Classical conditioning with electrical stimulation of cerebellum as both conditioned and unconditioned stimulus.

Stimulating electrodes were implanted in rabbit cerebellum, providing an electrical conditioned stimulus (CS) activating cortical parallel fibers and thence Purkinje and other cells, and an electrical unconditioned stimulus (US) activating underlying white matter and eliciting unconditioned responses. Paired CS-US presentations led to the development of conditioned responses, which showed extinction following CS-alone trials and reacquisition with significant savings on reinstatement of paired trials. Increased local excitability as a result of paired training (but not following unpaired stimulus presentations) was observed in cerebellar cortex, as manifested in substantial decreases in CS threshold for response elicitation in all subjects. This preparation offers a model for the study of plastic neuronal interactions within cerebellar networks critically involved in associative learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Leveraging information technology to achieve the IT2000 vision: the case study of an intelligent island

Although many developing and developed countries have major initiatives to promote the use of information technology (IT), Singapore is one of the few countries which not only has a comprehensive IT2000 vision, but which is also taking proactive steps to make the vision a reality. This paper examines how Singapore is currently leveraging IT applications to achieve the IT2000 vision. It also explores some of the uses of IT that will be deployed in the near future. Specifically, this paper discusses the use of IT applications to provide one-stop, non-stop government and business services, promote cashless transactions, provide more options for leisure, and facilitate easy commuting.     

Epidemiology of bluetongue in Central America and the Caribbean: initial entomological findings. Regional Bluetongue Team

Forty-four species of Culicoides (Diptera: Ceratopogonidae) were caught in insect light traps during the first 2 years of studies on the epidemiology of bluetongue virus in the Caribbean and Central America. Traps were operated near sentinel ruminants which were bled monthly for serologic evaluation and then virus isolation. More than 570,000 individuals were identified. Culicoides insignis Lutz accounted for 90% of the catch, C. filarifer Hoffman/C. ocumarensis Ortiz 5%, C. furens Poey 3% and C. pusillus Lutz 2%. Other species accounted for less than 1% of the total catch. Sentinel ruminants became seropositive when C. insignis populations were high at many study sites. At a few sites C. pusillus and C. filarifer/C. ocumarensis were predominant or were present in large numbers during seroconversions of sentinels. Virus isolations were obtained from sentinel ruminants during times when these same species were present in large populations.     

SPARC/osteonectin induces matrix metalloproteinase 2 activation in human breast cancer cell lines

Activation of the matrix metalloproteinase 2 (MMP-2) has been shown to play a major role in the proteolysis of extracellular matrix (ECM) associated with tumor invasion. Although the precise mechanism of this activation remains elusive, levels of the membrane type 1-MMP (MT1-MMP) at the cell surface and of the tissue inhibitor of MMP-2 (TIMP-2) appear to be two important determinants. Induction of MMP-2 activation in cells cultivated on collagen type I gels indicated that the ECM is important in the regulation of this process. In this study, we show that SPARC/osteonectin, a small ECM-associated matricellular glycoprotein, can induce MMP-2 activation in two invasive breast cancer cell lines (MDA-MB-231 and BT549) but not in a noninvasive counterpart (MCF-7), which lacks MT1-MMP. Using a set of peptides from different regions of SPARC, we found that peptide 1.1 (corresponding to the NH2-terminal region of the protein) contained the activity that induced MMP-2 activation. Despite the requirement for MT1-MMP, seen in MCF-7 cells transfected with MT1-MMP, the activation of MMP-2 by SPARC peptide 1.1 was not associated with increased steady-state levels of MT1-MMP mRNA or protein in either MT1-MMP-transfected MCF-7 cells or constitutively expressing MDA-MB-231 and BT549 cells. We did, however, detect decreased levels of TIMP-2 protein in the media of cells incubated with peptide 1.1 or recombinant SPARC; thus, the induction of MMP-2 activation by SPARC might be due in part to a diminution of TIMP-2 protein. We conclude that SPARC, and specifically its NH2-terminal domain, regulates the activation of MMP-2 at the cell surface and is therefore likely to contribute to the proteolytic pathways associated with tumor invasion.     

