Search PubMed⌕ Search

Biomedical subjects

M W Luttges

Publications and source records attributed to M W Luttges.

At least 37 records · Page 2Linked to original sources
PubMed1991

Effect of localized pulsed electromagnetic fields on tail-suspension osteopenia in growing mice.

Pulsed magnetic fields (PEMFs) have been used effectively to treat bone fractures and sciatic-nerve-section-induced osteopenias. Properly applied PEMFs are presumed to stimulate osteogenesis. Mouse-tail suspension has been implemented as a means of inducing an osteopenic response in the long bones of the hind limbs. To evaluate localized PEMF effects, the mouse-suspension model was modified to accommodate the use of miniature wire coils affixed directly to the rear legs. Laterally and axially orientated PEMF effects were compared. Three test groups of mice included (C) control mice, (S) tail-suspended mice with treatment apparatus attached, and (SF) tail-suspended mice with apparatus attached and PEMFs delivered. The SF group was divided into mice receiving axial or lateral PEMFs. Significant bone changes occurred in suspended as compared with control mice after a 2-week test period. The PEMF mice showed significantly fewer osteopenic effects than did untreated, suspended mice. These findings are based on biomechanical measures of stiffness, strength, ductility, and energy as well as whole-bone mass and porosity. The effects of PEMFs on these properties differ for axial and lateral exposures. The results are discussed in terms of mechanisms underlying PEMF effects.

Animals↗
PubMed1991

Effects of suspension-induced osteopenia on the mechanical behaviour of mouse long bones.

Whereas most studies of tail-suspension induced osteopenia have utilized rat femora, the present study investigated the effects of a 14 day tail-suspension on the mechanical behaviour of mice femora, tibiae and humeri. Force-deflection properties were obtained via three-point bending for long bones from suspended and control mice. Whole bone behaviour was characterized by converting the force-deflection values to stiffness, strength, ductility and energy parameters which were not normalized for specimen geometry. The effects of a systematic variation in the deflection rate over the range 0.1-10 mm min-1 were also evaluated. Statistical analysis indicated that the primary effect of the tail-suspension period was lowered bone mass which was manifested mechanically through lower values of the bone strength parameters. These effects were similar in the bones of both the fore and hind limbs. The results also demonstrated that the stiffness, ductility and energy characteristics were much less influenced by the tail-suspension. Whereas a significant dependence of the bone strength values upon deflection rate was observed for the femora and humeri, the other mechanical parameters were less sensitive. Based upon the nature of the physical and mechanical changes observed in the long bones following tail-suspension, the mouse appears to be a suitable animal model for the study of osteopenia.

Animals↗
PubMed1991

Recording of simultaneous single-unit activity in the dragonfly ganglia.

A technique for discriminating simultaneously active single units from multiple-unit data records has been developed. Multiple-unit records were obtained extracellularly from the dragonfly mesothoracic ganglion using two paired-electrode sets. The multiple-unit records were post processed based on the unique physical characteristics imparted to each spike via the tissue medium and spatial geometry of cells. It was assumed that the action potential amplitude falls off roughly as the inverse of distance squared from the recording electrode. Further, it was assumed that the tissue RC characteristics coupled with action potential amplitudes and neuron dipole characteristics impart a spike waveform unique to each cell. Accordingly, spikes were sorted by amplitude ratio as well as by matching of spike waveforms. Additional waveform characterization was derived from the spike angle (width) within grouped spikes. Decomposition of the multiple-unit records based on these parameters yielded clustered spike records from defined cellular sources. The defined clusters were combined to provide the cumulative record for a large number of simultaneously active single units.

Action Potentials↗
PubMed1991

Neural network analyses of stochastic information: application to neurobiological data.

Simultaneous recordings from over 50 neural cells were obtained from the dragonfly ganglia. To explore the biological information processing strategies reflected therein, data analysis methods were designed for use with artificial neural networks (ANN). Most methods are degraded by different cell spike trains that vary in mean firing frequencies by well over an order of magnitude. Based on underlying cell physiology, the occurrence of each spike is likely to be a stochastic function. To overcome such degradation problems in ANN use, a gaussian spike train representation was synthesized for each cell using raw data. This representation retained the exact spiking times and provided a biologically plausible probabilistic value for the time of occurrence for each spike. A 3-layer, feed-forward, ANN was trained on these data using a gradient descent learning algorithm. The task was to predict the neural activity at time (t + 1) given the neural activity at time (t). Following training, the network sum-squared prediction error was less than 0.01. Further, the temporal reproduction of the neural firing patterns was corroborated. The results indicated that the ANN could accurately reproduce the neural firing patterns in both the spatial and temporal domain using the stochastic spike train data. Encoding parameters for the spike trains using synthesized gaussian representations were optimized. The "lesion" studies were performed to determine the contribution of each cell to ANN predictions. The capability to "fine tune" both the information representation of spike trains and the ANN architecture provides significant advantages in the analysis of biological information processing by neural cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

A neural network simulation of simultaneous single-unit activity recorded from the dragonfly ganglia.

