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PubMed1988

Effect of load perturbations on EMG activity and trajectories of pointing movements.

Force perturbations were applied to the upper arm during pointing movements to a target. Following the perturbation, the trajectories of shoulder and elbow angular velocities converged on those obtained during trials in which no perturbation was imposed, but with a temporal offset. Changes in EMG activity in shoulder and elbow flexors evoked by the perturbation were similar to those observed previously under quasi-static conditions, the change in a given muscle depending on shoulder and elbow motion.

Arm↗
PubMed1988

The origins and trajectories of somatostatin reticulospinal neurons: a potential neurotransmitter candidate of the dorsal reticulospinal pathway.

Somatostatin (SOMA)-immunoreactive neurons present in the nucleus gigantocellularis and nucleus raphe magnus formed the origins of a descending pathway from the rostral medulla to the spinal cord. This descending pathway was traced through the central medullary tegmentum and dorsolateral funiculus to innervate the dorsal horn. The location, trajectories and presumed inhibitory nature of SOMA in the spinal cord suggest that SOMA maybe a potential neurotransmitter candidate for the classic dorsal reticulospinal pathway.

Animals↗
PubMed1989

An analysis of mandibular movement trajectories and masticatory muscle EMG activity during drinking in the guinea pig.

Electromyographic (EMG) activity of the anterior digastric, lateral pterygoid, and deep masseter muscles as well as the associated jaw movements during drinking were studied in the awake guinea pig. Drinking was characterized by rhythmic, vertically directed jaw movements with little or no associated lateral movements. The jaw opening phase of each cycle was associated with bilaterally synchronized EMG activity in the digastric and lateral pterygoid muscles, and the jaw closing phase with bilaterally synchronized activity in the masseter muscles. The mean EMG burst durations (+/- 1 S.E.) in the digastric and masseter muscles were 164.2 +/- 14.93 ms and 94.3 +/- 26.44 ms, respectively. The digastric muscle EMG burst duration was significantly correlated with drinking cycle time and with masseter muscle EMG onset; on the other hand, masseter muscle EMG burst duration was not correlated with cycle time. These patterns of EMG activity and jaw movement trajectories are similar to those induced by apomorphine in the ketamine-anesthetized guinea pig.

Animals↗
PubMed1991

Differential sensitivity to hypoxia of the peripheral versus central trajectory of primary afferent axons.

Myelinated primary afferent fibers have both peripheral and central nervous system components. As the fibers course through peripheral nerve and dorsal roots they are myelinated by Schwann cells, but after they invade the spinal cord they become myelinated by oligodendrocytes and have associations with astrocytes. This presents the opportunity to compare the pathophysiology of PNS (Schwann cell-associated) vs. CNS (oligodendrocyte/astrocyte-associated) portions of the same axonal trunk located in the dorsal roots and dorsal columns, respectively. Dorsal spinal roots and slices of dorsal columns isolated from adult rats were studied in a sucrose gap chamber from which compound action potential and membrane potential changes could be recorded. The results indicate that the peripheral component of the afferent fibers is resistant to hypoxia as evidenced by stable action and membrane potential when O2 in the bathing medium was completely replaced with N2 for periods up to 2 h. In contrast, the axons become sensitive to hypoxia as they project through the dorsal columns as evidenced by rapid reduction in action potential amplitude accompanied by membrane depolarization when O2 is replaced by N2. This differential response to hypoxia, observed on the same axon branches but over CNS vs. PNS trajectories, suggests that differences related to the extracellular environment or in axo-glial organization in dorsal root vs. dorsal column may confer different degrees of susceptibility to anoxia.

Action Potentials↗
PubMed1991

Trajectory of redirected corticospinal axons after unilateral lesion of the sensorimotor cortex in neonatal rat; a phaseolus vulgaris-leucoagglutinin (PHA-L) tracing study.

