Jan Drukker

Effect of the notochord on the differentiation of a floor plate area in the neural tube of the chick embryo

SummaryThe role of a notochord fragment on the origin of an additional floor plate area in the neural tube is investigated by quantitative morphological methods. In 1.5 to 2 day chick embryos a notochordal fragment was implanted in close apposition to the lateral wall of the neural groove in the region between prospective wing and leg bud. At 4 days, adjacent to the implant a distinct area of the neural wall was present, which resembled the natural floor plate with respect to its thickness, the abluminal location of elongated nuclei and the absence of neuroblasts. The mitotic density of this area was reduced. This “additional floor plate” was distinct when the experiment was performed at 1.5 days but was hardly recognizable when it was carried out at 2 days.From these results it is concluded that a) the notochord induces floor plate like structures and diminishes proliferation, and b) that the period of floor plate induction by the notochord is very restricted.

Strength training in patients with myotonic dystrophy and hereditary motor and sensory neuropathy: A randomized clinical trial

A randomized clinical trial on the effects of strength training was performed in myotonic dystrophy (MyD) patients and patients with hereditary motor and sensory neuropathy (HMSN). Training and most measurement tools involved the proximal lower extremity muscles. The participants trained 3 times a week for 24 weeks with weights adapted to their force. Strength was evaluated by isokinetically measured knee torque. Fatiguability was assessed by the time an isometric contraction could be sustained. Functional performance was measured by timed motor performance and by questionnaires on functional performance. Serum myoglobin (Mb) levels were determined to detect changes in muscle fiber membrane permeability. The MyD group included 33 participants, and the HMSN group included 29 participants. Within each diagnostic group, patients were individually matched and subsequently randomized for treatment allocation. In the MyD patients, none of the measurement techniques showed any training effect. Neither were there signs of deterioration caused by the training. In the HMSN group, knee torques increased. Timed motor performance did not change, although the questionnaires showed an improvement on items related to upper-leg function. Mb levels did not change significantly as a result of the training. In conclusion, the MyD group showed neither positive nor negative effects of the training protocol, whereas the training produced a moderate increase in strength and leg-related functional performance in the HMSN group.

Does problem‐based learning lead to deficiencies in basic science knowledge? An empirical case on anatomy

Introduction  Problem‐based learning (PBL) is supposed to enhance the integration of basic and clinical sciences. In a non‐integrative curriculum, these disciplines are generally taught in separate courses. Problem‐based learning students perceive deficiencies in their knowledge of basic sciences, particularly in important areas such as anatomy. Outcome studies on PBL show controversial results, sometimes indicating that medical students at PBL schools have less knowledge of basic sciences than do their colleagues at more traditional medical schools. We aimed to identify differences between PBL and non‐PBL students in perceived and actual levels of knowledge of anatomy.

Cervical spine motion in the sagittal plane. II. Position of segmental averaged instantaneous centers of rotation--a cineradiographic study.

Anteflexion and retroflexion movements of the cervical spine were recorded cineradiographically during three measuring sessions to determine reproducibility as well as intraindividual and interindividual variability of segmental instantaneous centers of rotation [recorded as “averaged” and “standard”). Segmental averaged instantaneous centers of rotation were based on data obtained from all frames of the cineradiographic film by the use of the average pentagon and moving average method. Only the first and last frame were used to construct the segmental standard instantaneous centers of rotation. Contrary to segmental range of motion, a parameter of quanityt of motion, the position of the averaged Instantaneous centers of rotation (better than the standard), a parameter of quality of movements, shows a variability of such low extent that it seems feasible to use it to diagnose abnormal mobility or in assessing therapy in the neck region.

Effect of a notochordal implant on the early morphogenesis of the neural tube and neuroblasts: histometrical and histological results.

The role of the notochord on the early development of ventral horn neuroblasts was investigated in chick embryos by implanting an additional notochord fragment near the right side of the thoracic neural tube. When the implant was located directly lateral to the neural tube, an enlargement of the right half of the neural tube and of the area of neuroblasts occurred, and axons were found to pass through the outer membrane of the neural tube over a broad dorsoventral trajectory. When the notochord was located ventrolaterally a population of neuroblasts including their efferent axons was found at a more dorsal location. It is concluded that a notochordal implant is able to influence the differentiation of neuroblasts.

Development of new muscle synergies in postural control in spinal cord injured subjects.

The development of new patterns of postural control in patients with a complete thoracic spinal cord injury (SCI) during their active clinical rehabilitation was studied. Especially the role of non-postural muscles, like the latissimus dorsi (LD) and the trapezius pars ascendens (TPA), in maintaining and restoring sitting balance during standardized bimanual task performance was investigated. Twelve patients, diagnosed with an acute complete thoracic SCI between spinal cord level T2 and T12, participated in a longitudinal experimental study. Changes in the centre of pressure (CP) and electromyographic activity of the erector spinae (ES) at level L3, T9 and T3, the LD, the TPA, the pectoralis major (PM), the serratus anterior and the oblique abdominal muscles were investigated at several moments in the rehabilitation process. Results show a gradual development of specific muscle activation patterns for both high and low thoracic SCI patients. These patterns seem to be related to a combination of restoration of function of the ES-L3 and ES-T9 in the low thoracic SCI subjects and increased compensatory muscle use of the LD, TPA and PM in high SCI patients. The range in which low thoracic SCI patients can actively vary their CP increased slightly during rehabilitation.