Techniques are described that allow the use of multiple neuron spike data in a computational neural network architecture. The network architecture was devised to match the number of actual neurons from which data were obtained. The network was successfully trained to accurately predict the multiple neuron spike trains. Simultaneous spike histories of 44 neurons were modeled by a network architecture consisting of 44 input units, 88 hidden units with recurrent connections and 44 output units. The activation function of each unit was determined by data unique to a single neuron. These data were coupled with an analog gradient that preserved both the exact spiking times and the relative spiking tendency of each neuron. The input activation values were compared to network output target values calculated to occur 5 msec forward in the composite spiking records of all neurons. Following 2000 training cycles with the gradient data, the average error of each unit in the network was 0.0016. Discrete output values for each network unit were correlated with those of all other units. These correlations were comparable to those done using the actual neuron data. Both correlations reveal a functional connectivity pattern among the units and neurons. These connectivity patterns indicate that the networks may synthesize patterns of activity needed for biological function; in this case, flight patterns carried out in the mesothoracic ganglion of the dragonfly. This model represents, to the best of our knowledge, the first computer based network simulation using actual experimental neural data obtained from a large number of spontaneously active cells in a small intact ganglion.

Action Potentials↗
PubMed1990

Age dependent development of osteopenia in the long bones of tail-suspended mice.

The microgravity, or weightlessness, of space causes measurable bone deterioration in humans and rats. The use of tail-suspension to simulate weightlessness in rats is well-documented. Our studies have focused on mice, as their smaller size suggests more efficient space-based experimentation. Using mice ranging from 1.3-12 months in age, the results of a 2-wk suspension were ascertained through measurement of bone mass and mechanical (3-pt bending) characteristics. Significant differences between tail-suspended (S) and control (C) mice were noted for mice less than 6 months old. Such significance was not observed for the older mice. In addition, for the 1.3 month and 1.7 month old mice, a group of mice were sacrificed (designated PC, or pre-control) with ages matching those of the S mice prior to suspension. These were assayed to determine if the effects of tail-suspension are predominantly on growth-suppression or on bone atrophy. Our results show that tail-suspension effects are best explained by growth-suppression, as both the C and S groups showed growth when compared to the PC groups. 4-wk tail-suspensions of 10 month old mice were implemented to determine if increased suspension time would produce deterioration in older mice. An indication of longer periods of suspension being effective was found, but significant differences like those obtained for younger mice were not seen in the numbers of mice used.

Aging↗
PubMed1988

Changes in neurotransmitter uptake in the spinal cord following peripheral nerve injury.

Changes in neurotransmitter systems of the spinal cord were studied in response to peripheral nerve injury. The uptake and compartmentalization of radiolabeled spinal cord neurotransmitters and transmitter precursors were examined as a function of time following unilateral sciatic nerve crush in adult mice. Accumulation of transmitter was measured within synaptosomally enriched fractions prepared using combinations of differential and density gradient centrifugations. The amount of transmitter substance recovered from these fractions was strongly dependent upon the amount of time following nerve injury and on the specific transmitter or precursor being examined (GABA, glutamate, glycine, and choline chloride). However, for each of these substances, uptake values returned to control levels within nine to twelve days after nerve crush. Localization of GABA changes postcrush revealed reciprocal differences between ipsilateral and contralateral sides of the spinal cord, as well as differences between segmental levels. Altered GABA uptake may reflect changes in the postcrush microchemical environment present during tissue processing, but may also be related to direct changes in the synaptic binding, transport, and compartmentalization of transmitter substance. The time course, magnitude, and direction of these neurochemical changes follow those observed neurophysiologically, and may thus underlie injury-induced short-term (days) alterations reported in primary afferent depolarizations, cross cord responses, and other spinal mechanisms.

Aminooxyacetic Acid↗
PubMed1986

Structural properties of spinal nerve roots: biomechanics.

The biomechanics of spinal nerve roots obtained from normal and nerve-crushed mice were evaluated. Photographs and longitudinal force measurements were taken as nerve roots were elongated through mechanical failure. Proportional limit stress and strain as well as the apparent modulus were calculated from photographic and force measurements to characterize nerve root strength, elasticity, and stiffness, respectively. Resulting mechanical data were indicative of an extremely weak material. Comparisons of nerve and nerve root mechanical properties revealed major differences. While nerve root elasticity was comparable to nerve, nerve root strength was only 10% that of nerve and root stiffness was only 20% of nerve values. Differences in nerve and root mechanics are attributed to the large discrepancies in relative amounts of connective tissue. Also in sharp contrast with peripheral nerve, unilateral nerve crush produced no significant alterations in root mechanics. Comparisons of nerve and nerve root strengths suggested possible pathways for dissipation of peripherally applied forces through epineurial and dural structures.

Animals↗
PubMed1986

Structural properties of spinal nerve roots: protein composition.

