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R B Stein

Publications and source records attributed to R B Stein.

At least 73 records · Page 4Linked to original sources
PubMed1996

Neural signals for command control and feedback in functional neuromuscular stimulation: a review.

In current functional neuromuscular stimulation systems (FNS), control and feedback signals are usually provided by external sensors and switches, which pose problems such as donning and calibration time, cosmesis, and mechanical vulnerability. Artificial sensors are difficult to build and are insufficiently biocompatible and reliable for implantation. With the advent of methods for electrical interfacing with nerves and muscles, natural sensors are being considered as an alternative source of feedback and command signals for FNS. Decision making methods for higher level control can perform equally well with natural or artificial sensors. Recording nerve cuff electrodes have been developed and tested in animals and demonstrated to be feasible in humans for control of dorsiflexion in foot-drop and grasp in quadriplegia. Electromyographic signals, being one thousand times larger than electroneurograms, are easier to measure but have not been able to provide reliable indicators (e.g., of muscle fatigue) that would be useful in FNS systems. Animal studies have shown that information about the shape and movement of arm trajectories can be extracted from brain cortical activity, suggesting that FNS may ultimately be directly controllable from the central nervous system.

Electric Stimulation Therapy↗
PubMed1995

STAT protein complexes activated by interferon-gamma and gp130 signaling molecules differ in their sequence preferences and transcriptional induction properties.

Activation of members of the STAT (signal transducers and activators of transcription) family of latent transcription factors is an early event following the binding of many cytokines to their cognate receptors. Although the patterns of STATs activated by different cytokines are well described, the consequences of differential STAT activation are less well studied. We show by mutational analysis that STAT binding elements (SBEs) exist that discriminate between STAT complexes containing STAT1 alpha, STAT3 or both, and that these elements show altered cytokine responsiveness. We also show that in the context of a minimal promoter, single and multiple SBEs exhibit strikingly different patterns of transcriptional activation in response to IFN-gamma, IL-6, OSM or LIF. These differences in transcriptional activation are correlated with the differential ability of these cytokines to activate STAT1 alpha, STAT3 or both. Our results show that the pattern of STATs activated by a cytokine and the arrangement and sequence of the SBEs in the responding promoter have a profound effect on the ability of the cytokine to elicit a transcriptional response.

Animals↗
PubMed1995

Cellular mechanisms which distinguish between hormone- and antihormone-activated estrogen receptor.

The use of reverse genetics has permitted a definition of the structural features within estrogen receptor required for its productive association with the transcription apparatus. These sequences, transactivation function 1 (TAF1) in the amino terminus and TAF2 at the carboxyl terminus, display distinct transcriptional functions. Using specific receptor mutations it has been shown that on some promoters both TAF1 and TAF2 are required for maximal transcriptional activity, whereas on others, additional factors bound to the target promoter can functionally substitute for TAF1 or TAF2. Estrogen functions as an ER agonist by promoting functional synergism between TAF1 and TAF2. Conversely, 4-OH-tamoxifen inhibits TAF2 activity and functions as an antagonist in cell contexts where TAF2 is required. Alternatively, if a 'TAF2 function' is supplied by another factor, 4-OH tamoxifen can manifest ER agonist activity. These data indicate that alterations in the cellular expression of proteins which mimic TAF1 or TAF2 activity can have a profound effect on the pharmacology of ER modulators. Thus the identification of the cellular proteins which interact with ER and its TAF regions will allow a definition of the mechanism used by the cell to distinguish between hormone- and antihormone-activated estrogen receptor.

Animals↗
PubMed1995

Spacing of palindromic half sites as a determinant of selective STAT (signal transducers and activators of transcription) DNA binding and transcriptional activity.

