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R Sigal

Publications and source records attributed to R Sigal.

At least 55 records · Page 3Linked to original sources
PubMed1991

Stability patterns and trophic structure in a Delaware Bay plankton community.

Using qualitative loop analysis we have extended our examination of a Delaware Bay plankton community to include an investigation of the roles played by the various entities (population, guild or nutrient) in the community. In an entity removal exercise, we used stability relationships as a probe into community structure. Six types of stability change are possible as a result of entity removal from the system: stable to stable (s-->s); stable to unstable (s-->u); stable to disconnected (s-->d); unstable to stable (u-->s); unstable to unstable (u-->u); unstable to disconnected (u-->d). Using these changes as an investigative tool, we found that in order to account for the stability-instability patterns, it was necessary to construct a refined trophic structure model. The observed connections between the entities in the larger model could be grouped into two different types of stability substructures: a simple pattern and a more complex branching pattern. These patterns map easily onto the refined trophic structure model. Using stability analysis it is also possible to model community structure in ways other than the traditional trophic approach. Patterns of system necessity and relative contribution to stability are observed. These patterns match the refined trophic structure model derived previously. The roles that the various entities play in the overall community were followed over an annual cycle. Entities were seen to change their roles as a function of time and status within a subgroup. These results show that stability determinations have the potential to be used as a valuable tool in community analysis.

Animals↗
PubMed1991

[The normal cranial nerves in MRI. Description and visualization frequency].

In order to assess the value of MR in the depiction of intracranial nerves, we retrospectively reviewed 60 patients investigated over a period of 2 years. The aim of this study was: 1) to assess the score of MR in the detection of cranial nerves III to XII; 2) to determine accurate landmarks allowing for easy detection of those cranial nerves. Cranial nerves III, V, VII, VIII are well seen (70 to 100%), very often in both axial, sagittal and coronal sections. Nerves IX to XII are correctly studied only on axial planes [81 and 83%), but it is difficult to distinguish between the vagal nerve and the glossopharyngeal and spinal nerves. Due to their oblique direction and small size, fourth and sixth nerves are rarely visualized. The more important landmarks are the chiasma, the colliculi, the Meckel's cave, the internal auditory canal, the jugular foramen, the hypoglossal canal and the different brainstem structures. We suggest the following scanning protocol: short spin echo sequences (TR = 600 ms, TE = 20 msec), 3 to 5 continuous sections, 16 to 20 cm field of vue with respectively 4 or 2 excitations, 256 x 256 matrix, with at least one acquisition plane (axial), but preferably two or three planes. Thus MR is sensitive exam in the recognition of cranial nerves, and it must be the first step exam in patients presenting with cranial nerve disease.

Adult↗
PubMed1990

The influence of protein malnutrition on T cell, natural killer cell, and lymphokine-activated killer cell function, and on biological responsiveness to high-dose interleukin-2.

Protein malnutrition is prevalent in cancer patients, however the influence of protein-calorie malnutrition on anti-tumor immune effector mechanisms is unclear. In addition, the effect of malnutrition on host immunological and biological responsiveness to recombinant interleukin-2 (rIL-2) is unknown. In Swiss mice (n = 100), we observed that T cell activation, T cell response to rIL-2, T suppressor cell generation, cytotoxic T lymphocyte development, and the cytolytic activity of LAK cells were not significantly impaired by two or three weeks of feeding with a 2.5% protein diet compared with mice fed an isocaloric diet in which protein calories constituted 24% of the total. In CBA/J mice (n = 100), we observed a significant (P less than 0.05) impairment of poly(I:C)-inducible natural killer cell function in mice ingesting the 2.5% diet. In both A/J (n = 40) and Swiss mice (n = 40), cytotoxic responses after 3 days treatment with rIL-2 (5 X 10(6) U/kg body wt. three times daily) were comparable in both dietary groups. These studies demonstrate that protein depletion is associated with impaired poly (I:C)-induced natural killer cell function in CBA/J mice. However, T cell function and biological responsiveness to high-dose rIL-2 were not significantly impaired.

