You-Yin Chen

Imaging brain hemodynamic changes during rat forepaw electrical stimulation using functional photoacoustic microscopy

The present study reported the development of a novel functional photoacoustic microscopy (fPAM) system for investigating hemodynamic changes in rat cortical vessels associated with electrical forepaw stimulation. Imaging of blood optical absorption by fPAM at multiple appropriately-selected and distinct wavelengths can be used to probe changes in total hemoglobin concentration (HbT, i.e., cerebral blood volume [CBV]) and hemoglobin oxygen saturation (SO(2)). Changes in CBV were measured by images acquired at a wavelength of 570nm (lambda(570)), an isosbestic point of the molar extinction spectra of oxy- and deoxy-hemoglobin, whereas SO(2) changes were sensed by pixel-wise normalization of images acquired at lambda(560) or lambda(600) to those at lambda(570). We demonstrated the capacity of the fPAM system to image and quantify significant contralateral changes in both SO(2) and CBV driven by electrical forepaw stimulation. The fPAM system complements existing imaging techniques, with the potential to serve as a favorable tool for explicitly studying brain hemodynamics in animal models.

A New Scenario for Negative Functional Magnetic Resonance Imaging Signals: Endogenous Neurotransmission

Functional magnetic resonance imaging (fMRI) has revolutionized investigations of brain functions. Increases in fMRI signals are usually correlated with neuronal activation, but diverse explanations have been proposed for negative fMRI responses, including decreases in neuronal activity, the vascular-steal effect, and large increases in oxygen consumption. These possible scenarios, although encompassing a wide range of potential neurovascular responses, cannot yet be used to interpret certain types of negative fMRI signals. Recent studies have found that intravenous injection of dopamine D2 receptor (D2DR) agonist reduced the hemodynamic responses in the caudate–putamen (CPu); however, whether endogenous dopaminergic neurotransmission contributes to fMRI signals remains obscure. Since it has been suggested that the D2DR is involved in pain modulation, and the CPu shows equivocal fMRI signals during noxious stimulation, the present study established an animal model based on graded electrical stimulation to elicit different levels of nociception, and aimed to determine whether nociception-induced endogenous dopaminergic neurotransmission is sufficient to generate negative fMRI responses. Our results from cerebral blood volume (CBV)-weighted fMRI, Fos immunohistochemistry, and electrophysiological recording demonstrated a salient bilateral CBV decreases associated with heightened neuronal activity in the CPu induced by unilateral noxious electrical stimulation. In addition, preinjection of D2DR antagonist reduced the observed CBV decreases. Our findings reveal the role of the D2DR in regulating striatal vascular responses and suggest that endogenous neurotransmission-induced CBV decreases underlie negative fMRI signals. Hence, the influence of endogenous neurotransmission should be considered when interpreting fMRI data, especially in an area involved in strong vasoactive neurotransmission.

Multifunctional magnetically removable nanogated lids of Fe3O4–capped mesoporous silica nanoparticles for intracellular controlled release and MR imaging

In this study, a novel nanocarrier (MSN@Fe3O4) is constructed using a facile technology by capping mesoporous silica nanoparticles (MSN) with monodispersed Fe3O4 nanoparticles through chemical bonding. The chemical links provide adhesion, which permits the magnetic nanoparticles, as nano-caps, to efficiently cover the mesoporous pores on the mesoporous silica matrix and be tightly bonded with the matrix surface. Without magnetic stimulus, none or only a negligible amount of the drug can be released from the MSN@Fe3O4. However, when subjected to an external controllable magnetic field, a quantity of nano-caps can be remotely and precisely removed, giving tunable release profiles for an anticancer drug, (S)-(+)-camptothecin (CPT), with various dosages depending upon the strength and time period of magnetic induction. The transverse relaxivity (r2) of the MSN@Fe3O4 nanocarriers was measured to be about 121.57 s−1mM−1Fe, which is larger than that for the reported mesoporous silica nanoparticles decorated with magnetite nanocrystals. Therefore, MSN@Fe3O4 nanocarriers could perform well as T2- type MR contrast enhancement agents for cell or molecular imaging. In addition, the MSN@Fe3O4 nanocarriers also demonstrate fairly high cell uptake efficiency. Together with its versatile magnetic manipulation, this new type of MSN@Fe3O4 nanosystem can be considered as a new class of multifunctional nanodevice, with combined tunable drug release and nanoimaging modalities for a variety of biomedical uses.

