Vergleich zweier Modelle für laterale Inhibition

Summary Two semi-linear models for lateral inhibition are discussed. The interaction between receptor units is assumed to be linear, as demonstrated by Hartline and Ratliff in the eye of the horseshoe crab Limulus polyphemus. Yet a model of such an inhibitory system must be nonlinear, since the output values correspond to nerve activities, which cannot be negativ. Models with forward inhibition were used often to describe contrast phenomena in the human nervous system. However, in order to simulate the input-output relation in systems similar to the eye of Limulus, a model with backward inhibition must be constructed. Two important properties of backward inhibition not shared by forward inhibition are: (1) Inhibition in a receptor unit has an influence upon its excitation, as well as upon its ability to inhibit other units (Disinhibition). (2) The range of interaction between sensory units is not necessarily the same as the range of direct cross connections. It is shown in this paper, that also forward inhibition may possess these two properties, provided that it is repeated on subsequent levels. Some properties of systems with backward and forward inhibition are studied and compared in models consisting of three units. The input-output relation for large systems with backward inhibition was calculated under special assumptions concerning the inhibitory coefficients. If the inhibitory coefficients in a system with backward inhibition decrease like a power series, as a function of the distance between receptor units, only neighboring receptors have an effect upon each other. That is, in an equivalent system with forward inhibition the inhibitory interaction is confined to neighbouring receptors. Conversely, when backward inhibition exists only between neighbouring receptors, the inhibitory coefficients in an equivalent system with forward inhibition are described, as a function of the distance between the receptor units, by a power series with alternating sign.     

Enzymatic transformations of morphinane alkaloids

Horseradish peroxidase transforms morphinane alkaloids into N-oxides and morphine to pseudomorphine in the presence of hydrogen peroxide. The crude poppy enzyme fraction shows the same activities. The rates of reactions were influenced by phenolic compounds and their relation controlled by the concentration of hydrogen peroxide and the presence of ascorbic acid.     

The effect of continuous human lymphokine treatment on skin graft rejection in mice.

Continuous intraperitoneal treatment with human lymphokines produced by Con-A stimulated peripheral human lymphocytes caused the acceleration of skin graft rejection in mice.     

Ions and Inhibitors in the Binding Site of HIV Protease: Comparison of Monte Carlo Simulations and the Linearized Poisson-Boltzmann Theory

Proteins can be influenced strongly by the electrolyte in which they are dissolved, and we wish to model, understand, and ultimately control such ionic effects. Relatively detailed Monte Carlo (MC) ion simulations are needed to capture biologically important properties of ion channels, but a simpler treatment of ions, the linearized Poisson-Boltzmann (LPB) theory, is often used to model processes such as binding and folding, even in settings where the LPB theory is expected to be inaccurate. This study uses MC simulations to assess the reliability of the LPB theory for such a system, the constrained, anionic active site of HIV protease. We study the distributions of ions in and around the active site, as well as the energetics of displacing ions when a protease inhibitor is inserted into the active site. The LPB theory substantially underestimates the density of counterions in the active site when divalent cations are present. It also underestimates the energy cost of displacing these counterions, but the error is not consequential because the energy cost is less than k_BT, according to the MC calculations. Thus, the LPB approach will often be suitable for studying energetics, but the more detailed MC approach is critical when ionic distributions and fluxes are at issue.     

A case of central nervous system atypical teratoid / rhabdoid tumor

The atypical teratoid / rhabdoid tumour is a rare type of tumours of central nervous system appearing usually under 2 years of age, bearing a rather bad prognosis and it may cause serious differential diagnostic problem. The tumour is characterized histologically by the presence of the rhabdoid cells, immunohistochemically by vimentin, SMA, EMA positivity, the frequent presence of cytokeratin, GFAP positivity, but germ cell markers: AFP, hCG negativity, cytogenetically by aberrations of chromosome 22. The case of a one and half month old female infant is presented, who died 8 months after the appearance of the first symptoms. The diagnostic possibilities and the unsolved problem of the therapy are discussed.     

Imaging of pediatric brain tumors using somatostatin analogue 111Ih-DTPA-D-Phe1-octreotide

Malignant solid tumors and leukemias are the second most common causes of death in childhood. The most frequent pediatric solid tumors are brain tumors. Brain tumors, especially medulloblastoma should be treated by surgery, irradiation and chemotherapy. However, chemotherapy has only moderate effect. Pediatric brain tumors, especially medulloblastomas, express somatostatin receptors. The aim of this study was the investigation of the expression of somatostatin receptors in pediatric brain tumors for diagnostic and therapeutic purpose. Fifty-six scintigraphic imagings (111In-DTPA-D-Phe1-octreotide) made in 45 children treated with brain tumor at the Unit of Oncology of the 2nd Department of Pediatrics, Semmelweis University. The diagnosis was medulloblastoma in 21 cases (46.7%). MRI scans have been performed parallel with the Octreoscan images. Octreoscan images were positive in 27 of 56 (48.2%) cases. The 27 positive Octreoscan images consisted of 16 medulloblastomas, 4 ependymomas, 4 astrocytomas and 3 glioblastomas. In 37 (66.1%) cases the results of Octreoscans were the same as those of the MRI scans. However, in 19 scans (33.9%) the outcome was different. Octreoscan imaging is not suitable for differential diagnosis in pediatric brain tumors, including medulloblastomas. Isotopes specifically binding to the somatostatin receptors (111In-DTPA-D-Phe1-octreotide) can be applied in medulloblastomas for diagnosis and follow-up treatment. In Octreoscan-positive tumors the Octreoscan images establish the opportunity to somatostatin analogue and/or specifically targeted radiation therapies.     

