Minah Suh

The control of neural cell-to-cell interactions through non-contact electrical field stimulation using graphene electrodes

Electric field stimulation has become one of the most promising therapies for a variety of neurological diseases. However, the safety and effectiveness of the stimulator are critical in determining the outcome. Because there are few safe and effective in vivo and/or in vitro stimulator devices, we demonstrate a method that allows for non-contact electric field stimulation with a specific strength that is able to control cell-to-cell interaction in vitro. Graphene, a form of graphite, and polyethylene terephthalate (PET) was used to create a non-cytotoxic in vitro graphene/PET film stimulator. A transient non-contact electric field was produced by charge-balanced biphasic stimuli through the graphene/PET film electrodes and applied to cultured neural cells. We found that weak electric field stimulation (pulse duration of 10 s) as low as 4.5 mV/mm for 32 min was particularly effective in shaping cell-to-cell interaction. Under weak electric field stimulation, we observed a significant increase in the number of cells forming new cell-to-cell couplings and in the number of cells strengthening existing cell-to-cell couplings. The underlying mechanism of the altered cellular interactions may be related to an altered regulation of the endogenous cytoskeletal proteins fibronectin, actin, and vinculin. In conclusion, this technique may open a new therapeutic approach for augmenting cell-to-cell coupling in cell transplantation therapy in the central nervous system.

A novel array-type transcranial direct current stimulation (tDCS) system for accurate focusing on targeted brain regions

In this paper, we propose a new array-type transcranial direct current stimulation (tDCS) system, which can modulate cortical excitability of human brain in a more effective manner. Once a target location inside a brain is determined, optimal injection current/potential at each electrode is calculated automatically by solving a constrained optimization problem. Current density distribution in a realistic head model was evaluated using the 3-D finite element method (FEM) adopting the superposition principle. Simulation results demonstrated that the proposed tDCS system enables effective and accurate field concentration on targeted brain areas.In this paper, we propose a new transcranial direct current stimulation (tDCS) system which uses multiple electrode arrays. Once a target location inside a human brain is selected, optimal injection current at each electrode is determined by solving a constrained optimization problem, of which the objective function is evaluated by 3D finite element method (FEM) adopting the superposition principle for enhanced computational efficiency. Simulation studies demonstrated that the proposed tDCS system enables more effective and accurate focusing on targeted brain areas than the conventional system.

Effect of cognitive load on eye-target synchronization during smooth pursuit eye movement

In mild traumatic brain injury (mTBI), the fiber tracts that connect the frontal cortex with the cerebellum may suffer shear damage, leading to attention deficits and performance variability. This damage also disrupts the enhancement of eye-target synchronization that can be affected by cognitive load when subjects are tested using a concurrent eye-tracking test and word-recall test. We investigated the effect of cognitive load on eye-target synchronization in normal and mTBI patients using the nonlinear dynamical technique of stochastic phase synchronization. Results demonstrate that eye-target synchronization was negatively affected by cognitive load in mTBI subjects. In contrast, eye-target synchronization improved under intermediate cognitive load in young (≤40years old) normal subjects.

Study of the primo vascular system utilizing a melanoma tumor model in a green fluorescence protein expressing mouse.

A melanoma tumor is a representative malignant tumor. Melanoma tumor growth involves vigorous angiogenesis around the tumor and a vasculogenic-like network inside an aggressive tumor. Primo vessels (PVs) are also found on the surface of the tumor and coexist alongside blood vessels (BVs), and sometimes within the BVs. We hypothesized that the primo vessels system plays a significant role in regulating the development of a melanoma tumor, and therefore has a tight coupling with BVs and angiogenesis. To prove this hypothesis, we developed a murine melanoma model by inoculating melanoma cell lines into the abdominal region. We used a green fluorescent protein (GFP) expressing mouse as a host to distinguish the endogenous source of the tumor PVs. We found strong formation of PVs on the tumor that coexisted with BVs and expression of GFP. PVs also had a tight coupling with adipose tissues, especially with white adipose tissue. These data suggest that the PVs of an induced melanoma tumor evolve endogenously from the host body and may be highly related to BVs and adipose tissue. This model of PVs in an overexpressing GFP mouse is a useful system for observing PVs, primo nodes, and primo vessel networks, and has potential to be developed as a model for examining novel treatments for cancer metastasis.

