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S Landau

Publications and source records attributed to S Landau.

At least 19 recordsLinked to original sources
PubMed2001

Reliable short-term memory in the trion model: toward a cortical language and grammar.

It has previously been shown that Hebb learning in a single column in the trion model of cortical organization occurs by selection. Motivated by von Neumann's solution for obtaining reliability and by models of circulating cortical activity, we introduce Hebb intercolumnar couplings to achieve dramatic enhancements in reliability in the firing of connected columns. In order for these enhancements to occur, specific temporal phase differences must exist between the same inherent spatial-temporal memory patterns in connected columns. We then generalize the criteria of large enhancements in the global firing of the entire connected columnar network to investigate the case when different inherent memory patterns are in the columns. The spatial rotations as well as the temporal phases now are crucial. Only certain combinations of inherent memory patterns meet these criteria with the symmetry properties playing a major role. The columnar order of these memory patterns not in the same symmetry family can be extremely important. This yields the first higher-level architecture of a cortical language and grammar within the trion model. The implications of this result with regard to an innate human language and grammar are discussed.

Cerebral Cortex↗
PubMed2000

Preovulatory follicular status and diet affect the insulin and glucose content of follicles in high-yielding dairy cows.

Insulin and glucose may be limiting factors for ovarian function in dairy cows genetically selected for high milk yield. The effects of nutrition on the intrafollicular content of insulin and glucose were investigated in Israeli Holstein dairy cattle fed a basic total mixed ration and producing 34-39kg of milk daily. In experiment 1, carried out in 11 oestrus-synchronised cows, little variation in insulin concentration was found in plasma sampled during the luteal phase, but high variation was found in plasma sampled during the follicular phase. Therefore, in order to prevent confounding the effects of diet and of phase in cycle in the following experiments, experimental diets were fed during the luteal phase of synchronised oestrus cycles. In experiment 2, designed as Latin-Square, six cows received sequentially diets containing 17.1 (control) or 19.7% of crude protein, using two sources of supplementary protein, i.e. soyabean meal (SBM) and corn gluten meal (CGM), differing in ruminal degradability and leucine content. When dry matter intake was used as covariant, plasma insulin on day 16 was 29.5 and 26.4% higher in cows fed diets containing SBM and CGM than in the control (P<0.05). In experiment 3, 17 cows were individually fed the basic diet and then switched to isoenergetic diets containing SBM (n=5), CGM (n=6) or corn grain (CG, n=6) given from day 10 to 16 of the synchronised oestrus cycle. On the eve of day 16, and in the morning of day 17, they were administered PGF(2alpha) and the content of 26 largest follicles was aspirated by using the transvaginal ovum pick-up technique. Follicles were sorted into two classes (preovulatory and subordinate) according to oestradiol concentration and the progesterone:oestradiol ratio in follicular fluid (FF). Higher concentrations of insulin (0.282 versus 0.127ng/ml, P<0.0001) and of glucose (0.614 versus 0.386g/l, P<0.002), were found in FF from preovulatory follicles. The insulin concentration in the FF of cows fed the CG diet was 26% higher than in their counterparts fed CGM (P<0.04), SBM being intermediate. Dietary effects did not reach significance in subordinate follicles. The finding that preovulatory follicular status is associated with increased intrafollicular insulin and glucose suggests that insulin is involved in follicular maturation. The nutritional effect on intrafollicular glucose and insulin may have practical implications to optimise feeding in dairy cows during phases of the oestrus cycle.

Animal Feed↗
PubMed2000

Short-term changes in eating patterns explain the effects of condensed tannins on feed intake in heifers.