Triiodothyronine accelerates differentiation of rat liver progenitor cells into hepatocytes

The 2-acetaminofluorene/partial hepatectomy (AAF/Phx) model is widely used to induce oval/progenitor cell proliferation in the rat liver. We have used this model to study the impact of a primary hepatocyte mitogen, triiodothyronine (T3) on the liver regenerating by the recruitment of oval/progenitor cells. Administration of T3 transiently accelerates the proliferation of the oval cells, which is followed by rapid differentiation into small hepatocytes. The oval cell origin of the small hepatocytes has been proven by tracing retrovirally transduced and BrdU marked oval cells. The differentiating oval cells become positive for hepatocyte nuclear factor-4 and start to express hepatocyte specific connexin 32, α1 integrin, Prox1, cytochrom P450s, and form CD 26 positive bile canaliculi. At the same time oval cell specific OV-6 and alpha-fetoprotein expression is lost. The upregulation of hepatocyte specific mRNAs: albumin, tyrosine aminotransferase and tryptophan 2,3-dioxygenase detected by real-time PCR also proves hepatocytic maturation. The hepatocytic conversion of oval cells occurs on the seventh day after the Phx in this model while the first small hepatocytes appear 5 days later without T3 treatment. The administration of the primary hepatocyte mitogen T3 accelerates the differentiation of hepatic progenitor cells into hepatocytes in vivo, and that may have therapeutic potential. Supported by OTKA T 42674 and ETT 32/2006.     

Phytochemical and pharmacological investigation of <Emphasis Type="Italic">Spiraea chamaedryfolia</Emphasis>: a contribution to the chemotaxonomy of <Emphasis Type="Italic">Spiraea</Emphasis> genus

Objective

Diterpene alkaloids are secondary plant metabolites and chemotaxonomical markers with a strong biological activity. These compounds are characteristic for the Ranunculaceae family, while their occurrence in other taxa is rare. Several species of the Spiraea genus (Rosaceae) are examples of this rarity. Screening Spiraea species for alkaloid content is a chemotaxonomical approach to clarify the classification and phylogeny of the genus. Novel pharmacological findings make further investigations of Spiraea diterpene alkaloids promising.

Results

Seven Spiraea species were screened for diterpene alkaloids. Phytochemical and pharmacological investigations were performed on Spiraea chamaedryfolia, the species found to contain diterpene alkaloids. Its alkaloid-rich fractions were found to exert a remarkable xanthine-oxidase inhibitory activity and a moderate antibacterial activity. The alkaloid distribution within the root was clarified by microscopic techniques.

     

The interaction between visual edge fixation and skototaxis in the mealworm beetle Tenebrio molitor

Summary (1) It has been shown in earlier experiments that during the visually guided orientation response of the mealworm beetle,Tenebrio molitor, edge fixation and skototaxis interact. Under certain stimulus conditions these two effects act against each other and relative movement between the retina and the surroundings shifts the balance in favour of edge fixation. In this paper, three further parameters are described which change the contribution of the two mechanisms to the turning tendency of the animals. (2) When the centre of a broad black stripe lies on one side and one of the edges on the other side of the animal (Fig. 1B, C) then motion of an edge from front to back (progressive movement) more effectively increases the relative weight of edge fixation than do regressive movements (motion of an edge from back to front). (3) In the same situation temporal modulation of the overall illumination weakens skototaxis, dimming more than brightening (Fig. 2 A). From this it was predicted — and confirmed — that the dependence on the direction of motion will be reversed if both the centre and the edge closest to the midline of a broad black stripe lie on the same side of the animal (Fig. 2 B). (4) Animals with one eye blinded can fixate an edge (Fig. 3). Furthermore, edge fixation is mediated mainly by the ventral part of the eyes and skototaxis by the dorsal (Fig. 5). (5) The possible significance of the results for the animal's natural behaviour and for the underlying neural circuitry is discussed.     

Pupillenreaktionen auf sinusförmige Leuchtdichteänderungen

Summary Nonlinear properties of the human pupillary light reflex have been studied using binocular light stimuli of sinusoidally varying intensity. As reported earlier, the pupil responds with a net contraction to the modulation of the light intensity within a wide range of modulation frequencies. Results of the present experiments show that the net contraction does not depend upon the relative phase difference of the binocular light stimuli. However in the lower frequency range, where the in-phase stimuli result in a periodic light reflex, the out-of-phase stimuli fail to do so. These results allow certain conclusions to be drawn regarding the localisation within the photopupil reflex arc of the nonlinearities involved.