Imaging Of Brain Tissue Research Articles

Multiscale vision model highlights spontaneous glial calcium waves recorded by 2-photon imaging in brain tissue

Intercellular glial calcium waves (GCW) constitute a signaling pathway which can be visualized by fluorescence imaging of cytosolic Ca(2+) changes. Reliable detection of calcium waves in multiphoton imaging data is challenging because of low signal-to-noise ratio. We modified the multiscale vision model (MVM), originally employed to detect faint objects in astronomy data to process stacks of fluorescent images. We demonstrate that the MVM identified and characterized GCWs with much higher sensitivity and detail than pixel thresholding. Origins of GCWs were often associated with prolonged secondary Ca(2+) elevations. The GCWs had variable shapes, and secondary GCWs were observed to bud from the primary, larger GCW. GCWs evaded areas shortly before occupied by a preceding GCW instead circulating around the refractory area. Blood vessels uniquely reshaped GCWs and were associated with secondary GCW events. We conclude that the MVM provides unique possibilities to study spatiotemporally correlated Ca(2+) signaling in brain tissue.

FTIR Imaging of Brain Tissue Reveals Crystalline Creatine Deposits Are an ex Vivo Marker of Localized Ischemia during Murine Cerebral Malaria: General Implications for Disease Neurochemistry

Phosphocreatine is a major cellular source of high energy phosphates, which is crucial to maintain cell viability under conditions of impaired metabolic states, such as decreased oxygen and energy availability (i.e., ischemia). Many methods exist for the bulk analysis of phosphocreatine and its dephosphorylated product creatine; however, no method exists to image the distribution of creatine or phosphocreatine at the cellular level. In this study, Fourier transform infrared (FTIR) spectroscopic imaging has revealed the ex vivo development of creatine microdeposits in situ in the brain region most affected by the disease, the cerebellum of cerebral malaria (CM) diseased mice; however, such deposits were also observed at significantly lower levels in the brains of control mice and mice with severe malaria. In addition, the number of deposits was observed to increase in a time-dependent manner during dehydration post tissue cutting. This challenges the hypotheses in recent reports of FTIR spectroscopic imaging where creatine microdeposits found in situ within thin sections from epileptic, Alzheimer's (AD), and amlyoid lateral sclerosis (ALS) diseased brains were proposed to be disease specific markers and/or postulated to contribute to the brain pathogenesis. As such, a detailed investigation was undertaken, which has established that the creatine microdeposits exist as the highly soluble HCl salt or zwitterion and are an ex-vivo tissue processing artifact and, hence, have no effect on disease pathogenesis. They occur as a result of creatine crystallization during dehydration (i.e., air-drying) of thin sections of brain tissue. As ischemia and decreased aerobic (oxidative metabolism) are common to many brain disorders, regions of elevated creatine-to-phosphocreatine ratio are likely to promote crystal formation during tissue dehydration (due to the lower water solubility of creatine relative to phosphocreatine). The results of this study have demonstrated that although the deposits do not occur in vivo, and do not directly play any role in disease pathogenesis, increased levels of creatine deposits within air-dried tissue sections serve as a highly valuable marker for the identification of tissue regions with an altered metabolic status. In this study, the location of crystalline creatine deposits were used to identify whether an altered metabolic state exists within the molecular and granular layers of the cerebellum during CM, which complements the recent discovery of decreased oxygen availability in the brain during this disease.

Digital confocal microscope

We demonstrate experimentally a scanning confocal microscopy technique based on digital holography. The method relies on digital holographic recording of the scanned spot. The data collected in this way contains all the necessary information to digitally produce three-dimensional images. Several methods to treat the data are presented. Examples of reflection and transmission images of epithelial cells and mouse brain tissue are shown.

High resolution imaging of neuronal connectivity

Connectomics is an emerging field that aims to generate and analyse neuronal connectivity data with high-throughput to gain knowledge about the brain. The realization of this goal largely depends on the development of innovative microscopy techniques that can produce large-scale three-dimensional images of brain tissue at nanoscale resolution and automated analysis tools that can extract relevant information from these images. This review surveys the challenges associated with generating the images needed for neuronal connectivity maps and how these challenges may be overcome by novel optical methods that allow sub-diffraction-limit imaging.