Design and fabrication of a polyimide-based microelectrode array: Application in neural recording and repeatable electrolytic lesion in rat brain

The design and testing of a new microelectrode array, the NCTU (National Chiao Tung University) probe, was presented. Evaluation results showed it has good biocompatibility, high signal-to-noise ratio (SNR: the root mean square of background noise to the average peak-to-peak amplitude of spikes) during chronic neural recordings, and high reusability for electrolytic lesions. The probe was a flexible, polyimide-based microelectrode array with a long shaft (14.9 mm in length) and 16 electrodes (5 microm-thick and 16 microm in radius); its performance in chronic in vivo recordings was examined in rodents. To improve the precision of implantation, a metallic, impact-resistant layer was sandwiched between the polyimide layers to strengthen the probe. The three-dimensional (3D) structure of electrodes fabricated by electroplating produced rough textures that increased the effective surface area. The in vitro impedance of electrodes on the NCTU probe was 2.4+/-0.52 MOmega at 1 kHz. In addition, post-surgical neural recordings of implanted NCTU probes were conducted for up to 40 days in awake, normally behaving rats. The electrodes on the NCTU probe functioned well and had a high SNR (range: 4-5) with reliable in vivo impedance (<0.7 MOmega). The electrodes were also robust enough to functionally record events, even after the anodal current (30 microA, 10s) was repeatedly applied for 60 times. With good biocompatibility, high and stable SNR for chronic recording, and high tolerance for electrolytic lesion, the NCTU probe would serve as a useful device in future neuroscience research.

A vision-based analysis system for gait recognition in patients with Parkinson's disease

Recognition of specific Parkinsonian gait patterns is helpful in the diagnosis of Parkinsons disease (PD). However, there are few computer-aided methods to identify the specific gait patterns of PD. We propose a vision-based diagnostic system to aid in recognition of the gait patterns of Parkinsons disease. The proposed system utilizes an algorithm combining principal component analysis (PCA) with linear discriminant analysis (LDA). This scheme not only addresses the high data dimensionality problem during image processing but also distinguishes different gait categories simultaneously. The feasibility of the proposed system for the recognition of PD gait was tested by using gait videos of PD and normal subjects. The efficiency of feature extraction using PCA and LDA coefficients are also compared. Experimental results showed that LDA had a recognition rate for Parkinsonian gait of 95.49%, which is higher than the conventional PCA feature extraction method. The proposed system is a promising aid in identifying the gait of Parkinsons disease patients and can discriminate the gait patterns of PD patients and normal people with a very high classification rate.

Design and characterization of a novel amphiphilic chitosan nanocapsule-based thermo-gelling biogel with sustained in vivo release of the hydrophilic anti-epilepsy drug ethosuximide

Thermo-gelling injectable nanogels, with no burst release of loaded drug, were prepared by a simple route by combining self assembled nanocapsules of amphiphilically modified chitosan with glycerophosphate di-sodium salt and glycerol. The potential as a depot drug delivery system was demonstrated in vivo through the therapeutic effect of ethosuximide (ESM) loaded nanogels, suppressing spike wave discharges (SWDs) in Long Evan rat model. Simultaneously clearance of gels from the site of administration was monitored non-invasively using MRI. The gel structure was characterized using TEM and SEM, confirming the gels to be an assembly of nanocapsules and using two-photon microscopy to visualize the network structure. In vitro drug release studies using ESM revealed that the nanogels exhibited extended, mostly Fickian release. Finally, all investigated formulations displayed excellent cytotoxicity data determined by MTT assay using human retinal pigmented epithelium cells. All presented properties are highly desirable for injectable depot gels for drug delivery.

Magnetic core-shell nanocapsules with dual-targeting capabilities and co-delivery of multiple drugs to treat brain gliomas.