The protein compositions of dorsal and ventral spinal nerve roots were determined using sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Protein readily soluble in sodium dodecyl sulfate (SDS) sample buffer made up 8.1% of the wet weight of dorsal and ventral roots. Spinal root protein samples consisted predominantly (60%) of myelin-associated proteins. Other major proteins including those tentatively identified as tubulin, actin, nuclear histones, and others accounted for the remainder of recovered protein. The protein constituents of nerve roots were similar to those of peripheral nerve but differed from those of spinal cord. Nerve roots and peripheral nerve were characterized by fewer major protein bands but greater concentrations of myelin proteins. Collagen which did not readily solubilize in SDS sample buffer was estimated by assaying for hydroxyproline. Nerve roots consisted of approximately 0.4% collagen by weight which was only one-fifth the amount estimated for nerve but six times more than spinal cord. It was apparent that the biomechanical frailty of roots compared with peripheral nerve might be explained by differences in the relative collagen contents of these tissues. The protein constituents of nerve roots after unilateral nerve crush were relatively stable compared with the profound changes seen in ipsilateral nerve and modest changes seen in contralateral uninjured nerve.

Animals↗
PubMed1986

Postinjury changes in the biomechanics of nerves and roots in mice.

The biomechanical characteristics of sciatic nerve and associated spinal roots of mice were investigated. Both normal and postcrush nerve materials were tested in the same fashion using superimposed elongation, force and geometry data. The results show that nerve and roots differ considerably both in the force they sustain before failure and in the other biomechanics they exhibit. The nerves and associated structures transmit and absorb large amounts of force. The roots, in comparison, are mechanically frail but exhibit similar elongation before failure. The behavior of these elements of the nervous system are discussed with regard to implications for integrated nerve, root and spinal cord mechanical integrity.

Animals↗
PubMed1984

Alterations in the mechanical properties of peripheral nerve following crush injury.

The mechanical properties of injured nerves have been studied. At specific times following unilateral nerve crush, the sciatic nerves of mice were tested mechanically. Photographs and longitudinal force measurements were obtained as nerve segments were elongated to mechanical failure. Stress and strain at the proportional limit and apparent elastic modulus were used as indicators of strength, elasticity and stiffness. Injury led to time-dependent increases in strength and stiffness and decreases in elasticity. These changes were apparent in both damaged and contralateral, undamaged nerves. Many of the changes appear to be related to the epineurium. Some mechanical changes in nerve could have important consequences for the integrity and function of nerves and mechanically interfaced structures.

Animals↗
PubMed1984

Relationships between the electrocardiogram and phonocardiogram: potential for improved heart monitoring.

Improvements in current heart monitoring techniques could reduce the number of heart attacks and resulting deaths. The potential for using time intervals measured between waveforms of the electrocardiogram (ECG), phonocardiogram (PCG), and peripheral blood flow pulse (PP) for heart monitoring was studied. The waveform locations identified in the simultaneously recorded signals included the R- and T-wave peaks of the ECG, the first (S1) and second (S2) sounds of the PCG, and the systolic peak of the PP. The signals were found to be highly consistent from one cardiac cycle to the next. Further, the time intervals measured between the different signals were stable with time. Strong relationships were found between the intervals R to T and R to S2 and the R to R interval. In contrast, R to PP and R to S1 correlated poorly with the R to R but strongly with each other. Additional differences between the measured intervals were revealed by studying changes due to exercise and different body positions. The relationships between the measured intervals were found to be independent of PCG recording location. This study demonstrates the feasibility and potential of using the electrical-contractile indices of heart function for monitoring heart patients. Design of a computer-based monitor using the techniques specified in this study is discussed along with relative strengths and weaknesses of such a system.

Adult↗
PubMed1983

Protein composition and synthesis in the adult mouse spinal cord.

Properties of spinal cord proteins were studied in adult mice subjected to unilateral crush or electrical stimulation of sciatic nerve. The protein composition of spinal tissue was determined using SDS-polyacrylamide gel electrophoresis coupled with subcellular fractionation. Comparisons of mouse spinal cord and brain revealed similarities in the types but differences in the concentrations of myelin associated proteins, nuclear histones and other proteins. Comparisons with sciatic nerve proteins demonstrated differences in types of proteins but similarities in the concentration of myelin proteins and nuclear histones. The short term (less than 2 hrs.) incorporation of radioactive amino acids into spinal cord proteins revealed heterogeneous rates of incorporation. Neither nerve crush six days prior to testing nor sciatic nerve stimulation had a significant effect on the protein composition or amino acid incorporation rates of spinal cord tissue. These observations suggest that known differences in spinal cord function following alterations in nerve input may be dependent upon different mechanisms than have been found in the brain.

Animals↗
PubMed1979

Postnatal alpha-methylphenylalanine treatment effects on adult mouse locomotor activity and avoidance learning.

Neonatal mice were injected for five days with a combination of alpha-methylphenylalanine and phenylalanine to determine the influences of excess phenylalanine during development upon the behavior of these mice as adults. Spontaneous activity, bolus production, passive avoidance learning, simple active avoidance learning and complex active avoidance learning were tested in mice treated at two different postnatal periods. The results show that the treatments during development produced adult behavioral alterations compared to controls. The effects were most pronounced in mice treated in the postnatal period immediately after birth. The behavioral effects can be summarized as increased emotionality and generalized, stimulus-induced activity as well as decreased passive avoidance performance and complex active avoidance performance. These behavioral deficits are consistent with those usually reported in various models of human phenylketonuria.

Animals↗