Ingestion of condensed tannins decreases feed intake in ruminants. Polyethylene glycol (PEG) forms high-affinity complexes with tannins. In two experiments carried out on Holstein heifers, quebracho (Q) from the Aspidosperma quebracho served as source of condensed tannins. The aims of the study were (i) to quantify the effect of Q on feed intake and eating behaviour in cattle fed complete mixed diets (CMDs); (ii) to clarify if changes induced in ingestive behaviour and feed intake by Q in cattle can be reversed by feeding PEG; and (iii) to clarify if the decrease in feed intake is associated with short-term (astringency, post-ingestive malaise) or longer-term effects. In experiment 1, 500 g/day of Q was found to be the minimal dose that decreased feed intake in heifers. A ratio of PEG:Q equal to 1:12.5 did not fully restore feed intake. In experiment 2, four heifers received a random sequence of four rations in a Latin-square design with feeding cycles of ca. 7 days: CMD containing no supplements (C), or supplemented with 625 g/day of Q without PEG (Q), with 625 g/day of Q and 250 g/day of PEG (Q-PEG), or with 250 g/day of PEG without Q (PEG). Individual rations were continuously weighed in the trough and the behaviour of heifers was observed for 180 min after distribution of CMD. Overall, feeding Q was associated with lowered feed intake and shorter duration of eating bouts, mainly of the first eating bout, immediately after distribution of the diet. A larger portion of the diet was consumed subsequent to 180 min after distribution in Q-fed heifers. Eating rate and the water to food ratio were not affected by Q. The effects of Q on feed intake were attenuated by feeding PEG. Heifers adapted effectively to condensed tannins by increasing the number of eating bouts and the portion of diet consumed subsequent to 180 min after distribution, so that no differences in feed intake were noted on the last day of each feeding cycle. Data are interpreted to show that: (i) negative effects of Q on feed intake derive from astringency of CT and short-term post-ingestive malaise; (ii) the increased number of eating bouts and their wider partition throughout the day are means to preserve the ruminal environment in Q-fed heifers; (iii) PEG has the potential to neutralize negative effects of condensed tannins in cattle.

Journal Article↗
PubMed2000

Short-term dietary effects on reproductive wastage after induced ovulation and artificial insemination in primiparous lactating Sarda ewes.

Short-term effects of nutrition on conception rate (CR), ovulation rate (OR), ova and embryo losses (OEL) during the first 50 days following insemination and total reproductive wastage after ovulation (TRW), were investigated in primiparous lactating Sarda ewes after oestrous synchronisation and cervical [corrected] artificial insemination (AI). Eighty ewes grazing a green high-quality pasture were offered one of three iso-energetic supplements from day 14 before to day 2 after AI: whole maize grain (M); soyabean meal (S); maize gluten meal (G); or served as controls (C). Supplements G and S were iso-nitrogenous but provided different amounts of rumen undegradable digestible protein. The intake of herbage and digestible dry matter, measured by the n560 mg/l was associated with lower CR. Ranking by ovulation groups of CR was single<double=triple; and of TRW was double<triple<single. In conclusion, OR in primiparous lactating Sarda ewes grazing on a good quality pasture is high, and CR after AI is reduced by ova as well as embryo loss, especially following single ovulations. Short-term supplementation with a soyabean-based concentrate may help alleviate these losses.

Alkanes↗
PubMed1999

School psychologists: strategic allies in the contemporary practice of primary care pediatrics.

Immense changes in the developmental/behavioral aspects of primary care pediatrics have resulted from revisions in special education laws, introduction of managed care, widened dissemination of information about disabilities to parents, and the changing character of American society. Challenges associated with contemporary pediatric practice can be diminished by routine collaboration with school psychologists. An alliance with school-based psychologists permits pediatricians access to children in their natural environments and potential collaboration for preventing illness and emotional/behavior problems. Further, school psychologists can provide a partner for assessing and treating both common and low-incident disorders without the constraints imposed by managed care.

Attention Deficit Disorder with Hyperactivity↗
PubMed1999

Group treatment of auditory hallucinations. Exploratory study of effectiveness.

BACKGROUND: Cognitive-behavioural therapy has been shown to be effective in reducing psychotic symptoms, but few patients have access to these services. Group cognitive treatment may provide a less costly service with similar benefits. AIMS: To explore the effectiveness of group cognitive-behavioural therapy on insight and symptoms, particularly auditory hallucinations. METHOD: Twenty-one DSM-IV diagnosed patients with schizophrenia with treatment-resistant, distressing auditory hallucinations were referred to a group programme consisting of six sessions of cognitive treatment following a strict protocol which emphasised individual power and control as well as coping strategies. RESULTS: There were significant changes in all three main outcome measures following treatment; those changes were maintained at follow-up and were greater than changes over the waiting-list period. Specifically, there were changes in perceived power and distress as well as increases in the number and effectiveness of the coping strategies. CONCLUSIONS: Group treatment for auditory hallucinations needs further investigation but does look promising and may provide a less costly alternative to individual cognitive treatment.

Adaptation, Psychological↗
PubMed1998

The use of multivariate statistical methods in psychiatry.

Multivariate methods such as factor analysis and cluster analysis have been used for many years by psychiatric researchers primarily for investigating the problems of psychiatric diagnosis. In more recent times, the range of multivariate techniques used has been extended as has the number of areas in which they are being applied.