Animals↗
PubMed1990

Components of energy expenditure in tumor-bearing animals.

Single snapshot measurements of resting energy expenditure (REE) suggest that hypermetabolism contributes to cancer cachexia, but tumor impact on total 24-hr energy expenditure (TEE) is unknown. Automated multicage indirect calorimetry was employed to measure daily energy expenditure in adult Buffalo rats (n = 16) randomized to tumor inoculation or controls. Measurements included baseline REE, activity EE (AEE), thermic response to food (TEF), and TEE. Rats (n = 16) were randomized. Metabolic measurements, tumor size, and body weight were recorded weekly. Animals were sacrificed at Week 5 for analysis of host and tumor composition. Significant depletion of total lean body mass occurred in TB rats (greater than 15% wt loss, ANOVA P less than 0.001) which inversely correlated with tumor growth (r = -0.81, P less than 0.001). REE, TEF, AEE, and TEE did not change in controls (ANOVA P = n.s.). In TB rats, a 19.5% increase in REE occurred (119.4 +/- 3.3 to 138.7 +/- 1.8 kcal/kg LBM/day, P less than 0.01). TEE remained unchanged (157.3 +/- 5.6 vs 152.9 +/- 3.6 kcal/kg LBM/day, P = n.s.) due to a 66% decrease in AEE (32.9 +/- 3.1 to 10.5 +/- 1.7 kcal/kg LBM/day, P = 0.01). TEF did not change (4.7 +/- 0.8 vs 5.0 +/- 0.3 kcal/kg LBM/day, P = n.s.). Both TB and controls demonstrated a decreased REE in response to a 24-hr fast (7.9% vs 4.8%, P = n.s.). Respiratory quotient decreased in both groups when comparing fed to fasted values: TB (0.86 to 0.76) and controls (0.86 to 0.71), but the decline was greater in controls (P = 0.04).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Stability-complexity relationships within models of natural systems.

Drawing on the qualitative loop analysis models prepared by Lane for a Delaware Bay plankton community, we evaluated 12 systems that ranged from 14 to 18 entities (population, guild or nutrient). Our approach was to study models of extended trophic biotic communities and examine the stability-complexity issue not only as it exists between systems (the traditional approach) but also with respect to the entities and relationships within a given system. We found no statistically significant inverse relationship for stability and complexity between systems. Within a system, a significant inverse relationship at the entity level was observed embedded in an increasing stability positively related to increasing subsystem size. Also, within a system and from system to system, several entities were seen to vary their roles with respect to stability. These results extend the stability-complexity issue to models of relatively large biotic communities and raise issues concerning the roles, with respect to stability, played by entities within communities.

Animals↗
PubMed1990

Immunologic effects of arginine supplementation in tumor-bearing and non-tumor-bearing hosts.

Supplemental dietary arginine has anti-tumor properties but the degree and mechanisms are unclear. In non-tumor-bearing CBA/J mice (n = 60), 1% arginine supplementation significantly enhanced thymic weight, spleen cell mitogenesis, and interferon-activated natural killer cell activity; no further enhancement was observed with 2% or 4% supplementation. Supplemental 1% arginine, when compared with 1.7% glycine, enhanced interferon-induced natural killer cell activity, lymphokine-activated killer cell generation, and macrophage cytotoxicity. In A/J mice (n = 420), bearing either a moderately immunogenic (C1300) or weakly immunogenic (TBJ) murine neuroblastoma, 1% arginine significantly (p less than 0.05) retarded tumor growth and prolonged median survival time compared with glycine or no supplementation. Dietary arginine enhanced T-cell function and significantly increased responsiveness to autologous C1300 tumor in a mixed lymphocyte tumor cell culture (MLTC). The immunomodulatory effects of arginine provide nutritional and immunologic support of the tumor-bearing host and may be helpful when given concommitant with immunotherapy.

