bluuebunny/crossref_metadata_2025_split huggingface dataset:
Regulation of cerebral microvascular permeability by histamine in the anaesthetized rat
Authors: Sarker M. H. , Easton A. S. , Fraser P. A. 
Published: September 2004

The permeability response of slightly leaky pial venular capillaries to histamine was investigated using the single microvessel occlusion technique.
Histamine dose‐response curves showed that concentrations between 5 nm and 5 μM increased permeability, while concentrations from 50 μM to 5 mM reduced it.
The H2 receptor antagonist cimetidine (2 μM) blocked the effects of lower concentrations of histamine, while the H1 receptor antagonist mepyramine (3 nM) blocked those of higher concentrations of histamine.
The effects of lower doses of histamine were mimicked by the H2 receptor agonist dimaprit, and the effects of higher doses of histamine were mimicked by the H1 receptor agonist α‐2‐(2‐aminoethyl)pyridine (AEP).
Low concentrations of histamine, which normally increase the permeability of Lucifer Yellow (PLY), reduced it when co‐applied with the phosphodiesterase 4 (PDE4) inhibitor rolipram. Rolipram also potentiated the response to AEP, but had no effect on that to dimaprit.
The effects of dimaprit were blocked by reducing extracellular Ca2+ from 2.5 mM to nominally Ca2+ free, or by applying the calcium entry blocker SKF 96365.
Mechanical advantage of the human parasternal intercostal and triangularis sterni muscles
Authors: De Troyer André , Legrand Alexandre , Gevenois Pierre‐Alain , Wilson Theodore A. 
Published: September 2004

Previous studies in dogs have demonstrated that the maximum change in airway pressure (ΔPao) produced by a particular respiratory muscle is the product of three factors, namely the mass of the muscle, the maximal active muscle tension per unit cross‐sectional area (∼3.0 kg cm−2), and the fractional change in muscle length per unit volume increase of the relaxed chest wall (i.e. the muscle's mechanical advantage). In the present studies, we have used this principle to infer the ΔPao values generated by the parasternal intercostal and triangularis sterni muscles in man.
The mass of the muscles and the direction of the muscle fibres relative to the sternum were first assessed in six cadavers. Seven healthy individuals were then placed in a computed tomographic scanner to determine the orientation of the costal cartilages relative to the sternum and their rotation during passive inflation to total lung capacity. The fractional changes in length of the muscles during inflation, their mechanical advantages, and their ΔPao values were then calculated.
Passive inflation induced shortening of the parasternal intercostals in all interspaces and lengthening of the triangularis sterni. The fractional shortening of the parasternal intercostals decreased gradually from 7.7% in the second interspace to 2.0% in the fifth, whereas the fractional lengthening of the triangularis sterni increased progressively from 5.9 to 13.8%. These rostrocaudal gradients were well accounted for by the more caudal orientation of the cartilages of the lower ribs.
Since these fractional changes in length corresponded to a maximal inflation, the inspiratory mechanical advantage of the parasternal intercostals was only 2.2–0.6% l−1, and the expiratory mechanical advantage of the triangularis sterni was only 1.6–3.8% l−1. In addition, whatever the interspace, parasternal and triangularis muscle mass was 3–5 and 1–3 g, respectively. As a result, the magnitude of the ΔPao values generated by a maximal contraction of the parasternal intercostals or triangularis sterni in all interspaces would be only 1–3 cmH2O.
These studies therefore confirm that the parasternal intercostals in man have an inspiratory action on the lung whereas the triangularis sterni has an expiratory action. However, these studies also establish the important fact that the pressure‐generating ability of both muscles is substantially smaller than in the dog.
InsP3, but not novel Ca2+ releasers, contributes to agonist‐initiated contraction in rabbit airway smooth muscle
Authors: Iizuka Kunihiko , Yoshii Akihiro , Dobashi Kunio , Horie Takeo , Mori Masatomo , Nakazawa Tsugio 
Published: September 2004

