Central and peripheral modulation of exercise pressor reflex sensitivity after nonfatiguing work

Autonomic blood pressure control is fundamentally altered during a single bout of exercise, as evidenced by the downward resetting of the baroreflex following exercise (postexercise hypotension). However, it is unclear if an acute bout of exercise is also associated with a change in the sensitivity of the exercise pressor response to a controlled stimulus, such as a static contraction. This study tested the hypothesis that the blood pressure response to a controlled static contraction would be attenuated after unilateral cycling of the contralateral (opposite) leg, but preserved after cycling of the ipsilateral (same) leg. To test this, the blood pressure response to 90 s of isometric plantar flexion [50% maximal voluntary contraction (MVC)] was compared before and after 20 min of contralateral and ipsilateral single-leg cycling at 20% peak oxygen consumption and rest (control) in 10 healthy subjects (three males and seven females). The mean arterial pressure response was significantly attenuated after contralateral single-leg cycling (+9.8 ± 7.5% ∆mmHg vs. +6.7 ± 6.6% ∆mmHg pre and postexercise, respectively, P = 0.04) and rest (+9.0 ± 7.5% ∆mmHg vs. +6.6 ± 5.2% ∆mmHg pre and postexercise, respectively, P = 0.03). In contrast, the pressor response nonsignificantly increased following ipsilateral single-leg cycling (+5.5 ± 5.2% ∆mmHg vs. +8.9 ± 7.2% ∆mmHg pre and postexercise, respectively, P = 0.08). The heart rate, leg blood flow, and leg conductance responses to plantar flexion were not affected by any condition ( P ≥ 0.12). These results are consistent with the notion that peripheral, but not central mechanisms promote exercise pressor reflex sensitivity after exercise.

‘‘Pranayama and yoga’’ : A boon to motherhood

Yoga is multi dimensional practice that originated in India and is becoming increasingly recognized and used in developed nations as a health practice for a variety of immu nological, neuromuscular, psychological, and pain condi- tions. Pregnancy in a woman is a condition in which woman changes both from inside as well as outside. These changes create obstacles in the normal life of a pregnant woman and yoga in pregnancy can help the women to go through these changes and challenges. Practicing yoga during pregnancy provides a great range of activity and benefits to unborn child and mother by numerous ways. Yoga soothes the mind, refocus the energy and prepare the woman physiologically and psychologically for labour. Different breathing techniques impart invaluable neuro-muscular control and helps in coordinated relaxation and contraction of uterus. Different type of asanas (postures),are described in Ayurveda and Yoga darshan texts which can be performed by a pregnant woman as they consume low energy and provide greater benefits. Yoga practicing includes physical postures and breathing techniques which minimizes the complication of pregnancy, like pregnancy induced hypertension, intrauterine growth retardation and pre-term delivery etc. Western exercises bring about what is known as phase contraction of muscles while yogic exercises create a static contraction which maintains a muscle under tension without causing repeated motions.

ASIC1a plays a key role in evoking the metabolic component of the exercise pressor reflex in rats

The role of the acid-sensing ion channel 1a (ASIC1a) in evoking the exercise pressor reflex is unknown, despite the fact that ASIC1a is opened by decreases in pH in the physiological range. This fact prompted us to test the hypothesis that ASIC1a plays an important role in evoking the exercise pressor reflex in decerebrated rats with freely perfused hindlimb muscles. To test this hypothesis, we measured the effect of injecting two ASIC1a blockers into the arterial supply of the triceps surae muscles on the reflex pressor responses to four maneuvers, namely 1) static contraction of the triceps surae muscles (i.e., the exercise pressor reflex), 2) calcaneal tendon stretch, 3) intra-arterial injection of lactic acid, and 4) intra-arterial injection of diprotonated phosphate. We found that the 2 ASIC1a blockers, psalmotoxin-1 (200 ng/kg) and mambalgin-1 (6.5 μg/kg), decreased the pressor responses to static contraction as well as the peak pressor responses to injection of lactic acid and diprotonated phosphate. In contrast, neither ASIC1a blocker had any effect on the pressor responses to tendon stretch. Importantly, we found that ASIC1a blockade significantly decreased the pressor response to static contraction after a latency of at least 8 s. Our results support the hypothesis that ASIC1a plays a key role in evoking the metabolic component of the exercise pressor reflex. NEW & NOTEWORTHY The role played by acid-sensing ion channel 1a (ASIC1a) in evoking the exercise pressor reflex remains unknown. In decerebrated rats with freely perfused femoral arteries, blocking ASIC1a with psalmotoxin-1 or mambalgin-1 significantly attenuated the pressor response to static contraction, lactic acid, and diprotonated phosphate injection but had no effect on the pressor response to stretch. We conclude that ASIC1a plays a key role in evoking the exercise pressor reflex by responding to contraction-induced metabolites, such as protons.

