Gi Ja Lee

Microdialysis applications in neuroscience

Abstract Background: Microdialysis is a technique to monitor extracellular changes in living tissue. Substances present in the extracellular space, such as neurotransmitters and metabolites transported between cells and capillaries in the extracellular fluid (ECF), are major object. Results: Since its introduction to the research of the nervous system, microdialysis has become a popular method for the measurements of brain chemistry and greatly affected in the fields of neuropharmacology, neuroanatomy and neurophysiology. Most of published papers using microdialysis have focused on the area of neuroscience, recently more biomedical application. Conclusion: In this review, we focused on cerebral microdialysis as a monitoring tool for physiologic and pathophysiologic changes in chemical processes in the brain. Then we presented the principle and various applications of cerebral microdialysis.

The effect of extracellular glutamate release on repetitive transient ischemic injury in global ischemia model.

During operations, neurosurgeons usually perform multiple temporary occlusions of parental artery, possibly resulting in the neuronal damage. It is generally thought that neuronal damage by cerebral ischemia is associated with extracellular concentrations of the excitatory amino acids. In this study, we measured the dynamics of extracellular glutamate release in 11 vessel occlusion (VO) model to compare between single occlusion and repeated transient occlusions within short interval. Changes in cerebral blood flow were monitored by laser-Doppler flowmetry simultaneously with cortical glutamate level measured by amperometric biosensor. From real time monitoring of glutamate release in 11 VO model, the change of extracellular glutamate level in repeated transient occlusion group was smaller than that of single occlusion group, and the onset time of glutamate release in the second ischemic episode of repeated occlusion group was delayed compared to the first ischemic episode which was similar to that of single 10 min ischemic episode. These results suggested that repeated transient occlusion induces less glutamate release from neuronal cell than single occlusion, and the delayed onset time of glutamate release is attributed to endogeneous protective mechanism of ischemic tolerance.

Investigation of aging effects in human hair using atomic force microscopy

Background: A thorough characterization of the morphological structure and physical properties is essential for an understanding of human hair. A number of techniques such as scanning electron microscopy, transmission electron microscopy and confocal microscopy have been used to study hair surfaces. Recently, atomic force microscopy (AFM) has emerged as an ideal method for the non‐invasive examination of hair surfaces.

Enhanced biocompatibility and wound healing properties of biodegradable polymer-modified allyl 2-cyanoacrylate tissue adhesive.

As poly L-lactic acid (PLLA) is a polymer with good biocompatibility and biodegradability, we created a new tissue adhesive (TA), pre-polymerized allyl 2-cyanoacrylate (PACA) mixed with PLLA in an effort to improve biocompatibility and mechanical properties in healing dermal wound tissue. We determined optimal mixing ratios of PACA and PLLA based on their bond strengths and chemical structures analyzed by the thermal gravimetric analysis (TGA) and Fourier transform infrared (FT-IR) spectroscopy. In vitro biocompatibility of the PACA/PLLA was evaluated using direct- and indirect-contact methods according to the ISO-10993 cytotoxicity test for medical devices. The PACA/PLLA have similar or even better biocompatibility than those of commercially available cyanoacrylate (CA)-based TAs such as Dermabond® and Histoacryl®. The PACA/PLLA were not different from those exposed to Dermabond® and Histoacryl® in Raman spectra when biochemical changes of protein and DNA/RNA underlying during cell death were compared utilizing Raman spectroscopy. Histological analysis revealed that incised dermal tissues of rats treated with PACA/PLLA showed less inflammatory signs and enhanced collagen formation compared to those treated with Dermabond® or Histoacryl®. Of note, tissues treated with PACA/PLLA were stronger in the tensile strength compared to those treated with the commercially available TAs. Therefore, taking all the results into consideration, the PACA/PLLA we created might be a clinically useful TA for treating dermal wounds.

Correlation between extracellular glutamate release and neuronal cell death in an eleven vessel occlusion model in rat

The aim of this study was to define the effects of glutamate release on cell death in an eleven vessel rat occlusion model. Male Sprague-Dawley rats (250-350g) were used for the 11 vessel occlusion ischemic model, which was induced by a 5- and 10-min transient occlusion. During the surgical procedure, the extracellular glutamate concentration was measured in real-time using a microdialysis amperometirc biosensor with cerebral blood flow. In order to confirm neuronal cell death, brains were removed 72h after ischemia for the detection of the neuron-specific nuclear protein and cleaved caspase-3 levels, using double-immunofluorescence. A significant decrease in % cerebral blood flow was observed in both the 5- and 10-min 11 vessel occlusion models, while an increase in glutamate release was detected after the onset of ischemia that continued to rise during the ischemic period. However, a significantly higher level of glutamate release was observed in the 10-min ischemia group compared to the 5-min group. Unlike the small amount of brain damage in the 5-min group, the increased glutamate levels in the 10-min group resulted in ischemic cell death in the hippocampal region with the activation of cleaved caspase-3 and the inhibition of neuron-specific nuclear protein expression. This study suggests that the increased level of glutamate release induces apoptotic cell death in the 11 vessel occlusion ischemic model.

Effects of Stray Field Distribution Generated by Magnetic Beads on Giant Magnetoresistance Sensor for Biochip Applications

This study examined the effects of the stray field distribution, which depends on the relative orientation of the magnetic bead and sensor, on the sensing performance of a giant magnetoresistance (GMR) sensor for biochip applications. The beads were magnetized in two different ways: parallel and perpendicular to the sensor surface. In the case of the parallel magnetized bead, it was saturated in either the same (-x direction) or opposite (+x direction) direction to the free layer magnetization. A significant difference in the magnetization configuration of the free layer was observed with the stray field distribution. The MR values of the sensor were dependent on the stray field distribution. The largest MR value was obtained at B para (parallel magnetized bead in +x direction). However, the smallest MR was observed at –B para (parallel magnetized bead in -x direction). A moderate MR value was observed at B perp (perpendicularly magnetized bead). The dependence of MR on the distance (h) between the bead and sensor was also different from that of the stray field: the MR values at B para and B perp increase with increasing h, while MR at –B para decreases.

Dynamic Movement and Property Changes in Live Mesangial Cells by Stimuli

Atomic force microscopy (AFM) has become an important device to visualize various cells and biological materials for non-invasive imaging. The major advantage of AFM compared to the conventional optical and electron microscopes is its convenience. Sample preparation for AFM does not need special coating or vacuum as a procedure. AFM can detect samples even under the aqueous condition. Although the AFM is originally used to obtain surface topography of sample, it can measure precisely the interactions between its probe tip and the sample surface from force-distance measurements.

The probe type CNT network junctions for real-time detection of neurotransmitter

In order to detect L-glutamate, we immobilized L-glutamate oxidase (GLOD) on the probe-type carbon nanotube (CNT) network junctions by a non-covalent functionalized method to preserve their electronic characteristics. After immobilizing GLOD on the CNT network, the excess reactive groups of linker molecule remaining on its surface were deactivated and blocked by ethanolamine. The electrical property of the GLOD-immobilized CNT network transistor was characterized as source-drain current that depended on liquid gate voltage. The real time electronic response of the GLOD-coated CNT network junctions was conducted with a glutamate standard solution in vitro and the 11 vessel occlusion (11VO) rat model in vivo. The ultrahigh sensitivity, selectivity, and fast response time of GLOD-immobilized CNT-FET (field-effect transistor) could provide great potential for the real time electronic detection of extracellular glutamate levels in the brain.