Basin boundary metamorphoses in the canonical escape equation

A study is made of the escape boundary, in the space of the starting values of displacement and velocity, for a sinusoidally driven nonlinear oscillator. The oscillator has constant inertia and linear viscous damping, with a restoring force that corresponds to a cubic potential well. This cubic form of the total potential energy has the universal canonical form encountered by all metastable mechanical systems as they approach a generic fold catastrophe under a single control parameter. The basin boundary metamorphoses are observed, and an engineering integrity diagram is proposed, quantifying the rapid erosion of area that is triggered under increasing excitation by a homoclinic tangency. The pictures show clearly the fractal basin associated with the developed homoclinic tangle. The boundary crisis, at which the final chaotic attractor loses its stability, is examined in terms of an accessible saddle point, which is here a directly unstable subharmonic of order six.     

Intestinal cell cycle regulations. Interactions of cyclin D1, Cdk4, and p21Cip1

OBJECTIVE: The p21Cip1 protein is a potent stoichiometric inhibitor of cyclin-dependent kinase activity, and p21Cip1 mRNA expression is localized to the nonproliferative compartment of the intestinal villus, suggesting an in vivo growth-inhibitory role in the gut. The authors determined whether nontransformed rat intestinal epithelial cells (IECs) underwent reversible cell cycle arrest by contact inhibition, and determined whether increases in the relative amount of p21 associated with cyclin D/Cdk4 protein complexes were associated with cell growth arrest. METHODS: Density arrest was achieved by prolonged culture IEC-6 in confluent conditions (5 or more days). Release from density arrest was achieved by detaching the cells from the culture plate and reseeding them at a 1:4 ratio. The DNA synthesis was estimated by [3H]-thymidine incorporation and expressed as mean plus or minus standard error of the mean (n = 4). Cyclin D1, Cdk4, and p21 mRNA and protein levels were determined by standard Northern and Western blot analyses, respectively. Cyclin D1, Cdk4, and p21 protein complex formation was analyzed by immunoprecipitating the complexes from cell lysates with an antibody to one of the constituents, followed by SDS polyacrylamide gel electrophoresis (SDS-PAGE) and Western blot analysis of the precipitated complexes using antibodies to the other proteins. The kinase activity of the immunoprecipitated Cdk4 was determined using recombinant Rb as substrate. RESULTS: The IEC-6[3H]-thymidine incorporation was decreased 7.5-fold from day 1 confluence to day 7 of confluence. Twenty-four hours after release from density arrest, there was a 43-fold increase in [3H]-thymidine incorporation. Cyclin D1 and Cdk4 mRNA levels remained relatively constant during contact inhibition, whereas immunoblotting showed that the levels of cyclin D1 and Cdk4 proteins decreased by 70.9% and 68.7%, respectively, comparing day 3 with day 9 during density arrest. The levels of cyclin D1 increased 5.8-fold and Cdk4 increased by 4.4-fold by 24 hours after reseeding the day 9 density-arrested cultures, coincident with the increase in DNA synthesis. The amount of p21 associated with the cyclin D1 and Cdk4 complex in the density-arrested cells was 170% of that observed in the reseeded, proliferating cells. More important, the p21::Cdk4 ratio was 6.4-fold higher in the density-arrested (quiescent) cells as compared with rapidly proliferating cells by 24 hours after release from growth arrest. Recovery of Cdk4-dependent kinase activity occurred by 4 hours after release from growth arrest, coincident with decreased binding of p21 to the complex. CONCLUSIONS: Intestinal epithelial cells in culture can undergo density-dependent growth arrest. This process involves downregulation of cyclin D1 and Cdk4 at the level of protein expression, whereas the mRNA levels remain relatively unchanged. Further, during contact inhibition, there is more p21 associated with cyclin D1/Cdk4, which further contributes to the inhibition of the kinase complex. The authors also have shown that the process of contact inhibition is reversible, which may explain partly the ability of the intestinal epithelium to increase proliferative activity in response to injury.