Time Course Of Signal Research Articles

Multiparametric imaging of brain hemodynamics and function using gas-inhalation MRI

Diagnosis and treatment monitoring of cerebrovascular diseases routinely require hemodynamic imaging of the brain. Current methods either only provide part of the desired information or require the injection of multiple exogenous agents. In this study, we developed a multiparametric imaging scheme for the imaging of brain hemodynamics and function using gas-inhalation MRI. The proposed technique uses a single MRI scan to provide simultaneous measurements of baseline venous cerebral blood volume (vCBV), cerebrovascular reactivity (CVR), bolus arrival time (BAT), and resting-state functional connectivity (fcMRI). This was achieved with a novel, concomitant O2 and CO2 gas inhalation paradigm, rapid MRI image acquisition with a 9.3min BOLD sequence, and an advanced algorithm to extract multiple hemodynamic information from the same dataset. In healthy subjects, CVR and vCBV values were 0.23±0.03%/mmHg and 0.0056±0.0006%/mmHg, respectively, with a strong correlation (r=0.96 for CVR and r=0.91 for vCBV) with more conventional, separate acquisitions that take twice the scan time. In patients with Moyamoya syndrome, CVR in the stenosis-affected flow territories (typically anterior-cerebral-artery, ACA, and middle-cerebral-artery, MCA, territories) was significantly lower than that in posterior-cerebral-artery (PCA), which typically has minimal stenosis, flow territories (0.12±0.06%/mmHg vs. 0.21±0.05%/mmHg, p<0.001). BAT of the gas bolus was significantly longer (p=0.008) in ACA/MCA territories, compared to PCA, and the maps were consistent with the conventional contrast-enhanced CT perfusion method. FcMRI networks were robustly identified from the gas-inhalation MRI data after factoring out the influence of CO2 and O2 on the signal time course. The spatial correspondence between the gas-data-derived fcMRI maps and those using a separate, conventional fcMRI scan was excellent, showing a spatial correlation of 0.58±0.17 and 0.64±0.20 for default mode network and primary visual network, respectively. These findings suggest that advanced gas-inhalation MRI provides reliable measurements of multiple hemodynamic parameters within a clinically acceptable imaging time and is suitable for patient examinations.

The Differential Hormonal Milieu of Morning versus Evening May Have an Impact on Muscle Hypertrophic Potential.

Substantial gains in muscle strength and hypertrophy are clearly associated with the routine performance of resistance training. What is less evident is the optimal timing of the resistance training stimulus to elicit these significant functional and structural skeletal muscle changes. Therefore, this investigation determined the impact of a single bout of resistance training performed either in the morning or evening upon acute anabolic signalling (insulin-like growth factor-binding protein-3 (IGFBP-3), myogenic index and differentiation) and catabolic processes (cortisol). Twenty-four male participants (age 21.4±1.9yrs, mass 83.7±13.7kg) with no sustained resistance training experience were allocated to a resistance exercise group (REP). Sixteen of the 24 participants were randomly selected to perform an additional non-exercising control group (CP) protocol. REP performed two bouts of resistance exercise (80% 1RM) in the morning (AM: 0800 hrs) and evening (PM: 1800 hrs), with the sessions separated by a minimum of 72 hours. Venous blood was collected immediately prior to, and 5 min after, each resistance exercise and control sessions. Serum cortisol and IGFBP-3 levels, myogenic index, myotube width, were determined at each sampling period. All data are reported as mean ± SEM, statistical significance was set at P≤0.05. As expected a significant reduction in evening cortisol concentration was observed at pre (AM: 98.4±10.5, PM: 49.8±4.4 ng/ml, P<0.001) and post (AM: 98.0±9.0, PM: 52.7±6.0 ng/ml, P<0.001) exercise. Interestingly, individual cortisol differences pre vs post exercise indicate a time-of-day effect (AM difference: -2±2.6%, PM difference: 14.0±6.7%, P = 0.03). A time-of-day related elevation in serum IGFBP-3 (AM: 3274.9 ± 345.2, PM: 3605.1 ± 367.5, p = 0.032) was also evident. Pre exercise myogenic index (AM: 8.0±0.6%, PM: 16.8±1.1%) and myotube width (AM: 48.0±3.0, PM: 71.6±1.9 μm) were significantly elevated (P<0.001) in the evening. Post exercise myogenic index was greater AM (11.5±1.6%) compared with PM (4.6±0.9%). No difference was observed in myotube width (AM: 48.5±1.5, PM: 47.8±1.8 μm) (P>0.05). Timing of resistance training regimen in the evening appears to augment some markers of hypertrophic potential, with elevated IGFBP-3, suppressed cortisol and a superior cellular environment. Further investigation, to further elucidate the time course of peak anabolic signalling in morning vs evening training conditions, are timely.