Signal transducers and activators of transcription (STAT proteins) bind to palindromic sequence elements related to interferon gamma (IFN-gamma) activation sites, which were first identified in the promoters of IFN-gamma-inducible genes. Although the sequences of the natural palindromic STAT-binding elements vary considerably, they conform to the general structure TT(N)5AA. We have systematically examined the effects of the spacing between the TT and AA core half sites on the binding of the STAT complexes activated by IFN-gamma, interleukin (IL) 6, granulocyte-macrophage colony-stimulating factor, and IL-4. We show that (i) as suggested earlier, a core palindromic TT--AA motif with a 5-bp spacing displays general STAT binding, (ii) a palindromic motif with a spacing of 4 bp selectively binds to complexes containing Stat3, and (iii) a motif with a 6-bp spacing selectively binds the STAT complexes activated by IL-4. We have examined natural elements in the promoters of cytokine-responsive genes that differ in half-site spacing and found that they display binding properties predicted from the synthetic binding sites. Furthermore, the observed differential selective binding characteristics for the most part correlate with the ability to mediate transcriptional activation of transfected test genes in response to the cytokines tested. Our results thus demonstrate that the specificity of STAT-directed transcription in response to particular cytokines or cytokine families depends in part on the spacing of half sites within the conserved response element sequence.

Base Sequence↗
PubMed1995

Optimal control for an above-knee prosthesis with two degrees of freedom.

Our previous research and clinical tests of a self-contained powered above-knee prosthesis (AKP) showed that a knee joint with one degree of freedom (DOF) increases the energy cost of walking with respect to able-bodied subjects. Better symmetry of the gait can improve performance, so we suggest here the integration of a second powered DOF into the knee joint mechanism to control the internal-external rotation of the shank-foot complex. The control for the AKP with two DOFs is based on a method of optimal tracking. The data used for analysis were collected in able-bodied subjects braced with an ankle splint to experimentally duplicate a gait like that of amputees using a two-DOF prosthesis. The simulation showed the following: (1) the technique of optimal programming can be used for simulation of the artificial leg during locomotion; (2) the optimal tracking method is an efficient tool for selection of actuators for the above-knee prosthesis, ensuring that the tracking remains within limits. Limitation of joint torque is desirable in order to reduce the size of the motor, but beyond a certain point limiting maximal torques lead to tracking errors that are associated with higher energy costs and hence the need for a larger power source. The errors are also associated with higher forces at the interface between the socket and the prosthesis. The optimal tracking method allows the optimization of tracking with constraints on the size of the motor used and its energy cost.

Adult↗
PubMed1995

Presynaptic inhibition in humans.

Presynaptic inhibition plays an important role in controlling sensory processing of information in humans, as in other animals. However, because of experimental constraints the methods for measuring presynaptic inhibition are necessarily more indirect in humans. The most common method uses the modulation of the H-reflex by vibratory or electrical inputs. However, these stimuli can produce postsynaptic as well as presynaptic changes so it is important to use very short periods of stimulation and measure changes at a latency where presynaptic changes predominate. In addition, the stimuli should be superimposed upon a steady background of EMG activity, preferably in a single motor unit, to maintain the postsynaptic state at a constant level. Recent studies indicate that presynaptic inhibition is used as part of the program for voluntary movement and that it can be rapidly and dramatically adapted to the task being carried out. This task-dependent modulation is produced by pattern generators within the central nervous system as well as sensory feedback from the periphery, but the relative importance of the two remains uncertain. Clinical disorders, such as spasticity, affect the ability of humans to modulate presynaptic inhibition, and contribute to the deficits observed. Improved methods for treating the symptoms pharmacologically and electrically can improve function in these patients.

Electromyography↗
PubMed1995

Machine learning in control of functional electrical stimulation systems for locomotion.

