Head Swing Research Articles

Myosin head mechanical performance under different conformational change mechanisms

The present paper puts forward a mathematical approach to model the conformational changes of the myosin head due to ATP hydrolysis, which determine the head swinging and consequent sliding of the actin filament. Our aim is to provide a simple but effective model simulating myosin head performance to be integrated into the overall model of sarcomere mechanics under development at our Laboratory (J. Biomech. 34 (2001) 1607). We began by exploring myosin head mechanics in recent findings about myosin ultrastructure, morphology and energetics in order to calculate the working stroke distance (WS) and the force transmitted to the actin filament during muscle contraction. Two different working stroke mechanisms were investigated, assuming that the swinging of the myosin head occurs either as a consequence of purely conformational changes (Science 261 (1993a) 58) or by thermally driven motion (ratchet mechanism) followed by conformational changes (Cell 99 (1999) 421). Our results show that force and WS values vary markedly between the two models. The maximum force generated is about 10 pN for the first model and 31 pN for the second model, and the WSs are about 13 and 4 nm, respectively. These results are then discussed and compared with published data. The experimental data used for comparison are scarce and non-homogeneous; hence, the final remarks do not lead to definite conclusions. In any event, relatively speaking, the first model is more coherent with experimental findings.

Myosin head mechanical performance under different conformational change mechanisms

The present paper puts forward a mathematical approach to model the conformational changes of the myosin head due to ATP hydrolysis, which determine the head swinging and consequent sliding of the actin filament. Our aim is to provide a simple but effective model simulating myosin head performance to be integrated into the overall model of sarcomere mechanics under development at our Laboratory (J. Biomech. 34 (2001) 1607). We began by exploring myosin head mechanics in recent findings about myosin ultrastructure, morphology and energetics in order to calculate the working stroke distance (WS) and the force transmitted to the actin filament during muscle contraction. Two different working stroke mechanisms were investigated, assuming that the swinging of the myosin head occurs either as a consequence of purely conformational changes (Science 261 (1993a) 58) or by thermally driven motion (ratchet mechanism) followed by conformational changes (Cell 99 (1999) 421). Our results show that force and WS values vary markedly between the two models. The maximum force generated is about 10 pN for the first model and 31 pN for the second model, and the WSs are about 13 and 4 nm, respectively. These results are then discussed and compared with published data. The experimental data used for comparison are scarce and non-homogeneous; hence, the final remarks do not lead to definite conclusions. In any event, relatively speaking, the first model is more coherent with experimental findings.

Neural network model to generate head swing in locomotion of Caenorhabditis elegans

Computer simulation of the neural network composed of the head neurons of Caenorhabditis elegans was performed to reconstruct the realistic changes in the membrane potential of motoneurons in swinging the head for coordinated forward locomotion. The model neuron had ion channels for calcium and potassium, whose parameters were obtained by fitting the experimental data. Transmission properties of the chemical synapses were set as graded. The neural network involved in forward movement was extracted by tracing the neuronal activity flow upstream from the motoneurons connected to the head muscles. Simulations were performed with datasets, which included all combinations of the excitatory and inhibitory properties of the neurons. In this model, a pulse input entered only from motoneuron VB1, and activation of the stretch receptors on SAA neurons was necessary for the periodic bending. The synaptic output property of each neuron was estimated for the alternate contraction of the dorsal and ventral muscles. The AIB neuron was excitatory, RIV and SMD neurons seemed to be excitatory and RMD and SAA neurons seemed to be inhibitory. With datasets violating Dale's principle for the SMB neuron, AIB neuron was excitatory and RMD neuron was inhibitory. RIA, RIV and SMD neurons seemed to be excitatory.

Targeted expression of tetanus toxin reveals sets of neurons involved in larval locomotion in Drosophila

The Drosophila larva is widely used for studies of neuronal development and function, yet little is known about the neuronal basis of locomotion in this model organism. Drosophila larvae crawl over a plain substrate by performing repetitive waves of forward peristalsis alternated by brief episodes of head swinging and turning. To identify sets of central and peripheral neurons required for the spatial or temporal pattern of larval locomotion, we blocked neurotransmitter release from defined populations of neurons by targeted expression of tetanus toxin light chain (TeTxLC) with the GAL4/UAS system. One hundred fifty GAL4 lines were crossed to a UAS-TeTxLC strain and a motion-analysis system was used to identify larvae with abnormal movement patterns. Five lines were selected that show discrete locomotor defects (i.e., increased turning and pausing) and these defects are correlated with diverse sets of central neurons. One line, 4C-GAL4, caused an unusual circling behavior that is correlated with approximately 200 neurons, including dopaminergic and peptidergic interneurons. Expression of TeTxLC in all dopaminergic and serotonergic but not in peptidergic neurons, caused turning deficits that are similar to those of 4C-GAL4/TeTxLC larvae. The results presented here provide a basis for future genetic studies of motor control in the Drosophila larva.