Progressive resistance training in neuromuscular patients. Effects on force and surface EMG

In a randomized clinical trial the efficacy of strength training was studied in patients with myotonic dystrophy (n = 33) and in patients with Charcot-Marie-Tooth disease (n = 29). Measurements were performed at the start and after 8, 16 and 24 weeks of progressive resistance training. Surface electromyography (SEMG) of proximal leg muscles was recorded during isometric knee extension at maximum voluntary contraction (MVC) and at 20, 40, 60 and 80% of MVC. Changes in MVC, maximum electrical activity and torque-EMG ratios (TER) were calculated. Fatigue was studied by determining the changes in endurance and in the decline of the median frequency (Fmed) of the SEMG during a sustained contraction at 80% MVC. These parameters showed no significant changes after the training in either of the diagnostic groups. Only the Charcot-Marie-Tooth training group showed a gradual significant increase in mean MVC over the whole training period (21%). After 24 weeks, the increase in mean RMS was similar (25%), but this was mainly due to a sharp rise during the first 8 weeks of training (20%). The findings indicate that the initial strength increase was due to a neural factor, while the subsequent increase was mainly due to muscle hypertrophy.

Postural muscle responses in the spinal cord injured persons during forward reaching.

To compensate for postural muscle function loss spinal cord injured (SCI) people have to use parts of the sensorimotor system which are still intact. In this study, postural control was investigated in high and low thoracic SCI people and in able-bodied controls, using a bimanual forward-reaching task. Muscle activity was recorded bilaterally from the erector spinae (ES) at level L3, T9 and T3, latissimus dorsi (LD), ascending part of the trapezius muscle (TPA), serratus anterior (SA), sternocostal head of the pectoralis major (PM) and the oblique abdominal muscles (OA) by means of surface electromyography. Sitting balance was monitored by measuring the changes in the location of the centre of pressure (CP) using a force platform. Muscle activity analyzed in different phases of the movement showed that SCI people adopt different postural adjustments to face the balance changes due to the reaching movement. SCI people make alternative use of non-postural muscles like the LD and TPA to maintain their sitting balance.

Surface EMG of proximal leg muscles in neuromuscular patients and in healthy controls. Relations to force and fatigue

In an effort to find parameters to evaluate patients with neuromuscular disorders, surface electromyography (SEMG) of proximal leg muscles was performed in 33 patients with myotonic dystrophy (MyD), 29 patients with Charcot-Marie-Tooth (CMT) disease and 20 healthy controls. The root mean square (RMS) of the SEMG amplitude (microV) was calculated at different torque levels. Endurance (seconds) and median frequency (Fmed) of the SEMG power spectrum, used as parameters of fatigue, were determined at 80% of MVC. Maximum voluntary contraction (MVC) was found to be decreased in patients; the ratio between RMS values of antagonists and agonists was increased and torque-EMG ratios (Nm/microV) were decreased. These differences with respect to controls were more pronounced in MyD than in CMT. The initial Fmed value was lowest in CMT. The greatest decrease in Fmed was found in MyD. SEMG data in relation to force have not been determined before in groups of MyD or CMT patients. In both disorders, parameters differed from controls, which means that adding SEMG to strength measurements could be useful in studying the progress of the disorder and the effects of interventions.

Quadriceps strength and timed motor performances in myotonic dystrophy, Charcot–Marie–Tooth disease, and healthy subjects

Background and purpose: The leading hypothesis was that a relation exists between muscular strength and functional abilities. Therefore a study was undertaken to quantify such a relationship in a population of subjects with different muscular strengths. This population consisted of healthy subjects and subjects with slowly progressive neuromuscular disorders. Methods: The study included 33 patients with myotonic dystrophy, 29 patients with Charcot–Marie–Tooth disease and 20 healthy subjects. Isokinetic and isometric knee torques were measured on an isokinetic dynamometer at various velocities. The following activities were timed: descending and ascending stairs, rising from a chair, rising from supine, walking at natural speed and walking at maximum speed. Results: The population covered a wide range of the variables: whereas the healthy subjects performed best (i.e. had the highest knee torques and performed the activities most quickly), the myotonic dystrophy group included the subjects with the lowest knee torques. The natural logarithms (ln) of isokinetic extension torque at the highest velocity (120°/s) and those of the time taken to perform the described activities showed the highest levels of correlation. It was found that after correction for age and weight, 56% (walking at natural speed) to 73% (descending stairs) of the variance in the ln of the time taken could be attributed to the variance in the ln of the torques. Conclusion and discussion: A strong relation between quadriceps strength and timed motor performances were demonstrated. The impact of strength reduction on time taken was most obvious in subjects with considerably decreased strength. Therefore, it is feasible to try to influence muscle strength in patients with relevant strength reduction in order to achieve better functional ability.