Biomedical subjects

G Wittenberg

Publications and source records attributed to G Wittenberg.

46 records · Page 3Linked to original sources

PubMed1993

[Interobserver variability of dialysis shunt flow measurements using color coated duplex sonography].

A prospective study extending over 4 months was carried out in which 142 shunt volume flow measurements were performed on 43 patients; two up to four operators with varying degrees of experience took part. Flow volumes varied between 51 and 2409 ml/min with an average blood flow volume of 521 ml/min. Comparison of measurements of individual operators showed errors of between 0.5 and 19.8%. Average error was calculated as 11.3%. Shunt flow measurements by colour Doppler sonography provide an easily appreciated and reproducible method for quantifying changes in shunt flow.

Adult↗

PubMed1992

Analysis and modeling of the multisegmental coordination of shortening behavior in the medicinal leech. I. Motor output pattern.

1. To understand how a multisegmental animal coordinates motor activity over more than one segment, we studied shortening behavior in the medicinal leech, in which several segments contract longitudinally in response to a moderately strong mechanical stimulus. 2. We first demonstrated that the neuronal activity responsible for shortening behavior occurred in semi-intact and isolated nerve cord preparations, and then characterized the responses of motor neurons in isolated preparations. The motor output during shortening was simultaneous excitation of motor neurons innervating dorsal longitudinal muscle and of motor neurons innervating ventral longitudinal muscle. 3. The stronger the stimulus, the more segments produced the shortening motor output, with the segments nearest the stimulus recruited first. 4. Although the shortening response was produced in several segments near the site of stimulation, it was never produced in the stimulated segment, where the local bending motor output pattern was produced. The motor pattern suggests that shortening, initially considered a very simple behavior, requires the involvement of at least few segmentally iterated interneurons.

Acetates↗

PubMed1992

Analysis and modeling of the multisegmental coordination of shortening behavior in the medicinal leech. II. Role of identified interneurons.

1. Mechanical stimulation of the leech, Hirudo medicinalis, elicits withdrawal behavior that has two components: local bending in the segment stimulated and shortening in outlying segments. Local bending is characterized by excitation of longitudinal muscle on one side of the segment and inhibition on the other side. In shortening, all longitudinal muscles are excited. We wished to understand how these distinct motor patterns are produced by a nervous system with segmentally iterated neurons, a configuration that places some limitations on the complexity of connection patterns. 2. We searched for neurons in the segmental nervous system that subserved shortening behavior, expecting to find at least one interneuron in each segment that was involved in shortening behavior exclusively. We found instead that all interneurons involved in shortening are also involved in local bending, and no individual interneuron can completely account for shortening. 3. The motor output caused by individual identified interneurons is not entirely consistent with the shortening motor output pattern. For instance, one interneuron, cell 115, has the same pattern of motor effects from segment to segment, causing excitation of dorsal excitatory motor neurons and inhibition of ventral excitatory motor neurons. These effects would cause dorsal local bending, not shortening, in a few segments. Only one interneuron, cell 125, has motor effects that would cause shortening. 4. Individual interneurons were hyperpolarized while single sensory cells were stimulated, to quantify the contributions of individual interneurons to the observed motor pattern. Interneurons 115 and 125, and the inhibitory motor neuron, cell 1, were found to have significant roles in producing the shortening motor output. 5. A quantitative estimate of the role of each interneuron type showed that the identified interneurons account for most of the excitation of dorsal motor neurons, but for very little of the excitation of ventral motor neurons. This predicts that at least one additional interneuron type remains to be identified, one that would provide excitation to ventral motor neurons in several segments. 6. A back-propagation trained neural network model was constructed to predict the connections of the as yet unidentified interneurons. To match the known properties of interneurons, it was necessary to include a segmental similarity constraint in the training algorithm for segmentally iterated model neurons. The modeled networks predicted that there are at least two kinds of interneurons yet to be found. Also, the modeling showed that interneurons can have input and output patterns that differ very little from segment to segment but yet produce major differences in the motor output.