Animals↗
PubMed1990

Occult cerebrovascular malformations: follow-up with MR imaging.

The clinical and magnetic resonance (MR) imaging findings in 20 patients with MR evidence of occult cerebrovascular malformations (OCVMs) were retrospectively analyzed. Of 27 lesions followed up throughout a mean period of 18 months, eight showed obvious evolution on MR images (four cases of regression and four cases of new bleeding). Three new independent lesions were disclosed. Clinical evolution was discordant with MR findings in five patients. In the other patients, topography of the lesion, mass effect, and location of the hemorrhage could explain clinical data. The dynamic nature of OCVMs must be considered in decisions on therapeutic management.

Adult↗
PubMed1990

Visibility of cranial nerves at MRI.

In order to assess the value of MRI in the depiction of intracranial nerves, we retrospectively reviewed 60 patients investigated over a 2-year period. The purposes of this study were: 1) to determine the score of MRI in detecting cranial nerves III to XII, and 2) to establish accurate landmarks for easy detection of these nerves. Cranial nerves III, V, VII and VIII are well seen (70 to 100%), very often on axial, sagittal and coronal sections. Nerves IX to XII are correctly studied only on axial planes (81 and 83%), but it is difficult to distinguish between the vagus nerve and the glossopharyngeal and spinal nerves. Due to their oblique direction and small size, nerves IV and VI are seldom visualized. The most important landmarks are the chiasma, the colliculi, Meckel's cavity, the internal auditory canal, the jugular foramen, the hypoglossal canal and the brainstem structures. We suggest the following scanning technique: short spin-echo sequences (TR 600 ms, TE 20 ms), 3 to 5 mm thick contiguous sections, 16 to 20 cm field of view with 4 or 2 excitations respectively, 256 x 256 matrix, and at least one acquisition plane (axial plane), but preferably two or three planes. MRI is a sensitive examination in the recognition of cranial nerves. It should be the first-step exploratory procedure in patients with cranial nerve pathology.

Adolescent↗
PubMed1989

[Diagnosis of diseases of the spinal cord and the vertebral column].

Magnetic resonance imaging (MRI) nowadays plays a predominant role in the diagnosis and evaluation of spinal canal pathologies and has reduced the other exploratory methods, including computerized tomography (CT) and myelography, to an ancillary role. These pathologies are divided into three groups: those where MRI is the only imaging method (syringomyelia, tumours in the spinal canal, phakomatoses, external pachymeningitis, spinal cord injuries, myelitis); those where MRI is the initial method and is completed by other examinations (vascular malformations, dysraphism, myelopathies due to cervical osteoarthritis) and those where MRI still play a lesser role than CT (degenerative lesions of the lumbar column).

Humans↗
PubMed1989

The influence of natural killer cells in neuroblastoma.

Human neuroblastoma (NRB) cell lines are markedly sensitive to natural killer (NK) cell lysis in vitro, but patients with NRBs have low or absent NK activity. This study evaluated the NK sensitivity of murine NRBs (C1300 and TBJ) in the regulation of NRB growth and determined the effects of recombinant (r) interferon gamma and recombinant interleukin 2 (rIL-2). Both basal (8% +/- 3% specific cytotoxicity) and induced (20% +/- 3%) NK lyses of C1300-NRB were observed. In vivo depletion of NK cells with anti-asialo GM-1 significantly enhanced growth of C1300-NRB and decreased survival. Treatment with r-interferon gamma or rIL-2 on days 1 through 3 after C1300-NRB inoculation significantly prolonged the mean tumor latency period, decreased the tumor growth rate, and enhanced in vitro NK killing of C1300-NRB and YAC-1. The effects of r-interferon gamma and IL-2 were abrogated by pretreatment with anti-asialo GM-1. These results demonstrated that NK cells form one important component of regulation of a murine NRB, but immunomodulation with potent lymphokines requires cooperation of more than one cell type.