Contributions of Superior and Inferior Tentacles to Learned Food-Avoidance Behavior in Limax marginatus

We investigated learned food-avoidance behavior of conditioned slugs in detail, and examined the effect of removing the inferior or superior tentacles (ITs and STs) on the avoidance behavior. The conditioning procedure significantly lowered the preference level of slugs to the conditioned odor, and the decrease of the preference was maintained for at least 48 hr. Video analysis experiments showed that change in the crawling direction during an aversion response occurred consistently accompanied by an average of 1.2 head swings. The first head swing was usually observed within 1 cm from the conditioned odor. Removal of the ITs after conditioning reversed the trend towards a lowered preference level. On the other hand, removal of the STs did not change the level. These results suggest that the IT inputs are needed to induce conditioned behavior. The contribution of STs to the conditioning behavior is indicated by the significant increase in the average number of head swings (3.6 swings) in a trial after their removal. In some trials, the slugs lacking STs avoided the odor source after crossing it. These observations indicate that removal of STs decreases the orientation ability of conditioned slugs.

Consideration of the relevance of ethological animal models for human repetitive behavioral spectrum disorders

Treatment successes of various stereotyped behaviors in animals and humans has renewed interest in ethologic animal models for the study of psychiatric disorders. This report presents another such behavior occurring in horses to weaving. This anomalous, repetitive, and purposeless behavior draws analogies to human compulsive spectrum behaviors. A "weaver" provided an opportunity to evaluate serotonin, dopamine, and opioid neurotransmitter system contributions by probing each with a selective agent in A-B-A-C-A-D design. The horse was treated in sequential 1-month periods separated by 1-month washouts with a serotonin transport inhibitor (SRI), opiate antagonist (OA), and neuroleptic (DA). Videotape was taken weekly and analyzed by two blind raters. Frequency of head swings, latency to onset, and severity were recorded. The SRI showed > 95% symptom reduction, the DA 40%, and OA 30%. The findings suggest that neurochemical explanations of disturbance based on single drug vs. placebo trials may be oversimplified. Multiple-system probes are needed to dissect complex interactive biological systems. Animal model research can have an important role in such investigations.

The pattern of locomotor activity after cocaine treatment in the rat

The present study used a computerised technique to assess the behavioural effects on locomotor activity of i.p. cocaine administration in the rat. This computerised method provides considerable information about various behavioural responses, as well as accuracy by measuring the frequency and duration of every behavioural event. Cocaine induced an increase in behavioural events related to motor activity, such as moving, sniffing and rearing, while standing was reduced. Cocaine increased the frequency of the behavioural responses recorded, but decreased their mean duration. No stereotyped behavioural element, such as head swinging, head bobbing, licking, stereotyped mouth moving or stereotyped sniffing, was recorded after cocaine treatment. Cocaine, unlike d-amphetamine, induced a specific behavioural pattern characterised predominantly at all doses by a stimulated motor activation involving an increase in moving and sniffing and a decrease in standing behaviour.

The effect of a simple conversion of a tether house on sow welfare

A survey of dry sow housing across England (Baynes and Hunter, 1993) indicated that 30% of producers currently with confinement systems would like to convert their existing sow buildings to conform with the ban on stall and tether systems in 1999. This study assessed the feasibility of a minimal cost conversion of part of a tether house in which the sows were liquid fed.Sows were housed in a 21 year old tether house capable of housing 152 sows in four rows. The middle section of the house consisted of two rows of tethers, back to back, and part of this was gated off to create two pens, each capable of holding 10 sows in two rows of five. Total space allowance was 14m2/sow. Sows were of mixed weights and parities and all had previous experience of the tether house. Both groups were observed for three hours immediately after mixing, for two hours feeding on the following day, and for two hours on nine subsequent days. Eight categories of agonistic interaction (head swing with mouth closed, head swing with mouth open, push, attempted bite/slash, bite/slash, mount, vulva bite and fight of more than ten seconds), space usage and skin lesions (scored from one to five on eight regions of the body - Stewartet al, 1993) were recorded during each observation period. Sow weight and condition (scored from one to five - Whittemore, 1980) were assessed on entry to the building at four weeks post-weaning and on exit, approximately five days pre-farrowing.

