bluuebunny/crossref_metadata_2025_split huggingface dataset:
Co‐activation of tongue protrudor and retractor muscles during chemoreceptor stimulation in the rat
Authors: Fuller David , Mateika Jason H. , Fregosi Ralph F. 
Published: September 2004

Our primary purpose was to test the hypothesis that the tongue protrudor (genioglossus, GG) and retractor (styloglossus, SG and hyoglossus, HG) muscles are co‐activated when respiratory drive increases, and that co‐activation will cause retraction of the tongue. This was addressed by performing two series of experiments using a supine, anaesthetized, tracheotomized rat in which tongue muscle force and the neural drive to the protrudor and retractor muscles could be measured during spontaneous breathing. In the first series of experiments, respiratory drive was increased progressively by occluding the tracheal cannula for thirty respiratory cycles; in the second series of experiments, the animals were subjected to hyperoxic hypercapnia and poikilocapnic hypoxia.
Airway occlusion for thirty breaths caused progressive, quantitatively similar increases in efferent motor nerve activity to protrudor and retractor tongue muscles. Net tongue muscle force was always consistent with tongue retraction during occlusion, and peak force rose in parallel with the neural activites. When airway occlusion was repeated following section of the lateral XIIth nerve branch (denervation of retractor muscles) the tongue either protruded (15/21 animals; 10 ± 2 mN at the 30th occluded breath) or retracted weakly (6/21 animals; 6 ± 2 mN at 30th occluded breath).
To ensure that our findings were not the result of damage to the muscle nerves, occlusion experiments were also done in eight animals in which GG EMG activity was recorded instead of nerve activities. Changes in peak integrated GG electryomyogram (EMG) activity and peak retraction force during occlusion were highly correlated (r2= 0.86, slope = 1.05).
In separate experiments in fourteen rats, we found that hyperoxic hypercapnia and poikilocapnic hypoxia also result in parallel increases in the respiratory‐related EMG activity of the GG and HG muscles. Also, as in the occlusion experiments, augmentations of protrudor and retractor muscle EMG activities were associated with parallel changes in tongue retraction force.
These studies in anaesthetized rats demonstrate that tracheal occlusion and independent stimulation of central or peripheral chemoreceptors results in inspiratory‐related co‐activation of the protrudor and retractor muscles, and proportional changes in tongue retraction force. These observations also demonstrate that recording GG EMG activity in isolation could lead to erroneous conclusions about respiratory‐related movements of the tongue.
Electrocortical activity in fetal sheep in the last seven days of gestation
Authors: Shinozuka Norio , Nathanielsz Peter W. 
Published: September 2004

Electrocorticogram (ECoG) and myometrial electromyogram (EMG) were recorded continuously in chronically instrumented late gestation sheep fetuses (n= 9) to analyse: (1) 24 h ECoG patterns, (2) relationships between ECoG and myometrial contractility, and (3) 24 h ECoG patterns at the spontaneous onset of labour.
Spontaneous onset of labour was determined from the myometrial EMG. ECoG signals were purified by a denoising procedure of wavelet decomposition. High‐voltage slow ECoG activity (HV) and low‐voltage fast ECoG activity (LV) were determined mathematically, and HV‐LV cycle periodicity was calculated by periodogram analysis.
Twenty‐four hour rhythms were present in fetal ECoG HV‐LV cycles in the 3–5 days prior to spontaneous onset of labour (P < 0.01). Cycle frequency was lower at 08.00–12.00 h and higher at 16.00–20.00 h (lights on at 07.00 h, lights off at 21.00 h). LV duration was longer at 20.00–24.00 h, and HV was shorter at 16.00–20.00 h. No relationship was found between ECoG cycles and myometrial contracture cycles. Twenty‐four hour ECoG rhythms disappeared 1 day before the spontaneous onset of labour.
ECoG patterns changed 7 to 4 h prior to spontaneous onset of labour, percentage of time spent and duration of HV ECoG increased, and percentage of time spent in LV decreased significantly. ECoG HV‐LV cyclicity was reduced 4–5 h prior to spontaneous onset of labour, indicating that the altered fetal hormonal and blood gas environment around the spontaneous onset of labour alter fetal neural function.
Electromyographic study of the contractile and electrical properties of the human triceps surae muscle in a simulated microgravity environment
Authors: Koryak Yuri 
Published: September 2004

