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121.
Simple cells in primary visual cortex are believed to extract local contour information from a visual scene. The 2D Gabor
function (GF) model has gained particular popularity as a computational model of a simple cell. However, it short-cuts the
LGN, it cannot reproduce a number of properties of real simple cells, and its effectiveness in contour detection tasks has
never been compared with the effectiveness of alternative models. We propose a computational model that uses as afferent inputs
the responses of model LGN cells with center–surround receptive fields (RFs) and we refer to it as a Combination of Receptive
Fields (CORF) model. We use shifted gratings as test stimuli and simulated reverse correlation to explore the nature of the
proposed model. We study its behavior regarding the effect of contrast on its response and orientation bandwidth as well as
the effect of an orthogonal mask on the response to an optimally oriented stimulus. We also evaluate and compare the performances
of the CORF and GF models regarding contour detection, using two public data sets of images of natural scenes with associated
contour ground truths. The RF map of the proposed CORF model, determined with simulated reverse correlation, can be divided
in elongated excitatory and inhibitory regions typical of simple cells. The modulated response to shifted gratings that this
model shows is also characteristic of a simple cell. Furthermore, the CORF model exhibits cross orientation suppression, contrast
invariant orientation tuning and response saturation. These properties are observed in real simple cells, but are not possessed
by the GF model. The proposed CORF model outperforms the GF model in contour detection with high statistical confidence (RuG
data set: p < 10−4, and Berkeley data set: p < 10−4). The proposed CORF model is more realistic than the GF model and is more effective in contour detection, which is assumed
to be the primary biological role of simple cells. 相似文献
122.
Hristov KL Parajuli SP Soder RP Cheng Q Rovner ES Petkov GV 《American journal of physiology. Cell physiology》2012,302(11):C1632-C1641
Overactive bladder syndrome is frequently associated with increased detrusor smooth muscle (DSM) contractility. We tested the hypothesis that pharmacological activation of the large-conductance voltage- and Ca(2+)-activated K(+) (BK) channel with NS-1619, a selective BK channel opener, reduces the excitability and contractility of human DSM. We used the amphotericin-perforated whole cell patch-clamp technique on freshly isolated human DSM cells, live-cell Ca(2+) imaging, and isometric DSM tension recordings of human DSM strips obtained from open bladder surgeries. NS-1619 (30 μM) significantly increased the amplitude of the voltage step-induced whole cell BK currents, and this effect was abolished by pretreatment with 200 nM iberiotoxin (IBTX), a selective BK channel inhibitor. In current-clamp mode, NS-1619 (30 μM) significantly hyperpolarized the resting membrane potential, and the hyperpolarization was reversed by IBTX (200 nM). NS-1619 (30 μM) significantly decreased the intracellular Ca(2+) level in isolated human DSM cells. BK channel activation with NS-1619 (30 μM) significantly inhibited the amplitude, muscle force, frequency, duration, and tone of the spontaneous phasic and pharmacologically induced DSM contractions from human DSM isolated strips. IBTX (200 nM) suppressed the inhibitory effects of NS-1619 on spontaneous contractions. The amplitude of electrical field stimulation (0.5-50 Hz)-induced contractions was significantly reduced by NS-1619 (30 μM). Our data suggest that pharmacological activation of BK channels could represent a novel treatment option to control bladder dysfunction in humans. 相似文献
123.
Graber JH Churchill GA Dipetrillo KJ King BL Petkov PM Paigen K 《Journal of experimental zoology. Part A, Comparative experimental biology》2006,305(9):683-688
The physical and functional organizations of a genome are correlated outcomes of evolution. Inbred strains of mice provide a unique opportunity for exploring these relationships, representing as they do, diverse genomes originally separated by millions of generations that were then scrambled in the laboratory and subjected to intense selection during inbreeding to homozygosity. Here we show that the resulting pattern of chromosome organization includes regional domains of functionally related elements that promote the co-inheritance and survival of compatible sets of alleles. There are also patterns of linkage disequilibrium between domains on separate chromosomes; these are distinctly non-random and form networks with scale-free architecture. The strong conservation of gene order among mammals suggests that the domains and networks we find likely characterize all mammals, and possibly beyond. 相似文献
124.
Epigenetic re-programming is an important event in the development of primordial germ cells (PGC) into functional gametes, characterized by genome-wide erasure of DNA methylation and re-establishment of epigenetic marks, a process essential for restoration of the potential for totipotency. In this study changes in the methylation status of centromeric repeats and two IGF2-H19 differentially methylated domain (DMD) sequences were examined in porcine PGC between Days 24 and 31 of pregnancy. The methylation levels of centromeric repeats and IGF2-H19 DMD sequences decreased rapidly from Days 24 to 28 in both male and female PGC. At Days 30 and 31 of pregnancy centromeric repeats and IGF2-H19 DMD sequences acquired new methylation in male PGC, while in female PGC these sequences were completely demethylated by Day 30 and remained hypomethylated at Day 31. To characterize methylation changes that PGC undergo in culture, the methylation status of embryonic germ cells (EGCs) derived from PGC at Day 26 of pregnancy was examined. Centromeric repeats and IGF2-H19 DMD sequences were similarly methylated in both male and female EGC and hypermethylated in female EGC compared with female PGC at the same embryonic age. Our results show that, similar to murine PGC, porcine PGC undergo genome-wide DNA demethylation shortly after arrival in the genital ridges. When placed in culture porcine PGC terminate their demethylation program and may acquire new DNA methylation marks. To our knowledge, this is the first report regarding epigenetic re-programming of genital ridge PGC in the pig. 相似文献
125.
126.
The innervation of the pancreatic duct was studied in the European Hare (Lepus europaeus) by the cholinesterase technique. The duct was accompanied by thick myelinated and thin non-myelinated nerve fibres, which subsequently formed a plexi. The plexi were associated with the fibres of the plexi of the islet of Langerhans, or with ganglia, blood vessels or neural networks. No chain of ganglia was observed on or near the duct and the ductules. 相似文献
127.
128.
The administration of captopril (CP, 30 mg/kg) limited the arterial hypertension induced by the coarctation of the renal arteria and cardiac hypertrophy in rats. CP prevented the activation of MB-KK and glucoso-6-phosphate dehydrogenase. Besides CP decreased the activity of pyruvate kinase and increased that of malate dehydrogenase. These data demonstrate, that CP prevents both the cardiac hypertrophy and metabolic changes in animals with the renal hypertension. 相似文献
129.
130.
Summary A and B cells in the pancreatic islets of cattle are interlaced with one another. The histochemical characteristics of the islet cells is similar to that of some other mammals. Series of differences are however detected concerning: the positive reaction for glucose-6-phosphatase in the A cells and in the epithelium of the excretory ducts, the simultaneous presence of alkaline phosphatase in the A and B cells, a higher contents of phospholipids in the B cells and a lack of histochemically provable zinc. These differences in the histochemistry of the pancreatic islets of cattle are in authors, opinion an expression of peculiarity of the species. 相似文献