Influence of ionic conductances on spike timing reliability of cortical neurons for suprathreshold rhythmic inputs

Spike timing reliability of neuronal responses depends on the frequency content of the input. We investigate how intrinsic properties of cortical neurons affect spike timing reliability in response to rhythmic inputs of suprathreshold mean. Analyzing reliability of conductance-based cortical model neurons on the basis of a correlation measure, we show two aspects of how ionic conductances influence spike timing reliability. First, they set the preferred frequency for spike timing reliability, which in accordance with the resonance effect of spike timing reliability is well approximated by the firing rate of a neuron in response to the DC component in the input. We demonstrate that a slow potassium current can modulate the spike timing frequency preference over a broad range of frequencies. This result is confirmed experimentally by dynamic-clamp recordings from rat prefrontal cortical neurons in vitro. Second, we provide evidence that ionic conductances also influence spike timing beyond changes in preferred frequency. Cells with the same DC firing rate exhibit more reliable spike timing at the preferred frequency and its harmonics if the slow potassium current is larger and its kinetics are faster, whereas a larger persistent sodium current impairs reliability. We predict that potassium channels are an efficient target for neuromodulators that can tune spike timing reliability to a given rhythmic input.     

Mechanism(s) promoting HIV-1 infection of primary unstimulated T lymphocytes in autologous B cell/T cell co-cultures

Resting CD4(+) T cells in the lymphoid tissue (LT) are essential producers of virions at the beginning of HIV infection in vivo. We previously developed a model that allowed in vitro infection of non-prestimulated T lymphocytes in the presence of autologous B lymphocytes and complement. In this study, we try to clarify the mechanism(s) responsible for virus transmission in unstimulated autologous B cell/T cell co-cultures. Ex vivo analyses of patient plasma samples revealed that HIV was opsonized. Flow cytometry showed that opsonized virus preferentially bound to complement receptor (CR)-2 on B lymphocytes in primary B cell/T cell co-cultures. As indicated by cytokine measurements and transwell experiments, soluble factors seemed to play a minor role in enabling infection. Rather, direct interaction between B and T lymphocytes and direct binding of opsonized virus to CR2 on B cells turned out to be essential for productive infection. Antibodies blocking cell-cell adhesion inhibited p24 antigen production. An anti-CR2 antibody blocking C3d-CR2 binding also significantly reduced viral replication. Since the infection of unstimulated T cells by opsonized primary HIV isolates in the presence of B cells was highly efficient independent of the tropism of the virus, this mechanism may be critical in the pathogenesis of HIV.     

Lymphocyte transformation and production of a human mononuclear leucocyte chemotactic factor in patients with Hodgkin''s disease

Human peripheral lymphocytes stimulated in vitro with phytohaemagglutinin (PHA) produce a factor with chemotactic activity for homologous monocytes. The production of this factor and lymphocyte transformation was investigated in patients with Hodgkin's disease. It has been found that the PHA response as measured by incorporation of [³H]thymidine was markedly depressed in patients when compared to the response of normal lymphocytes. In contrast, the production of the chemotactic factor was not significantly depressed in patients with Hodgkin's disease.     

Interaction of Angiotensin with Disseminated Intravascular Coagulation: A Possible Mechanism in the Genesis of Acute Renal Failure

Because of the importance of the renin-angiotensin system in renal homeostatic mechanisms, the effect of angiotensin administration upon disseminated intravascular coagulation has been studied in rabbits. An infusion of angiotensin II (0.1 μg/kg/min for 2 hours) produced neither histologic abnormalities in the kidneys nor an elevation of creatinine. After an infusion of thrombin (2.0 units/kg/min for 2 hours) only 3 of 10 rabbits, when sacrified 24 hours later, showed histologic lesions comprised of occasional fibrin thrombi and foci of tubular necrosis. Creatinine levels did not rise. In contrast, the combination of angiotensin and thrombin resulted in renal lesions in 12 of 14 animals. Four had frank cortical necrosis, while combinations of tubular necrosis, glomerular thrombosis and segmental glomerular infarction occurred in the others, together with elevated creatinine levels. Blockade of α-adrenoreceptors with phenoxybenzamine in 12 animals did not prevent either these histologic changes or creatinine elevation, showing that the effect of angiotensin was independent of α-adrenoreceptor stimulation. The synergistic interaction between angiotensin and disseminated intravascular coagulation was not explained by differences in the consumption of plasma fibrinogen but apparently was due to localization of fibrin thrombi within glomerular capillaries by the vasomotor actions of angiotensin, as has previously been shown to occur with α-adrenoreceptor simulation. Such a mechanism might contribute to renal glomerular deposition of fibrin in acute ischemic renal failure.     

Recombinant allergens promote expression of CD203c on basophils in sensitized individuals

BACKGROUND: Traditionally, the diagnosis of type I allergies is based on clinical data, skin test results, and laboratory test results with allergen extracts. During the past few years, several attempts have been made to refine diagnostic assays in clinical allergy by introducing recombinant allergens and novel markers of IgE-dependent cell activation. OBJECTIVES: We have identified the ectoenzyme CD203c as a novel basophil antigen that is upregulated on IgE receptor cross-linkage. In this study we applied CD203c and a panel of recombinant allergens to establish a novel basophil test that allows for a reliable quantification of IgE-dependent responses at the effector cell level. METHODS: Patients allergic to birch (Bet v 1, n = 15; Bet v 2, n = 8) and grass (Phl p 1, n = 15; Phl p 2, n = 10; Phl p 5, n = 14) pollen allergens, as well as 10 nonallergic donors, were examined. Basophils were exposed to various concentrations of recombinant allergens for 15 minutes and then examined for expression of CD203c by means of flow cytometry. CD203c upregulation was correlated with the increase in CD63. RESULTS: Exposure to recombinant allergens resulted in a dose-dependent increase in expression of CD203c on peripheral blood basophils in sensitized individuals, whereas no increase was seen in healthy control subjects. The effects of the recombinant allergens on CD203c expression were also time dependent. There was a good correlation between allergen-induced upregulation of CD203c and upregulation of CD63 (R = 0.76). CONCLUSION: Flow cytometric quantitation of CD203c on blood basophils exposed to recombinant allergens is a useful approach to determine the allergic state in sensitized individuals and represents a basis for a sensitive novel allergy test.     