The effects of 7 days of simulated space flight, achieved with the technique of ‘dry’ water immersion, on human triceps surae muscle function have been investigated.
The maximal voluntary contraction (MVC) was reduced by 33.8 % (P < 0.01) while the electrically evoked maximal tetanic contraction force (Po) decreased by 8.2 % (P > 0.05). This suggests that most of the force loss is due to a reduction in motor drive.
The decrease in Po was associated with a small increase in maximal rates of tension development (7.2 %). The twitch tension (Pt) was not significantly changed and the Pt : Po ratio was decreased by 8.7 % after immersion.
A standard fatigue test, consisting of sixty 1 s intermittent isometric contractions (50 impulses s−1) separated by 1 s rest decreased tetanic force to approximately 60 % of initial values, but force reduction was not significantly different before and after immersion: the fatigue index was 36.2 ± 5.4 % before and 38.6 ± 2.8 % after immersion (P > 0.05). Whilst there were similar changes in mechanical output between control and disused muscles, there were differences in the pattern of electrical activity.
Absence of viscerosomatic inhibition with injections of lobeline designed to activate human pulmonary C fibres
Authors: Gandevia S. C. , Butler J. E. , Taylor J. L. , Crawford M. R. 
Published: September 2004

Activation of pulmonary C fibres (J receptors) in animals produces inhibition of spinal motoneurones. Intravenous bolus injections of lobeline are believed to activate pulmonary C fibres (J receptors) in human subjects and to produce characteristic sensations and cardiorespiratory responses. This study quantified the respiratory sensations evoked by such injections and then used a range of suprathreshold doses of lobeline and tested for the presence of reflex or descending inhibition of motoneuronal output.
Injections of lobeline produced dose‐dependent sensations of respiratory discomfort referred to the throat and upper chest beginning within about 10 s and often associated with coughing. As the dose increased the latency for the sensations decreased while their duration and intensity increased. Reflex changes in blood pressure, heart rate and ventilation also occurred.
Injections of lobeline at doses sufficient to evoke respiratory discomfort lasting 25‐32 s (37‐73 μg kg−1) increased the size of the H reflex in soleus with an onset latency of about 10 s and lasting about 20 s.
The size of EMG responses evoked in upper limb muscles by transcranial magnetic stimulation of the motor cortex increased shortly after injections and remained elevated for about 30‐35 s.
Injections of lobeline during sustained voluntary contractions of the elbow flexors at submaximal or maximal levels did not impair the ability to produce force.
Walking was not disrupted by repeated suprathreshold doses of lobeline.
It is concluded that injections of lobeline sufficient to evoke cardiorespiratory reflexes and sensations of severe respiratory discomfort are not associated with functionally important inhibition of motor performance. The results cast doubt on the ability of the J reflex to limit exercise in humans.
Effect of sodium perturbations on rat chemoreceptor spike generation: implications for a Poisson model
Authors: Donnelly David F. , Panisello Jose M. , Boggs Dona 
Published: September 2004

The sensitivity of arterial chemoreceptor spike generation to reductions in excitability was examined using rat chemoreceptors in vitro. Axonal excitability was reduced by reducing extracellular sodium concentration ([Na+]o) by 10‐40 % or by applying low doses of tetrodotoxin (TTX).
In normoxia and in hypoxia, an isosmotic reduction in [Na+]o caused a proportional decrease in single‐fibre, spiking nerve activity. For a 20 % reduction in [Na+]o, nerve activity decreased to 54 ± 7 % of control in normoxia and 41 ± 5 % in hypoxia.
Low doses of TTX (25‐50 nM) caused a similar decrease in spiking frequency, but this response was variable amongst fibres, with some fibres unaffected by TTX.
A reduction in [Na+]o by 20 % caused a slowing of conduction velocity, measured using an electrical stimulus delivered to an electrode placed in the carotid body. Threshold current for spike generation was increased by about 2·7 ± 1·4 %. Threshold current increased by 6·5 ± 3·7 % following a 40 % reduction in [Na+]o.
The spike generation process was modelled as a Poisson process in which depolarizing events summate and give rise to an action potential. The experimental data were best fitted to a high order process characterized by a large number of events and high event threshold.
This result is not consistent with depolarization events caused by episodic transmitter release, but suggests that afferent spike generation is an endogenous process in the afferent nerve fibres, perhaps linked to random channel activity or to thermal noise fluctuations.
Exercise metabolism in human skeletal muscle exposed to prior eccentric exercise
Authors: Asp Sven , Daugaard Jens R. , Kristiansen Søren , Kiens Bente , Richter Erik A. 
Published: September 2004