Two machine learning techniques were evaluated for automatic design of a rule-based control of functional electrical stimulation (FES) for locomotion of spinal cord injured humans. The task was to learn the invariant characteristics of the relationship between sensory information and the FES-control signal by using off-line supervised training. Sensory signals were recorded using pressure sensors installed in the insoles of a subject's shoes and goniometers attached across the joints of the affected leg. The FES-control consisted of pulses corresponding to time intervals when the subject pressed on the manual push-button to deliver the stimulation during FES-assisted ambulation. The machine learning techniques used were the adaptive logic network (ALN) [1] and the inductive learning algorithm (IL) [2]. Results to date suggest that, given the same training data, the IL learned faster than the ALN, while both performed the test rapidly. The generalization was estimated by measuring the test errors and it was better with an ALN, especially if past points were used to reflect the time dimension. Both techniques were able to predict future stimulation events. An advantage of the ALN over the IL was that ALN's can be retrained with new data without losing previously collected knowledge. The advantages of the IL over the ALN were that the IL produces small, explicit, comprehensible trees and that the relative importance of each sensory contribution can be quantified.

Adult↗
PubMed1995

Nonlinear behavior of muscle reflexes at the human ankle joint.

1. Pulse inputs (similar to tendon jerks) were applied to the human ankle joint with the use of a hydraulic actuator. Inputs of only 1-2 degrees could elicit large responses (> 20% of maximum voluntary contraction). The magnitude of the response depended nonlinearly on a number of factors: the amplitude, direction, and duration of the pulse; the angle of the ankle; and the level of voluntary activation of the ankle muscles. 2. Pulses that flexed or extended the ankle could both produce reflex torques in the same direction (extensor torque). Although an extension of the ankle did not itself produce a response, it could affect the response to a subsequent flexion for up to 1 s. 3. The influence of random perturbations on the stretch reflex at the ankle was assessed. Responses to pulse displacements alone and to pulses superimposed on random perturbations were compared at the same level of voluntary activity. Reflex responses decreased in a graded manner with increasing amplitude or bandwidth of the random perturbations. 4. These results demonstrate that stretch reflexes can generate substantial torques, but in a highly nonlinear manner. In particular, passive joint movements markedly alter stretch reflex gain, and these changes must be considered in interpreting the functional significance of reflex actions.

Ankle↗
PubMed1995

Analysis of short-latency reflexes in human elbow flexor muscles.

1. A motor and digital controller have been developed to apply rapid stretches to the human elbow joint. The digital controller returns the forearm to the initial position before the reflex contraction. Thus short-latency reflex responses can be cleanly separated in time from the mechanical effects of the stretch under a wide variety of loading conditions. 2. The reflex force varies linearly with the velocity of stretch over nearly 2 orders of magnitude. The reflex force also varies linearly with the tonic level of force over the entire range of forces studied (0-100 N). This contrasts sharply with, for example, the human ankle joint, which shows a very limited linear range. 3. As the digital controller is made more compliant (less stiff), reflex shortening increases dramatically and becomes more prolonged, whereas the reflex force becomes somewhat smaller and shorter. With compliant loads and the brief stretches we applied, the reflex shortening is approximately equal to the stretch that generated it. 4. Simulations of the results confirm that the dependence of reflex shortening and force on the stiffness of the load is mainly determined by the mechanics of the limb and muscles. The simulations also indicate that 1) the gain of the reflex is as high as it can be without causing instability and 2) the presence of a rectification nonlinearity (e.g., lengthening the muscle produces a reflex, but shortening the muscle does not) is mainly responsible for preserving the stability of the elbow system.

Adult↗
PubMed1995

Nonsteroidal human progesterone receptor modulators from the marine alga Cymopolia barbata.