To examine the contributions of the putative Ca2+ releasers, inositol 1,4,5‐trisphosphate (InsP3), cyclic ADP ribose (cADPR), and nicotinate adenine dinucleotide phosphate (NAADP), to carbachol (CCh)‐induced contraction in airway smooth muscle, we measured force development of permeabilized rabbit tracheal smooth muscle, human bronchial smooth muscle and guinea‐pig ileum longitudinal smooth muscle.
In the presence of 50 μm GTP, CCh and InsP3 contracted α‐toxin‐permeabilized tracheal smooth muscle dose dependently; the EC50 values for CCh and InsP3 were 1.84 μm and 363 μm, and the maximum responses (normalized to the 30 mM caffeine response) to 100 μm CCh and to 800 μm InsP3 were 206 ± 13.4 % (mean ± s.e.m.) and 84.4 ± 5.3 %, respectively.
However, cADPR (10‐300 μm), β‐NAD+ (2.5 mM), FK506 (30 μm) and NAADP (100 μm) neither contracted the strip by themselves nor affected the subsequent CCh (1 μm) response. α‐Toxin‐permeabilized bronchial smooth muscle and ileum smooth muscle also responded to caffeine, InsP3 and CCh but not to cADPR.
Both 100 μm 8‐amino‐cADPR, a selective cADPR antagonist, and 100 μm thionicotinamide‐NADP, a selective NAADP antagonist, failed to inhibit the CCh response, although procaine abolished the caffeine, InsP3 and CCh responses in the permeabilized tracheal smooth muscle.
Although inhibition of the caffeine response by 30 μm ryanodine was nearly complete, approximately 30 % of the InsP3 (300 μm) plus GTP (50 μm) response was retained, and the resultant response disappeared after the caffeine response was evoked in the presence of ryanodine.
Heparin (300 μg ml−1) blocked InsP3 (300 μm) and CCh (3 μm) responses in β‐escin‐permeabilized tracheal smooth muscle, while Ruthenium Red (100 μm) partially inhibited the CCh response.
Collectively, InsP3 but not cADPR or NAADP plays a key role in CCh‐initiated contraction, and InsP3 utilizes a single compartment of the caffeine/ryanodine‐sensitive stored Ca2+ in airway smooth muscle.
Sympathetic attenuation of parasympathetic vasodilatation in oro‐facial areas in the cat
Authors: Izumi Hiroshi , Ito Yutaka 
Published: September 2004

The present study was designed to examine the interaction between sympathetic and parasympathetic influences on blood flow in oro‐facial areas such as lower lip, palate and submandibular gland (SMG) and in the common carotid artery (CCA) in anaesthetized cats.
Section of the ipsilateral superior cervical sympathetic trunk (CST) increased the basal CCA blood flow significantly. The control level with the nerve intact was comparable with that seen at 0.5‐1 Hz CST stimulation, suggesting a spontaneous discharge of around 0.5‐1 Hz in the CST fibres innervating the beds supplied by the CCA. The basal blood flow at all sites examined was reduced by CST stimulation in a frequency‐dependent manner.
Electrical stimulation of the central end of the lingual nerve (LN) evoked blood flow increases in the lower lip and palate. These blood flow increases were markedly reduced by concurrent CST stimulation in a manner that was frequency dependent, but not simply related to the vasoconstrictor effect of CST stimulation. This effect of CST stimulation was not observed in tongue or SMG, even though CST stimulation evoked vasoconstriction in these tissues. A significant reduction in the level of CCA blood flow attained during LN stimulation was observed on repetitive CST stimulation only at 10 Hz, indicating that this response behaved in a fashion different from that seen in the lower lip, palate, tongue and SMG.
The present study suggests that concurrent repetitive CST stimulation reduces parasympathetically mediated blood flow increases in certain oro‐facial areas (such as the lower lip and palate), but not in the tongue and SMG. This inhibitory action was not a simple additive effect (between vasoconstriction and vasodilatation) and it disappeared rapidly after the cessation of CST stimulation.
The compliance of the porcine pulmonary artery depends on pressure and heart rate
Authors: Kornet L. , Jansen J. R. C. , te Nijenhuis F. C. A. M. , Langewouters G. J. , Versprille A. 
Published: September 2004