The effects of unaccustomed eccentric exercise on exercise metabolism during a subsequent bout of graded concentric exercise were investigated in seven healthy male subjects. Arterial and bilateral femoral venous catheters were inserted 2 days after eccentric exercise of one thigh (eccentric thigh) and blood samples were taken before and during graded two‐legged concentric knee‐extensor exercise. Muscle biopsies were obtained from the eccentric and control vastus lateralis before (rest) and after (post) the concentric exercise bout.
Maximal knee‐extensor concentric exercise capacity was decreased by an average of 23 % (P < 0.05) in the eccentric compared with the control thigh.
The resting muscle glycogen content was lower in the eccentric thigh than in the control thigh (402 ± 30 mmol (kg dry wt)−1vs. 515 ± 26 mmol (kg dry wt)−1, means ± s.e.m., P < 0.05), and following the two‐legged concentric exercise this difference substantially increased (190 ± 46 mmol (kg dry wt)−1vs. 379 ± 58 mmol (kg dry wt)−1, P < 0.05) despite identical power and duration of exercise with the two thighs.
There was no measurable difference in glucose uptake between the eccentric and control thigh before or during the graded two‐legged concentric exercise. Lactate release was higher from the eccentric thigh at rest and, just before termination of the exercise bout, release of lactate decreased from this thigh (suggesting decreased glycogenolysis), whereas no decrease was found from the contralateral control thigh. Lower glycerol release from the eccentric thigh during the first, lighter part of the exercise (P < 0.05) suggested impaired triacylglycerol breakdown.
At rest, sarcolemmal GLUT4 glucose transporter content and glucose transport were similar in the two thighs, and concentric exercise increased sarcolemmal GLUT4 content and glucose transport capacity similarly in the two thighs.
It is concluded that in muscle exposed to prior eccentric contractions, exercise at a given power output requires a higher relative workload than in undamaged muscle. This increases utilization of the decreased muscle glycogen stores, contributing to decreased endurance.
Function of sural nerve reflexes during human walking
Authors: Zehr E. P. , Stein R. B. , Komiyama T. 
Published: September 2004

The functions of ipsilateral cutaneous reflexes were studied with short trains of stimuli presented pseudorandomly to the sural nerve during human walking. Electromyograms (EMG) of lower (tibialis anterior (TA), soleus, lateral (LG) and medial (MG) gastrocnemius) and upper leg (vastus lateralis and biceps femoris) muscles were recorded, together with ankle, knee and hip joint angles. Net reflex EMG responses were quantified in each of the sixteen parts of the step cycle. The kinematic measurements included ankle eversion‐ inversion, and ankle, knee and hip flexion‐extension.
The function of the sural reflexes depended upon the part of the step cycle in which the nerve was stimulated and the intensity of stimulation. During stance, reflexes in MG and TA muscles in response to a medium intensity of stimulation (1.9 × radiating threshold, × RT) were closely associated with ankle eversion and dorsiflexion responses, respectively. These responses could assist in accommodation to uneven terrain that applies pressure to the lateral side of the foot (sural innervation area). Non‐noxious, high intensity (2.3 × RT) stimulation resulted in strong suppression of LG and MG during stance which was correlated to a small reduction in ankle plantarflexion. At this higher intensity the response would function to prevent the foot from moving more forcefully onto a potentially harmful obstacle.
During swing, ankle dorsiflexion increased and was significantly correlated to the net TA EMG response after both medium and high intensity stimulation. Knee flexion was increased throughout swing at both intensities of stimulation. These responses may serve in an avoidance response in which the swing limb is brought past an obstacle without destabilizing contact.
The net EMG and kinematic responses suggest that cutaneous reflexes stabilize human gait against external perturbations produced by an uneven surface in stance or obstacles encountered during swing.
Epiglottic movements during breathing in humans
Authors: Amis T. C. , O'Neill N. , Somma E. Di , Wheatley J. R. 
Published: September 2004