Action Potentials↗

PubMed1991

[Color-coded duplex sonography of the extracranial arteries supplying the brain: diagnostic significance and sources of error in comparison with i.a. DSA].

The findings of color Doppler flow imaging of the extracranial cerebral arteries in 75 patients were compared with i.a. DSA. Carotid stenoses greater than 50% and carotid occlusions were shown by sonography with a sensitivity of 91% and a specificity of 97%. The severity of the stenosis was in agreement in 88% of cases using the two methods. Sonography of the vertebral arteries achieved a sensitivity of only 65% and a specificity of 88%. Sonographic examination of the ophthalmic artery in order to demonstrate carotid stenosis achieved a sensitivity of only 29% and provided no additional information. Retrobulbar kinking of the ophthalmic artery was found in 30/178 vessels and may be a cause of misinterpretation.

Angiography, Digital Subtraction↗

PubMed1990

Segmental specialization of neuronal connectivity in the leech.

1. Every segmental ganglion of the leech Hirudo medicinalis contains two serotonergic Retzius cells. However, Retzius cells in the two segmental ganglia associated with reproductive function are morphologically distinct from Retzius cells elsewhere. This suggested that these Retzius cells might be physiologically distinct as well. 2. The degree of electrical coupling between Retzius cells distinguishes the reproductive Retzius cells; all Retzius cells are coupled in a non-rectifying manner, but reproductive Retzius cells are less strongly coupled. 3. Retzius cells in standard ganglia depolarize following swim motor pattern initiation or mechanosensory stimulation while Retzius cells in reproductive ganglia either do not respond or hyperpolarize. 4. In standard Retzius cells the depolarizing response caused by pressure mechanosensory neurons has fixed latency and one-to-one correspondence between the mechanosensory neuron action potentials and Retzius cell EPSPs. However, the latency is longer than for most known monosynaptic connections in the leech. 5. Raising the concentration of divalent cations in the bathing solution to increase thresholds abolishes the mechanosensory neuron-evoked EPSP in standard Retzius cells. This suggests that generation of action potentials in an interneuron is required for production of the EPSP, and therefore that the pathway from mechanosensory neuron to Retzius cell is polysynaptic. 6. P cells in reproductive segments have opposite effects on reproductive Retzius cells and standard Retzius cells in adjacent ganglia. Thus the difference in the pathway from P to Retzius is not localized specifically in the P cell, but elsewhere in the pathway, possibly in the type of receptor expressed by the Retzius cells.

Animals↗

PubMed1989

Function of identified interneurons in the leech elucidated using neural networks trained by back-propagation.

Mechanical stimulation of the body surface of the leech causes a localized withdrawal from dorsal, ventral and lateral stimuli. The pathways from sensory to motor neurons in the reflex include at least one interneuron. We have identified a subset of interneurons contributing to the reflex by intracellular recording, and our analysis of interneuron input and output connections suggests a network in which most interneurons respond to more than one sensory input, most have effects on all motor neurons and in which each form of the behaviour is produced by appropriate and inappropriate effects of many interneurons. To determine whether interneurons of this type can account for the behaviour, or whether additional types are required, model networks were trained by back-propagation to reproduce the physiologically determined input-output function of the reflex. Quantitative comparisons of model and actual connection strengths show that model interneurons are similar to real ones. Consequently, the identified subset of interneurons could control local bending as part of a distributed processing network in which each form of the behaviour is produced by the appropriate and inappropriate effects of many interneurons.

Animals↗

PubMed1988

Multifunctional interneurons in behavioral circuits of the medicinal leech.

We are using the medicinal leech to study the neuronal basis of behavioral choice. In particular, we are recording from neurons, both extracellularly and intracellularly, in preparations that can express three different behaviors: the shortening reflex, crawling and swimming. We have found that particular mechanosensory neurons can elicit any of the behaviors, and that the movements are produced by just four sets of muscles, each controlled by a small number of motor neurons. Hence, there must be three different pattern-generating neuronal circuits, each of which can be activated by the same set of sensory neurons. We are studying how the choice is made among the three behaviors by recording, while one behavior is being performed, from neurons known to be involved in the initiation of the other two. We have found that an interneuron, cell 204, which is known to initiate and maintain swimming, is also active during shortening and crawling. The activity level in this interneuron can influence whether a mechanosensory stimulus produces shortening or swimming. The neuronal mechanisms by which this choice is normally effected awaits further elucidation of the circuits that elicit and generate shortening and crawling.