Ongoing Slow Fluctuations in V1 Impact on Visual Perception.

The human brain’s ongoing activity is characterized by intrinsic networks of coherent fluctuations, measured for example with correlated functional magnetic resonance imaging signals. So far, however, the brain processes underlying this ongoing blood oxygenation level dependent (BOLD) signal orchestration and their direct relevance for human behavior are not sufficiently understood. In this study, we address the question of whether and how ongoing BOLD activity within intrinsic occipital networks impacts on conscious visual perception. To this end, backwardly masked targets were presented in participants’ left visual field only, leaving the ipsi-lateral occipital areas entirely free from direct effects of task throughout the experiment. Signal time courses of ipsi-lateral BOLD fluctuations in visual areas V1 and V2 were then used as proxies for the ongoing contra-lateral BOLD activity within the bilateral networks. Magnitude and phase of these fluctuations were compared in trials with and without conscious visual perception, operationalized by means of subjective confidence ratings. Our results show that ipsi-lateral BOLD magnitudes in V1 were significantly higher at times of peak response when the target was perceived consciously. A significant difference between conscious and non-conscious perception with regard to the pre-target phase of an intrinsic-frequency regime suggests that ongoing V1 fluctuations exert a decisive impact on the access to consciousness already before stimulation. Both effects were absent in V2. These results thus support the notion that ongoing slow BOLD activity within intrinsic networks covering V1 represents localized processes that modulate the degree of readiness for the emergence of visual consciousness.

Revealing the time course of signals influencing the generation of secondary saccades using Aalen’s additive hazards model

Saccadic eye movements are frequently followed by smaller secondary saccades which are generally assumed to correct for the error in primary saccade landing position. However, secondary saccades can also occur after accurate primary saccades and they are often as small as microsaccades, therefore raising the need to further scrutinize the processes involved in secondary saccade generation. Following up a previous study, we analyzed secondary saccades using rate analysis which allows us to quantify experimental effects as shifts in distributions, therefore going beyond comparisons of mean differences. We use Aalen’s additive hazards model to delineate the time course of key influences on the secondary saccade rate. In addition to the established effect of primary saccade error, we observed a time-varying influence of under- vs. overshooting – with a higher risk of generating secondary saccades following undershoots. Moreover, increasing target eccentricity influenced the programming of secondary saccades, therefore demonstrating that error-unrelated variables co-determine secondary saccade programs. Our results provide new insights into the generative mechanisms of small saccades during postsaccadic fixation that need to be accounted for by secondary saccade models.

Matrix pencil decomposition of time-resolved proton MRI for robust and improved assessment of pulmonary ventilation and perfusion.

To present an improved and robust method of pulmonary function assessment from time-resolved proton MRI using a matrix pencil (MP) method in combination with a linear least squares analysis. Simulations of the signal time course in lung parenchyma were performed to compare the accuracy of Fourier decomposition (FD) and MP methods for the estimation of respiratory and cardiac amplitudes. Series of two-dimensional time-resolved lung images were acquired in healthy volunteers at 1.5 T using ultra-fast steady-state free precession. Qualitative lung ventilation- and perfusion-weighted images as well as a quantitative map of fractional ventilation, perfusion, and blood arrival time were calculated using the proposed MP method and compared with the contemporary FD technique. A region-of-interest analysis was performed on the quantitative data. The signal analysis performed using MP decomposition resulted in reduced variability of the estimated respiratory and cardiac amplitudes in comparison with FD for both simulated and in vivo data. MP decomposition provides an automatic, robust, and more accurate estimation of amplitudes of respiratory and cardiac signal modulations in the lung parenchyma than the contemporary FD technique. Magn Reson Med 77:336-342, 2017. © 2016 Wiley Periodicals, Inc.