Real-time evaluation of nitric oxide (NO) levels in cortical and hippocampal areas with a nanopore-based electrochemical NO sensor

Nitric oxide (NO) is an important biomolecule for regulating various brain functions, such as the control of neurovascular tone. NO, however, cannot be stored inside cells where NO is produced and immediately diffuses through the cellular membrane and decays rapidly, which makes the detection of NO extremely hard in an in vivo setting. We constructed an amperometric NO nanosensor and utilized it to directly measure NO release in the living brain. The NO nanosensor uses nanopores (pores with an opening radii <500 nm) in which NO is oxidized at the porous platinum surface. The nanopore-based sensor was inserted vertically into the brains of anesthetized mice up to the end of the hippocampal CA 3 region, or to a depth of about 3mm. The sensor was slowly advanced in the brain in 0.5 μm increments and in 0.05 s temporal steps. Different levels of NO release were monitored by the nanopore NO sensor during the course of the penetration. The hippocampal CA3 region had the highest level of NO release, which was followed by CA2 and CA1 of the hippocampus and the cortex. The levels of NO release were not uniformly distributed within the cortical and hippocampal areas of living brain. In sum, the nanopore-based NO sensor was able to grossly measure NO contents within living brain in real time and with high sensitivity. This study may provide good insights about the relationship between the distributions of NOS-immunoreactive neurons and the directly measured levels of NO release in brain.

A soft, transparent, freely accessible cranial window for chronic imaging and electrophysiology

Chronic in vivo imaging and electrophysiology are important for better understanding of neural functions and circuits. We introduce the new cranial window using soft, penetrable, elastic, and transparent, silicone-based polydimethylsiloxane (PDMS) as a substitute for the skull and dura in both rats and mice. The PDMS can be readily tailored to any size and shape to cover large brain area. Clear and healthy cortical vasculatures were observed up to 15 weeks post-implantation. Real-time hemodynamic responses were successfully monitored during sensory stimulation. Furthermore, the PDMS window allowed for easy insertion of microelectrodes and micropipettes into the cortical tissue for electrophysiological recording and chemical injection at any location without causing any fluid leakage. Longitudinal two-photon microscopic imaging of Cx3Cr1+/− GFP transgenic mice was comparable with imaging via a conventional glass-type cranial window, even immediately following direct intracortical injection. This cranial window will facilitate direct probing and mapping for long-term brain studies.

Depth-dependent cerebral hemodynamic responses following Direct Cortical Electrical Stimulation (DCES) revealed by in vivo dual-optical imaging techniques

We studied depth-dependent cerebral hemodynamic responses of rat brain following direct cortical electrical stimulation (DCES) in vivo with optical recording of intrinsic signal (ORIS) and near-infrared spectroscopy (NIRS). ORIS is used to visualize the immediate hemodynamic changes in cortical areas following the stimulation, whereas NIRS measures the hemodynamic changes originating from subcortical areas. We found strong hemodynamic changes in relation to DCES both in ORIS and NIRS data. In particular, the signals originating from cortical areas exhibited a tri-phasic response, whereas those originating from subcortical regions exhibited multi-phasic responses. In addition, NIRS signals from two different sets of source-detector separation were compared and analyzed to investigate the causality of perfusion, which demonstrated downstream propagation, indicating that the upper brain region reacted faster than the deep region.

