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Biomedical subjects

J Hirsch

Publications and source records attributed to J Hirsch.

At least 217 records · Page 12Linked to original sources
PubMed1985

Comment on "Line-separation discrimination curve in the human fovea: smooth or segmented"?

In a recent publication, Westheimer concluded that the foveal line-separation discrimination function was smooth [J. Opt. Soc. Am. A 1, 683-684 (1984)]. However, when the Westheimer data are replotted in the Weber-fraction (delta s/s) form, segments in the discrimination function similar to those previously described by Hirsch and Hylton [J. Opt. Soc. AM. 72, 1367-1374 (1984)] can be observed.

Discrimination, Psychological↗
PubMed1985

Attention to television: intrastimulus effects of movement and scene changes on alpha variation over time.

Central and occipital EEG alpha were used as an on-line measure of momentary changes in covert attention during television viewing. Alpha was recorded during nine 30-second commercials shown embedded in a half-hour situation comedy. Two time series were constructed for data analysis. A stimulus series consisted of codes representing the presence or absence of scene changes or person and object movement for each half-second interval of the commercials. The alpha series consisted of median alpha scores for each half-second interval, aggregated across 26 subjects. The alpha series was regressed on the movement and scene change series, both of which produced significant increments in R, even after autocorrelational effects inherent in the alpha series were removed. As a validity check on the attentional interpretation of alpha, it was shown that mean alpha for each commercial was significantly (negatively) correlated with recall and recognition of commercial contents. The results are discussed in terms of their implications for further use of continuously-recorded alpha in research on factors that influence attention to television.

Adult↗
PubMed1985

Metabolic characterization of obesity.

Body composition (adiposity) is a regulated characteristic with multicomponent controls having redundant and interconnecting loops. The nature of the relevant control processes and of their interactions is poorly understood. Components of the system include complex mechanisms controlling food intake; energy expenditure; and the production, location, and filling of adipocytes. Recent studies in humans have implicated three systems in this overall control process: systemic energy homeostasis, adipocyte-related substrate flux, and adrenoreceptor function in adipocytes. These studies indicate that the formerly obese state is characterized by changes in systemic energy expenditure and adipocyte metabolism that may favor regaining weight. The anatomic distribution of adipose tissue, influencing risk of metabolic complications at any absolute level of adiposity, may be partially controlled by the status of adrenergic receptors in the adipocytes of the relevant anatomic sites.

Adipose Tissue↗
PubMed1985

Health implications of obesity: an NIH Consensus Development Conference.

A Consensus Development Conference on the Health Implications of Obesity was held in February 1985 at the National Institutes of Health in Bethesda, Maryland, USA. After presentations by 19 experts in relevant subject areas, a panel of 15 impartial senior level professionals presented their consensus of findings and recommendations. This paper summarizes the results of the conference and provides reference tables of body mass index (BMI) values and weight goals, along with nomograms of the BMI determined from height and weight scales, to show comparisons with weight goals. The goals are taken from two widely available tables of mortality data by weight. These reference aids are included to illustrate the potential clinical value of wider use of the BMI, as recommended in the conference.

Body Height↗
PubMed1985

Selection for central excitation in Drosophila melanogaster.

In two populations of Drosophila melanogaster, bidirectional selection and single-pair matings for high and low expression of central excitatory state (CES) succeeded in producing from one a high, but not a low, CES line, and from the other a low, but not a high, CES line. Compared with results from the selection studies of the blow fly, Phormia regina, in which one major gene correlate of CES has been found, the results from this study suggest that in D. melanogaster there are several gene correlates of CES, opposite alleles of some of which have become fixed in the divergent lines.

Animals↗
PubMed1985

Evolution of an instinct under long-term divergent selection for geotaxis in domesticated populations of Drosophila melanogaster.