Age Effects in L2 Grammar Processing as Revealed by ERPs and How (Not) to Study Them

In this study we investigate the effect of age of acquisition (AoA) on grammatical processing in second language learners as measured by event-related brain potentials (ERPs). We compare a traditional analysis involving the calculation of averages across a certain time window of the ERP waveform, analyzed with categorical groups (early vs. late), with a generalized additive modeling analysis, which allows us to take into account the full range of variability in both AoA and time. Sixty-six Slavic advanced learners of German listened to German sentences with correct and incorrect use of non-finite verbs and grammatical gender agreement. We show that the ERP signal depends on the AoA of the learner, as well as on the regularity of the structure under investigation. For gender agreement, a gradual change in processing strategies can be shown that varies by AoA, with younger learners showing a P600 and older learners showing a posterior negativity. For verb agreement, all learners show a P600 effect, irrespective of AoA. Based on their behavioral responses in an offline grammaticality judgment task, we argue that the late learners resort to computationally less efficient processing strategies when confronted with (lexically determined) syntactic constructions different from the L1. In addition, this study highlights the insights the explicit focus on the time course of the ERP signal in our analysis framework can offer compared to the traditional analysis.

Differential fMRI Activation Patterns to Noxious Heat and Tactile Stimuli in the Primate Spinal Cord.

Mesoscale local functional organizations of the primate spinal cord are largely unknown. Using high-resolution fMRI at 9.4 T, we identified distinct interhorn and intersegment fMRI activation patterns to tactile versus nociceptive heat stimulation of digits in lightly anesthetized monkeys. Within a spinal segment, 8 Hz vibrotactile stimuli elicited predominantly fMRI activations in the middle part of ipsilateral dorsal horn (iDH), along with significantly weaker activations in ipsilateral (iVH) and contralateral (cVH) ventral horns. In contrast, nociceptive heat stimuli evoked widespread strong activations in the superficial part of iDH, as well as in iVH and contralateral dorsal (cDH) horns. As controls, only weak signal fluctuations were detected in the white matter. The iDH responded most strongly to both tactile and heat stimuli, whereas the cVH and cDH responded selectively to tactile versus nociceptive heat, respectively. Across spinal segments, iDH activations were detected in three consecutive segments in both tactile and heat conditions. Heat responses, however, were more extensive along the cord, with strong activations in iVH and cDH in two consecutive segments. Subsequent subunit B of cholera toxin tracer histology confirmed that the spinal segments showing fMRI activations indeed received afferent inputs from the stimulated digits. Comparisons of the fMRI signal time courses in early somatosensory area 3b and iDH revealed very similar hemodynamic stimulus-response functions. In summary, we identified with fMRI distinct segmental networks for the processing of tactile and nociceptive heat stimuli in the cervical spinal cord of nonhuman primates. Significance statement: This is the first fMRI demonstration of distinct intrasegmental and intersegmental nociceptive heat and touch processing circuits in the spinal cord of nonhuman primates. This study provides novel insights into the local functional organizations of the primate spinal cord for pain and touch, information that will be valuable for designing and optimizing therapeutic interventions for chronic pain management.

