Length-dependent activation and sensitivity in arterial ring segments

This study examines the effect of length on the dose-response (D-R) relationship and the effect of agonist concentration on the length-tension (L-T) relationship in vascular smooth muscle. The experiments used 2-mm rings from isolated segments of the dog anterior tibial artery. In D-R experiments the length (internal ring circumference) for maximum active force (L_max) was determined first. D-R relationships were obtained from cumulative responses to increasing concentrations of norepinephrine (NE) or potassium (K⁺). L-T relationships were obtained from individual responses to a specific concentration of agonist as the ring was stretched in increments of L₀ (the initial length for resting force). Dimensions of the arterial rings were measured with a video caliper. For NE and K⁺ stimulations at lengths equal to and less than L_max: (a) The concentration for half maximal response (ED₅₀) was lowest (most sensitive) at L_max and increased significantly as length decreased from L_max; (b) When the direction of length change was reversed, the direction of change in ED₅₀ was reversed; and (c) The ED₅₀ of repeated dose-response experiments at L_max was not significantly different. For NE: (a) the ED₅₀ decreased significantly when length was increased from L_max; and (b) the ED₅₀ increased significantly when length was decreased to L_max. The results of L-T experiments show L_max is significantly longer for a low concentration of NE (10⁻⁶ M) than for a high concentration (10⁻⁵ M). With force normalized to the maximum force, the L-T curve is significantly lower, and the initial length for an active response was 80% longer for 10⁻⁶ M than for 10⁻⁵ M NE. It may be concluded that vascular smooth muscle has a length-dependent dose-response relationship and a concentration-dependent length-tension relationship.     

The relationship between the electromyogram-amplitude and isometric extension torques of neck muscles at different positions of the cervical spine

A group of 12 healthy men volunteered for the experiment. Electromyograms (EMG) were obtained from semispinalis capitis, splenius capitis, levator scapulae, and trapezius muscles. The flexion angle of the cervical spine was precisely adjusted to 0°, 10°, 20°, and 30° relative to the horizontal, with a constant angle of the atlanto-occipital joint. The subjects made eight short (about 2 s) vertical extension forces (6%, 12%,18%, 24%, 30%, 36%, 42%, and 48% of maximal voluntary peak contraction force). For each position, the centre of pressure under the head was determine as the basis for the calculation of the external lever arm. The presence of motor endplate regions was ascertained by multiple surface electrodes. The slopes of individual linear regression lines for the root mean square (rms)-values were dependent on the existence of endplates in the area of the electrodes — endplates caused smaller rms values per Newton metres of external torque. Significant intersubject differences between regression equations could not be eliminated by the normalization of EMG-parameters and/or torques. The elimination of gravity, the continuous monitoring of positions, and the consideration of localization of motor endplate regions were essential prerequisites for the acquisition of reliable relationships between EMG of different neck muscles and external torques. Two important conclusions were derived for the prediction of torques from EMG measurements: firstly, individual regression equations which take into account the position of the head and neck should be used; secondly, normalization procedures do not justify the application of average regressions to a group of subjects.     

The force-velocity relationship of arm flexion in untrained males and females and arm-trained athletes

Summary The force-velocity curve (FVC) of arm flexion was established in 123 untrained males and 110 untrained females aged from 15 to 36 years, and 48 arm-trained athletes competing in different sport disciplines. The FVC was described by Hill's equation and defined by the parameters: maximal static moment (M₀), maximal angular velocity (₀), maximal power (P₀) and the concavity of the FVC (H). Within the given age range the level of the curve parameters of both untrained men and women was independent of age.On average, H was the same in all three groups. As compared to M₀ of the untrained males, M₀ of the athletes was 33% higher and M₀ of the females was 38% lower; with regard to P₀ these differences were +30% and –43% respectively. ₀ was the same for trained and untrained males, wherease ₀ of the women was 10% lower than ₀ of the men.     

Changes in the angle-force curve of human elbow flexors following eccentric and isometric exercise

The aim of this study was to explore and compare the magnitude and time-course of the shift in the angle-force curves obtained from maximal voluntary contractions of the elbow flexors, both before and 4 consecutive days after eccentric and isometric exercise. The maximal isometric force of the elbow flexors of fourteen young male volunteers was measured at five different elbow angles between 50° and 160°. Subjects were then divided into two groups: the eccentric group (ECC, n=7) and the isometric group (ISO, n=7). Subjects in the ECC group performed 50 maximal voluntary eccentric contractions of the elbow flexors on an isokinetic dynamometer (30°^.s^–1), while subjects in the ISO group performed 50 maximal voluntary isometric muscle contractions with the elbow flexors at a lengthened position. Following the ECC and ISO exercise protocols, maximal isometric force at the five angles, muscle soreness, and the relaxed (RANG) and flexed (FANG) elbow angles were measured at 24 h intervals for 4 days. All results were presented as the mean and standard error, and a quadratic curve was used to model the maximal isometric force data obtained at the five elbow angles. This approach not only allowed us to mathematically describe the angle-force curves and estimate the peak force and optimum angle for peak force generation, but also enabled us to statistically compare the shift of the angle-force curves between and within groups. A large and persistent shift of the angle-force curve towards longer muscle lengths was observed 1 day after eccentric exercise (P<0.01). This resulted in a ~16° shift of the optimum angle for force generation, which remained unchanged for the whole observation period. A smaller but also persistent shift of the angle-force curve was seen after isometric exercise at long muscle length (P<0.05; shift in optimum angle ~5°). ECC exercise caused more muscle damage than ISO exercise, as indicated by the greater changes in RANG and ratings of muscle soreness (P<0.05). It was suggested that the shift in the angle-force curve was proportional to the degree of muscle damage and may be explained by the presence of overstretched sarcomeres that increased in series compliance of the muscle.     

