pre-period, which documents the existence of adaptation to distorted visual feedback. We further found that adaptation can transfer fully to untrained amplitudes (Exp. 1), although the amount of transfer may be reduced if trained and untrained amplitudes are substantially different (Exp. 2). However, selective adaptation of one amplitude but not another can also be yielded if the paradigm explicitly asks for it (Exp. 3), and if the two amplitudes differ by more than about 10 cm (Exp. 4). We conclude from these findings that the adapted mechanism consists of amplitude-specific elements, tuned to amplitude spans of some 10 cm.     

Characteristics of the muscle mechanoreflex during quadriceps contractions in humans

We examined muscle sympathetic nerve activity (MSNA) in the nonexercising lower limb during repetitive static quadriceps contraction paradigm at 25% maximal voluntary contraction in eight men. Subjects performed 20-s contractions with 5-s rest periods for up to 12 contractions. Although the workload was constant, we found that MSNA amplitude rose as a function of contraction number [0.6 ln (amplitude/min)/contraction]; this suggests chemical sensitization of the muscle reflex response. We employed signal-averaging techniques and then integrated the data to examine the onset latency of the MSNA response as a function of the 25-s contraction-rest period. We observed an onset latency of approximately 4-6 s. Moreover, although the onset latency did not appear to vary as a function of contraction number, the rate of MSNA increase took approximately four contractions to reach a steady-state rate of rise; this suggests contraction-induced sensitization. The onset latency reported here is similar to findings in recent animal studies, but it is at odds with latencies determined in prior human handgrip contraction studies. We believe our data suggest that 1) mechanically sensitive afferents contribute importantly to the MSNA response to the paradigm employed and 2) these afferents may be sensitized by the chemical products of muscle contraction.     

Doublet potentiation during eccentric and concentric contractions of cat soleus muscle

The addition of an extra stimulus pulse, or doublet, at the beginning of a low-frequency train has been shown to substantially increase isometric force. This study examined the effects of muscle movement on this doublet potentiation. The soleus muscles of anesthetized cats were stimulated at 10 Hz for 1 s, with and without an added doublet (0.01-s interval). Isovelocity releases reduced but did not eliminate peak and early doublet potentiation (average 0.0-0.5 s after the doublet). Large releases, >0.4 s after the doublet, completely abolished sustained doublet potentiation (average 0.5-1.0 s after the doublet). In contrast, early isovelocity stretches boosted peak doublet potentiation. Yet, large stretches later in the stimulus almost completely eliminated sustained doublet potentiation. This suggests that a different mechanism is responsible for early and sustained doublet potentiations. Because peak and average initial doublet potentiation were not strongly affected by movement, doublets still offer a viable control strategy to increase force during movement while minimizing the number of stimulus pulses.     

Task-dependent facilitation of motor evoked potentials during dynamic and steady muscle contractions

Task-dependent differences in the facilitation of motor evoked potentials (MEPs) following cortex stimulation were studied in a proximal (deltoid) and a distal muscle (abductor digiti minimi; ADM) in 23 healthy subjects during both dynamic and steady contractions of the target muscle under isometric and under nonisometric conditions. In the deltoid, MEP amplitudes were significantly greater if stimulation was performed during dynamic contractions than during steady contractions, despite equal background electromyographic levels just prior to the stimulus. The same task-specific extra facilitation of deltoid MEP amplitudes was also found with magnetic stimulation of the brain stem instead of the cortex in 3 subjects. In the ADM, no such task-dependent extra facilitation of MEPs during dynamic contractions was found. It is concluded that in the deltoid, during dynamic contractions, a greater proportion of the spinal motoneurons is close to depolarization threshold (greater "subliminal fringe") whereas the number of firing motoneurons is similar to that during steady contraction. The lack of task-dependent extra facilitation of MEPs in the ADM is explained by the predominant recruitment principle for force gradation in small hand muscles, which is in contrast to the predominant frequency principle used in proximal muscles.     