Cluster Analysis↗
PubMed1997

Predicting wheat yields: the search for valid and precise models.

Interest in predicting wheat yield in terms of physiological, cultural and meteorological variables is more than a century old. Early attempts involved statistical analyses of relationships between yield and observational data on precipitation, temperature, radiation, etc., and scientific study of physiological and cultural influences such as dates of sowing or anthesis, farming procedures and soil treatments. More recently these have been augmented by large-scale mechanistic models of phenological development, such as AFRCWHEAT, CERES and SIRIUS, incorporating some simulation facilities. All approaches implicitly involve fitting models of some sort: statistical, mechanistic or (preferably) a hybrid of these forms. Levels of success on this important matter are highly variable. After reviewing the field, we consider the results of recent efforts to contrast and evaluate the (large-scale) mechanistic approaches, using spatial/temporal methods for interpolating the required climatological input variables. The work employs a substantial database of wheat yields assembled for this purpose. After assessing the validity of the large-scale mechanistic models (with some intriguing conclusions), we then consider some results from a current approach to parsimonious hybrid modelling, based on statistical study of accessible climatological data interpreted in terms of physiological knowledge of key influences on plant development.

Models, Biological↗
PubMed1996

Adenosine A2 receptor occupancy regulates stimulated neutrophil function via activation of a serine/threonine protein phosphatase.

Adenosine modulates generation of superoxide anion by neutrophils via occupancy of specific adenosine A2A receptors. However, the intracellular signal transduction pathways by which occupancy of neutrophil adenosine A2A receptors inhibits superoxide anion generation (O2.-) are not well understood. We, therefore, tested the hypothesis that signaling at polymorphonuclear leukocyte (PMN) adenosine receptors proceeds via activation of a serine/threonine protein phosphatase (pp). Both the specific pp1 inhibitor calyculin A (10 nM) and the pp2A inhibitor okadaic acid (10 microM) enhanced O2.- generation (185 +/- 24 and 189 +/- 35% of control, respectively, p < 0.0001 for both, n = 8), as reported previously. Calyculin A, but not okadaic acid, completely reversed inhibition of stimulated O2.- generation by the adenosine A2 receptor agonist 5'-N-ethylcarboxamidoadenosine (NECA; IC50 = 30 nM; p < 0.0001, analysis of variance). Calyculin A also reversed the adenosine receptor-mediated desensitization of bound chemoattractant receptors in neutrophils. Treatment of PMNs with NECA increased the pp1 activity of crude membrane preparations in a time- and dose-dependent fashion (EC50 = 40 nM; p < 0.001, analysis of variance, n = 5). NECA inhibited cytosolic protein phosphatase activity by 78 +/- 12% (p < 0.003, n = 6) but did not shift pp1 catalytic subunit from cytosol to plasma membrane. Similar changes were observed in neutrophil cytoplasts depleted of organelles and nucleus. Moreover, the selective protein kinase A inhibitor KT5720 (10 microM) reversed the capacity of dibutyryl cAMP but not NECA to increase pp1 activity (p < 0.01, n = 5) in keeping with its effects on O2.- generation. Western blot analysis of PMN subcellular fractions demonstrated the presence of pp1alpha and pp1gamma1 but not pp1gamma2 isotypes in both cytosol and plasma membrane but not in azurophil or specific granules. We conclude from these studies that signal transduction by adenosine in PMN proceeds via a novel pathway: cAMP-independent activation of a serine/threonine protein phosphatase in the plasma membrane.

Adenosine↗
PubMed1996

Protein sources affect follicular dynamics in ewes near the onset of the breeding season.

The influence of source of protein during the luteal phase before a synchronized oestrus on the dynamics of follicular development, observed daily by ultrasonography, was assessed in ewes that were beginning the sexual season. Iso-nitrogenous amounts of soybean meal (SBM) or of a corn-gluten meal-ground-corn grain mixture (CGM-GC), or an iso-energetic amount of ground-corn grain (GC), were fed from four days before to four days after treatment with prostaglandin F2 alpha (PGF2 alpha). Feeding with SBM was associated with a higher frequency of short luteal phases (P < 0.02). Dynamics of follicular population were studied in ewes that ovulated after normal cycles. More follicles > or = 2 mm in diameter were observed on the ovaries of ewes fed SBM four days before PGF2 alpha treatment (P < 0.02), but the highest number was seen in ewes fed CGM-GC at the time of injection of PGF2 alpha (P < 0.08). Ewes fed SBM had larger follicles at last detection and ovulated earlier after PGF2 alpha treatment than their counterparts fed other diets (P < 0.001). Ovulatory follicles developed over a greater range of days in ewes with twin ovulations compared with ewes with single ovulations (P < 0.08). Serum concentrations of insulin were increased after four days of feeding with CGM-GC (P < 0.01), but not with SBM or GC, and reached a peak at the time of oestrus. In summary: (1) the source of dietary protein during the late-luteal phase affected follicular maturation after PGF2 alpha treatment; (2) insulin and glucose may be involved in this response and may play a role in ovarian follicular activity; and (3) twin ovulations appeared to result from both reduced atresia and increased recruitment of follicles.