Confocal Laser Endomicroscopy for Diagnosis and Histomorphologic Imaging of Brain Tumors In Vivo

Early detection and evaluation of brain tumors during surgery is crucial for accurate resection. Currently cryosections during surgery are regularly performed. Confocal laser endomicroscopy (CLE) is a novel technique permitting in vivo histologic imaging with miniaturized endoscopic probes at excellent resolution. Aim of the current study was to evaluate CLE for in vivo diagnosis in different types and models of intracranial neoplasia. In vivo histomorphology of healthy brains and two different C6 glioma cell line allografts was evaluated in rats. One cell line expressed EYFP, the other cell line was used for staining with fluorescent dyes (fluorescein, acriflavine, FITC-dextran and Indocyanine green). To evaluate future application in patients, fresh surgical resection specimen of human intracranial tumors (n = 15) were examined (glioblastoma multiforme, meningioma, craniopharyngioma, acoustic neurinoma, brain metastasis, medulloblastoma, epidermoid tumor). Healthy brain tissue adjacent to the samples served as control. CLE yielded high-quality histomorphology of normal brain tissue and tumors. Different fluorescent agents revealed distinct aspects of tissue and cell structure (nuclear pattern, axonal pathways, hemorrhages). CLE discrimination of neoplastic from healthy brain tissue was easy to perform based on tissue and cellular architecture and resemblance with histopathology was excellent. Confocal laser endomicroscopy allows immediate in vivo imaging of normal and neoplastic brain tissue at high resolution. The technology might be transferred to scientific and clinical application in neurosurgery and neuropathology. It may become helpful to screen for tumor free margins and to improve the surgical resection of malignant brain tumors, and opens the door to in vivo molecular imaging of tumors and other neurologic disorders.

High resolution biomedical imaging—multimodal ultrasound microscope and combination with optics

High frequency ultrasound imaging has evolved from classical acoustic microscopy to the multimodal ultrasound microscope which is available for quantitative C-mode, surface acoustic impedance mode and 3D-mode imaging. The evolution has realized both quantitative parametric imaging and easier observation. Quantitative C-mode representing two-dimensional distribution of attenuation or sound speed is realized by frequency-domain analysis of a single pulse by a high speed digitizer. Because the square of sound speed is proportional to the tissue elasticity, sound speed imaging provides biomechanical information of the tissues which is especially important in cardiology and orthopedic surgery. The data also help understanding clinical echo features, especially important in grading of liver fibrosis. Surface acoustic impedance mode without thin-slicing has been applied for imaging of fresh brain tissues and real time observation of high-intensity focused ultrasound procedures. High frequency 3D-mode imaging has visualized 3D structure of sebaceous gland in dermis. Compared with optical coherence tomography which provides higher resolution imaging, ultrasound is superior in the penetration depth and assessment of tissue elasticity. Photoacoustic imaging provides not only morphology but also small blood flow distribution. Both ultrasound and optical methods should develop together to realize high resolution and “gentle” biomedical imaging.

C60 Secondary Ion Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

Secondary ion mass spectrometry (SIMS) has seen increased application for high spatial resolution chemical imaging of complex biological surfaces. The advent and commercial availability of cluster and polyatomic primary ion sources (e.g., Au and Bi cluster and buckminsterfullerene (C(60))) provide improved secondary ion yield and decreased fragmentation of surface species, thus improving accessibility of intact molecular ions for SIMS analysis. However, full exploitation of the advantages of these new primary ion sources has been limited, due to the use of low mass resolution mass spectrometers without tandem MS to enable enhanced structural identification capabilities. Similarly, high mass resolution and high mass measurement accuracy would greatly improve the chemical specificity of SIMS. Here we combine, for the first time, the advantages of a C(60) primary ion source with the ultrahigh mass resolving power and high mass measurement accuracy of Fourier transform ion cyclotron resonance mass spectrometry. Mass resolving power in excess of 100 000 (m/Δm(50%)) is demonstrated, with a root-mean-square mass measurement accuracy below 1 part-per-million. Imaging of mouse brain tissue at 40 μm pixel size is shown. Tandem mass spectrometry of ions from biological tissue is demonstrated and molecular formulas were assigned for fragment ion identification.

Adaptive optics microscopy with direct wavefront sensing using fluorescent protein guide stars

We introduce a direct wavefront sensing method using structures labeled with fluorescent proteins in tissues as guide stars. An adaptive optics confocal microscope using this method is demonstrated for imaging of mouse brain tissue. A dendrite and a cell body of a neuron labeled with yellow fluorescent protein are tested as guide stars without injection of other fluorescent labels. Photobleaching effects are also analyzed. The results shows increased image contrast and 3× improvement in the signal intensity for fixed mouse tissues at depths of 70 μm.