Aberrant functioning of the putamen links delusions, antipsychotic drug dose, and compromised connectivity in first episode psychosis—Preliminary fMRI findings

The dopamine theory proposes the relationship of delusions to aberrant signaling in striatal circuitries that can be normalized with dopamine D2 receptor-blocking drugs. Localization of such circuitries, as well as their upstream and downstream signaling, remains poorly known. We collected functional magnetic resonance images from first-episode psychosis patients and controls during an audiovisual movie. Final analyses included 20 patients and 20 controls; another sample of 10 patients and 10 controls was used to calculate a comparison signal-time course. We identified putamen circuitry in which the signal aberrance (poor correlation with the comparison signal time course) was predicted by the dopamine theory, being greater in patients than controls; correlating positively with delusion scores; and correlating negatively with antipsychotic-equivalent dosage. In Granger causality analysis, patients showed a compromised contribution of the cortical salience network to the putamen and compromised contribution of the putamen to the default mode network. Results were corrected for multiple comparisons at the cluster level with primary voxel-wise threshold p<0.005 for the salience network contribution, but liberal primary threshold p<0.05 was used in other group comparisons. If replicated in larger studies, these findings may help unify and extend current hypotheses on dopaminergic dysfunction, salience processing and pathogenesis of delusions.

Widespread Vestibular Activation of the Rodent Cortex

Much of our understanding of the neuronal mechanisms of spatial navigation is derived from chronic recordings in rodents in which head-direction, place, and grid cells have all been described. However, despite the proposed importance of self-reference information to these internal representations of space, their congruence with vestibular signaling remains unclear. Here we have undertaken brain-wide functional mapping using both fMRI and electrophysiological methods to directly determine the spatial extent, strength, and time course of vestibular signaling across the rat forebrain. We find distributed activity throughout thalamic, limbic, and particularly primary sensory cortical areas in addition to known head-direction pathways. We also observe activation of frontal regions, including infralimbic and cingulate cortices, indicating integration of vestibular information throughout functionally diverse cortical regions. These whole-brain activity maps therefore suggest a widespread contribution of vestibular signaling to a self-centered framework for multimodal sensorimotor integration in support of movement planning, execution, spatial navigation, and autonomic responses to gravito-inertial changes.

A Stochastic Delay Differential Model of Cerebral Autoregulation

Mathematical models of the cardiovascular system and of cerebral autoregulation (CAR) have been employed for several years in order to describe the time course of pressures and flows changes subsequent to postural changes. The assessment of the degree of efficiency of cerebral auto regulation has indeed importance in the prognosis of such conditions as cerebro-vascular accidents or Alzheimer. In the quest for a simple but realistic mathematical description of cardiovascular control, which may be fitted onto non-invasive experimental observations after postural changes, the present work proposes a first version of an empirical Stochastic Delay Differential Equations (SDDEs) model. The model consists of a total of four SDDEs and two ancillary algebraic equations, incorporates four distinct delayed controls from the brain onto different components of the circulation, and is able to accurately capture the time course of mean arterial pressure and cerebral blood flow velocity signals, reproducing observed auto-correlated error around the expected drift.

Delayed Activation of Muscle Protein Synthesis following Resistance Exercise in Mice is mTORC1‐Dependent

The activation of the mechanistic target of rapamycin-complex-1 (mTORC1) is important for muscle hypertrophy following resistance exercise. However, our present understanding of the dynamics of anabolic signaling and muscle protein synthesis (MPS) following an acute bout of resistance exercise in mice is lacking. PURPOSE: To determine the time course of anabolic signaling and MPS in response to an acute bout of resistance exercise in mice. METHODS: Three month old C57BL/6 mice (n = 56) were anesthetized, the sciatic nerve exposed before the point of trifurcation, and all of the muscles of the right distal hindlimb were stimulated for 10 sets of 6 repetitions with 1 minute rest between sets. Both control and stimulated tibialis anterior (TA) muscles were collected 0, 0.75, 1.5, 3, 4.5, 6, 9, 12 and 24 hours post-loading. Thirty minutes prior to collection animals were injected with 100 μL of 0.04 μmol/g puromycin. Two additional groups of mice were injected with 110 μL of 1.5 μg/g rapamycin or saline immediately prior to loading and collected 6h later. Muscles were processed for western blot analysis of proposed anabolic signaling molecules and MPS via SUnSET. RESULTS: ERK1/2 phosphorylation peaked at 0.75h (2.76 ± 0.60) and pS6K1 Thr389 was significantly higher 1.5h (4.18 ± 2.75) and 3h (5.39 ± 0.62) post-loading (p < 0.05). MPS showed two peaks, the first at 0.75h (1.27 ± 0.14) and the second at 6h (1.27 ± 0.10) post-loading. Rapamycin abolished the peak at 6h even though mTORC1 activity was not elevated at this timepoint. CONCLUSION Following acute resistance exercise in mice, there are two peaks of anabolic activity. The first corresponds with an increase in ERK1/2 activity 0.75h after loading and the second, at 6h, is dependent on mTORC1 activation.