Animals↗

PubMed1987

Macrophage handling of a tolerogen and the role of IL 1 in tolerance induction in a helper T cell clone in vitro.

The human gamma-globulin (HGG)-specific helper T cell clone AB.7.D7 can reconstitute the plaque-forming cell response of HGG-primed B cells. Tolerance induction at the level of T cell help results from exposure of the AB.7.D7 cells to 10 micrograms monomeric HGG. The monokine IL 1 was found to interfere with tolerance induction in AB.7.D7 cells in a dose-dependent manner. Furthermore, interference with tolerance induction was dependent upon the T cells being presented with IL 1 at the same time as monomeric HGG, the tolerogen. IL 1 and monomeric HGG could not be demonstrated to interact to make nontolerogenic soluble aggregates, however. It was found that monomeric HGG was unable to stimulate the production of either membrane or secreted IL 1 by splenic macrophages and in addition was not degraded by peritoneal exudate cells. Heat-aggregated HGG, which is highly antigenic and nontolerogenic, is a good stimulus for IL 1 production and is processed by macrophages into peptides of varying sizes. These data are consistent with the suggestion that a tolerogenic signal results from T cell recognition of a nondegraded antigen in the absence of a signal from IL 1. It is possible, however, that small amounts of processed antigen, undetectable by us, are involved.

Animals↗

PubMedDate not supplied

Long-term results of vena cava filters: experiences with the LGM and the Titanium Greenfield devices.

PURPOSE: Vena cava filter (VCF) application is the method of choice to prevent recurrent pulmonary embolism in patients with deep venous thrombosis. Because of the reported complications after VCF placement we summarize our long-term follow-up results with the LGM and Titanium Greenfield (TG) devices. METHODS: Eighty-seven LGM VCF and 17 TG VCF were placed in 104 patients (average age 64 years). The follow-up examinations were performed by color-coded duplex sonography, plain radiographs, cavography, and computed tomography (CT). The maximum observation time was 81 months. RESULTS: Filter migration occurred in 11% (8/76) of the LGM VCF and 15% (2/13) of the TG VCF. Vena cava thrombosis was seen in 17% (13/76) of the patients with an LGM VCF and in 31% (4/13) of those with a TG VCF. The patency rate was 95% (72/76) for the LGM VCF and 92% (12/13) for the TG VCF. Pulmonary embolism was noted in 3 patients after LGM VCF insertion and in no patient after TG VCF insertion. CONCLUSION: A VCF should only be inserted in a patient after pulmonary embolism and when there is strict proof of the indication.

Adult↗

PubMedDate not supplied

Treatment of inoperable tracheobronchial obstructive lesions with the Palmaz stent.

PURPOSE: The treatment of inoperable tracheobronchial stenoses with Palmaz stents is analyzed in terms of the clinical effect, typical complications, and long-term follow-up. METHODS: Twenty-seven Palmaz stents were placed in 22 patients with the help of a rigid bronchoscope. RESULTS: Stents were implanted in the distal trachea, the main bronchi, and the lower lobe bronchi. Twenty-one of 22 patients reported an immediate subjective improvement in their respiratory situation. The mean survival time was 12 months; in two patients the stents were well tolerated for up to 40 months. A redilation of three stents was successful up to 33 months. In three cases a dislocation of the stent was observed; after bronchoscopic retraction a new stent was successfully implanted in each case. CONCLUSIONoff Treatment of inoperable tracheobronchial stenoses with the Palmaz stent is a safe procedure that provides an immediate improvement of the patient's pulmonary situation. The Palmaz stent shows a minimal complication rate in the long-term follow-up.

Adult↗