Contralateral hyperperfusion and ipsilateral hypoperfusion by ictal SPECT in patients with mesial temporal lobe epilepsy

Ictal Single Proton Emission Computed Tomography (SPECT) has demonstrated high levels of sensitivity in localizing seizures among patients with epilepsy of the mesial temporal lobe (mTLE). However, incorrect information on the lateralization of mTLE has also been reported. In order to investigate the causes of these incorrect localizations, the authors assessed clinical symptoms, as well as the electroencephalography (EEG) and brain SPECT scan data of five patients with mTLE experiencing ictal hyperperfusion of the contralateral temporal lobe. All patients underwent presurgical evaluations, including an interictal and ictal brain SPECT scan. A subtraction ictal SPECT co-registered with Magnetic Resonance Imaging (MRI) procedure or SISCOM was performed. Hyperperfusion (ictal perfusion greater than interictal perfusion) and hypoperfusion (ictal perfusion lower than interictal perfusion), results of SISCOM were analyzed and compared with seizure and ictal EEG pattern patterns. All the five patients had unilateral hippocampal sclerosis, and the radiotracer for the ictal SPECT was injected after the ictal EEG pattern had propagated to the contralateral side. The average delay between the ictal EEG onset and the radiotracer injection was 29.7+/-9.6s. All hyperperfusion SISCOM results revealed hyperperfusion in the contralateral temporal region with a more intense ictal EEG build-up. However, hypoperfusion SISCOM results demonstrated significant hypoperfusion in the epileptogenic temporal lobe of three of the five patients, but no hypoperfusion finding in the other two patients. This study demonstrates that early ictal EEG pattern propagation to the contralateral side in mTLE may be associated with contralateral ictal hyperperfusion with or without ipsilateral temporal hypoperfusion. The authors recommend simultaneous interpretations of ictal SPECT and ictal EEG propagation patterns at the time of the injection of radiotracers.

Primo Vascular System of Murine Melanoma and Heterogeneity of Tissue Oxygenation of the Melanoma

Murine melanoma requires the complex development of lymphatic, vascular, and non-vascular structures. A possible relationship between the primo vascular system (PVS) and the melanoma metastasis has been proposed. In particular, the PVS may be involved in oxygen transport. Vasculogenic-like networks, similar to the PVS, have been found within melanoma tumors, but their functional relationship with the PVS and meridian structures are unclear. Herein, we report on the use of an electrochemical O(2) sensor to study oxygenation levels of melanoma tumors in mice. We consistently found higher tissue oxygenation in specific sites of tumors (n=5). These sites were strongly associated with vascular structures or the PVS. Furthermore, the PVS on the tumor surface was associated with adipose tissue. Our findings suggest that the PVS is involved in the regulation of metastasis.

Hyperspectral fluorescence imaging for cellular iron mapping in the in vitro model of Parkinson’s disease

Abstract. Parkinson’s disease (PD) is characterized by progressive dopaminergic cell loss in the substantia nigra (SN) and elevated iron levels demonstrated by autopsy. Direct visualization of iron with live imaging techniques has not yet been successful. The aim of this study is to visualize and quantify the distribution of cellular iron using an intrinsic iron hyperspectral fluorescence signal. The 1-methyl-4-phenylpyridinium (MPP+)-induced cellular model of PD was established in SHSY5Y cells exposed to iron with ferric ammonium citrate (FAC, 100 μM). The hyperspectral fluorescence signal of iron was examined using a high-resolution dark-field optical microscope system with signal absorption for the visible/near infrared spectral range. The 6-h group showed heavy cellular iron deposition compared with the 1-h group. The cellular iron was dispersed in a small particulate form, whereas the extracellular iron was aggregated. In addition, iron particles were found to be concentrated on the cell membrane/edge of shrunken cells. The iron accumulation readily occurred in MPP+-induced cells, which is consistent with previous studies demonstrating elevated iron levels in the SN. This direct iron imaging could be applied to analyze the physiological role of iron, and its application might be expanded to various neurological disorders involving metals, such as copper, manganese, or zinc.