The influence of mean pulmonary arterial pressure (mean Ppa) on dynamic (Cd) and pseudo‐static compliance (Cps) of the pulmonary artery was studied at a constant and a changing heart rate. Cd is the change in cross‐sectional area (CSA) relative to the change in Ppa throughout a heart cycle. Cps is the change in mean CSA relative to the change in mean Ppa. If Cd is known, pulmonary blood flow can be computed from the Ppa using a windkessel model. We investigated whether Cps can be interchanged with Cd.
In nine anaesthetized pigs, we determined the mean CSA and Cd of the pulmonary artery at various Ppa levels, ranging from approximately 30 to 10 mmHg, established by bleeding. Two series of measurements were carried out, one series at a spontaneously changing heart rate (n= 9) and one series at a constant heart rate (n= 6). To determine CSA a conductance method was used.
C
ps depended on pressure. The mean CSA versus mean Ppa curves were sigmoid and steepest in the series with the increasing heart rate (established by bleeding). The CSA versus Ppa loop during a heart cycle, giving Cd, was approximately linear and almost closed. The Cdversus mean Ppa relationship was bell shaped. Its width was smaller if the heart rate increased during the series of measurements. The pressure, where Cd was maximum, was higher at higher heart rates. Furthermore, the maximum Cd was not affected by the heart rate.
Because the pulmonary artery constricts with increasing heart rate, Cps will be overestimated during procedures where heart rate increases. Cd should be determined on a beat‐to‐beat basis to calculate flow because it changes with mean pulmonary arterial pressure and heart rate.
The canine phrenic‐to‐intercostal reflex
Authors: De Troyer André 
Published: September 2004

Paralysis of the diaphragm in the dog causes a non‐vagal, non‐chemical increase in the activity of the inspiratory intercostal muscles. In the present studies, the hypothesis was tested that phrenic afferent fibres may elicit a reflex inhibition of inspiratory intercostal activity.
The electrical activity of the three groups of inspiratory intercostal muscles (parasternal intercostals, external intercostals, levator costae) was recorded in twenty vagotomized, spontaneously breathing dogs, and the proximal end of one or both C5 phrenic nerve roots was stimulated during inspiration.
Stimulation of the ipsilateral and contralateral C5 phrenic roots caused an immediate reduction in inspiratory intercostal activity. This reduction was abolished when phrenic stimulation was repeated after section of the C5 dorsal roots.
The reduction in external intercostal and levator costae activity during bilateral C5 afferent stimulation appeared when the stimulus strength was 3 times the motor threshold and it increased in magnitude when stimulus intensity was increased further. In contrast, the reduction in parasternal intercostal activity occurred only when the stimulus strength was 12 times the motor threshold.
These observations confirm the hypothesis that diaphragmatic receptors may reflexly inhibit efferent activity to the inspiratory intercostal muscles, in particular the external intercostals and levator costae. This inhibition appears to be primarily mediated by small myelinated fibres.
Activity‐dependent hyperpolarization of human motor axons produced by natural activity
Authors: Vagg Rebecca , Mogyoros Ilona , Kiernan Matthew C. , Burke David 
Published: September 2004

The changes in excitability of motor axons produced by natural activity were measured in six healthy subjects using voluntary contractions lasting 15 s, 30 s and 1 min, by recording the changes in stimulus current required to produce a compound muscle action potential of ≈60 % of maximum.
On cessation of the contractions there was a prominent increase in the current required to produce the target potential, accompanied by an increase in rheobase, a decrease in strength‐duration time constant, and an increase in axonal supernormality. These changes indicate that the hypoexcitability was due to axonal hyperpolarization.
The activity‐dependent hypoexcitability increased in depth and duration the longer the contraction. Following a 1 min contraction, it produced a 24 % increase in threshold, waning over 15 min. The hypoexcitability was greater than in cutaneous afferents tetanized to produce an equivalent rate‐dependent stress.
It is concluded that natural activity results in substantial hyperpolarization of active axons and that, for similar discharge rates, the degree of hyperpolarization is greater in motor axons than cutaneous afferents. The greater effect of activity on the excitability of motor axons could be due to less inward rectification and less persistent Na+ conductance than in sensory axons. It is suggested that motor axons may therefore be more susceptible than cutaneous afferents to conduction block at sites of impaired safety margin for impulse conduction.
Signalling of static and dynamic features of muscle spindle input by cuneate neurones in the cat
Authors: Mackie P. D. , Morley J. W. , Zhang H. Q. , Murray G. M. , Rowe M. J. 
Published: September 2004

