Near infrared imaging of intrinsic signals in cortical spreading depression observed through the intact scalp in hairless mice

Brain cooling was inevitable in both thinned and intact skull windows in neuroimaging in vivo of mice. Thus we proposed the novel imaging method leaving intact scalp on the skull using the light at 670, 785, and 975 nm. In this study, we used hairless mice (Hos:HR-1) since the deterioration of image quality was resulted from the hair. Cortical spreading depression was induced by KCl application through small incision and burr hole on the frontal bone. Intrinsic optical signals through the intact scalp in the observation area were detected. Time course of the signal showed a triphasic feature which was consistent with the intrinsic optical signals through the intact skull. In three pairs of signal amplitudes at the different wavelengths, no significant differences were observed. Although the intact scalp weakened the amplitudes significantly, e.g., 4.0 from 6.9 at 975 nm, the signals during cortical spreading depression were sufficient to be detected.

Systematic review of the pharmacological agents that have been tested against spreading depolarizations

Spreading depolarization (SD) occurs alongside brain injuries and it can lead to neuronal damage. Therefore, pharmacological modulation of SD can constitute a therapeutic approach to reduce its detrimental effects and to improve the clinical outcome of patients. The major objective of this article was to produce a systematic review of all the drugs that have been tested against SD. Of the substances that have been examined, most have been shown to modulate certain SD characteristics. Only a few have succeeded in significantly inhibiting SD. We present a variety of strategies that have been proposed to overcome the notorious harmfulness and pharmacoresistance of SD. Information on clinically used anesthetic, sedative, hypnotic agents, anti-migraine drugs, anticonvulsants and various other substances have been compiled and reviewed with respect to the efficacy against SD, in order to answer the question of whether a drug at safe doses could be of therapeutic use against SD in humans.

Evidence that adenosine contributes to Leao's spreading depression in vivo

Leao's spreading depression of cortical activity is a propagating silencing of neuronal activity resulting from spreading depolarization (SD). We evaluated the contributions of action potential (AP) failure and adenosine A₁ receptor (A₁R) activation to the depression of evoked and spontaneous electrocorticographic (ECoG) activity after SD in vivo, in anesthetized mice. We compared depression with SD-induced effects on AP-dependent transmission, and synaptic potentials in the transcallosal and thalamocortical pathways. After SD, APs recovered rapidly, within 1-2 min, as demonstrated by evoked activity in distant projection targets. Evoked corticocortical postsynaptic potentials recovered next, within ∼5 min. Spontaneous ECoG and evoked thalamocortical postsynaptic potentials recovered together, after ∼10-15 min. The duration of ECoG depression was shortened 20% by systemic (10 mg/kg) or focal (30 µM) administration of A₁R competitive antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX). ECoG depression was also shortened by focal application of exogenous adenosine deaminase (ADA; 100 U/mL), and conversely, was prolonged 50% by the non-competitive ADA inhibitor deoxycoformycin (DCF; 100 µM). We concluded that while initial depolarization block is brief, adenosine A₁R activation, in part, contributes to the persistent secondary phase of Leao's cortical spreading depression.

Spreading Depression, Spreading Depolarizations, and the Cerebral Vasculature

Spreading depression (SD) is a transient wave of near-complete neuronal and glial depolarization associated with massive transmembrane ionic and water shifts. It is evolutionarily conserved in the central nervous systems of a wide variety of species from locust to human. The depolarization spreads slowly at a rate of only millimeters per minute by way of grey matter contiguity, irrespective of functional or vascular divisions, and lasts up to a minute in otherwise normal tissue. As such, SD is a radically different breed of electrophysiological activity compared with everyday neural activity, such as action potentials and synaptic transmission. Seventy years after its discovery by Leão, the mechanisms of SD and its profound metabolic and hemodynamic effects are still debated. What we did learn of consequence, however, is that SD plays a central role in the pathophysiology of a number of diseases including migraine, ischemic stroke, intracranial hemorrhage, and traumatic brain injury. An intriguing overlap among them is that they are all neurovascular disorders. Therefore, the interplay between neurons and vascular elements is critical for our understanding of the impact of this homeostatic breakdown in patients. The challenges of translating experimental data into human pathophysiology notwithstanding, this review provides a detailed account of bidirectional interactions between brain parenchyma and the cerebral vasculature during SD and puts this in the context of neurovascular diseases.

Cortical spreading depression and calcitonin gene-related peptide: a brief review of current progress

Although detailed disease mechanisms of migraine remain poorly understood, migraine is known to have a complex pathophysiology with both vascular and neuronal mechanisms. The neuronal mechanisms of migraine may be attributed to cortical spreading depression (CSD); consequently, CSD has been widely studied for understanding the pathophysiology of migraine. Well validated CSD models have been developed for evaluating anti-migraine drugs. Neuropeptides, mainly, calcitonin gene-related peptide (CGRP), have been proposed as an emerging class of effective drugs against migraine headache. The central role of this neuropeptide has led to research into CSD for understanding disease mechanisms of migraine. This review briefly summarizes our current understanding of CSD and CGRP involvement in CSD. Although CSD can also worsen strokes, this brief paper has excluded the possible connection between the neuropeptide and CSD associated with them. Instead it has focused solely on CGRP in CSD associated with migraine.