Complement-mediated enhancement of HIV-1 neutralisation by anti-HLA antibodies derived from polytransfused patients

We have recently shown that 'alloimmune sera' derived from polytransfused patients (PTP sera) are able to recognise and neutralise HIV in vitro. In this study we try to identify the protein(s), which are recognised by the PTP sera and elucidate mechanisms responsible for the neutralising capacity of these sera. The PTP sera allowed immunoprecipitation (IP) of HLA class II molecules on HIV-infected cells. To detect a potential cross-reactivity of alloreactive antibodies (Ab) with the HIV envelope protein gp160 or its subunits gp120/gp41 and HLA proteins, ELISA and FACS analyses were performed. The lack of reactivity of the PTP sera against rsgp160 in ELISA or FACS analysis indicated that recognition of cells was independent of HIV infection. To clarify whether interaction of the PTP sera with target cells has any effect on the infection process, virus neutralisation assays were performed. Inhibition of HIV infection was observed only when virus was pre-incubated with the PTP sera. Complement enhanced neutralisation of HIV-1 significantly. This enhancement was not due to complement-mediated lysis, because pre-incubation of the target cells with PTP sera did not inhibit HIV replication. Therefore, the neutralising effect of the Ab was due to blocking of the viral attachment/fusion process and not to negative signalling after infection. Since steric hindrance is possible only when HLA and gp120/gp41 are in close vicinity, isolation of rafts and IP assays were performed. These experiments revealed that gp120 and MHC class II molecules are indeed co-localised. The close physical association of gp120/gp41 and HLA strongly supports a mechanism for neutralisation of HIV by anti-HLA-Ab based on steric hindrance.     

Using literature-based discovery to identify disease candidate genes

We present BITOLA, an interactive literature-based biomedical discovery support system. The goal of this system is to discover new, potentially meaningful relations between a given starting concept of interest and other concepts, by mining the bibliographic database MEDLINE. To make the system more suitable for disease candidate gene discovery and to decrease the number of candidate relations, we integrate background knowledge about the chromosomal location of the starting disease as well as the chromosomal location of the candidate genes from resources such as LocusLink and Human Genome Organization (HUGO). BITOLA can also be used as an alternative way of searching the MEDLINE database. The system is available at http://www.mf.uni-lj.si/bitola/.     

Mouse macrophage development in the absence of the common γ chain: defining receptor complexes responsible for IL-4 and IL-13 signaling

The common γ chain (γ_c) forms a critical component of the receptors for interleukins (IL)-2, IL-4, IL-7, IL-9, and IL-15. We analyzed γ_c-deficient mice to define a role for γ_c signaling in the development and function of the macrophage lineage. No major differences in absolute cell numbers, cell surface phenotype, or in vitro function of γ^?_c compared to γ⁺_c macrophages were observed. We therefore conclude that signaling through the γ_c chain is not essential for the differentiation of mouse macrophages. Although B and T cells require γ_c for IL-4 responses, IL-4 up-regulated major histocompatibility class II molecules and inhibited nitric oxide production from γ^?_c macrophages following stimulation with lipopolysaccharide and interferon-γ. γ^?_c macrophages could also respond to IL-13, consistent with the model of a type II IL-4 receptor α/IL-13R which can function in the absence of γ_c. Both IL-4 and IL-13 responses could be completely inhibited with the mouse IL-4 antagonist QY, suggesting that all of the observed IL-13 responses pass through the type II receptor, making it the primary signaling receptor complex for IL-13 in mouse macrophages.     

Secretion of kallikrein and its role in vasodilatation in the submaxillary gland

1. The effects of parasympathetic (chorda) and sympathetic nerve stimulation on the concentration and output of kallikrein secreted in saliva from the cat's submaxillary gland were compared. Sympathetic stimulation always produced a much higher concentration (up to 500 times) and output (up to 390 times) of kallikrein than parasympathetic stimulation. In the dog, in which sympathetic nerve stimulation produces little or no secretion from the submaxillary gland, there was also a marked increase in the secretion of kallikrein when sympathetic was superimposed on parasympathetic secretion. This effect did not occur, however, in the rabbit's submaxillary gland.2. It was possible to deplete the cat's submaxillary gland of kallikrein, either by ligation of the duct for several days or by duct ligation and sympathetic nerve stimulation, so that it was undetectable either in the gland or in saliva after stimulation of the chorda. Such glands, nevertheless, responded to chorda stimulation with a normal atropine-resistant vasodilatation.3. There is a close parallelism between the rate of secretion of salvia and vasodilatation over a range of frequencies of chorda stimulation, but the output (and concentration) of kallikrein in saliva is distinctly different for the same frequencies of nerve stimulation.4. Our results are consistent with the view that vasodilator nerves exist in the parasympathetic nerves to the submaxillary gland. We suggest that they are cholinergic in nature despite the fact that chorda vasodilatation is resistant to atropine. It is further suggested that neither the kallikrein-kinin system nor adrenergic vasodilator nerve fibres play a significant role in chorda vasodilatation.