Motor patterns and kinematics during backward walking in the pacific giant salamander: evidence for novel motor output

Kinematic and motor patterns during forward and backward walking in the salamander Dicamptodon tenebrosus were compared to determine whether the differences seen in mammals also apply to a lower vertebrate with sprawling posture and to measure the flexibility of motor output by tetrapod central pattern generators. During treadmill locomotion, electromyograms (EMGs) were recorded from hindlimb muscles of Dicamptodon while simultaneous high-speed video records documented movement of the body, thigh, and crus and allowed EMGs to be synchronized to limb movements. In forward locomotion, the trunk was lifted above the treadmill surface. The pelvic girdle and trunk underwent smooth side-to-side oscillations throughout the stride. At the beginning of the stance phase, the femur was protracted and the knee joint extended. The knee joint initially flexed in early stance and then extended as the foot pushed off in late stance, reaching maximum extension just before foot lift-off. The femur retracted steadily throughout the stance. In the swing phase, the femur rapidly protracted, and the leg was brought forward in an "overhand crawl" motion. In backward walking, the body frequently remained in contact with the treadmill surface. The pelvic girdle, trunk, and femur remained relatively still during stance phase, and most motion occurred at the knee joint. The knee joint extended throughout most of stance, as the body moved back, away from the stationary foot. The knee flexed during swing. Four of five angles showed significantly smaller ranges in backward than in forward walking. EMGs of forward walking showed that ventral muscles were coactive, beginning activity just before foot touchdown and ceasing during the middle of stance phase. Dorsal muscles were active primarily during swing. Backward locomotion showed a different pattern; all muscles except one showed primary activity during the swing phase. This pattern of muscle synergy in backward walking never was seen in forward locomotion. Also, several muscles demonstrated lower burst rectified integrated areas (RIA) or durations during backward locomotion. Multivariate statistical analysis of EMG onset and RIA completely separated forward and backward walking along the first principal component, based on higher RIAs, longer durations of muscle activity, and greater synergy between ventral muscles during early stance in forward walking. Backward walking in Dicamptodon uses a novel motor pattern not seen during forward walking in salamanders or during any other locomotor activity in previously studied tetrapods. The central neuronal mechanisms mediating locomotion in this primitive tetrapod are thus capable of considerable plasticity.     

Training induced adaptation of skeletal muscle and metabolism during submaximal exercise

1. Six subjects were trained using a one-leg bicycle exercise for 2 months. The untrained leg served as control. After the training period, muscle oxidative capacity, determined as succinate dehydrogenase activity, was 27% higher in the trained (as opposed to the control) leg (P < 0.05).2. When the subjects in this situation performed a 1 h two-legged submaximal bicycle exercise bout (150-225 W), determinations of V(O2) of the single leg (leg blood flow x (A-V)(O2) difference) revealed that they appeared to choose to work harder with their trained than with their untrained leg, so as to make the relative loads for the two legs the same.3. Determinations of O(2) and CO(2) on femoral arterial and venous blood demonstrated that the R.Q. was lower in the trained as compared to the untrained leg, 0.91 cf. 0.96 (10 min) and 0.91 cf. 0.94 (50 min) (P < 0.05).4. That metabolism of fat was more pronounced in the trained leg was further supported by the finding of a significant net uptake of free fatty acids in this leg only. Moreover, a lower release of lactate from the trained leg was demonstrated.5. It is suggested that the shift towards a more pronounced metabolism of fat in the trained leg is a function of an increased muscle oxidative capacity.     

Calcium handling by the sarcoplasmic reticulum during oscillatory contractions of skinned skeletal muscle fibres

Isometric ATP consumption and force were investigated in mechanically skinned fibres from iliofibularis muscle of Xenopus laevis. Measurements were performed at different [Ca2+], in the presence and absence of caffeine (5 nM). In weakly Ca2+-buffered solutions without caffeine, spontaneous oscillations in force and ATPase activity occurred. The repetition frequency was [Ca2+]-and temperature-dependent. The Ca2+ threshold (+/- SEM) for the oscillations corresponded to a pCa of 6.5 +/- 0.1. The maximum ATP consumption associated with calcium uptake by the sarcoplasmic reticulum (SR) reached during the oscillations was similar to the activity under steady-state conditions at saturating calcium concentrations in the presence of caffeine. Maximum activity was reached when the force relaxation was almost complete. The calculated amount of Ca2+ taken up by the SR during a complete cycle corresponded to 5.4 +/ 0.4 mmol per litre cell volume. In strongly Ca2+-buffered solutions, caffeine enhanced the calcium sensitivity of the contractile apparatus and, at low calcium concentrations, SR Ca uptake. These results suggest that when the SR is heavily loaded by net Ca uptake, there is a massive calcium-induced calcium release. Subsequent net Ca uptake by the SR then gives rise to the periodic nature of the calcium transient.     