Animals↗
PubMed1989

Magnetic resonance investigations of non-acoustic petrous lesions.

Twenty cases of intrapetrous lesions were studied by a 1.5 T magnetic resonance (MR) unit. In all cases, comparisons were made between MR, CT and clinical findings. Our present material included 9 cholesteatomas, 1 cholesterol cyst, 3 primary epidermoid carcinomas, 2 metastatic neoplasms, 1 glomus jugulare tumor and 4 facial neurinomas. Gadolinium was injected in 7 cases and seemed to be the best method for studying the intrapetrous tumors. MR permitted accurate topographic study and assessment of tumoral extension, as well as a ready demonstration of tumor vascularity. The present findings also showed that MR is not capable of defining small bony detail or calcifications.

Adolescent↗
PubMed1989

[MRI in the diagnosis of recurrent cholesteatoma of the petrous bone].

Nine cases of recurrent petrous cholesteatomas have been studied by a 1,5 T MR unit. Gadolinium was injected in 1 case. In all cases, comparison between MR, CT and clinical findings were made. MR allows for accurate topographic study and assessment of cholesteatomas extension, in particular in the posterior fossa and skull base. Relationships with the internal carotid artery and the jugular vein are clearly depicted.

Adult↗
PubMed1988

Immunomodulatory mechanisms of arginine.

Dietary supplementation with the amino acid arginine augments T-lymphocyte activation in response to mitogens in clinical and experimental studies. In experimental models arginine enhances specific T cell antitumor immunity. The mechanism of these immunostimulatory effects of arginine on T cell function is unclear, and the scope and specificity of arginine's influence on other components of the effector immune response such as natural killer (NK) cells and macrophages are unknown. To evaluate the role of arginine in these responses, CBA/J mice (n = 100) were randomized to receive either 1% arginine supplementation or isonitrogenous (1.7%) glycine supplementation for at least 10 days. There was no significant differences in mean body weight between groups during feeding. Arginine supplementation significantly (p less than 0.05) enhanced cytotoxic T-lymphocyte development, poly IC-inducible NK activity, and the kinetics of interleukin-2 receptor expression on activated T cells. Basal- and endotoxin-induced macrophage interleukin-1 and superoxide production were not significantly influenced by supplemental arginine although macrophage cytotoxicity in response to gamma-interferon was augmented (p = 0.07). In subsequent in vitro studies we established that certain effects (NK, cytotoxic T-lymphocyte, and T cell activation) were reproducible after preincubation for 72 hours in pharmacologic levels of arginine. The data strongly suggest that arginine mediates a direct effect on components of the immune system, which results in enhanced production or use of lymphokines.

Animals↗
PubMed1988

MRI features of craniopharyngiomas at 1.5 Tesla. A series of 13 cases.

Thirteen patients with craniopharyngioma were explored with a 1.5 Tesla magnetic resonance imager. The results were compared with those of CT and with operative findings. The MRI signals were correlated with the biochemical composition of the cysts (proteins, lipids, iron, LDH) in 5 cases; 2 patients were studied after an intravenous injection of gadolinium DOTA. MRI proved vastly superior to CT to evaluate the spread and identify the various components of craniopharyngiomas (cysts, fleshy parts, haemorrhages), except for calcifications. Gadolinium improved the detection of fleshy parts and "active" cysts. The signals emitted by cysts were extremely variable on T1-weighted sequences. The correlation between MRI and biochemical data was complex, but it appeared that protein, lipid and iron concentrations had a major influence on cyst signals. MRI with gadolinium may be envisaged as first-line examination to improve the evaluation of spread, determine the prognosis and detect recurrences of craniopharyngiomas. CT could be reserved to difficult cases with invasion of bones and sinuses.

Adolescent↗