Analysis of Variance↗
PubMed1994

Rat cluster of differentiation 1 molecule: expression on the surface of intestinal epithelial cells and hepatocytes.

BACKGROUND/AIMS: Cluster of differentiation 1 (CD1) is a family of nonpolymorphic, major histocompatibility complex class I-like molecules with prominent expression in the liver and intestinal epithelium of humans and mice. Models of intestinal and hepatobiliary inflammation and experimental liver transplantation are conducted in the rat, yet nothing is known of CD1 expression in this species. METHODS: Monoclonal antibodies against murine CD1 were used to identify a rat CD1 homologue. Tissue messenger RNA expression was confirmed by Northern blot analysis with a murine CD1 complementary DNA probe. RESULTS: Immunoperoxidase staining detected CD1 in intestinal epithelial and liver cells but not in the thymus. Immunofluorescence of isolated hepatocytes and a rat fetal intestinal cell line, SLC-44, showed cell surface expression of CD1. Metabolic labeling and immunoprecipitation of the SLC-44 cell line and a mouse intestinal epithelial cell line, MODE-K, showed a protein of 55 kilodaltons. Immunoblotting of CD1 in isolated intestinal epithelial cells and hepatocytes showed a molecule of 55 kilodaltons. Northern blot analysis showed a single message of approximately 2.2 kilobases in hepatocytes. CONCLUSIONS: A CD1 homologue exists in the rat. Expression in the rat intestine and liver are similar to those in the human and mouse. The rat may be useful as a model for the study of CD1 function.

Animals↗
PubMed1994

Cardiac electrophysiologic effects of diltiazem in dogs receiving either enflurane or chloralose anesthesia.

Previously we have described impaired myocardial conduction in patients receiving diltiazem and enflurane. The present study examines the possible mechanism(s) which may account for our clinical observation and presents methods of reversing adverse interactions. Nineteen mongrel dogs were randomized into two exposure groups: enflurane or chloralose anesthesia. Stepwise increasing doses of diltiazem were administered until predetermined endpoints were reached. Sinus and atrioventricular (AV) node function was assessed at all levels of diltiazem infusions, and after reversal drugs. Depression of AV nodal conduction and refractoriness after diltiazem administration was greater during enflurane anesthesia when compared with chloralose. There was severe sinus node dysfunction in enflurane-anesthetized animals. These effects were only reversed by isoproterenol. Patients may be at increased risk for severe sinus node depression when diltiazem is administered during enflurane anesthesia. This is due to a potent interaction between diltiazem and enflurane on the sinoatrial node.

Anesthesia, Inhalation↗
PubMed1994

Patency of the internal jugular vein following modified radical neck dissection.

Although the internal jugular vein is commonly preserved in modified radical neck dissections, the English literature contains only a single study assessing postoperative vein patency including only 13 patients. The present study was instituted to better determine the patency of the internal jugular vein following modified radical neck dissection and to identify factors associated with venous occlusion. Preoperative and postoperative computed tomography or magnetic resonance imaging was performed on 69 patients undergoing 79 vein sparing neck dissections. Sixty-eight veins (86%) were patent postoperatively. A retrospective chart review revealed that compression by either a musculocutaneous flap or recurrent carcinoma in the neck was associated with venous occlusion. We conclude that the internal jugular vein is likely to remain patent after modified radical neck dissection with vein preservation.

Combined Modality Therapy↗
PubMed1994

Comparison of thallium-201 and F-18 FDG SPECT uptake in squamous cell carcinoma of the head and neck.