A mechanochemical model for the steady and transient contractions of the skeletal muscle

A mechanochemical model for muscle contraction was presented which consisted of three subsystems: the regulatory mechanism of contraction by Ca ion, the cross-bridge cycle coupled with actin-myosin interaction and the dynamics of contraction with an external load. It was assumed that both the rate constant of the cross-bridge cycle and the net force of the cross-bridge were linear functions of the sliding velocity. Most parameters in the model were determined from the experimental data, but several were estimated by simulation techniques. The model adequately described the force-load-velocity relation, the rates of energy and heat output as well as some basic mechanical properties of muscle. Not only the steady-state contraction but also the twitch response could be explained by the model. Time courses of tension and shortening during isometric and isotonic twitches were calculated by the model on a digital computer. The calculated curves agreed satisfactorily with the experimental ones obtained from the frog semitendinosus muscle. The rate of tension rise of the isometric twitch was shown to attain the peak at nearly the same time as does the calculated Ca concentration curve.     

Functional state of the cardiovascular system of miners during prolonged adaptation to extreme circumstances

The hospital files of 410 patients with hematological malignancy treated at our clinic between 1977 and 1990 were reviewed to determine the importance of infections as a cause of death. The total number of infections was 203 (49.5%). A microbiologically documented infection was detected in 27.3%, a clinically documented infection in 9.5% and a possible infection in 12.7% of the patients. Gram-positive bacteria were responsible for 25.9%, gram-negative bacteria for 31.3%, anaerobic bacteria for 2.7%, viruses for 4.5% and fungi for 25.9% of the microbiologically documented infections. Of 29 systemic fungal infections only 2 were diagnosed before the patients died. The remaining diagnoses rested on autopsy findings. Empiric antifungal therapy was introduced in 1983; still, 74.2% of systemic fungal infections in 1977-1990 were detected after 1982. Patients with a verified infection had statistically significantly higher CRP concentrations than patients who died of other causes (152 mg/l vs. 117.5 mg/l, p = 0.018). We conclude that infection is a significant cause of death in patients with these diseases. The number of systemic fungal infections is increasing, despite the widespread use of antifungal medication and thus better diagnostic methods and more effective treatment are needed.     

Load pattern and pressure pain threshold in the upper trapezius muscle and psychosocial factors in medical secretaries with and without shoulder/neck disorders

OBJECT: A current hypothesis for the genesis of muscular complaints in the shoulder/neck region postulates that short periods with a completely relaxed muscle are essential to avoid complaints. Another hypothesis is that these disorders are related to psychosocial conditions at work. In order to test these hypotheses, 23 medical secretaries were investigated. METHODS: The load pattern during work in the upper trapezius muscle bilaterally was assessed with electromyographic (EMG) technique and exposure variation analysis (EVA). In addition, pressure pain threshold (PPT) was measured on the trapezius muscle bilaterally and on the sternum. Psychosocial conditions at work were assessed with a questionnaire. RESULTS: The medical secretaries with complaints had significantly fewer episodes with totally or close to totally relaxed muscle compared with the healthy group. The group with complaints tended to have a more monotonous load pattern at low levels (approx. 1%-5% maximum voluntary contraction) while the healthy group had more frequent pauses but also somewhat more frequent short load peaks. The group with complaints showed lower PPT readings compared with the healthy group. However, the whole group had considerably lower PPTs than is usually reported in the literature. Of the 12 questions in the psychosocial questionnaire only one regarding work task satisfaction showed a significant difference between the two groups. CONCLUSION: Support is found for hypothesis that secretaries without complaints have more frequent episodes with totally relaxed muscle. A significant difference is found regarding work task satisfaction.     