The corticospinal neurons of the rat project almost exclusively to the contralateral spinal cord. Retrograde and anterograde tracing experiments showed that only about 2-4% of the corticospinal neurons of the sensorimotor cortex project to the ipsilateral spinal cord in the normal rat. The large majority of corticospinal axons (more than 90%) travel at spinal level at the base of the contralateral dorsal funiculus; in addition a few axons run in the contralateral lateral funiculus and at the base of the dorsal horn. The undecussated axons run in the ipsilateral dorsal (about 1-2%) and ventral (about 1-2%) funiculi. The rearrangement of the corticospinal projections was studied with various tracing methods in rats subjected to unilateral lesion of the sensorimotor cortex at Postnatal Day 2 to 4. Spinal injections of the tracer WGA-HRP that were restricted to the side opposite to the cortical lesion showed a significant increase of retrogradely labeled corticospinal neurons in the intact cortex as compared to the proportion of ipsilateral projections in control experiments. This was consistent with an increased density of anterogradely labeled corticospinal terminals in the spinal cord ipsilateral to an injection of WGA-HRP in the motor cortex opposite to neonatal lesion, in comparison to normal rats. The trajectory of these "aberrant" ipsilateral corticospinal projections resulting from the neonatal lesion of the opposite sensorimotor cortex was analyzed by means of the anterograde tracer phaseolus vulgaris-leucoagglutinin (PHA-L), injected in the motor cortex. These data indicated that decussated corticospinal axons recross at spinal levels, close to their terminal zone, where they appear to ramify and terminate in the spinal gray including the motoneurons. Such recrossing axons thus represent one new possible mechanism, among other previously reported ones, contributing to the increase of ipsilateral corticospinal projections in rats subjected to neonatal cortical lesion.

Animals↗
PubMed1986

Geometrical principal component analysis of planar-segments of the three-channel Lissajous' trajectory of human auditory brain stem evoked potentials.

Three-Channel Lissajous' Trajectories (3CLTs) of Auditory Brain Stem Evoked Potentials (ABEP) were obtained from 15 normal humans. Planar-segments of 3CLT were identified and the orientations of the first two geometrical principal components, which interact to produce the planar-segments, were calculated. Each principal component's orientation in voltage space was quantified by its coefficients (A, B and C). Intersubject variability of these orientations was comparable to the variability of plane orientations. The principal components of planar-segments can indicate the type of generator activity that is involved in the formation of planar-segments. The results of this analysis indicate that planarity of each 3CLT component is produced by the interaction of simultaneous multiple generators, or by a single synchronous generator which changes its orientation. The coefficients of these principal components may complement plane coefficients as quantitative indices of 3CLT of ABEP.

Adult↗
PubMed1985

A molecular dynamics study of the C-terminal fragment of the L7/L12 ribosomal protein. Secondary structure motion in a 150 picosecond trajectory.

A 150 picosecond molecular dynamics computer simulation of the C-terminal fragment of the L7/L12 ribosomal protein from Escherichia coli is reported. The molecular dynamics results are compared with the available high-resolution X-ray data in terms of atomic positions, distances and positional fluctuations. Good agreement is found between the molecular dynamics results and the X-ray data. The form and parameters of the interaction potential energy function and the procedures for deriving it are discussed. Some current misunderstandings concerning the ways of evaluating the efficiency of molecular dynamics algorithms and of application of bond-length constraints in protein simulations are cleared up. The 150 picosecond trajectory has been scanned in a search for correlated motions within and between secondary structure elements. The beta-strands have diffusional stretching modes, and uncorrelated transversal displacements. The dynamic analysis of alpha-helices shows a variety of features. The atomic fluctuations differ between the helix ends; this effect reflects long time-scale motions. Two alpha-helices, alpha A and alpha C, show diffusive longitudinal stretching modes. The third helix, alpha B, has a correlated asymmetric longitudinal stretching; the N-terminal part dominates this behaviour. Furthermore, alpha B presents a librational motion with respect to the other parts of the molecule with a frequency of approximately 5 cm-1. This motion is coupled to helix stretching. Interestingly, the regions of highly conserved residues contain the most mobile parts of the molecule.

Bacterial Proteins↗
PubMed1992

Optimal protocol and trajectory visualization for conformational searches of peptides and proteins.

Conformational searches by molecular dynamics and different types of Monte Carlo or build-up methods usually aim to find the lowest-energy conformation. However, this is often misleading, as the energy functions used in conformational calculations are imprecise. For instance, though positions of local minima defined by the repulsive part of the Lennard-Jones potential are usually altered only slightly by functional modification, the relative depths of the minima could change significantly. Thus, the purpose of conformational searches and, correspondingly, performance criteria should be reformulated and appropriate methods found to extract different local minima from the search trajectory and allow visualization in the search space. Attempts at convergence to the lowest-energy structure should be replaced with efforts to visit a maximum number of different local energy minima with energies within a certain range. We use this quantitative criterion consistently to evaluate performances of different search procedures. To utilize information generated in the course of simulation, a "stack" of low energy conformations is created and stored. It keeps track of variables and visit numbers for the best representatives of different conformational families. To visualize the search, projection of multidimensional walks onto a principal plane defined by a set of reference structures is used. With Met-enkephalin as a structural example and a Monte Carlo procedure combined with energy minimization (MCM) as a basic search method, we analyzed the influence on search efficiency of different characteristics as temperature schedules, the step size for variable modification, constrained random step and response mechanisms to search difficulties. Simulated annealing MCM had comparable efficiency with MCM at constant and elevated temperature (about 600 K). Constraining the randomized choice of side-chain chi angles to optimal values (rotamers) on every MCM step did not improve, but rather worsened, the search efficiency. Two low-energy Met-enkephalin conformations with parallel Tyr1 and Phe4 rings, a gamma-turn around the Gly2 residue, and Phe4 and Met5 side-chains forming together a compact hydrophobic cluster were found and are suggested as possible structural candidates for interaction with a receptor or a membrane.