Quasi-static contraction during runaway gas accretion onto giant planets

Gas-giant planets, like Jupiter and Saturn, acquire massive gaseous envelopes during the approximately 3 Myr-long lifetimes of protoplanetary discs. In the core accretion scenario, the formation of a solid core of around ten Earth masses triggers a phase of rapid gas accretion. Previous 3D grid-based hydrodynamical simulations found that runaway gas accretion rates correspond to approximately 10 to 100 Jupiter masses per Myr. Such high accretion rates would result in all planets with larger than ten Earth-mass cores to form Jupiter-like planets, which is in clear contrast to the ice giants in the Solar System and the observed exoplanet population. In this work, we used 3D hydrodynamical simulations, that include radiative transfer, to model the growth of the envelope on planets with different masses. We find that gas flows rapidly through the outer part of the envelope, but this flow does not drive accretion. Instead, gas accretion is the result of quasi-static contraction of the inner envelope, which can be orders of magnitude smaller than the mass flow through the outer atmosphere. For planets smaller than Saturn, we measured moderate gas accretion rates that are below one Jupiter mass per Myr. Higher mass planets, however, accrete up to ten times faster and do not reveal a self-driven mechanism that can halt gas accretion. Therefore, the reason for the final masses of Saturn and Jupiter remains difficult to understand, unless their completion coincided with the dissipation of the solar nebula.

Exaggerated cardiovascular responses to muscle contraction and tendon stretch in UCD type-2 diabetes mellitus rats

Patients with type-2 diabetes mellitus (T2DM) have exaggerated sympathetic activity and blood pressure responses to exercise. However, the underlying mechanisms for these responses, as well as how these responses change throughout disease progression, are not completely understood. For this study, we examined the effect of the progression of T2DM on the exercise pressor reflex, a critical neurocardiovascular mechanism that functions to increase sympathetic activity and blood pressure during exercise. We also aimed to examine the effect of T2DM on reflexive cardiovascular responses to static contraction, as well as those responses to tendon stretch when an exaggerated exercise pressor reflex was present. We evoked the exercise pressor reflex and mechanoreflex by statically contracting the hindlimb muscles and stretching the Achilles tendon, respectively, for 30 s. We then compared pressor and cardioaccelerator responses in unanesthetized, decerebrated University of California Davis (UCD)-T2DM rats at 21 and 31 wk following the onset of T2DM to responses in healthy nondiabetic rats. We found that the pressor response to static contraction was greater in the 31-wk T2DM [change in mean arterial pressure (∆MAP) = 39 ± 5 mmHg] but not in the 21-wk T2DM (∆MAP = 24 ± 5 mmHg) rats compared with nondiabetic rats (∆MAP = 18 ± 2 mmHg; P < 0.05). Similarly, the pressor and the cardioaccelerator responses to tendon stretch were significantly greater in the 31-wk T2DM rats [∆MAP = 69 ± 6 mmHg; change in heart rate (∆HR) = 28 ± 4 beats/min] compared with nondiabetic rats (∆MAP = 14 ± 2 mmHg; ∆HR = 5 ± 3 beats/min; P < 0.05). These findings suggest that the exercise pressor reflex changes as T2DM progresses and that a sensitized mechanoreflex may play a role in exaggerating these cardiovascular responses. NEW & NOTEWORTHY This is the first study to provide evidence that as type-2 diabetes mellitus (T2DM) progresses, the exercise pressor reflex becomes exaggerated, an effect that may be due to a sensitized mechanoreflex. Moreover, these findings provide compelling evidence suggesting that impairments in the reflexive control of circulation contribute to exaggerated blood pressure responses to exercise in T2DM.