Accuracy and Precision of Head Motion Information in Multi-Channel Free Induction Decay Navigators for Magnetic Resonance Imaging.

Free induction decay (FID) navigators were found to qualitatively detect rigid-body head movements, yet it is unknown to what extent they can provide quantitative motion estimates. Here, we acquired FID navigators at different sampling rates and simultaneously measured head movements using a highly accurate optical motion tracking system. This strategy allowed us to estimate the accuracy and precision of FID navigators for quantification of rigid-body head movements. Five subjects were scanned with a 32-channel head coil array on a clinical 3T MR scanner during several resting and guided head movement periods. For each subject we trained a linear regression model based on FID navigator and optical motion tracking signals. FID-based motion model accuracy and precision was evaluated using cross-validation. FID-based prediction of rigid-body head motion was found to be with a mean translational and rotational error of 0.14±0.21 mm and 0.08±0.13°, respectively. Robust model training with sub-millimeter and sub-degree accuracy could be achieved using 100 data points with motion magnitudes of ±2 mm and ±1° for translation and rotation. The obtained linear models appeared to be subject-specific as inter-subject application of a "universal" FID-based motion model resulted in poor prediction accuracy. The results show that substantial rigid-body motion information is encoded in FID navigator signal time courses. Although, the applied method currently requires the simultaneous acquisition of FID signals and optical tracking data, the findings suggest that multi-channel FID navigators have a potential to complement existing tracking technologies for accurate rigid-body motion detection and correction in MRI.

High-contrast imaging of reversibly switchable fluorescent proteins via temporally unmixed multispectral optoacoustic tomography.

Photocontrol of reversibly switchable fluorescent proteins (RSFPs) was used to program optoacoustic signal time courses that were temporally unmixed to increase the proteins' contrast-to-noise-ratios (CNRs) in optoacoustic imaging. In this way, two variants of the RSFP Dronpa with very similar optoacoustic spectra could be readily discriminated in the presence of highly absorbing blood. Addition of temporal unmixing to multispectral optoacoustic tomography (tuMSOT) in conjunction with synthetic or genetically encoded photochromic contrast agents and customized photoswitching schedules can increase the performance of multiplexed and high-contrast molecular optoacoustic imaging.

Visualization and Quantification of Differences in Interaction Strength of Sensory and Motor Networks in the Human Brain using Differential Correlation Analysis and Graph Theory