化合物构效关系的模糊极小极大神经网络识别研究

应用模糊极小极大神经网络研究了化合物复杂结构和性能（QSAR）之间的关系，用该法进行几组化合物致癌的识别，结果优于线性回归的方法，对此作出一些分析。     

Molecular Evidence for the Existence of Two Distinct Subgroups in Cucumber Mosaic Cucumovirus

Infectious full-length cDNA clones from the genomic RNAs of a subgroup II cucumber mosaic cucumovirus strain (Trk7) were obtained. Sequence analysis of the whole genome revealed strong homology (99%) to the genome of Q-CMV, the only subgroup II strain whose entire genomic nucleotide sequence had been available in the database, and an overall 75% homology to those of subgroup I strains. We provide sequence comparisons of different parts of 1a, 2a and 2b proteins of Cucumovirus species, and propose phylogenetic trees based on these protein sequences.     

Effect of postactivation potentiation on dynamic knee extension performance

Six men and four women performed, in separate trials, maximal dynamic knee extensions with loads of 15%, 30%, 45% and 60% of maximal isometric knee extension peak torque (MVC). The dynamic extensions were done after postactivation potentiation (PAP) had been induced with a 10-s MVC, and in a control trial without PAP. PAP, measured as the increase in evoked twitch torque, was 53 (4)% (SE) and 43 (3)% at the time of the first and second extensions with each load. PAP failed to increase the attained peak velocity with any load; on the contrary, there was a trend for peak velocity to decrease in the first extension, which occurred ≅15 s after the 10-s MVC. The results suggest that fatigue produced by the 10-s MVC suppressed any benefit that could be derived from the induced PAP. A surface electromyogram (EMG) recorded from one muscle of quadriceps femoris gave no indication of activation failure in the first knee extension; however, activation impairment specific to the rate of force development cannot be ruled out. It is concluded that the strategy employed, namely of having knee extensions performed soon after the 10-s MVC to maximize PAP at the time of performance, was unsuccessful because there had been insufficient time for recovery from fatigue. It is possible that a longer recovery time, even at the cost of a diminished PAP, may have proved beneficial. Accepted: 27 July 2000     

Summation of fibre potentials and the e.m.g.-force relationship during the voluntary movement of a forearm

A linear mathematical model of the electromyogram (e.m.g.) has been developed for the biceps muscle. The number of motor units (and therefore muscle fibres) contributing to the resultant e.m.g. at any stage of movement has been found from the force analysis of elbow flexion. The depths of various motor units and the phase difference between the recruitment of any two motor units have been formulated using a spiral spread of recruitment sequence. The attenuation of individual motor-unit action potentials due to varying depths has been taken into consideration, and due regard has been taken of the length-tension diagram of a muscle while performing the force analysis. Attention has been focused on the flexion of the elbow joint, in which a method of finding the individual contribution of the biceps and brachialis muscles has been developed and applied. The results predicted by the model have been verified by experiments. The model can also be extended to the e.m.g. of other fast skeletal muscles. The conditions and limitations for such generalisations have been stated and discussed.     

The influence of social environmental condition on the production of stress-induced 22 kHz calls in adult male Wistar rats

Adult rats emit 22 kHz ultrasonic vocalizations (USVs) in response to aversive stimuli, and these sounds are suggested to have communicative information among conspecifics. It is conceivable that social environment during development of rats has relevance to the emission of 22 kHz USVs. To examine the effects of social environment after weaning on production of stress-induced USVs, we compared the amount of emission of USVs among three groups of rats reared under different conditions after weaning. One group of rats was housed individually, and the other two groups were housed in pairs, in which social hierarchy of the pair was determined by social dominance-subordination relationships. The USVs were induced by acute mild somatic stimuli on the back and neck. Individually reared rats emitted much fewer USVs than pair-reared rats. In addition, socially subordinate rats emitted more USVs compared with socially dominant ones. These results suggest that not only social interaction but also the status in social hierarchy may play an important role in the process of the development of USVs induced by somatic stimuli.     

Radiotherapy alone in breast cancer. I. Analysis of tumor parameters, tumor dose and local control: the experience of the Gustave-Roussy Institute and the Princess Margaret Hospital

This retrospective study involved 463 breast cancer patients treated by radiotherapy alone at the Princess Margaret Hospital and at the Institut Gustave-Roussy. These patients either had operable tumors, but were unfit for general anesthesia, or had inoperable tumors due to local contraindications to surgery. Results were analyzed according to tumor response, local recurrence rate, tumor size, tumor fixation, nodal fixation and tumor dose. Conventional statistical analysis of local control showed two significant factors: tumor dose and tumor size. Multivariate analysis permitted to define an "individual risk" (IR) of local recurrence according to three independent factors: tumor size, tumor fixation, and nodal fixation. It was shown that the IR was a good prognostic factor for local control. Increase in tumor dose gave a similar effect in the local recurrence relative risk for all the IR groups. According to the slope of the dose-effect curve, it was deduced that a dose increase of 15 Gy can decrease the relative risk of local recurrence 2-fold. In fact, it was shown that tumor dose was the most significant independent factor on local control, able to produce up to a 10-fold increase compared to 2-fold decrease for tumor size. If the IR of local recurrence is known, a theoretical predictive value on local control, taking into account the tumor dose, can be determined according to the present data.