Amino Acid Sequence↗
PubMed1981

The prefrontal cortico-oculomotor trajectories in the monkey.

Prefrontal corticofugal systems, as studied with anterograde HRP histochemistry, revealed projections to preoculomotor and oculomotor centers in the diencephalon and brainstem which may underlie direct cortical influence on eye movement. Because of the location of these preoculomotor trajectories, stimulation and lesion experiments affecting ocular motility may be explained by having involved prefrontal projections which have their origin in sulcus principalis or prearcuate area 8 (frontal eye field) cortex.

Animals↗
PubMed1987

Inferring limb coordination strategies from trajectory kinematics.

This paper discusses the method of kinematic modeling and matching to human arm trajectories in order to ascertain the motor control system's coordination strategy. The planning variables of joint angles and endpoint Cartesian coordinates are contrasted, under linear and staggered interpolation strategies. It is shown that distinguishing the two variable planning sets depends critically on the region of the workspace in which movement takes place.

Arm↗
PubMed1994

The spatial relationship between the cerebral cortex and fiber trajectory through the corpus callosum of the cat.

We related fiber trajectory through the feline corpus callosum to the site of fiber origin in the cortical mantle and to functional modality. The cortical fields which contribute axons to the different portions of the corpus callosum were revealed by applying horseradish peroxidase (HRP) to the cut ends of selected groups of callosal axons in twelve adult cats. Overall, the application of HRP at progressively more caudal positions in the corpus callosum labels fields of neurons at successively more caudal positions in the cerebral cortex. Comparison of these data to functionally distinct cortical zones shows that the callosal body conveys a mixture of fibers arising from functionally diverse regions of the cerebrum, whereas portions of the rostral and caudal ends appear to be essentially unimodal, conveying motor and visual signals, respectively.

Animals↗
PubMed1990

Effects of unexpected perturbations on trajectories and EMG patterns of rapid wrist flexion movements in humans.

To investigate how motor programs can be modified by sensory inputs we recorded kinematic and EMG patterns from normal human subjects performing well-practised wrist flexion movements in response to an auditory tone. On random trials unexpected wrist perturbations were introduced at varying times after the signal to move had been given. Extension perturbations delivered before agonist EMG onset resulted in an increased maximum velocity (MV) during the wrist flexion movement and in an increased target overshoot even though the wrist was further from the target than expected by the subject at the onset of the movement. The first agonist EMG burst and the antagonist burst were both increased in magnitude in these perturbed trials. Flexion perturbations delivered before the agonist EMG onset moved the hand nearer to the target just prior to movement onset. These resulted in a reduced MV, but the expected increased target overshoot did not occur. The first agonist burst was reduced in magnitude, and the antagonist burst was increased in magnitude. Perturbations delivered after agonist EMG onset produced less change in the first agonist and antagonist EMG burst, and less compensation for the perturbation was evident in wrist position and velocity recordings. These results indicate that, at least in some situations, motor programs for rapid voluntary movements can be modified by afferent inputs. This interaction between central motor commands and sensory feedback might occur at the cortical or spinal level, depending on when perturbations occur relative to onset of EMG and movement. The timing of the EMG changes suggest that both reflex mechanisms and longer latency 'voluntary' adjustments contribute to the compensatory changes in movement trajectory.

Adult↗
PubMedDate not supplied

Wave III of brain-stem auditory evoked potentials analysed both with 3-channel Lissajous' trajectory and dipole localization method.