Lactoferrin (Lf)-tethered magnetic double emulsion nanocapsules (Lf-MDCs) are assembled from polyvinyl alcohol (PVA), polyacrylic acid (PAA), and iron oxide (IO) nanoparticles. The core-shell nanostructure of the Lf-MDCs (particle diameters from 100 to 150 nm) can simultaneously accommodate a hydrophilic drug, doxorubicin (Dox), and a hydrophobic drug, curcumin (Cur), in the core and shell, respectively, of the nanocapsules for an efficient drug delivery system. The release patterns of the two drugs can be regulated by manipulating the surface charges and drug-loading ratios, providing the capability for a stepwise adjuvant release to treat cancer cells. The results demonstrate that the dual (Dox+Cur)-drug-loaded nanocapsule can be effectively delivered into RG2 glioma cells to enhance the cytotoxicity against the cells through a synergistic effect. The combined targeting, i.e., magnetic guidance and incorporation of Lf ligands, of these Lf-MDCs results in significantly elevated cellular uptake in the RG2 cells that overexpress the Lf receptor. Interestingly, an intravenous injection of the co-delivered chemotherapeutics follows by magnetic targeting in brain tumor-bearing mice not only achieve high accumulation at the targeted site but also more efficiently suppress cancer growth in vivo than does the delivery of either drug alone.

Transcranial imaging of functional cerebral hemodynamic changes in single blood vessels using in vivo photoacoustic microscopy.

Optical imaging of changes in total hemoglobin concentration (HbT), cerebral blood volume (CBV), and hemoglobin oxygen saturation (SO 2 ) provides a means to investigate brain hemodynamic regulation. However, high-resolution transcranial imaging remains challenging. In this study, we applied a novel functional photoacoustic microscopy technique to probe the responses of single cortical vessels to left forepaw electrical stimulation in mice with intact skulls. Functional changes in HbT, CBV, and SO 2 in the superior sagittal sinus and different-sized arterioles from the anterior cerebral artery system were bilaterally imaged with unambiguous 36 × 65-μm2 spatial resolution. In addition, an early decrease of SO 2 in single blood vessels during activation (i.e., ‘the initial dip’) was observed. Our results indicate that the initial dip occurred specifically in small arterioles of activated regions but not in large veins. This technique complements other existing imaging approaches for the investigation of the hemodynamic responses in single cerebral blood vessels.

Whole-brain functional magnetic resonance imaging mapping of acute nociceptive responses induced by formalin in rats using atlas registration-based event-related analysis

Nociceptive neuronal activation in subcortical regions has not been well investigated in functional magnetic resonance imaging (fMRI) studies. The present report aimed to use the blood oxygenation level‐dependent (BOLD) fMRI technique to map nociceptive responses in both subcortical and cortical regions by employing a refined data processing method, the atlas registration‐based event‐related (ARBER) analysis technique. During fMRI acquisition, 5% formalin (50 μl) was injected into the left hindpaw to induce nociception. ARBER was then used to normalize the data among rats, and images were analyzed using automatic selection of the atlas‐based region of interest. It was found that formalin‐induced nociceptive processing increased BOLD signals in both cortical and subcortical regions. The cortical activation was distributed over the cingulate, motor, somatosensory, insular, and visual cortices, and the subcortical activation involved the caudate putamen, hippocampus, periaqueductal gray, superior colliculus, thalamus, and hypothalamus. With the aid of ARBER, the present study revealed a detailed activation pattern that possibly indicated the recruitment of various parts of the nociceptive system. The results also demonstrated the utilization of ARBER in establishing an fMRI‐based whole‐brain nociceptive map. The formalin induced nociceptive images may serve as a template of central nociceptive responses, which can facilitate the future use of fMRI in evaluation of new drugs and preclinical therapies for pain.

A Programmable Implantable Microstimulator SoC With Wireless Telemetry: Application in Closed-Loop Endocardial Stimulation for Cardiac Pacemaker

A low-power, wireless, and implantable microstimulator system on chip with smart powering management, immediate neural signal acquisition, and wireless rechargeable system is proposed. A system controller with parity checking handles the adjustable stimulus parameters for the stimulated objective. In the current paper, the rats intra-cardiac electrogram is employed as the stimulated model in the animal study, and it is sensed by a low-voltage and low-power monitoring analog front end. The power management unit, which includes a rectifier, battery charging and detection, and a regulator, is used for the power control of the internal circuits. The stimulation data and required clock are extracted by a phase-locked-loop-based phase shift keying demodulator from an inductive AC signal. The full chip, which consumes 48 μW only, is fabricated in a TSMC 0.35 μm 2P4M standard CMOS process to perform the monitoring and pacing functions with inductively powered communication in the in vivo study.