Consequences of trapezius relaxation on the distribution of shoulder muscle forces: an electromyographic study

Recent experiments have suggested a pathway of genes that regulate left-right asymmetry in vertebrate embryogenesis. The most downstream member of this cascade is nodal (XNR-1 in frogs), which is expressed in the left-side lateral mesoderm. Previous work in the chick [Levin, 1998] suggests that an inductive interaction by Shh (Sonic hedgehog) present at the midline was needed for the left-sided expression of nodal, which by default would not be expressed. Interestingly, it has been reported [Lohr et al., 1997] that in Xenopus, right-side mesoderm that is explanted at st. 15 and allowed to develop in culture, goes on to express nodal, suggesting that lateral mesoderm expresses this gene by default and that a repression of nodal by the midline is needed to achieve asymmetry. Such a contradiction raises interesting questions about the degree of conservation of the mechanisms upstream of nodal asymmetry and, in general, about the differences in the LR pathway among species. Thus we examined this issue directly. We show that in the chick, as in the frog, explanted mesoderm from both sides does, indeed, go on to express nodal, including both the medial and lateral expression domains. Ectopic nodal expression in the medial domain on the right side is not sufficient to induce an ectopic lateral domain. We also show that explanted lateral tissue regenerates node/notochord structures exhibiting Shh expression. Furthermore, we show that Xenopus explants done at st. 15 also regenerate notochord by the stage at which XNR-1 would be expressed. Thus explants are not isolated from the influence of the midline. In contrast to the midline repressor model previously suggested [Lohr et al., 1997] to explain the presence of nodal expression in explants, we propose that the expression is due to induction by signals secreted by regenerating node and notochord tissue (Shh in the chick). Thus our results are consistent with Shh being necessary for nodal induction in both species, and we provide an explanation for both sets of data in terms of a single conserved mechanism upstream of nodal expression.     

Primary prevention of cardiovascular disease: Communitywide strategies for youth.

National interest in health promotion and disease prevention has led naturally to a concern with primary prevention and with youth. This attention to youth has been particularly notable in efforts to prevent injuries and chronic diseases. Specific behavior patterns that are learned in childhood and adolescence are implicated in the development of chronic diseases. These behavior patterns logically become the targets for early intervention. Over the past two decades, studies on the prevention of cardiovascular disease (CVD), the primary cause of mortality in the Western world, have become numerous and comprehensive and have included substantial work with youth. This article provides a rationale for that focus. We review promising communitywide strategies for youth and argue that communitywide strategies ought to be most efficient and efficacious for primary prevention. Both interest in and research on communitywide strategies are relatively recent; consequently, few strategies can be recommended unequivocally. The need for future research in this area by multidisciplinary teams is identified. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Infectious complications: prevention and strategies for their control

Despite major advances in burn wound management and other supportive care regimens, infection remains the leading cause of morbidity in the thermally injured patient. Changes in nursing practices and patient isolation have played a significant role in reducing the incidence of burn wounds and other infections, particularly those that result from cross-contamination in the hospitalized burn patient. This article focuses on the sources of the most common infections seen in burn centers today and on the infection control strategies developed for their prevention and treatment.     

Asymmetrical hemispheric activation and behavioral persistence: effects of unilateral muscle contractions

OBJECTIVE: To compare pubertal maturation, sex steroid hormones, and lipoproteins and their interrelationships in male offspring of parents with premature coronary heart disease (cases) and a control group. DESIGN: This was a cross-sectional comparison of cases and members of a control group 10 to 15 years of age. SUBJECTS AND METHODS: Offspring were recruited from patient lists of area physicians. Members of the control group were recruited from area schools. Body mass (kg/m2), serum lipids, lipoproteins, apolipoproteins, estradiol, and free testosterone were measured. RESULTS: Differences in age were not significant, but offspring were taller, heavier, and more mature. Offspring had higher total and low density lipoprotein cholesterol. Offspring had lower estradiol levels in early puberty but higher levels in late puberty. With family history and body mass in the regression models for lipid parameters, free testosterone was a significant explanatory factor for total cholesterol, low-density lipoprotein cholesterol, and high-density lipoprotein, and estradiol was a significant predictor for apolipoprotein B. The percent of the variance in the lipid parameters explained by testosterone and estradiol was small. CONCLUSION: Sex hormone concentrations appear to be modest but significant predictors of lipoprotein and apolipoprotein concentrations in offspring and a control group in cross-sectional analysis. After controlling for pubertal maturation, hormone and lipid concentrations differed in offspring and the control group.     