Using X‐ray fluoroscopy we measured antero‐posterior (A–P) and cranio‐caudal (C–C) displacements of the epiglottic tip (ET), corniculate cartilage and hyoid bone in seven seated, normal human subjects (age 34 ± 3 years; mean ±s.e.m.; 4 males, 3 females) breathing via a nasal mask or mouthpiece with (RL) and without (UB) a fixed resistive load.
During UB, via either mouth or nose, there were no significant A‐P ET movements. During RL via the nose the ET at peak expiratory flow was 2.6 ± 1.3 mm cranial to its position at peak inspiratory flow (P < 0.05, ANOVA). C–C movements of the ET correlated strongly with C‐C movements of the corniculate cartilage and hyoid bone.
The ET, corniculate cartilage and hyoid bone (at zero airflow) were situated more caudally during oral UB than for any other condition.
When present, epiglottic movements during breathing do not appear to be independent of those of the larynx and hyoid. Furthermore, epiglottic position may be related to the level of upper airway resistance.
Movement detection at the human big toe
Authors: Refshauge Kathryn M. , Taylor Janet L. , McCloskey D. I. , Gianoutsos M. , Mathews P. , Fitzpatrick Richard C. 
Published: September 2004

To be detected, movements of the interphalangeal joint of the big toe must be greater than at other joints. This poor acuity may arise because the anatomy of the foot and ankle results in poor coupling between the toe and the muscles that operate it. To vary this coupling, the effect of ankle position on proprioceptive acuity at the toe was measured.
We measured proprioceptive acuity at the toe with the ankle in different positions and found that ankle plantarflexion did improve acuity. This implies that, with the ankle at mid‐range or dorsiflexed, toe movement is inadequately transferred to muscle fascicles.
To determine actual changes in fascicle length of the toe extensor, movements of extensor hallucis longus near the toe and at the muscle‐tendon junction were measured during surgical exposure in one subject. Ankle position greatly affected movement transfer from toe to muscle‐tendon junction: no tendon movement was transferred with the ankle dorsiflexed, but all movement was transferred with the ankle plantarflexed.
When the relationship between joint rotation and muscle fascicle length measured in vivo was used to express the smallest detectable movements of the toe as proportional changes in muscle fascicle length, these detectable changes were similar to those at all other limb joints. This suggests that change in muscle fascicle length is of major interest to the nervous system.
Control of motility patterns in the human colonic circular muscle layer by pacemaker activity
Authors: Rae M. G. , Fleming N. , McGregor D. B. , Sanders K. M. , Keef K. D. 
Published: September 2004

This study characterized the electrical and mechanical activities of human colonic muscle strips obtained from either the ascending, descending or sigmoid colon of patient volunteers during elective colon resections.
Rhythmic contractile activity was observed in colonic circular muscle strips in the absence of external stimuli. This activity persisted in the presence of atropine, phentolamine, propranolol, tetrodotoxin and Nω‐nitro‐L‐arginine but was abolished by nifedipine.
The activity of whole circular muscle (WCM) was compared with that of the myenteric half (MCM), the submucosal half (SCM) and the interior (ICM) of the circular muscle layer. WCM exhibited a prominent 2–4 contractions min−1 contractile pattern which was also present in strips of SCM. In contrast, MCM and ICM exhibited slow (0.3–0.6 contractions min−1), long duration contractions with superimposed higher frequency contractions (17–18 contractions min−1).
Resting membrane potential (Vm), recorded at various positions through the thickness of WCM strips did not differ and averaged −50 mV.
Slow waves were observed in 83 % of muscles. They averaged 12 mV in amplitude, 9.4 s in duration and had a frequency of 2–4 contractions min−1. Slow waves were greatest in amplitude near the submucosal edge and decreased with distance away from this edge. Each slow wave was associated with a transient contraction.
Near the myenteric edge, rapid fluctuations of Vm with a mean frequency of 18 contractions min−1 were recorded in 67 % of muscles. Spiking activity was common and was superimposed upon slow waves and rapid Vm fluctuations.
In summary, slow waves were identified in the human colonic circular muscle layer which arise at or near the submucosal edge. These electrical events give rise to a 2–4 contractions min−1 contractile rhythm which is characteristic of the intact muscle layer. Thus, the nature and spatial organization of pacemaker activity in the human colon bears significant resemblance to other animal models, such as the dog and pig.
Vasopressin, angiotensin II and renal responses during water immersion in hydrated humans
Authors: Hammerum Mette Schou , Bie Peter , Pump Bettina , Johansen Lars Bo , Christensen Niels Juel , Norsk Peter 
Published: September 2004