S4‐02‐06: Gene therapy utilizing growth factors

Brain-derived neurotrophic factor (BDNF) potently prevents the death and stimulates the function of cortical neurons in several rodent and primate models of Alzheimer's disease (AD). We previously reported that BDNF administration to the entorhinal cortex improved hippocampal-dependent learning and memory, enhanced synaptic function, and reduced neuronal loss (Nagahara et al., Nature Medicine 2009). Effects were observed in both the entorhinal cortex and hippocampus. We are now assessing the safety and toxicity of adeno-associated virus serotype 2 (AAV2) BDNF gene delivery at escalating doses in rodent and primate models. As part of potential clinical translation, it is essential to develop methods to accurately target AAV2-BDNF vector delivery to the entorhinal cortex. We have developed a “real-time” magnetic resonance imaging delivery system that enables accurate identification of vector infusion sites in the entorhinal cortex in rhesus monkeys, and that monitors spread of vector in each subjects at the time of active infusion. This system may be essential both in this AAV2-BDNF infusion program, and in other gene delivery programs targeting AD and other neurodegenerative brain disorders. Young rhesus monkeys underwent delivery of BDNF-AAV2 into the entorhinal cortex with the Clearpoint system (Surgivision) that uses a MRI-compatible head mounted frame (Smartframe), cannula system, and software to establish the cannula trajectory based real-time MRI. Using the real-time MRI, convection-enhanced delivery of BDNF-AAV2 mixed with 1mM gadoteridol (MRI contrast agent) into the entorhinal cortex is monitored during the infusion procedure. 1 month following vector delivery, monkeys are perfused and the brain is examined to confirm delivery of the BDNF-AAV2 to the targeted region. Real-time MRI during the infusion procedure allowed accurate targeting of BDNF-AAV2 to the entorhinal cortex. Comparison of BDNF immunolabeling in brain tissue and MR images of the vector infusion during surgery confirmed that real-time MRI accurately reflects targeting and spread of BDNF-AAV2. BDNF-AAV2 transduced only neurons, resulting in accurate vector delivery to the intended cellular targets. These findings demonstrate that real-time MRI during the infusion procedure can enable accurate targeting of gene delivery into entorhinal cortex of non-human primates. This represents a feasible method to deliver vectors into specific brain regions with 0.5 mm accuracy. The use of this system can allow accurate delivery of vector into this brain region in AD.

Chemoselective imaging of mouse brain tissue via multiplex CARS microscopy

The fast and reliable characterization of pathological tissue is a debated topic in the application of vibrational spectroscopy in medicine. In the present work we apply multiplex coherent anti-Stokes Raman scattering (MCARS) to the investigation of fresh mouse brain tissue. The combination of imaginary part extraction followed by principal component analysis led to color contrast between grey and white matter as well as layers of granule and Purkinje cells. Additional quantitative information was obtained by using a decomposition algorithm. The results perfectly agree with HE stained references slides prepared separately making multiplex CARS an ideal approach for chemoselective imaging.

Label-free live brain imaging and targeted patching with third-harmonic generation microscopy

The ability to visualize neurons inside living brain tissue is a fundamental requirement in neuroscience and neurosurgery. Especially the development of a noninvasive probe of brain morphology with micrometer-scale resolution is highly desirable, as it would provide a noninvasive approach to optical biopsies in diagnostic medicine. Two-photon laser-scanning microscopy (2PLSM) is a powerful tool in this regard, and has become the standard for minimally invasive high-resolution imaging of living biological samples. However, while 2PLSM-based optical methods provide sufficient resolution, they have been hampered by the requirement for fluorescent dyes to provide image contrast. Here we demonstrate high-contrast imaging of live brain tissue at cellular resolution, without the need for fluorescent probes, using optical third-harmonic generation (THG). We exploit the specific geometry and lipid content of brain tissue at the cellular level to achieve partial phase matching of THG, providing an alternative contrast mechanism to fluorescence. We find that THG brain imaging allows rapid, noninvasive label-free imaging of neurons, white-matter structures, and blood vessels simultaneously. Furthermore, we exploit THG-based imaging to guide micropipettes towards designated neurons inside live tissue. This work is a major step towards label-free microscopic live brain imaging, and opens up possibilities for the development of laser-guided microsurgery techniques in the living brain.