Event Abstract Back to Event Visualization and Quantification of Differences in Interaction Strength of Sensory and Motor Networks in the Human Brain using Differential Correlation Analysis and Graph Theory Christof Karmonik1*, Jeff Anderson2, Steve Fung3, Amit Verma4 and Robert Grossman1 1 Houston Methodist Research Institute, Neurosurgery, United States 2 Houston Methodist Research Institute, Translational Imaging, United States 3 Houston Methodist Research Institute, Radiology, United States 4 Houston Methodist Hospital, Neurology, United States Purpose: To compare the interaction strength of sensory and motor networks between healthy controls and subjects diagnosed with complex partial seizures (CPS) when initiating a willed activity using a new graph-theoretical analysis approach Methods: Functional magnetic resonance images (fMRI) (TR=1300 ms) were obtained during the performance of a visual presentation of 10 faces (10 sec, interspersed by green background, 60 sec). Subjects (9 healthy controls (HC), 6 male, average age: 34.7, 5 CPS subjects, male, average age: 28.4) were instructed to squeeze a ball if a face was perceived as unpleasant. Interictal spikes indicative of anomalous brain activity were identified with simultaneous EEG recordings during the fMRI examinations of the CPS subjects. For each subject, a difference correlation map was calculated using a BOLD signal time course from the primary visual cortex (sensory input) and one from the motor cortex (motor output). Networks using a 2D spring-embedded design and using the 3D anatomical Talairach space with correlation coefficients of signal time courses as edge weights were created. Statistical significance between the networks for the two groups was investigated for selected network parameters. 3D printing technology was used to create replica of computer-generated 3D networks. Results: On average, visual cortex, cuneus, precuneus, dorsal lateral prefrontal cortex (DLPC), cingulate gyrus, parahippocampal gyrus, thalamus, lentiform nucleus, caudate and substantia nigra exhibited stronger correlation with the sensory (input) time course, while postcentral gyrus, supplementary motor area, precentral gyrus, insula and regions in the cerebellum showed stronger correlation with the motor (output) time course. Graph-theoretical analysis showed a larger cluster coefficient in the CPS group (p-value<0.05), as well as larger diameter, average path length and larger first eigenvalue (p-value <0.17). Conclusion: Differential correlation analysis in combination with a graph-theoretical approach revealed a stronger small-world character in CPS subjects of the sensory and motor brain networks activated during the performance of a willed motor activity initiated by an emotional stimulus potentially as a result of compensatory mechanisms. Keywords: functional MRI, brain connectivity, simultaneous EEG-fMRI, Graph-theoretical analysis, initiation of willed activity Conference: XII International Conference on Cognitive Neuroscience (ICON-XII), Brisbane, Queensland, Australia, 27 Jul - 31 Jul, 2014. Presentation Type: Poster Topic: Methods Development Citation: Karmonik C, Anderson J, Fung S, Verma A and Grossman R (2015). Visualization and Quantification of Differences in Interaction Strength of Sensory and Motor Networks in the Human Brain using Differential Correlation Analysis and Graph Theory. Conference Abstract: XII International Conference on Cognitive Neuroscience (ICON-XII). doi: 10.3389/conf.fnhum.2015.217.00285 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 19 Feb 2015; Published Online: 24 Apr 2015. * Correspondence: Dr. Christof Karmonik, Houston Methodist Research Institute, Neurosurgery, Houston, United States, ckarmonik@houstonmethodist.org Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Christof Karmonik Jeff Anderson Steve Fung Amit Verma Robert Grossman Google Christof Karmonik Jeff Anderson Steve Fung Amit Verma Robert Grossman Google Scholar Christof Karmonik Jeff Anderson Steve Fung Amit Verma Robert Grossman PubMed Christof Karmonik Jeff Anderson Steve Fung Amit Verma Robert Grossman Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

The time course of the aversive conflict signal.

The idea that conflicts are aversive signals recently has gained strong support by both physiological as well as psychological evidence. However, the time course of the aversive signal has not been subject to direct investigation. In the present study, participants had to judge the valence of neutral German words after being primed with conflict or non-conflict Stroop stimuli in three experiments with varying SOA (200 ms, 400 ms, 800 ms) and varying prime presentation time. Conflict priming effects (i.e., increased frequencies of negative judgments after conflict as compared to non-conflict primes) were found for SOAs of 200 ms and 400 ms, but absent (or even reversed) with a SOA of 800 ms. These results imply that the aversiveness of conflicts is evaluated automatically with short SOAs, but is actively counteracted with prolonged prime presentation.