PURPOSE: To compare the uptake of 2-[F-18] fluoro-2-deoxy-D-glucose (fludeoxyglucose F-18; F-18 FDG) and thallous chloride Tl 201, using single-photon emission CT (SPECT), for the detection and location of squamous cell carcinoma of the head and neck. METHODS: Five patients with biopsy-proved squamous cell carcinoma of the upper aerodigestive tract underwent both F-18 FDG and thallium-201 SPECT on the same day. F-18 FDG SPECT was performed using a dual-head gamma camera equipped with commercially available, extremely high-energy collimators (full width half-maximal height, 17 mm for 511 keV photons). Tumor size was estimated at 1.0 to 5.0 cm3 in these cases. RESULTS: F-18 FDG SPECT showed five of five primary tumors. In two of the five cases, normal salivary gland activity severely limited thallium SPECT, and the tumors could not be definitively identified. Two of four lymph node groups that were positive for metastatic disease by CT criteria were shown by F-18 FDG SPECT. None were seen with thallium imaging. In one case, F-18 FDG SPECT was able to show a tumor that was not visible on CT. CONCLUSIONS: F-18 FDG has advantages over Tl-201 as a squamous cell carcinoma imaging agent (primarily because of its reduced salivary activity). F-18 FDG SPECT has potential as a viable, less expensive alternative to F-18 FDG positron emission tomography. The ultimate value of F-18 FDG SPECT imaging for detecting occult malignancy, monitoring therapeutic effectiveness, or evaluating tumor recurrence remains to be determined in patients with squamous cell carcinoma of the head and neck.

Biopsy↗
PubMed1993

Private speech of learning disabled and normally achieving children in classroom academic and laboratory contexts.

Learning disabled (LD) children are often targets for cognitive-behavioral interventions designed to train them in effective use of a self-directed speech. The purpose of this study was to determine if, indeed, these children display immature private speech in the naturalistic classroom setting. Comparisons were made of the private speech, motor accompaniment to task, and attention of LD and normally achieving classmates during academic seatwork. Setting effects were examined by comparing classroom data with observations during academic seatwork and puzzle solving in the laboratory. Finally, a subgroup of LD children symptomatic of attention-deficit hyperactivity disorder (ADHD) was compared with pure LD and normally achieving controls to determine if the presumed immature private speech is a function of a learning disability or externalizing behavior problems. Results indicated that LD children used more task-relevant private speech than controls, an effect that was especially pronounced for the LD/ADHD subgroup. Use of private speech was setting- and task-specific. Implications for intervention and future research methodology are discussed.

Attention Deficit Disorder with Hyperactivity↗
PubMed1993

A randomized comparative study of the electrophysiological and electrocardiographic effects of isradipine vs verapamil.

Isradipine is a new dihydropyridine calcium antagonist reported to have minimal effects on cardiac electrophysiology. Of 19 patients with normal cardiac electrophysiological profiles, 11 received isradipine intravenously at doses of 0.0010, 0.0020, 0.0040 and 0.0080 mg.kg-1 (0.0150 mg.kg-1 total dose), and eight received verapamil intravenously at 0.0125, 0.0250, 0.0500 and 0.1000 mg.kg-1 (0.1875 mg.kg-1 total dose). One patient experienced hypotension several minutes after receiving the third isradipine dose. With isradipine, systolic blood pressure (BP) decreased from 154 +/- 24 to 151 +/- 22, 143 +/- 25, 133 +/- 19 and 124 +/- 17 mmHg, respectively. Diastolic BP decreased from 83 +/- 10 (baseline) to 80 +/- 12, 76 +/- 10, 74 +/- 7 and 68 +/- 9 mmHg, respectively. With verapamil, systolic BP changed from 132 +/- 20 (baseline) to 135 +/- 29, 132 +/- 24, 130 +/- 25 and 115 +/- 17 mmHg, respectively, and diastolic BP changed from 80 +/- 14 to 84 +/- 14, 81 +/- 9, 78 +/- 6 and 73 +/- 5 mmHg, respectively. Isradipine had no significant effect on the PR, QRS, QT and QTc intervals, nor were there changes in the atrial-His (AH) and His-ventricle (HV) intervals, atrioventricular nodal effective refractory period. Wenckebach cycle length or sinus node recovery time. Similarly, verapamil at the doses studied did not significantly affect PR, QRS, QT, QTc, AH or HV intervals. However, with verapamil, the Wenckebach cycle length changed significantly from 394 +/- 82 (baseline) to 448 +/- 93 ms. Despite the significant fall in BP with isradipine, heart rate did not change significantly. These results support the electrophysiological neutrality of isradipine on the cardiac conduction system.

Adult↗