Wavelet Transform Method to Characterize Dendrites in Digital Images of Brain Tissue

The effects of normal (non-disease) aging in the brain can be characterized by impairments in memory and executive function. These impairments usually start developing in healthy people in their early twenties and progressing linearly until old age. This is usually labeled as the “normal” effects of age. The precise nature of these effects in the brain, however, are not known. Extensive studies have shown that neurons are not lost with age, in contrast with other neurodegenerative diseases such as Alzheimer's disease. In a previous joint computational and anatomical study, it was found that neurons in aged brains suffered from a loss of organization when compared with young subjects. This meant that neurons that are typically organized in anatomical structures known as microcolumns, would lose their columnar organization due to random small displacements of their positions. The current hypothesis is that the dendrites that surround and in a way support the neurons suffer atrophy with age. In this work we present a method to assess this atrophy from digital immunostained photomicrographs of brain tissue samples. By applying a wavelet transforms to digital images of brain tissue we characterize the widths and separation of bundles of dendrites. By correlating these quantities with age, we determine if they contribute to the anatomical changes found in neurons and cognitive impairment. A correlation between results from our wavelet transform method and the more time-consuming acquisition of data by measuring by hand will be presented as a validation of our method. By exploiting the parallel nature of image analysis, an NVIDIA CUDA implementation of our wavelet transform will be presented in which hardware acceleration increases execution by up to ten orders of magnitude.

Nucleus Accumbens Invulnerability to Methamphetamine Neurotoxicity

Methamphetamine (Meth) is a neurotoxic drug of abuse that damages neurons and nerve endings throughout the central nervous system. Emerging studies of human Meth addicts using both postmortem analyses of brain tissue and noninvasive imaging studies of intact brains have confirmed that Meth causes persistent structural abnormalities. Animal and human studies have also defined a number of significant functional problems and comorbid psychiatric disorders associated with long-term Meth abuse. This review summarizes the salient features of Meth-induced neurotoxicity with a focus on the dopamine (DA) neuronal system. DA nerve endings in the caudate-putamen (CPu) are damaged by Meth in a highly delimited manner. Even within the CPu, damage is remarkably heterogeneous, with ventral and lateral aspects showing the greatest deficits. The nucleus accumbens (NAc) is largely spared the damage that accompanies binge Meth intoxication, but relatively subtle changes in the disposition of DA in its nerve endings can lead to dramatic increases in Meth-induced toxicity in the CPu and overcome the normal resistance of the NAc to damage. In contrast to the CPu, where DA neuronal deficiencies are persistent, alterations in the NAc show a partial recovery. Animal models have been indispensable in studies of the causes and consequences of Meth neurotoxicity and in the development of new therapies. This research has shown that increases in cytoplasmic DA dramatically broaden the neurotoxic profile of Meth to include brain structures not normally targeted for damage. The resistance of the NAc to Meth-induced neurotoxicity and its ability to recover reveal a fundamentally different neuroplasticity by comparison to the CPu. Recruitment of the NAc as a target of Meth neurotoxicity by alterations in DA homeostasis is significant in light of the numerous important roles played by this brain structure.

Imaging the future of stroke: II. Hemorrhage

Bleeding into the brain or adjacent structures is one of the most devastating neurological conditions, incurring tremendous emotional, financial, and societal costs. Imaging is essential to differentiate variants of hemorrhage, as the clinical features may be insufficient. A comprehensive approach to hemorrhage therefore relies on imaging to disclose pathophysiology, elucidate mechanisms, and thereby open further avenues to effective treatment. Hemorrhage patterns from superficial to deep locations in the brain are surveyed in this work, noting myriad potential causes and the influential pathophysiology of arterial ischemia, venous hypertension, and microvascular dysfunction. Recent progress of imaging studies and novel techniques to evaluate hemorrhage are explored. For decades, only computed tomography was available to define a hematoma without corroborating evidence of other pathology whereas multimodal computed tomography and magnetic resonance imaging, including noninvasive imaging of brain tissue, vessels, and perfusion, have now radically altered clinical practice. Imaging of the blood-brain barrier, cerebral microbleeds, coexistent ischemia, associated vascular lesions, and markers of hemorrhage expansion is possible with routine protocols akin to diagnostic strategies for ischemic stroke. Imaging applications for hemorrhagic transformation, venous thrombosis, and microvascular disorders are considered with a perspective that balances concern for hemorrhage with prevention of ischemia as these processes are often intertwined and clinical conundrums arise. Imminent imaging advances are anticipated with increased use of detailed imaging for hemorrhage and overlap with cerebral ischemia. Numerous questions abound regarding optimal management of hemorrhage and definitive treatments are lacking, yet imaging of pivotal pathophysiology offers tremendous opportunity for future progress in combating this debilitating condition.