Hierarchical control and skilled typing: Evidence for word-level control over the execution of individual keystrokes.

Routine actions are commonly assumed to be controlled by hierarchically organized processes and representations. In the domain of typing theories, word-level information is assumed to activate the constituent keystrokes required to type each letter in a word. We tested this assumption directly using a novel single-letter probe technique. Subjects were primed with a visual or auditory word or a visually presented random consonant string and then probed to type a single letter from the prime or another randomly selected letter. Relative to randomly selected letters, probe responses were speeded for first, middle, and last letters contained in visual and auditory word primes but not for middle and last letters contained in random consonant primes. This suggests that word-level information causes parallel activation of constituent keystrokes, consistent with hierarchical processing. The role of hierarchical processing in typing and routine action is discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Romantic partners' individual coping strategies and dyadic coping: Implications for relationship functioning.

Individual coping strategies and dyadic coping independently predict partner well-being and relationship functioning; however, it is unclear whether the coping processes are inter-related and whether they uniquely contribute to romantic relationship functioning. One hundred heterosexual dating couples rated the individual coping strategy of negative mood regulation as well as positive and negative dyadic coping. Relationship functioning was assessed via partners' reports of relationship satisfaction and observers' ratings of negative interaction in conflict. Actor-Partner Interdependence Models (APIMs; Cook & Kenny, 2005; Kashy & Kenny, 2000) revealed associations between individual coping and dyadic coping in the predicted directions. APIMs also indicated the unique contributions of positive and negative dyadic coping to relationship functioning, above and beyond contributions of individual coping strategies. Implications of dyadic coping as a target of efforts to prevent or treat partner and/or relational distress are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Trajectories of adaptation in pediatric chronic illness: The importance of the individual.

This study used individual growth modeling to examine individual difference and group difference models of adaptation. The adaptation of 27 children with juvenile rheumatoid arthritis (JRA) and 40 children with insulin-dependent diabetes mellitus (IDDM) was tracked for 18 months from diagnosis. A control group of 62 healthy children was followed over the same time period. Clustering procedures indicated that child and family adaptation could be described by a number of distinct adaptation trajectories, independent of diagnostic group membership. In contrast, parental adaptation trajectory was associated with diagnostic group membership and control over disease activity for the JRA group and with diagnostic group membership for healthy controls. The observation of common patterns across trajectory sets, as well as the finding that trajectories were differentially related to a number of variables of interest, support the use of trajectories to represent adaptation to chronic disease. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Trigeminal-reticular connections: possible pathways for nociception-induced cardiovascular reflex responses in the rat

Cardiovascular regulatory neurons of the ventral medulla and pons are thought to have an important role in the mediation of trigeminal nociception-induced reflex cardiovascular responses. However, the neural pathways that link the spinal trigeminal nucleus with ventral medullary and pontine autonomic cell groups are poorly understood. The present study utilized injections of the highly sensitive anterograde tracer substance biotinylated dextran combined with immunocytochemistry for tyrosine hydroxylase, the synthesizing enzyme for catecholamines, to investigate the distribution and morphology of projections from the spinal trigeminal subnucleus caudalis to ventral medullary and pontine catecholaminergic cell groups. Injection of biotylinated dextran into the dorsal subnucleus caudalis produced dense anterograde labeling in dorsal regions of the medullary and pontine reticular formation including the dorsal medullary reticular field, the parvicellular reticular field, and the parvicellular reticular field pars anterior. In the ventral medullary and pontine reticular formation, light anterograde labeling tended to be distributed in close proximity to the distal dendrites of catecholaminergic neurons located in the C1, A1, and A5 regions. Injections of anterograde tracer into the dorsal medullary reticular field produced dense anterograde labeling in the ventral medullary and pontine reticular formation. Numerous terminal-like varicosities were observed in close proximity to catecholaminergic neurons located in the C1, A1, and A5 regions. These data suggest that trigeminal pain-induced reflex cardiovascular responses involve indirect projections that terminate in the dorsal medullary and pontine reticular formation before reaching ventral medullary and pontine catecholaminergic cell groups known to be involved in cardiovascular regulation.