Long-term divergent selection for geotaxis in lines of Drosophila melanogaster (the fruit fly) is described. After 26 years (600+ generations) of intermittent selection, the mean geotactic scores now remain stable upon relaxed selection, a result suggesting that evolutionary changes have occurred in these lines. Because the stability is not due to genetic fixation (homozygosity) of the lines, it must be due to either close linkage of genes associated with geotaxis (which would not result in enduring change) or the development of new coadapted gene complexes utilizing genes associated with extreme geotaxis expression (which should result in enduring change). Better evidence for the latter hypothesis is obtained from the low, than from the high, line. The notions of coadaptation and genetic homeostasis are considered, as well as the prospective use of the geotaxis lines to study such concepts experimentally. The geotactic behavior expressed in each line is defined as "instinctive": It increases reproductive success and is characteristic of a population.

Animals↗
PubMed1984

Diminished energy requirements in reduced-obese patients.

In assessing the reasons for the frequent regaining of weight by reduced-obese patients, we examined retrospectively the seven-day energy intake requirements for weight maintenance of 26 obese patients (12 males, 14 females) at maximum weight (152.5 +/- 8.4 kg) and after weight loss (100.2 +/- 5.7 kg). These results were compared with those obtained in 26 age- and sex-matched control patients who had never been obese (62.6 +/- 2.3 kg). The obese and control subjects required comparable caloric intakes: 1432 +/- 32 kcal/m2/d vs 1341 +/- 33 kcal/m2/d, respectively. Following weight loss, the reduced-obese subjects required only 1021 +/- 32 kcal/m2/d, a 28% decrease (P less than 0.001) in requirements relative to their obese state and a 24% decrease relative to the control patients (P less than 0.001). The mean individual energy requirement of the reduced-obese subjects (2171 kcal/d) was less than that for the control subjects (2280 kcal/d) despite the fact that they still weighed 60% more than the controls. In order to maintain a reduced weight, some reduced-obese or even partially reduced patients must restrict their food intake to approximately 25% less than that anticipated on the basis of metabolic body size. The reasons why this finding is unlikely to be an artifactual consequence of changes in lean body mass or body water content are discussed. This finding has implications with regard to the pathophysiology and treatment of obesity in humans.

Adult↗
PubMed1984

Quality of the primate photoreceptor lattice and limits of spatial vision.

Quantitative analysis of a primate photoreceptor lattice shows that the foveal lattice is a highly regular hexagonal structure with a positional correlation length of at least 130 photoreceptors. This result indicates that the photoreceptor lattice is not sufficiently disordered to prevent aliasing in the fovea, but rather could provide the metric with which the visual system determines spatial separation even for tasks involving hyperacuity .

Animals↗
PubMed1984

Measurement of glycerol turnover by infusion of nonisotopic glycerol in normal and injured subjects.

A new technique for measuring glycerol turnover in human subjects is presented using a staged infusion of unlabeled glycerol. A total of 105 measurements was made in normal subjects and postoperative or acutely ill patients. The relation between glycerol turnover rate (R tau) and concentration (C) (R tau = 31 + 2.07C) from 80 staged infusion measurements in 21 normal subjects did not differ significantly from observations of others made by isotope dilution. In 11 patients, glycerol turnover was also measured by dilution of isotopic glycerol. Mean values did not differ significantly between the two methods. The average difference, regardless of sign, for individual values was 17%. This agreement tends to validate the assumptions of both methods. Advantages of the staged infusion method are that it is quicker and easier to perform and does not entail a risk due to administration of radioactive materials. Evidence obtained in this study from a three-stage procedure indicates that satisfactory information may be obtained from a two-stage infusion at successive rates of 250 and 600 mumol/min for 70 min each, with a prime of 2 mmol given as a bolus at the start of each stage.

Adult↗
PubMed1984

Orientation dependence of visual hyperacuity contains a component with hexagonal symmetry.

Recently we reported that hyperacuity thresholds for separation-discrimination tasks were not smooth functions of spatial variables but rather were regularly segmented with sharp transitions between the segments. In this study we have measured the orientation dependence of two tasks involving visual hyperacuity, the discrimination of spatial frequencies and the discrimination of vernier offsets, in the vicinity of a transition between segments. The orientation dependence of both tasks contains a periodic component with a period of 60 degrees. We interpret this as evidence that the cortical substrate that processes spatial information has a hexagonal two-dimensional organization, preserving the hexagonal packing of the foveal photoreceptors.