The co-transfection assay is a novel functional assay using cells transiently transfected with plasmids encoding intracellular receptors and corresponding reporter genes. Using this assay, natural product extracts were tested to identify compounds that modulate intracellular receptor activity, measured as changes in reporter gene activity. A crude extract of the marine alga Cymopolia barbata was found to inhibit progesterone-stimulated reporter gene expression in cells transfected with the human progesterone receptor (hPR) and an appropriate reporter construct. Purification of the active constituents of the extract, guided by the co-transfection assay, yielded two diastereomers of cyclocymopol monomethyl ether, possessing opposing pharmacological activities with the hPR. The antagonist (3R)-cyclocymopol monomethyl ether (LG100127) blocked 1 nM progesterone-stimulated reporter gene expression with an IC50 value of 549 +/- 55 nM in the co-transfection assay. The agonist (3S)-cyclocymopol monomethyl ether (LG100128) had efficacy similar to that of progesterone and an EC50 value of 35 +/- 2 nM. Stimulation by progesterone of the hPR in the human breast cancer cell line T-47D results in enhanced expression of alkaline phosphatase; LG100127 blocked alkaline phosphatase expression stimulated either by progesterone or by LG100128, and LG100128 mimicked progesterone in this assay. Both diastereomers displaced [3H]progesterone from baculovirus-expressed hPR. LG100127 and LG100128 each interacted with the human androgen receptor but did not interact with the human glucocorticoid receptor, estrogen receptor, vitamin D receptor, or retinoid receptors. In summary, these in vitro studies describe the first nonsteroidal pharmacophores for the hPR and demonstrate the use of the co-transfection assay in their discovery.

Animals↗
PubMed1994

Rapid activation of the STAT3 transcription factor by granulocyte colony-stimulating factor.

Granulocyte colony-stimulating factor (G-CSF) is a glycoprotein that stimulates proliferation and differentiation of progenitor cells of neutrophils by signaling through its receptor (G-CSFR). Although the G-CSFR belongs to the cytokine receptor superfamily, which lacks an intracellular kinase domain, G-CSF-induced tyrosine phosphorylation of cellular proteins is critical for its biologic activities. We report here that JAK1 and JAK2 tyrosine kinases are tyrosine phosphorylated in response to G-CSF induction. We also demonstrate that the DNA-binding protein STAT3 (also called the acute-phase response factor [APRF], activated by interleukin-6) is an early target of G-CSF-induced tyrosine phosphorylation. G-CSF induces two DNA-binding complexes; the major complex contains tyrosine phosphorylated STAT3 protein and the minor complex appears to be a heterodimer of the STAT1 (previously p91, a component of DNA-binding complexes activated by interferons) and STAT3 proteins. Antiphosphotyrosine antibody interferes with the DNA binding activity of activated STAT3, indicating that tyrosine phosphorylation of STAT3 is important for the DNA binding activity. These results identify a signal transduction pathway activated in response to G-CSF and provide a mechanism for the rapid modulation of gene expression by G-CSF.

DNA↗
PubMed1994

Rapid activation of proteins that interact with the interferon gamma activation site in response to multiple cytokines.

Many cytokines and growth factors trigger rapid changes in gene expression upon binding to their receptors. In many cases, the mechanism by which these changes are affected is unknown. In this report, we show that interleukin-2 (IL-2), IL-3, IL-4, IL-6, leukemia inhibitory factor (LIF), erythropoietin (Epo), and granulocyte-macrophage colony-stimulating factor (GM-CSF) treatment of cells causes rapid activation of DNA-binding activities that recognize a DNA sequence element previously implicated in regulation of gene expression by interferon gamma (IFN gamma). The IL-4-, IL-6-, and GM-CSF-induced complexes can be distinguished from the recently characterized IFN gamma-activated protein p91 on the basis of mobility in polyacrylamide gels, sequence preferences, and lack of reactivity with an anti-p91 antiserum. The IL-4- and GM-CSF-induced complexes react with antiphosphotyrosine antibodies, demonstrating the presence of phosphotyrosine-containing proteins in these DNA-binding complexes. Transcriptional activation of a reporter gene linked to a synthetic IFN gamma-responsive promoter is observed in response to IFN gamma, IL-6, and LIF. These data suggest a pathway by which cytokines induce rapid changes in gene expression.

