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Biomedical subjects

M Zak

Publications and source records attributed to M Zak.

25 records · Page 2Linked to original sources

Creative dynamics approach to neural intelligence.

The thrust of this paper is to introduce and discuss a substantially new type of dynamical system for modelling biological behavior. The approach was motivated by an attempt to remove one of the most fundamental limitations of artificial neural networks-their rigid behavior compared with even simplest biological systems. This approach exploits a novel paradigm in nonlinear dynamics based upon the concept of terminal attractors and repellers. It was demonstrated that non-Lipschitzian dynamics based upon the failure of Lipschitz condition exhibits a new qualitative effect--a multi-choice response to periodic external excitations. Based upon this property, a substantially new class of dynamical systems--the unpredictable systems--was introduced and analyzed. These systems are represented in the form of coupled activation and learning dynamical equations whose ability to be spontaneously activated is based upon two pathological characteristics. Firstly, such systems have zero Jacobian. As a result of that, they have an infinite number of equilibrium points which occupy curves, surfaces or hypersurfaces. Secondly, at all these equilibrium points, the Lipschitz conditions fails, so the equilibrium points become terminal attractors or repellers depending upon the sign of the periodic excitation. Both of these pathological characteristics result in multi-choice response of unpredictable dynamical systems. It has been shown that the unpredictable systems can be controlled by sign strings which uniquely define the system behaviors by specifying the direction of the motions in the critical points. By changing the combinations of signs in the code strings the system can reproduce any prescribed behavior to a prescribed accuracy.(ABSTRACT TRUNCATED AT 250 WORDS)

Artificial Intelligence↗

Aminoglutethimide-stimulated corticotrophs. An immunocytologic, ultrastructural and immunoelectron microscopic study of the rat adenohypophysis.

Thirty-six rats of both sexes in two groups were treated with aminoglutethimide (AG), a steroid synthesis inhibitor, for 1 and 8 weeks respectively. The anterior pituitaries were investigated by light and electron microscopy, the techniques used including immunocytochemical and morphometric methods. Corticotrophs were identified by the avidinbiotin-peroxidase complex technique at the light and electron microscopic levels. AG administration resulted in hyperplasia of ACTH-containing cells. The increase in the volume density of corticotrophs was prevented by simultaneous medication with 3 mg corticosterone in male rats, whereas in female rats a larger dose of corticosterone was required to suppress pituitary corticotroph hyperplasia. Electron microscopy revealed that in AG-treated rats, corticotrophs were larger and contained more secretory granules than those in controls, the mean secretory granule diameter increasing from 100 nm to 165 nm. Under AG stimulation, corticotrophs showed considerable variations in structural features probably reflecting differences in their functional state. It was apparent that only one ACTH-producing cell type existed in the pars distalis of the rat adenohypophysis, although this cell type may undergo substantial morphologic alterations due to changes in endocrine activity. Gonadotrophs and thyrotrophs showed morphologic signs of stimulation and exhibited hyperplasia following AG treatment indicating that the effect of the drug was not restricted to corticotrophs.

Adrenal Glands↗

An assay of biological dosimetry from the changed number of lymphocytes and hypersegmented neutrophiles evaluated by means of statistical decision method.

The paper presented deals with the statistical utilization of changes in lymphocyte and hypersegmented neutrophiles counts in peripheral blood after irradiation for the biological detection of ionizing radiation. Both followed-up parameters are in a good correlation during simultaneous evaluation of their changes, and they fail during evaluation in various time intervals after irradiation. The changes of two hematological parameters after irradiation, lymphopenia and hypersegmentation of cellular nuclei of granulocytes were therefore utilized. The changes under examination were elaborated in the computer and avaluated by method of regression classification and by discriminatory analysis. This analytical way enables a new conception during the evaluation of individual hematological post-irradiation changes. This study is being continued in several lines. On the one hand, further statistical methods of making the results more precise will be used, on the other hand, other laboratory animals will be tested as well. Last but not least, the best statistical method will be used in an attempt to detect biologically the changes after the therapeutical irradiation in man.

Animals↗

Interleukin-1 receptor antagonist in neonates, children and adults, and in patients with pauci- and polyarticular onset juvenile chronic arthritis.

OBJECTIVE: The production of interleukin (IL) -1 alpha IL-1 beta and IL-1 receptor antagonist (IL-1ra) by blood mononuclear cells (MNC), as well as the corresponding serum levels of IL-1ra were examined in blood samples from umbilical cords (n = 11), children (n = 40) and adults (n = 20), and in 42 patients with juvenile chronic arthritis (JCA) of the pauci- or polyarticular onset type. RESULTS: IL-1ra serum levels were found to differ significantly between the three age groups, being higher in neonates (569 pg/ml) than in children (70 pg/ml) and adults (177 pg/ml). IL-1ra production in E. coli lipopolysacharide (LPS) stimulated-cultures of MNC was also significantly higher in neonates (median 2451 pg/ml) than in children (1526 pg/ml), but similar to that in adults (2107 pg/ml). IL-1ra levels in the sera of both subgroups of JCA patients were significantly elevated (median 257 pg/ml), but did not reflect paraclinical or clinical disease parameters. In samples of synovial fluid the IL-1ra levels tended to be fairly high, up to approximately 2 ng/ml, but they did not reflect the serum levels of IL-1ra. CONCLUSION: These findings suggests that the upregulation of IL-1ra production forms part of the immunoregulatory response in JCA patients, and that the insufficient production of IL-1ra is unlikely to contribute to the pathogenesis of JCA.

Adolescent↗