Wave III of the BAEP was analysed both with 3-channel Lissajous' trajectory (3-CLT) and a dipole localization method. The experiments were performed on 5 normally hearing subjects. The dipole analysis used an iterative algorithm assuming a spherical head model and homogeneous media. 3-CLT planar analysis was performed with a laboratory system. The parameters of plane C (azimuth and elevation) corresponding to wave III and those of the equivalent dipole showed a similar orientation of the plane and the dipole. This result is in agreement with previous investigations and confirms the interest of 3-CLT in far-field analysis and, at the same time, validates the dipole localization model used in this study, at least for BAEP analysis.

Adult↗
PubMed1994

Three-channel Lissajous' trajectory of the binaural interaction components in human auditory brain-stem evoked potentials.

The 3-channel Lissajous' trajectory (3-CLT) of the binaural interaction components (BI) in auditory brain-stem evoked potentials (ABEPs) was derived from 17 normally hearing adults by subtracting the response to binaural clicks (B) from the algebraic sum of monaural responses (L + R). ABEPs were recorded in response to 65 dB nHL, alternating polarity clicks, presented at a rate of 11/sec. A normative set of BI 3-CLT measures was calculated and compared with the corresponding measures of simultaneously recorded, single-channel vertex-left mastoid and vertex-neck derivations of BI and of ABEP L + R and B. 3-CLT measures included: apex latency, amplitude and orientation, as well as planar segment duration and orientation. The results showed 3 apices and associated planar segments ("BdII," "Be" and "Bf") in the 3-CLT of BI which corresponded in latency to the vertex-mastoid and vertex-neck peaks IIIn, V and VI of ABEP L + R and B. These apices corresponded in latency and orientation to apices of the 3-CLT of ABEP L + R and ABEP B. This correspondence suggests generators of the BI components between the trapezoid body and the inferior colliculus output. Durations of BI planar segments were approximately 1.0 msec. Apex amplitudes of BI 3-CLT were larger than the respective peak amplitudes of the vertex-mastoid and vertex-neck recorded BI, while their intersubject variabilities were comparable.

Adolescent↗
PubMed1992

A graphics program for the analysis and display of molecular dynamics trajectories.

The program SCARECROW has been developed to help the molecular modeler to analyze and display the very big and complex data files produced by molecular dynamics programs. The molecular graphics program SCARECROW is written to support the display, animation, and extensive analysis of molecular dynamics trajectories. Using the macro language it is easy to make scripts for video animation and for the automated display and analysis of time series. Extensive coloring and atom selection commands are included to help the user to focus on relevant regions of the molecule. Time series can be produced and viewed on the screen or transferred to other programs.

Chemical Phenomena↗
PubMed1983

Inactivation probability of heavy ion-irradiated Bacillus subtilis spores as a function of the radial distance to the particle's [correction of paricle's] trajectory.

The understanding of the radiobiological action of heavy ions requires the knowledge of the dependence of the inactivation probability on the distance between the particle's trajectory and the biological test organism (the impact parameter). Spores of Bacillus subtilis with a cytoplasmic core of about 0.22 micrometer cross section are suitable test objects for the study of this radial inactivation probability in its microscopic details. The spores are irradiated at low fluences of some 10(6) ions/cm2 with very heavy ions at different specific energies up to 10 MeV per atomic mass unit u while in fixed contact with visual nuclear track detectors. The methods are described by which the biological response of individual cells can be evaluated and the impact parameter be determined with an accuracy typically better than 0.2 micrometer. The results demonstrate that the common characteristics of inactivation, e.g., an effective range of inactivation extending to at least 3 micrometers, a nonmonotonic dependence of the inactivation probabilities on the radial distance, and the fact that the inactivation probability even for direct central hits on the cytoplasmic core is substantially below one, are nearly independent of the particle energy and type. The results are incompatible with the assumption that the radiobiological effectiveness can be attributed to the dose of secondary electrons as currently understood. They also demonstrate that the widely held notion of an "overkill" at low impact parameters does not apply for the spores even with the most densely ionizing ions.

Argon↗
PubMed1993

Variations in membrane potential trajectory of post-inspiratory neurons in the ventrolateral medulla of the cat.

In decerebrate cats, intracellular recordings were made in 124 expiratory neurons displaying either a plateau-phase of depolarization during post-inspiration or a steadily decrementing depolarization throughout expiration. Both groups consisted of vagal motoneurons and non-antidromically activated neurons. Five neurons were antidromically activated by both vagal and spinal cord stimuli. The pattern in membrane potential was changed from one type to another either spontaneously or experimentally. The present results suggest that the variable appearance of the membrane potential trajectory does not represent the different functional category of bulbar post-inspiratory neurons.

Anesthesia↗