Base Sequence↗
PubMed1994

Rapid activation of the interferon-gamma signal transduction pathway by inhibitors of tyrosine phosphatases.

Induction of gene expression by interferon-gamma involves the activation of a latent cytoplasmic transcription factor, p91, by phosphorylation on a single tyrosyl residue. This phosphorylation triggers dimerization, nuclear translocation, and the binding of p91 to interferon-gamma response elements present in the promoters of induced genes. Phosphorylation of p91 requires the activation of two tyrosine kinases, JAK1 and JAK2, that themselves become phosphorylated on tyrosyl residues shortly after interferon-gamma binds to its receptor. The importance of tyrosine phosphorylation in this pathway prompted us to investigate the role of protein tyrosine phosphatases in the regulation of the pathway. We find that in the absence of interferon-gamma, treatment of cells with an inhibitor of tyrosine phosphatases causes a rapid and potent activation of the components of the interferon-gamma signal transduction pathway and induces an interferon-gamma-responsive gene. This suggests that tyrosine phosphatases act both to repress the interferon-gamma signal transduction pathway in the absence of interferon-gamma and to downregulate the pathway after interferon-gamma induction.

Base Sequence↗
PubMed1994

Instrumentation for ENG and EMG recordings in FES systems.

An electronic circuit for analog processing of neural (electroneurogram or ENG) and muscular (electromyogram or EMG) signals in functional electrical stimulation (FES) systems is described in this paper. The basic circuit consists of a low-noise gated preamplifier, band-pass filter, amplifier, and a blanking circuit to minimize stimulation artifacts during electrical stimulation. This device was tested in chronic recordings using a triphasic cuff electrode for nerves and epimysial electrodes for muscles in the hind limbs of cats. The device was used for nerve recordings in the presence of electrical stimulation of muscles in the same leg. The recordings showed rejection of stimulation and muscle (M-wave) artifacts, while retaining the information of interest.

Amplifiers, Electronic↗
PubMed1994

The activity of interneurons during locomotion in the in vitro necturus spinal cord.

1. Less than two segments of the cervical spinal cord of the mudpuppy (Necturus maculatus) is sufficient to generate a locomotor rhythm with application of N-methyl-D-aspartic acid (NMDA). We have recorded intracellularly from rhythmically active interneurons in these segments and classified them according to their phase of firing within the step cycle and their afferent input. 2. Four classes of interneurons were found: flexor, flexor-->extensor, extensor, and extensor-->flexor. Interneurons that burst during the transition from flexion to extension or vice versa are referred to as "transitional" interneurons and represent the majority (68%) of rhythmically active interneurons studied in the mudpuppy spinal cord. 3. All flexor interneurons received only inhibitory input from cutaneous and dorsal root afferents, whereas the flexor-->extensor interneurons that responded received only excitatory input from dorsal root and cutaneous afferents. All extensor interneurons and all but one extensor-->flexor interneuron received no afferent input from the cutaneous or dorsal root afferents we stimulated. 4. Other interneurons have been classified as "tonic" cells. They fire continuously when the mudpuppy is walking and are silent when the mudpuppy is not walking. These interneurons receive no afferent input from the sources tested and may be responsible for turning locomotion on and off. 5. In conclusion, the presence of many transitional interneurons with specific patterns of afferent input may be required for the phasing of legged locomotion. We believe the in vitro preparation of the mudpuppy spinal cord and forelimb is an excellent model for studying the firing properties of interneurons during legged locomotion.

Afferent Pathways↗
PubMed1994

Human estrogen receptor transactivational capacity is determined by both cellular and promoter context and mediated by two functionally distinct intramolecular regions.