Skeletal muscle microvascular function in girls with Turner syndrome

BackgroundExercise intolerance is prevalent in individuals with Turner Syndrome (TS). We recently demonstrated that girls with TS have normal aerobic but altered skeletal muscle anaerobic metabolism compared to healthy controls (HC). The purpose of this study was to compare peripheral skeletal muscle microvascular function in girls with TS to HC after exercise. We hypothesized that girls with TS would have similar muscle blood-oxygen level-dependent (BOLD) magnetic resonance imaging (MRI) signal responses during recovery from exercise compared to HC. MethodsThirteen TS participants and 8 HC completed testing. BOLD MRI was used to measure skeletal muscle microvascular response during 60second recovery, following 60s of exercise at 65% of maximal workload. Exercise and recovery were repeated four times, and the BOLD signal time course was fit to a four-parameter sigmoid function. ResultsParticipants were 13.7±3.1years old and weighed 47.9±14.6kg. The mean change in BOLD signal intensity following exercise at the end of recovery, the mean response time of the function/the washout of deoxyhemoglobin, and the mean half-time of recovery were similar between the TS and HC groups. ConclusionsOur results demonstrate that compared to HC, peripheral skeletal muscle microvascular function following exercise in girls with TS is not impaired. General significanceThis study supports the idea that the aerobic energy pathway is not impaired in children with TS in response to submaximal exercise. Other mechanisms are likely responsible for exercise intolerance in TS; this needs to be further investigated.

BDNF-induced nitric oxide signals in cultured rat hippocampal neurons: time course, mechanism of generation, and effect on neurotrophin secretion.

BDNF and nitric oxide signaling both contribute to plasticity at glutamatergic synapses. However, the role of combined signaling of both pathways at the same synapse is largely unknown. Using NO imaging with diaminofluoresceine in cultured hippocampal neurons we analyzed the time course of neurotrophin-induced NO signals. Application of exogenous BDNF, NT-4, and NT-3 (but not NGF) induced NO signals in the soma and in proximal dendrites of hippocampal neurons that were sensitive to NO synthase activity, TrkB signaling, and intracellular calcium elevation. The effect of NO signaling on neurotrophin secretion was analyzed in BDNF-GFP, and NT-3-GFP transfected hippocampal neurons. Exogenous application of the NO donor sodium-nitroprusside markedly inhibited neurotrophin secretion. However, endogenously generated NO in response to depolarization and neurotrophin stimulation, both did not result in a negative feedback on neurotrophin secretion. These results suggest that a negative feedback of NO signaling on synaptic secretion of neurotrophins operates only at high intracellular levels of nitric oxide that are under physiological conditions not reached by depolarization or BDNF signaling.

234 Kinetic analysis of dynamic 11C-verapamil PET study: Compartmental v adaptive mixture models comparison

Background: Temporal aspects of dynamic positron emission tomography (PET) generally rely on compartmental models (CM), with questionable assumptions to summarise functional kinetics of injected radio-tracers in living tissues. Material and Methods: The tracer signal time-course is a combination of vascular delivery and tissue retention effects which do not always satisfy the assumptions of tissue homogeneity and instant mixing within compartments required by the CM. This tissue activity time-course can typically be expressed as a convolution between the signal of the tracer in the arterial supply and the tissue residue function. The residue represents the amount of tracer remaining in the tissue and provides a description of the tracer kinetics measurable by the PET scan. Thus, in statistical terms, the residue can be thought of as a survival function for the residence of the tracer in the tissue which does not require the physiological constraints intrinsic in the exponential-like residue needed for CM. Accordingly more flexible novel approaches − nonparametric and later adaptive mixture models − to estimate the residue based on a piecewise linear form have been developed. The new approaches have been successfully probed on two of the most well-established PET radiotracers, O-H2O and F-fluorodeoxyglucose, used for perfusion and glucose metabolism respectively. This study shows the extension of the new approaches to the multiple-drug resistance transporter P-glycoprotein (P-gp) highly present at the blood–brain barrier (BBB) using C-Verapamil (Vp) in healthy humans before and after inhibition of the P-gp by Cyclosporine (CsA) infusion. Previous PET studies on measuring BBB activity by CsA infusion using Vp have revealed difficulties for the CM to recover metabolic information as they require a full understanding of the tracers metabolisation in the tissue, which is still not certain for Vp. This problem is especially latent when the inhibition of the P-gp allows the tracer through the BBB where it is retained once at the brain tissue level. Results: This work examines and evaluate adaptive mixture model as an alternative to conventional compartment techniques in recovering metabolic information from dynamic PET studies with less biological restrictions. Key bioparameters such as flux, flow, blood volume and volume of distribution from the two different approaches are compared. Cross-validation is used to make regional comparisons and evaluate the fit of the two different estimated residue functions to the tissue activity curves. Conclusions: The accuracy of the standard models for Vp PET studies can be questionable, likely because behaviour of Vp metabolites in tissue is still unclear. Significant statistical evidence in favour of the new adaptivemixture models has been found. Supported by Science Foundation Ireland under SFI-PI 11/27 and by the National Institute of Health (NCI) under PO1-CA-42045.