Studies of anomalous diffusion in the human brain using fractional order calculus

It is well known that diffusion-induced MR signal loss deviates from monoexponential decay, particularly at high b-values (e.g., >1500 sec/mm(2) for human brain tissues). A number of models have been developed to describe this anomalous diffusion behavior and relate the diffusion measurements to tissue structures. Recently, a new diffusion model was proposed by solving the Bloch-Torrey equation using fractional order calculus with respect to time and space (Magin et al., J Magn Reson 2008;190:255-270; Zhou et al., Proc Int'l Soc Magn Reson Med 2008). Using a spatial Laplacian [symbol: see text], this model yields a new set of parameters to describe anomalous diffusion: diffusion coefficient D, fractional order derivative in space beta, and a spatial parameter mu (in units of microm). In this study, we demonstrate that the fractional calculus model can be successfully applied to analyzing diffusion images of healthy human brain tissues in vivo. Five human volunteers were scanned on a commercial 3-T scanner using a customized single-shot echo-planar imaging diffusion sequence with 15 b values ranging from 0 to 4700 sec/mm(2). The set of images was analyzed using the fractional calculus model, producing spatially resolved maps of D, beta, and mu. The beta and mu maps showed notable contrast between white and gray matter. The contrast has been attributed to the varying degree of complexity of the underlying tissue structures and microenvironment. Although the biophysical basis of beta and mu remains elusive, the potential utility of these parameters to characterize the environment for molecular diffusion, as a complement to apparent diffusion coefficient, may lead to a new way to investigate tissue structural changes in disease progression, intervention, and regression.

Bioimaging of metals in thin mouse brain section by laser ablation inductively coupled plasma mass spectrometry: novel online quantification strategy using aqueous standards

A novel solution-based calibration method for quantitative spatial resolved distribution analysis (imaging) of elements in thin biological tissue sections by LA-ICP-MS (laser ablation inductively coupled plasma mass spectrometry) is described. A dual flow of the carrier and nebulizer gas is used to transport the aerosol of the laser ablated solid sample (brain tissue) and that of the nebulized aqueous standard into inductively coupled plasma (ICP) source, respectively. Both aerosols are introduced separately in the injector tube inside a special ICP torch and then mixed in the inductively coupled plasma. Calibration curves were obtained via two different calibration strategies: (i) solution based calibration and (ii) with a set of well characterized homogeneous brain laboratory standards. In the first approach matrix matching is performed by solution nebulization of a series of aqueous standards with defined analyte concentrations and simultaneous laser ablation of brain homogenate followed by nebulization of 2% (v/v) HNO3 and laser ablation of a whole brain slice (line by line). In the second approach of calibration a set of brain homogenates with defined analyte concentrations is analyzed by LA-ICP-MS followed by the imaging of brain tissue under the same experimental conditions (dry plasma). Calibration curves of elements of interest (e.g., Li, Na, Al, K, Ca, Ti, V, Mn, Ni, Co, Cr, Cu, Zn, As, Se, Rb, Sr, Y, Cd, Ba, La, Ce, Nd, Gd, Hg, Pb, Bi and U) were obtained using (i) aqueous standards or (ii) the set of synthetic laboratory standards prepared from a mouse brain homogenate doped with elements at defined concentrations. The ratio of the slope of the calibration curves (obtained by using aqueous standards and solid standards) was applied to correct the differences of sensitivity among ICP-MS and LA-ICP-MS. Quantitative images of Li, Mn, Fe, Cu, Zn and Rb in mouse brain were obtained under wet plasma condition (nebulization of HNO3 solution in parallel with ablation of solid brain sample).

Micromirror-scanned dual-axis confocal microscope utilizing a gradient-index relay lens for image guidance during brain surgery

A fluorescence confocal microscope incorporating a 1.8-mm-diam gradient-index relay lens is developed for in vivo histological guidance during resection of brain tumors. The microscope utilizes a dual-axis confocal architecture to efficiently reject out-of-focus light for high-contrast optical sectioning. A biaxial microelectromechanical system (MEMS) scanning mirror is actuated at resonance along each axis to achieve a large field of view with low-voltage waveforms. The unstable Lissajous scan, which results from actuating the orthogonal axes of the MEMS mirror at highly disparate resonance frequencies, is optimized to fully sample 500x500 pixels at two frames per second. Optically sectioned fluorescence images of brain tissues are obtained in living mice to demonstrate the utility of this microscope for image-guided resections.