The capacity of cuneate neurones to signal information derived from muscle spindle afferent fibres about static stretch or vibration of forearm extensor muscles was examined electrophysiologically in anaesthetized cats.
Static stretch (<= 2 mm in amplitude) and sinusoidal vibration (at frequencies of 50‐800 Hz) were applied longitudinally to individual muscle tendons by means of a feedback controlled mechanical stimulator, and responses were recorded from individual cuneate neurones and from individual spindle afferent fibres.
Cuneate neurones sampled were located caudal to the obex and displayed a sensitivity to both vibration and static stretch of forearm muscles that was consistent with their input arising from primary spindle endings. In response to static muscle stretch, they displayed graded and approximately linear stimulus‐response relations, and a stability of response level at fixed lengths that was consistent with these neurones contributing discriminative information about static muscle stretch.
In response to sinusoidal muscle vibration the cuneate neurones also showed graded stimulus‐response relations (in contrast to spindle afferents which at low vibration amplitudes attain a plateau response level corresponding to a discharge of 1 impulse on each vibration cycle). Lowest thresholds were at 100‐300 Hz and bandwidths of vibration sensitivity extended up to ∼800 Hz.
Temporal precision in cuneate responses to muscle vibration was assessed by constructing phase scatter and cycle histograms from which measures of vector strength could be calculated. Cuneate responses displayed somewhat poorer phase locking (and lower vector strengths) than spindle afferent responses to vibration (a reflection of uncertainties associated with synaptic transmission). Nevertheless, the remarkable feature of cuneate responses to muscle vibration is the preservation of tight phase locking at frequencies up to 400‐500 Hz, which presumably enables these central neurones to contribute accurate temporal information for the kinaesthetic sense in a variety of circumstances involving dynamic perturbations to skeletal muscle.
Muscle history, fusimotor activity and the human stretch reflex
Authors: Gregory J. E. , Wise A. K. , Wood S. A. , Prochazka A. , Proske U. 
Published: September 2004

The previous history of contraction and length changes of a muscle influences the size of the stretch reflex and H reflex. Here we ask, is this dependence due to changes in mechanical properties of extrafusal fibres, intrafusal fibres of spindles, or both?
The soleus muscle of human subjects was conditioned using either a voluntary contraction or a contraction evoked by low‐strength electrical stimulation, in the range 0–25% of maximum. Following conditioning, reflexes were increased by more than twofold above the no‐contraction value by a voluntary contraction of 5% of maximum, or more, but not by electrical stimulation which presumably did not contract the intrafusal fibres of spindles.
When the muscle was conditioned with a contraction at a length shorter than the test length, rather than at the test length, a depressing effect on reflexes was attributed to both the burst of impulses generated in spindles when the muscle was stretched back to the test length and to a reduced stretch sensitivity of muscle spindles.
The experiments demonstrate the importance of keeping the muscle and its spindles in a defined mechanical state when measuring reflexes. They also point to the powerful facilitating influences of conditioning muscle contractions provided they recruit the intrafusal fibres of spindles.
Enhanced vasoconstrictor responses in renal and femoral arteries of the golden hamster during hibernation
Authors: Karoon Parastoo , Knight Gillian , Burnstock Geoffrey 
Published: September 2004