Impaired Ability to Suppress Excitability of Antagonist Motoneurons at Onset of Dorsiflexion in Adults with Cerebral Palsy

We recently showed that impaired gait function in adults with cerebral palsy (CP) is associated with reduced rate of force development in ankle dorsiflexors. Here, we explore potential mechanisms. We investigated the suppression of antagonist excitability, calculated as the amount of soleus H-reflex depression at the onset of ankle dorsiflexion compared to rest, in 24 adults with CP (34.3 years, range 18–57; GMFCS 1.95, range 1–3) and 15 healthy, age-matched controls. Furthermore, the central common drive to dorsiflexor motoneurons during a static contraction in the two groups was examined by coherence analyses. The H-reflex was significantly reduced by 37% at the onset of dorsiflexion compared to rest in healthy adults (P<0.001) but unchanged in adults with CP (P=0.91). Also, the adults with CP had significantly less coherence. These findings suggest that the ability to suppress antagonist motoneuronal excitability at movement onset is impaired and that the central common drive during static contractions is reduced in adults with CP.

PO-114 Effects of one-time exhaustive exercise on peripheral drive in rats

Objective In this study, we observed the effects of one-time exhaustive exercise on the grip strength, the time of grabbing, and the changes of the electromyography (EMG) of the hind limb flexor muscles and the flexor elbow muscles of the forelimbs, and revealed the effects of exercise fatigue on the peripheral motor drive level. Methods Male SD rats finished exhaustive fatigue exercise. A one-time exhaustive treadmill exercise fatigue model was established after one-week adaptive training in rats. The model was established by the modified Bedford incremental load motion program of the laboratory. The load is divided into 3 levels: the first stage movement speed 8.2 m/min, exercise time 15 min; second stage speed 15 m/min, exercise time 15 min; third stage speed at 20 m/min, exercise to exhaustion. At the same time, a miniature wireless acceleration sensor (18g) was worn in the tail of the rat to monitor the acceleration change of the running direction of the rat while running on the running platform. Three consecutive parallel experiments were performed using a rat grip tester (BioSEB GS3) to measure and compare the maximal muscle strength changes of the limbs before and after exercise fatigue in rats. Compared the static contraction of the rat muscle before and after exercise fatigue to overcome the length of time and gravity of the rod, and evaluated the muscle endurance after training the rats to learn to grab the rod. The EMG,square root amplitude (maxRMS), frequency domain analysis of EMG median frequency (MDF) and mean frequency (MPF) of the hind limb flexor and the forelimb flexor muscles (EMG) was measured by the Italian BTS FREEEMG ultra-miniature wireless surface electromyography tester to predict peripheral muscle tone and drive level. Results 1) The maximum holding force of the rat in resting state was 68.53 N/Kg, and the gripping force was significantly decreased (p<0.05) and reduced to 25.47 N/Kg after exercise fatigue .2) Exercise fatigue has a significant effect on the static grab time of rats. The rat has a grab time of 287.65s in a quiet state, and can only last for 27.78s after fatigue, and even can hardly maintain static contraction. The maxRMS of hindlimb flexor muscles in rats was significantly lower than that before fatigue (P<0.05) at rest, and there was no difference in forelimb flexor elbow muscle groups. MDF and MDF of forelimb flexor elbow muscle group and hind limb flexor muscle group were significant increased (P<0.05). 4) MaxRMS MDF and MDF of hind limb flexor muscle group and forelimb flexor elbow muscle group were significantly lower than those before fatigue (P<0.05) under the state of grabbing rod. Conclusions The sprinting ability in the running direction,maximum gripping force and grabbing time of the rats decreased significantly after exercise fatigue, revealing that the fatigue of the muscles may cause the decrease of the muscle static contraction ability. The inability of the hind limbs to maintain standing with exercise fatigue may be related to a significant decrease in hindlimb tension, and it was found that there was an explosive discharge and the phenomenon of tonic contraction in the muscles at rest. The muscle endurance and tension of the muscles were significantly reduced, and the contraction frequency of the muscle movement unit decreased significantly after exercise fatigue, causing insufficient peripheral driving level . (NSFC31401018, SKXJX2014014, [email protected]).