The hypothesis was tested that in hydrated humans the release of arginine vasopressin and angiotensin II is suppressed by water immersion (WI) and that this is a mechanism of the immersion‐induced diuresis and natriuresis. Seven male subjects on controlled sodium (65‐75 mmol per 24 h for 4 days) and water intake were studied.
Plasma vasopressin was promptly suppressed by WI, declining from 0·76 ± 0·13 to 0·23 ± 0·08 pg ml−1 (P < 0·05), with a concomitant increase in renal water output (CH2O) from ‐0·4 ± 0·2 to 4·4 ± 0·7 ml min−1 (P < 0·05). Subsequently, CH2O returned to the level of control, whereas plasma vasopressin remained suppressed. Plasma osmolality gradually increased from 285 ± 1 to 289 ± 1 mosmol kg−1 (P < 0·05). WI caused a 9‐fold increase in renal sodium excretion. Plasma angiotensin II decreased from 27·1 ± 5·3 to 4·3 ± 0·7 pg ml−1 (P < 0·05), and the intraindividual correlation coefficients between sodium excretion rates and angiotensin II concentrations varied between 0·73 and 0·96 (P < 0·002).
The data demonstrate that plasma vasopressin and angiotensin II concentrations decrease during WI in hydrated humans, concomitantly with initial increases in CH2O and sodium excretion. Therefore, vasopressin could constitute a mediator of CH2O and angiotensin II of the natriuresis of WI. The subsequent return of CH2O to the level of control is, however, also caused by other factors.
Role of receptor kinase in short‐term desensitization of cardiac muscarinic K+ channels expressed in Chinese hamster ovary cells
Authors: Shui Z. , Khan I. A. , Tsuga H. , Haga T. , Boyett M. R. 
Published: September 2004

The cardiac muscarinic receptor‐K+ channel system was reconstructed in Chinese hamster ovary (CHO) cells by transfecting the cells with the various components of the system. The activity of the muscarinic K+ channel was measured with the cell‐attached configuration of the patch clamp technique.
In CHO cells transfected with the channel (Kir3.1/Kir3.4), receptor (hm2) and receptor kinase (GRK2), on exposure to agonist, there was a decline in channel activity as a result of desensitization, similar to that in atrial cells.
Whereas the desensitization was almost abolished by not transfecting with the receptor kinase or by transfecting with a mutant receptor lacking phosphorylation sites, it was only reduced (by ≈39 %) by transfecting with a mutant receptor kinase with little kinase activity.
These results suggest that the receptor kinase is responsible for desensitization of the muscarinic K+ channel and that this involves phosphorylation‐dependent and ‐independent mechanisms.
Pore mutations alter closing and opening kinetics in Shaker K+ channels
Authors: Molina A. , Ortega‐Sáenz P. , López‐Barneo J. 
Published: September 2004

We have studied the effects of mutations of amino acids in the pore (positions 447 and 449) and the elevation of extracellular [K+] on the closing and opening kinetics of Shaker B K+ channels transiently expressed in Chinese hamster ovary (CHO) cells.
Mutant D447E had closing and C‐type inactivation kinetics which were faster than the wild‐type channel. These processes were slowed by increasing extracellular [K+] and in these conditions the channels exhibited linear instantaneous current‐voltage relationships. Thus, the mutation seems to produce uniform decrease of occupancy by K+ in sites along the channel pore where the cation competes with closing and C‐type inactivation.
In other mutants also showing K+‐dependent fast C‐type inactivation, closing was found to be slower than in the wild‐type channel and insensitive to variations in external [K+]. These characteristics were particularly apparent in mutant T449K which even in high [K+] has a non‐linear instantaneous current‐voltage relationship with marked saturation of the inward current recorded at negative membrane potentials. Hence, in this channel type occupation by K+ of the pore appears to be non‐uniform with low occupancy of sites near the outer entrance and saturation of the sites accessible from the internal solution.
The results show that channel closing is influenced by changes in the pore structure leading to alterations in the occupation of the channels by permeant cations. The differential effects of pore mutations and high external [K+] on closing and C‐type inactivation indicate that the respective gates are associated with separate domains of the molecule.
Point mutations in the pore sequence can also lead to modifications in channel opening. In general, channels with fast C‐type inactivation also show a fast rising phase of activation. However, these effects appear not to be due to primary modifications of the activation process but to arise from the coupling of activation and C‐type inactivation.
These data, demonstrating that the pore structure influences most of the gating parameters of K+ channels, give further insight into the mechanisms underlying the modulation of K+ channel function by changes in the ionic composition in the extracellular milieu.