Teaching Mathematics to Adolescents Classified as Educable Mentally Handicapped

This study examined the effects of teaching adolescents classified as having educable mental handicaps (EMH) to solve four-column subtraction problems involving regrouping through three different methods: (a) pencil and paper, (b) calculators, and (c) calculators employing a rehearsal strategy using problems containing visual cues. The students classified as EMH (five females and two males) were enrolled in a self-contained special education class in a junior high school. Forty-four eighth-grade general education students were selected from the same school to participate in a preexperimental, noninstructional, peer group assessment. An ABCD, single-case experimental design was used, with multiple probes introduced at staggered intervals. Days per phase ranged from 4 to 10. Two maintenance phases were scheduled, the first immediately after the last instructional phase, and the second 26 days later. The results indicated significant differences in performance favoring calculators over pencil and paper for each student classified as EMH. No difference in performance was found for the sample of general education students across computational modes; however, a split point (cutoff score) was found at 17.5 correct digits per minute with pencil and paper, which predicted a student's best computational mode. Rehearsal and visual cues significantly influenced correct performance for only one student classified as EMH. Maintenance of correct performance with calculators over time was excellent for each pupil. A positive relationship was found between the number of head swings used to input digits into a calculator and computational time. Without calculators, the students classified as EMH were markedly inferior to their general education peers; however, with calculators the performances were equivalent. Several clinical issues involved in conventional and calculator instruction for students with special needs are discussed.

On optimum frame structures of a motor cycle.

The frame structure of a motor cycle is required to be as rigid and as light as possible. In this paper, the minimum compliance design of the frame structure of a motor cycle is treated numerically. Torsional rigidity between the head pipe and swing arm pivots, which is very important for the driving stability of a motor cycle, is maximized under constraints of the total volume. Two typical cases of design are implemented. In the first case, cross-sectional areas of the frame members are taken as design variables. Shape optimization of the frame structure subjected to geometrical constraints, which are caused by keeping the driving function and the space of some parts, is carried out in the second case. In the latter case, positions and cross-sectional areas of frame members are varied simultaneously. Rigid and simple frame structures of the motor cycle are obtained for each design problem.

Ketamine-induced rotation: Interaction with GABA-transaminase inhibitors and picrotoxin

Ketamine in a dose of 100 mg/kg (IP) produced stereotypic behavior and vigorous rotation in adult male Sprague-Dawley rats. The first rotation phase, accompanied by head swinging, was short and terminated by the anesthetic phase which lasted 20–30 min. The second rotation phase began 1–3 min after the end of the anesthetic phase. A single dose of GABA-T inhibitors, γ-vinyl GABA (1200 mg/kg, IP) or γ-acetylenic GABA (100 mg/kg, IP) administered 4 hours prior to ketamine, shortened the first rotation phase, increased the anesthetic phase, changed the pattern of postanesthetic rotation and reduced total and net rotation scores. Picrotoxin (3 mg/kg) given 10 min prior to ketamine tended to act in the opposite direction although none of its effects reached statistical significance.

Segmental contribution to forces in vertical jump.

Performance of a vertical jump was analyzed with respect to the contribution of the different body segments to the forces acting on the whole body center of gravity. Both cinematograph and force-platform techniques were employed. The data disclosed that the take-off velocity in vertical jumps was caused by the different components as follows: knee extension 56%, plantar flexion 22%, trunk extension 10%, arm swing 10%, and head swing 2%. However, the average take-off velocity of the total performance (3.03 m/s) was only 76% from the theoretical maximum calculated from the segmental analyses. Optimal timing of the segmental performances was calculated to increase this "efficiency" to 84%. Great variance were observed among individuals in the total performance despite the similarities in utilization of the performance of individual segments.

Resistance of Cotton Plant Hairs to Mobility of First-Instars of the Pink Bollworm123

Movements of 1st-instars of pectinophora gossypiella (Saunders) on 6 varieties of cotton with leaves and petioles differing in amount of pubescence were observed, timed, and traced with a camera lucida. The 2 most pubescent varieties, SA-166 and TM-1(H2), appeared to confuse larvae and greatly impeded their movements. We conclude that high plant hair density in cotton is a promising mechanism for host plant resistance to the pink bollworm. Larvae paused regularly to head swing and to sample the substrate with their mandibles while moving on leaves and petioles. When leaf neclaries were encountered by larvae, feeding usually occurred.