Effect of dimethyl sulfoxide in cerebellar mutant Lurcher mice

DMSO has been many times described as harmless substance, beneficial in various diseases or pathological states, including brain injury or ischemia. Using Lurcher mutant mice suffering from genetically determined olivocerebellar degeneration and normal wild type mice, we examined the effect of DMSO on spontaneous motor activity and spatial learning and orientation ability. The acute effect of DMSO was studied in mice aged 3, 6, 9 and 22 weeks. DMSO treatment decreased spontaneous activity in the open field and swimming speed in the Morris water maze in both Lurcher mutant and wild type mice. While saline-treated Lurcher mice showed age-related decline of spatial memory in the Morris water maze in DMSO-treated ones such decline did not occur. The mechanism of the effect of DMSO remains unclear. A possible explanation could be modulation of the brain perfusion and metabolism in the aging brain. The improvement of learning ability could be also mediated by a tranquilizing effect of DMSO reducing stress-induced behavioral disinhibition which is supposed to interfere with learning process in Lurcher mutants. Future studies which would investigate DMSO effects in other models of neurodegenerative diseases are necessary to verify its potential therapeutic impact.

Simultaneous detection of hemodynamics, mitochondrial metabolism and light scattering changes during cortical spreading depression in rats based on multi-spectral optical imaging

Cortical spreading depression (CSD) is a self-propagating wave of cellular depolarization that plays an important role in the development of cerebral pathology following ischemia or trauma. Optical intrinsic signal (OIS) imaging has been widely used to investigate CSD. Sources of OIS are complex and related to the changes in brain tissue absorption and scattering. The absorbing chromophores may include oxy-hemoglobin, deoxy-hemoglobin, cytochromes, flavin adenine dinucleotide (FAD) and nicotinamide adenine dinucleotide (NADH). Considering only one or part of these elements in studies involving OIS may cause inaccurate results. Thus, we simultaneously calculated changes in HbO, HbR, FAD, cytochrome c, cytochrome aa3 and light scattering during CSD by applying multi-spectral OIS imaging at 450, 470, 500, 530, 550, 570, 600, 630, and 650 nm in the rat brain. We also showed that the hemodynamic changes during CSD may not be correctly estimated if the scattering and other chromophores such as FAD, cytochrome c and cytochrome aa3, are not included in the fitting model of multi-wavelength data analysis. As shown in our results, if considering the changes in scattering and other chromophores in data fitting model, deoxy-hemoglobin (HbR) showed a triphasic change while only a monophasic decrease in HbR will be resolved without considering changes in scattering and other chromophores as reported in previous studies. Moreover, our results showed that changes in cytochrome c was tightly related to OIS at 550 nm, cytochrome aa3 was closely related to OIS at 450, 600 and 650 nm, and FAD was closely related to OIS at 450 and 470 nm during CSD. It indicates that if the contribution by these related chromophores is not considered, using OIS at these wavelengths to determine the hemoglobin changes during CSD may lead to inaccurate results.

Dedicated hardware processor and corresponding system-on-chip design for real-time laser speckle imaging

Laser speckle imaging (LSI) is a noninvasive and full-field optical imaging technique which produces two-dimensional blood flow maps of tissues from the raw laser speckle images captured by a CCD camera without scanning. We present a hardware-friendly algorithm for the real-time processing of laser speckle imaging. The algorithm is developed and optimized specifically for LSI processing in the field programmable gate array (FPGA). Based on this algorithm, we designed a dedicated hardware processor for real-time LSI in FPGA. The pipeline processing scheme and parallel computing architecture are introduced into the design of this LSI hardware processor. When the LSI hardware processor is implemented in the FPGA running at the maximum frequency of 130 MHz, up to 85 raw images with the resolution of 640×480 pixels can be processed per second. Meanwhile, we also present a system on chip (SOC) solution for LSI processing by integrating the CCD controller, memory controller, LSI hardware processor, and LCD display controller into a single FPGA chip. This SOC solution also can be used to produce an application specific integrated circuit for LSI processing.

Simultaneous monitoring of intracellular pH changes and hemodynamic response during cortical spreading depression by fluorescence-corrected multimodal optical imaging

Cortical spreading depression (CSD) plays an important role in trauma, migraine and ischemia. CSD could induce pronounced hemodynamic changes and the disturbance of pH homeostasis which has been postulated to contribute to cell death following ischemia. In this study, we described a fluorescence-corrected multimodal optical imaging system to simultaneously monitor CSD associated intracellular pH (pH(i)) changes and hemodynamic response including hemoglobin concentrations and cerebral blood flow (CBF). CSD was elicited by application of KCl on rat cortex and direct current (DC) potential was recorded as a typical characteristic of CSD. The pH(i) shift was mapped by neutral red (NR) fluorescence which was excited at 516-556 nm and emitted at 625 nm. The changes in hemoglobin concentrations were determined by dual-wavelength optical intrinsic signal imaging (OISI) at 550 nm and 625 nm. Integration of fluorescence imaging and dual-wavelength OISI was achieved by a time-sharing camera equipped with a liquid crystal tunable filter (LCTF). CBF was visualized by laser speckle contrast imaging (LSCI) through a separate camera. Besides, based on the dual-wavelength optical intrinsic signals (OISs) obtained from our system, NR fluorescence was corrected according to our method of fluorescence correction. We found that a transient intracellular acidification followed by a small alkalization occurred during CSD. After CSD, there was a prolonged intracellular acidification and the recovery of pH(i) from CSD took much longer time than those of hemodynamic response. Our results suggested that the new multimodal optical imaging system had the potential to advance our knowledge of CSD and might work as a useful tool to exploit neurovascular coupling under physiological and pathological conditions.