We have used a series of human estrogen receptor (ER) mutants to evaluate the cell- and promoter-specific transcriptional activities of the TAF1 and TAF2 transactivation regions within the human ER. We show that the manifestation of TAF1 or TAF2 function depends strongly upon promoter context; on certain promoters, both the TAF1 and TAF2 activators are required for wild-type transcriptional activity, whereas on other promoters, the TAF1 and TAF2 activators function independently. Using these constructs, we show that the antagonist activity of the triphenylethylene-derived antiestrogens, e.g. tamoxifen, arises from their intrinsic inability to activate ER TAF2 function. However, on certain promoters, these antiestrogens efficiently activate gene transcription through ER. Consistent with this observation, the TAF2 function of the ER is not required on all promoters. In these TAF2-independent promoter contexts, TAF2 function may be provided by a separate transcription factor bound to the promoter. These data suggest that 1) TAF1 may be the major transcriptional activator of the ER; and 2) TAF2 functions as a transcriptional facilitator. On promoters where TAF2 function is provided independently of the ER, the TAF1 function of the ER can function independently of TAF2 activity, allowing triphenylethylene-derived antiestrogens to demonstrate partial agonist activity. These observations provide a possible molecular explanation for the tissue-specific partial agonist properties of tamoxifen and related triphenylethylene antiestrogens observed in vivo.

Binding, Competitive↗
PubMed1994

Cardiac electrophysiologic and antiarrhythmic actions of two long-acting spirobenzopyran piperidine class III agents, L-702,958 and L-706,000 [MK-499].

The cardiac electrophysiologic and antiarrhythmic actions of two Class III ketone- and alcohol-containing spirobenzopyran piperidine analogs, L-702,958 and L-706,000 [MK-499], respectively, were assessed in vitro and in vivo. L-702,958 and L-706,000 [MK-499] selectively blocked the rapidly activating component of the delayed rectifier K+ current in guinea pig isolated ventricular myocytes (IC50 values, 14.6 and 43.9 nM, respectively), and prolonged effective refractory period in ferret isolated papillary muscles (EC25 values, 10.5 and 53.8 nM, respectively). In anesthetized dogs, L-702,958 and L-706,000 [MK-499] increased ventricular refractory periods (ED20 values, 3.3 and 9.2 micrograms/kg i.v., respectively) and concomitantly increased ECG QT interval and left ventricular+dP/dt. Cumulative i.v. administrations of up to 100 micrograms/kg of L-702,958 and 300 micrograms/kg L-706,000 [MK-499] in anesthetized dogs increased atrial and ventricular refractoriness and prolonged the ECG QT interval, but did not alter atrial, atrioventricular nodal, His-Purkinje or ventricular conduction indices. In anesthetized dogs studied chronically (9.2 +/- 1.1 days) after anterior myocardial infarction, the cumulative i.v. administrations of 100 micrograms/kg of L-702,958 and 300 of micrograms/kg L-706,000 [MK-499] suppressed the induction of ventricular tachyarrhythmia by programmed ventricular stimulation (suppression rates: 8 of 10, 80% and 9 of 11, 82%, respectively) and reduced the incidence of lethal ventricular arrhythmias (incidence of lethal ischemic arrhythmias: 4 of 10, 40% and 1 of 11 9%, respectively, compared to 34 of 40, 85%, in vehicle controls. L-702,958 and L-706,000 [MK-499] (cumulative 100 and 300 micrograms/kg i.v., respectively) did not facilitate the induction of arrhythmias by programmed ventricular stimulation in postinfarction dogs. After equivalently effective p.o. doses in conscious dogs, L-702,958 (10 micrograms/kg) and L-706,000 [MK-499] (30 micrograms/kg) increased ECG QT interval with long durations of action of approximately 9 and 14 hr, respectively. L-706,000 [MK-499] elicited a more consistent and sustained prolongation of the QT interval than L-702,958. These findings show that both L-702,958 and L-706,000 [MK-499] are potentially useful agents for the prevention of malignant ventricular arrhythmias in the setting of myocardial ischemic injury.

Animals↗