Multi-photon Intracellular Sodium Imaging Combined with UV-mediated Focal Uncaging of Glutamate in CA1 Pyramidal Neurons

Multi-photon fluorescence microscopy has enabled the analysis of morphological and physiological parameters of brain cells in the intact tissue with high spatial and temporal resolution. Combined with electrophysiology, it is widely used to study activity-related calcium signals in small subcellular compartments such as dendrites and dendritic spines. In addition to calcium transients, synaptic activity also induces postsynaptic sodium signals, the properties of which are only marginally understood. Here, we describe a method for combined whole-cell patch-clamp and multi-photon sodium imaging in cellular micro domains of central neurons. Furthermore, we introduce a modified procedure for ultra-violet (UV)-light-induced uncaging of glutamate, which allows reliable and focal activation of glutamate receptors in the tissue. To this end, whole-cell recordings were performed on Cornu Ammonis subdivision 1 (CA1) pyramidal neurons in acute tissue slices of the mouse hippocampus. Neurons were filled with the sodium-sensitive fluorescent dye SBFI through the patch-pipette, and multi-photon excitation of SBFI enabled the visualization of dendrites and adjacent spines. To establish UV-induced focal uncaging, several parameters including light intensity, volume affected by the UV uncaging beam, positioning of the beam as well as concentration of the caged compound were tested and optimized. Our results show that local perfusion with caged glutamate (MNI-Glutamate) and its focal UV-uncaging result in inward currents and sodium transients in dendrites and spines. Time course and amplitude of both inward currents and sodium signals correlate with the duration of the uncaging pulse. Furthermore, our results show that intracellular sodium signals are blocked in the presence of blockers for ionotropic glutamate receptors, demonstrating that they are mediated by sodium influx though this pathway. In summary, our method provides a reliable tool for the investigation of intracellular sodium signals induced by focal receptor activation in intact brain tissue.

Multi-photon intracellular sodium imaging combined with UV-mediated focal uncaging of glutamate in CA1 pyramidal neurons.

Multi-photon fluorescence microscopy has enabled the analysis of morphological and physiological parameters of brain cells in the intact tissue with high spatial and temporal resolution. Combined with electrophysiology, it is widely used to study activity-related calcium signals in small subcellular compartments such as dendrites and dendritic spines. In addition to calcium transients, synaptic activity also induces postsynaptic sodium signals, the properties of which are only marginally understood. Here, we describe a method for combined whole-cell patch-clamp and multi-photon sodium imaging in cellular micro domains of central neurons. Furthermore, we introduce a modified procedure for ultra-violet (UV)-light-induced uncaging of glutamate, which allows reliable and focal activation of glutamate receptors in the tissue. To this end, whole-cell recordings were performed on Cornu Ammonis subdivision 1 (CA1) pyramidal neurons in acute tissue slices of the mouse hippocampus. Neurons were filled with the sodium-sensitive fluorescent dye SBFI through the patch-pipette, and multi-photon excitation of SBFI enabled the visualization of dendrites and adjacent spines. To establish UV-induced focal uncaging, several parameters including light intensity, volume affected by the UV uncaging beam, positioning of the beam as well as concentration of the caged compound were tested and optimized. Our results show that local perfusion with caged glutamate (MNI-Glutamate) and its focal UV-uncaging result in inward currents and sodium transients in dendrites and spines. Time course and amplitude of both inward currents and sodium signals correlate with the duration of the uncaging pulse. Furthermore, our results show that intracellular sodium signals are blocked in the presence of blockers for ionotropic glutamate receptors, demonstrating that they are mediated by sodium influx though this pathway. In summary, our method provides a reliable tool for the investigation of intracellular sodium signals induced by focal receptor activation in intact brain tissue.