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Seminars 2008

Energy Depletion Causes Endothelial Hyperpermeability in Hyperglycemia

Dr. Stewart Russell
Department of Biomedical Engineering
The City University of New York

Thursday, December 18, 11:30 AM
Schapiro Research Building

Diabetes is strongly correlated to an increased risk of cardiovascular disease (CVD). Reduced endothelial barrier function has been identified as a result of unregulated hyperglycemia in diabetes, and as risk factor in the development of atherosclerosis. Endothelial barrier dysfunction is measured by hyperpermeability to water and solutes, and by reduced dynamic response to a change in pressure. To investigate the relationship between endothelial dysfunction and high blood glucose we cultured bovine aortic endothelial cells (BAEC) in confluent monolayers on polycarbonate filters in a series of increasing glucose concentrations for use in a pressure-flow apparatus, with which we measured the hydraulic conductivity of water, and the convective and diffusive transport of low-density lipoprotein (LDL) through the monolayers in response to a 10-cmH2O transmural pressure gradient. The dynamic response of cells grown in high glucose was found to be significantly slower at physiological levels of hyperglycemia. Our results support the hypothesis that increased steady-state hydraulic conductivity and LDL permeability are strongly linked to ATP depletion independent of mechanism.


Modulation and migration of neural circuitry underlying reproductive functions

Dr. Siddharth Ramakrishnan
Department of Physiology

Friday, December 5, 11:00 AM
Interschool Lab, 750 CEPSR
Schapiro Research Building


Gonadotropin Releasing hormone (GnRH) neurons control reproduction and associated behaviors in most animals.This decapeptide has been conserved over evolution and has similar functions in organisms ranging from yeast to primates including humans. Here I present work from two different model systems to help us understand the role of GnRH neurons in circuit modulation and their migration over the course of development.

1. Central Pattern Generators (CPGs) are neural circuits that underlie rhythmic motor patterns controlling locomotion, feeding, etc. Some of these CPGs are multifunctional, i.e. they modulate the same set of muscles to execute different motor behaviors (e.g. walking vs. swimming vs. climbing stairs). Here I use the simple snail oral CPG to show that GnRH acts as a modulator that switches neural circuit output from feeding towards egg laying behavior. Simultaneous intracellular recordings from neurons and immunohistochemistry were used for this purpose.

2. GnRH neurons in the brain are born in the olfactory placode and move into the brain over the course of development. We have a transgenic line of zebrafish with GnRH neurons tagged with green fluoroscent protein that helps us understand this migration in a living intact embryo. We also show differences in electrical activity of these neurons using a patch clamp electrophysiology technique.


Time Correlated Photon Counting Instrumentation and Applications

Dr. Michael Wahl
PicoQuant GmbH
Berlin, Germany

Friday, November 14, 3:30 PM
Interschool Lab, 750 CEPSR
Schapiro Research Building

Time-Correlated Photon Counting (TCSPC) with multiple detector channels is an important tool in many applications over a growing range of vastly different disciplines. Despite many new developments in the recent past, existing instrumentation is often limited in its number of independent input channels. Solutions based on multiplexing several detectors into one timing channel provide input channels that are not truely independent, causing artifacts in correlation measurements and limiting applications with high count rates. On the other hand, parallel operation of complete TCSPC units, each with their own host computer interface, will result in multiple data streams arriving at the host computer. This causes complications in synchronization and real-time analysis of time-tagged photon data where the order and temporal relation of events across all channels is critical. Here we present recent advances in concept and technology leading to a new modular architecture allowing scalability in terms of the number of input channels, while using one common synchronization channel. Real-time sorting in hardware ensures delivering a single output data stream that contains time-tag records for all events from all inputs in correct temporal order, even at very high photon rates. Application results from Fluorescence Lifetime Imaging (FLIM) and new Single Molecule Spectroscopy (SMS) methods will be shown.


Biomedical instruments for patch-clamp recordings and voltage-sensitive dye imaging

Prof. Eugenio Culurciello
Electrical Engineering
Yale University

Thursday, October 30, 11:00 AM
Interschool Lab, 750 CEPSR
Schapiro Research Building

This talk has two components. First, I will present our work on integrated patch-clamp amplifiers for high-throughput screening of medical compounds. An integrated version of the patch-clamp amplifier not only reduces noise but also obtains better electrical performance, since cabling and parasitic capacitances that lower the measurement bandwidth are kept to a minimum. The integrated amplifier can be employed in high density parallel patch-clamp systems that would increase the throughput of drug testing in an effort to bring better and safer medicines to the consumer market. Second, I will present our work on voltage sensitive dye imaging systems for awake and freely moving animals. This device monitors fluorescent or intrinsic optical signals that reflect electrical, chemical or metabolic activity in the neural tissue. Our design innovates brain-machine interfaces by reducing the invasive and bias nature of traditional electrode array recording.


The effect of p-n junctions on quantum transport in graphene

Jimmy Williams
Department of Physics
Harvard University

Tuesday, October 14, 4:00 PM
Interschool Lab, 750 CEPSR
Schapiro Research Building

Recently, the ability to locally control the carrier density and type using the electric field effect in graphene has been reported. In order to realize clean bipolar graphene devices, care must be taken in controlling the graphene-local gate oxide interface. I will describe a method to create a functionalization layer on graphene that neither chemically dopes nor electrically degrades graphene, providing an ideal surface for subsequent local-gate oxide growth. Using these locally-gated graphene structures we study both the low and high magnetic field transport properties, demonstrating the ability to create a p (hole-like) region adjacent to an n (electron-like) region. In the quantum Hall regime, the presence of a p-n junction leads to unexpected plateaus in the conductance due to edge state mixing at the p-n interface. Finally, transport in devices where the majority of carriers approach the p-n interface at non-normal incidence is presented and its relationship to the Klein paradox and minimum conductivity problem in graphene is discussed.