Differentiation between normal and tumor vasculature of animal and human glioma by FTIR imaging

Malignant gliomas are very aggressive tumors, highly angiogenic and invading heterogeneously the surrounding brain parenchyma, making their resection very difficult. To overcome the limits of current diagnostic imaging techniques used for gliomas, we proposed using FTIR imaging, with a spatial resolution from 6 to 10 μm, to provide molecular information for their histological examination, based on discrimination between normal and tumor vasculature. Differentiation between normal and tumor blood vessel spectra by hierarchical cluster analysis was performed on tissue sections obtained from xenografted brain tumors of Rag-gamma mice 28 days after intracranial implantation of glioma cells, as well as for human brain tumors obtained in clinics. Classical pathological examination and immunohistochemistry were performed in parallel to the FTIR spectral imaging of brain tissues. First on the animal model, classification of FTIR spectra of blood vessels could be performed using spectral intervals based on fatty acyl (3050-2800 cm(-1)) and carbohydrate (1180-950 cm(-1)) absorptions, with the formation of two clusters corresponding to healthy and tumor parts of the tissue sections. Further data treatments on these two spectral intervals provided interpretable information about the molecular contents involved in the differentiation between normal and tumor blood vessels, the latter presenting a higher level of fatty acyl chain unsaturation and an unexpected loss of absorption from osidic residues. This classification method was further successfully tested on human glioma tissue sections. These findings demonstrate that FTIR imaging could highlight discriminant molecular markers to distinguish between normal and tumor vasculature, and help to delimitate areas of corresponding tissue.

Lymphocytic Choriomeningitis Virus-Induced Mortality in Mice Is Triggered by Edema and Brain Herniation

Although much is known about lymphocytic choriomeningitis virus (LCMV) infection and the subsequent immune response in its natural murine host, some crucial aspects of LCMV-mediated pathogenesis remain undefined, including the underlying basis of the characteristic central nervous system disease that occurs following intracerebral (i.c.) challenge. We show that the classic seizures and paresis that occur following i.c. infection of adult, immunocompetent mice with LCMV are accompanied by anatomical and histological changes that are consistent with brain herniation, likely of the uncal subtype, as a causative basis for disease and precipitous death. Both by water weight determinations and by magnetic resonance imaging of infected brain tissues, edema was detected only at the terminal stages of disease, likely caused by the leakage of cerebrospinal fluid from the ventricles into the parenchyma. Furthermore, death was accompanied by unilateral pupillary dilation, which is indicative of uncal herniation. While immunohistochemical analysis revealed periventricular inflammation and a loss of integrity of the blood-brain barrier (BBB), these events preceded seizures by 2 to 3 days. Moreover, surviving perforin knockout mice showed barrier permeability equivalent to that of moribund, immunocompetent mice; thus, BBB damage does not appear to be the basis of LCMV-induced neuropathogenesis. Importantly, brain herniation can occur in humans as a consequence of injuries that would be predicted to increase intracranial pressure, including inflammation, head trauma, and brain tumors. Thus, a mechanistic dissection of the basis of LCMV neuropathogenesis may be informative for the development of interventive therapies to prevent this typically fatal human condition.

Synchrotron light source imaging of brain tissue shows changes in iron concentration after chronic implantation of electrodes and electrical stimulation

PURPOSEVarious metallic electrodes are used in research and clinical applications because of their purported biological compatibility. However, little is known about the effects on surrounding tissue following subsequent stimulation. Using X‐ray fluorescence imaging, we examined metal distribution in the brain after stimulation with three types of electrodes.METHODSBilateral implantation of stainless steel, nickel‐chromium, or platinum‐iridium electrodes into amygdala was used in a rat preparation of epilepsy. Stage 5 seizures were kindled by a once‐daily application of electrical stimulation. Rapid scanning X‐Ray fluorescence and microprobe analysis of brain sections were performed using the imaging beam lines at the Stanford Synchrotron Radiation Lightsource.RESULTSImages showed elevated iron concentrations around the electrode tips in both control and kindled tissue. Concentrations varied according to electrode type and were greater in kindled tissue as compared to yoked controls.CONCLUSIONSChronic implantation of electrodes in the brain results in an increased concentration of iron around the electrode track, which is further increased by stimulation. These findings raise the issue of possible adverse effects from these metal depositions and suggest the need to evaluate the effects of chronic electrical stimulation in clinical settings.Support: NSERC, CIHR