Neural analogs of associative learning in {\it Aplysia\/}: Experimental and theoretical approaches

A change in synaptic strength arising from the activation of two neuronal pathways at approximately the same time is a form of associative plasticity and may underlie classical conditioning. Previously, a cellular analog of a classical conditioning protocol has been demonstrated to produce short-term associative plasticity at the connections between sensory and motor neurons in Aplysia. A similar training protocol produced long-term (24 hour) enhancement of excitatory postsynaptic potentials (EPSPs). EPSPs produced by sensory neurons in which activity was paired with a reinforcing stimulus were significantly larger than unpaired controls 24 hours after training. To examined whether the associative plasticity observed at these synapses may be involved in higher-order forms of classical conditioning, a neural analog of contingency was developed. In addition, computer simulations were used to analyze whether the associative plasticity observed in Aplysia could, in theory, account for second-order conditioning and blocking. ^

Molecular analysis of $\beta$1,4-galactosyl-transferase localization to the cell surface and participation in cell adhesion

$\beta$1,4-Galactosyltransferase (GalTase) is unusual among the glycosyltransferases in that it is found in two subcellular compartments where it performs different functions. In the trans-Golgi complex, GalTase participates in oligosaccharide biosynthesis as do other glycosyltransferases. GalTase is also found on the cell surface, where it associates with the cytoskeleton and functions as a receptor for extracellular oligosaccharide ligands. Although we know much regarding GalTase function on the cell surface, little is known about the mechanisms underlying its transport to the plasma membrane. Cloning of the GalTase gene revealed that there are two GalTase proteins (i.e., long and short) with different size cytoplasmic tails. This raises the possibility that differences in the cytoplasmic domain of GalTase may influence its subcellular distribution. The object of this study was to examine this hypothesis directly through the use of molecular, immunological, and biochemical approaches.^ To examine whether the two GalTase proteins are targeted to different subcellular compartments, F9 embryonal carcinoma cells were transfected with either long or short GalTase cDNAs and intracellular and cell surface enzyme levels measured. Cell surface GalTase activity was enriched in cells overexpressing the long, but not the form of short GalTase. Furthermore, a dominant negative mutation in cell surface GalTase was created by transfecting cells with GalTase cDNAs encoding a truncated version of long GalTase devoid of the extracellular catalytic domain. Overexpressing the complete cytoplasmic and transmembrane domains of long GalTase led to a loss of GalTase-dependent cellular adhesion by specifically displacing surface GalTase from its cytoskeletal associations. In contrast, overexpressing the analogous truncated protein of short GalTase had no effect on cell adhesion. Finally, chloramphenicol acetyltransferase (CAT) reporter proteins were used to determine directly whether the cytoplasmic domains of long and short GalTase were responsible for differential subcellular distribution. The cytoplasmic and transmembrane domains of long GalTase led to CAT expression on the ceil surface and its association with the detergent-insoluble cytoskeleton; the analogous fusion protein containing short GalTase was restricted to the Golgi compartment. These results suggest that the cytoplasmic domain unique to long GalTase is responsible for targeting a portion of this protein to the cell surface and associating it with the cytoskeleton, enabling it to function as a cell adhesion molecule. ^

TB research at UT-Houston--a review of cord factor: new approaches to drugs, vaccines and the pathogenesis of tuberculosis.

Tuberculosis remains a major threat as drug resistance continues to increase. Pulmonary tuberculosis in adults is responsible for 80% of clinical cases and nearly 100% of transmission of infection. Unfortunately, since we have no animal models of adult type pulmonary tuberculosis, the most important type of disease remains largely out of reach of modern science and many fundamental questions remain unanswered. This paper reviews research dating back to the 1950's providing compelling evidence that cord factor (trehalose 6,6 dimycolate [TDM]) is essential for understanding tuberculosis. However, the original papers by Bloch and Noll were too far ahead of their time to have immediate impact. We can now recognize that the physical and biologic properties of cord factor are unprecedented in science, especially its ability to switch between two sets of biologic activities with changes in conformation. While TDM remains on organisms, it protects them from killing within macrophages, reduces antibiotic effectiveness and inhibits the stimulation of protective immune responses. If it comes off organisms and associates with lipid, TDM becomes a driver of tissue damage and necrosis. Studies emanating from cord factor research have produced (1) a rationale for improving vaccines, (2) an approach to new drugs that overcome natural resistance to antibiotics, (3) models of caseating granulomas that reproduce multiple manifestations of human tuberculosis. (4) evidence that TDM is a key T cell antigen in destructive lesions of tuberculosis, and (5) a new understanding of the pathology and pathogenesis of postprimary tuberculosis that can guide more informative studies of long standing mysteries of tuberculosis.

Dielectrophoretic approaches to sample preparation and analysis

Dielectrophoresis (DEP) has been used to manipulate cells in low-conductivity suspending media using AC electrical fields generated on micro-fabricated electrode arrays. This has created the possibility of performing automatically on a micro-scale more sophisticated cell processing than that currently requiring substantial laboratory equipment, reagent volumes, time, and human intervention. In this research the manipulation of aqueous droplets in an immiscible, low-permittivity suspending medium is described to complement previous work on dielectrophoretic cell manipulation. Such droplets can be used as carriers not only for air- and water-borne samples, contaminants, chemical reagents, viral and gene products, and cells, but also the reagents to process and characterize these samples. A long-term goal of this area of research is to perform chemical and biological assays on automated, micro-scaled devices at or near the point-of-care, which will increase the availability of modern medicine to people who do not have ready access to large medical institutions and decrease the cost and delays associated with that lack of access. In this research I present proofs-of-concept for droplet manipulation and droplet-based biochemical analysis using dielectrophoresis as the motive force. Proofs-of-concept developed for the first time in this research include: (1) showing droplet movement on a two-dimensional array of electrodes, (2) achieving controlled dielectric droplet injection, (3) fusing and reacting droplets, and (4) demonstrating a protein fluorescence assay using micro-droplets. ^

A Path Forward: Evidence-Based Approaches to Educational Policy and Practice

In the complex landscape of public education, participants at all levels are searching for policy and practice levers that can raise overall performance and close achievement gaps. The collection of articles in this edition of the Journal of Applied Research on Children takes a big step toward providing the tools and tactics needed for an evidence-based approach to educational policy and practice.