Female↗
PubMed1984

Radioisotopic method for the measurement of lipolysis in small samples of human adipose tissue.

To facilitate the study of adrenoreceptor response in small needle biopsy samples of human subcutaneous adipose tissue, we developed a dual radioisotopic technique for measuring lipolysis rate. Aliquots (20-75 mg) of adipose tissue fragments were incubated in a buffered albumin medium containing [3H]palmitate and [14C]glucose, each of high specific activity. In neutral glycerides synthesized in this system, [14C]glucose is incorporated exclusively into the glyceride-glycerol moiety and 3H appears solely in the esterified fatty acid. Alpha-2 and beta-1 adrenoreceptor activation of tissue incubated in this system does not alter rates of 14C-labeled glyceride accumulation, but does produce a respective increase or decrease in the specific activity of fatty acids esterified into newly synthesized glycerides. This alteration in esterified fatty acid specific activity is reflected in the ratio of 14C:3H in newly synthesized triglycerides extracted from the incubated adipose tissue. There is a high correlation (r = 0.90) between the 14C:3H ratio in triglycerides and the rate of lipolysis as reflected in glycerol release into the incubation medium. The degree of adrenoreceptor activation by various concentrations of lipolytic and anti-lipolytic substances can be assessed by comparing this ratio in stimulated tissue to that characterizing unstimulated tissue or the incubation medium. This technique permits the study of very small, unweighed tissue biopsy fragments, the only limitation on sensitivity being the specific activity of the medium glucose and palmitate. It is, therefore, useful for serial examinations of adipose tissue adrenoreceptor dose-response characteristics under a variety of clinical circumstances.

Adipose Tissue↗
PubMed1984

Demonstration of de novo production of adipocytes in adult rats by biochemical and radioautographic techniques.

Adult rats of various strains show small increases in the number of adipocytes in the epididymal (Epi) fat pad and large increases in the retroperitoneal (RP) fat depot when they are fed a high-fat, high-sugar diet ( HFS ). In the present study, radioautographic techniques are used to demonstrate that these increases result from replication and differentiation of adipocyte precursors. In addition, both in vivo and in vitro biochemical techniques are used to demonstrate that HFS -induced acceleration of DNA synthesis differs between Epi and RP depots. Measures of levels of incorporation of radiolabeled thymidine into DNA in rats fed HFS for 4 weeks reveal significant elevation in the RP depot but not in the Epi pad. Analysis of radioautographs indicates that formation of precursors may be accelerated in the RP depot as early as the first week of HFS -feeding. Results obtained from the in vitro biochemical assay are of interest with regard to possible clinical application since current in vivo techniques for quantitative assessment of precursor synthesis cannot be applied directly to the study of adipose tissue growth in man. While data obtained from the in vitro assay contains a relatively high degree of variation, the information it provides is in general agreement with that provided by the in vivo assay.

Adipose Tissue↗
PubMed1983

Synthesis, benzodiazepine receptor binding, and anticonvulsant activity of 2,3-dihydro-3-oxo-5H-pyrido[3,4-b][1,4]benzothiazine-4-carbonitriles.

A series of oxopyridobenzothiazines (azaphenothiazines) were prepared and evaluated for binding to the benzodiazepine receptor, anticonvulsant activity in the pentylenetetrazole-induced convulsion assay, and, in two cases, ability to increase punished responding in a standard conflict test. While parent compound 1a showed binding affinity comparable to chlorodiazepoxide (CDP), its potency in the anticonvulsant assay and the anticonflict test was considerably weaker than CDP. Of the variety of derivatives synthesized, only the 7-chloro compound 1b showed receptor affinity comparable to 1a with slightly improved in vivo activity. The poor correlation between receptor binding and in vivo activity may be due to variability in absorption or pharmacological responses unrelated to affinity for the benzodiazepine receptor.

Animals↗