The present study assessed local regulation of vascular tone of euthermic (control), cold control and hibernating golden hamsters. Sympathetic neurotransmission in the renal artery, the long term effects of hibernation on perivascular nerve activity, and the responsiveness of femoral artery to a number of neurotransmitters and hormones with both constrictor and dilator actions during hibernation are described.
The contractile responses of the renal arterial rings to transmural nerve stimulation (80 V, 0.1 ms, 4–64 Hz, for 1 s) were negligible in controls, significantly increased at higher frequencies of stimulation in cold controls and markedly enhanced in the hibernating group at all frequencies tested. The contractile responses to exogenous noradrenaline (NA; 0.1–100 μm) were significantly increased in the renal arteries of hibernating hamsters compared with controls, but not compared with cold controls. Responses to exogenous ATP (1–3000 μm) and KCl (120 mm) were similar among all experimental groups.
The maximal contractile responses of femoral arterial rings to the sympathetic co‐transmitter ATP and 5‐hydroxytryptamine were increased by approximately 124 % and 99 %, respectively, in hibernating compared with cold control preparations without a change in the concentration of agonist that produces half‐maximal response. However, the responses to NA were not altered during hibernation.
Vasoconstriction of femoral arterial rings in response to arginine vasopressin was significantly enhanced in both cold controls and hibernating groups, while vasoconstriction in response to endothelin‐1 and KCl was unaltered.
The dilator responses of femoral arterial rings to acetylcholine, sodium nitroprusside and adenosine were not different among the groups.
It is suggested that the marked augmentation of sympathetic neurotransmission, selective supersensitivity of the vascular smooth muscle to sympathetic contractile agents and unaltered vasodilatory mechanisms may provide a means for maintenance of vascular tone and peripheral resistance during hibernation.
Infant stepping: a method to study the sensory control of human walking
Authors: Yang Jaynie F. , Stephens Marilee J. , Vishram Rosie 
Published: September 2004

Stepping responses were studied in infants between the ages of 10 days and 10 months while they were supported to step on a slowly moving treadmill belt. Surface electromyography (EMG) from muscles in the lower limb, force exerted by the feet on the treadmill belt, and the motion of the lower limbs were recorded.
Two groups of infants were studied, those who had a small amount of daily practice in stepping and those who did not. Practice resulted in a dramatic increase in the incidence of stepping recorded in the laboratory, particularly for the periods between 1 and 6 months of age.
The majority of infants showed clear alternation between the flexor and extensor muscles during walking, regardless of age. Co‐contraction between flexors and extensors, estimated by the overlap in area between rectified and smoothed EMG from a muscle pair, was greater for some muscle groups in the infant compared with the adult.
Practice resulted in a significantly lower co‐contraction index for the tibialis anterior‐ quadriceps muscle pair. Practice did not affect the mean step cycle duration.
Infants of all ages could step at a range of treadmill speeds by adjusting their step cycle duration. The relationship between the treadmill speed and cycle duration was well fitted by a power function, similar to those reported for intact cats and adult humans. The change in step cycle duration resulted almost entirely from a change in the extensor burst duration, whereas the flexor burst duration remained constant.
Airstepping could be elicited in some infants. The cycle durations for airstepping were close to the shortest cycles recorded on the treadmill.
In conclusion, the system for generating rhythmic, alternating activity of the lower limbs for stepping is clearly developed by birth. The stepping is sustained and regular, particularly if stepping practice is incorporated briefly each day. The infant population provides a good subject pool for studying the afferent control of walking in the human, before cerebral influences are fully developed. The characteristics and maturity of the system remain to be determined.
Glycolysis is independent of oxygenation state in stimulated human skeletal muscle in vivo
Authors: Conley Kevin E. , Kushmerick Martin J. , Jubrias Sharon A. 
Published: September 2004

We tested the hypothesis that the cytoplasmic control mechanism for glycolysis is affected by the presence of oxygen during exercise. We used a comparison of maximal twitch stimulation under ischaemic and intact circulation in human wrist flexor and ankle dorsiflexor muscles. 31P magnetic resonance spectroscopy followed the phosphocreatine (PCr), Pi and pH dynamics at 6–9 s intervals. Glycolytic PCr synthesis was determined during stimulation from pH and tissue buffer capacity, as well as the oxidative phosphorylation rate.
Ischaemic vs. aerobic stimulation resulted in similar glycolytic fluxes in the two muscles. The onset of glycolysis occured after fifty to seventy stimulations and the extent of glycolytic PCr synthesis was directly proportional to the number of stimulations thereafter.
Two‐fold differences in the putative feedback regulators of glycolysis, [Pi] and [ADP], were found between aerobic and ischaemic stimulation. The similar glycolytic fluxes in the face of these differences in metabolite levels eliminates feedback as a control mechanism in glycolysis.
These results demonstrate that glycolytic flux is independent of oxygenation state and metabolic feedback, but proportional to muscle activation. These results show a key role for muscle stimulation in the activation and maintenance of glycolysis. Further, this glycolytic control mechanism is independent of the feedback control mechanism that governs oxidative phosphorylation.