Beachdaichidh an t‑alt seo air cleachdadh teòiridh litreachasail iar-structarail an luchd-teoìridh Fhrangaich Gilles Deleuze is Gélix Guattari, gu sònraichte an aiste ainmeil aca ‘Qu’est-ce qu’une ...littérature mineure?’ ‘Dé th’ ann am mion-litreachas?’. Tòisichear le mìneachadh goirid air a’ choincheap de ‘mhion-litreachas’ agus an uair sin, a’ toirt iomradh an dà chuid air dùbhlanan a nochdas san aiste fhèin agus air breithneachaidhean o sgoilearan eile (Glissant agus Gauvin 2010, Jamison 2018, agus eile), feuchaidh an t‑alt ri ceist shònraichte a fhreagairt: ciamar a dh’fhaodadh an aiste seo — agus an teòiridh litreachasail nuadh-aimsireil is iar-nuadh-aimsireil san fharsaingeachd — a bhith cuideachail dhuinn ann a bhith a’ sgrùdadh litreachas na Gàidhlig? Bithear ag argamaid gu bheil feum aig teòiridhean a thogar ann an cànanan ceannasach air seallaidhean mhion-chànanan, a dh’fhaodas, air an dàrna làimh, cuid dhe na dùbhlanan aithnichte aca fhuasgladh agus, air an làimh eile, dùbhlanan agus dearmadan ùra a nochdadh air nach bi luchd-teòiridh chànanan ceannasach a’ smaoineachadh idir. Aig a’ cheart àm, ge-tà, bithear a’ dearbhadh gu bheil an t‑atharrachadh co-theacsa o Fhraingis gu Gàidhlig ag atharrachadh na teòiridh, cuideachd. Nithear sgrùdadh goirid air cuid de theacsaichean litreachasail Gàidhlig (dàin le Mona NicLeòid Wagner agus Lodaidh MacFhionghain agus nobhail le Aonghas Pàdraig Caimbeul), feuch ciamar a tha litreachas na Gàidhlig fhèin a’ dèiligeadh ri a staid mar ‘mhion-chànan’ agus ‘mhion-litreachas’, ann an teirmichean Deleuze is Guattari. Aig a’ cheann thall, dearbhaichear gur ann a dh’fhaodas teòiridhean litreachasail nuadh-aimsireil a bhith feumail ann a bhith a’ sgrùdadh litreachas na Gàidhlig ach gum feumar am freagarrachadh air neo an ath-chumadh ann an co-theacsa mion-chànain, agus togar ceistean nas fharsainge mu chiamar a dh’fhaodadh na teòiridhean seo a bhith feumail taobh a‑muigh an nua-litreachais a‑mhàin.
•Our goal is to validate layer-specific VASO fMRI with gold standard methods.•Layer-specific VASO sequences are implemented for 7T imaging in humans and rats.•Comparisons of VASO, optical imaging, ...and MION confirm the expected contrast origin.•We confirm that VASO is a valid measure to estimate layer-specific neural activity.
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Cerebral blood volume (CBV) has been shown to be a robust and important physiological parameter for quantitative interpretation of functional (f)MRI, capable of delivering highly localized mapping of neural activity. Indeed, with recent advances in ultra-high-field (≥7T) MRI hardware and associated sequence libraries, it has become possible to capture non-invasive CBV weighted fMRI signals across cortical layers. One of the most widely used approaches to achieve this (in humans) is through vascular-space-occupancy (VASO) fMRI. Unfortunately, the exact contrast mechanisms of layer-dependent VASO fMRI have not been validated for human fMRI and thus interpretation of such data is confounded. Here we validate the signal source of layer-dependent SS-SI VASO fMRI using multi-modal imaging in a rat model in response to neuronal activation (somatosensory cortex) and respiratory challenge (hypercapnia). In particular VASO derived CBV measures are directly compared to concurrent measures of total haemoglobin changes from high resolution intrinsic optical imaging spectroscopy (OIS). Quantified cortical layer profiling is demonstrated to be in agreement between VASO and contrast enhanced fMRI (using monocrystalline iron oxide nanoparticles, MION). Responses show high spatial localisation to layers of cortical processing independent of confounding large draining veins which can hamper BOLD fMRI studies, (depending on slice positioning). Thus, a cross species comparison is enabled using VASO as a common measure. We find increased VASO based CBV reactivity (3.1 ± 1.2 fold increase) in humans compared to rats. Together, our findings confirm that the VASO contrast is indeed a reliable estimate of layer-specific CBV changes. This validation study increases the neuronal interpretability of human layer-dependent VASO fMRI as an appropriate method in neuroscience application studies, in which the presence of large draining intracortical and pial veins limits neuroscientific inference with BOLD fMRI.
Contrast-enhanced cerebral blood volume-weighted (CBVw) fMRI response peaks are specific to the layer of evoked synaptic activity (Poplawsky et al., 2015), but the spatial resolution limit of CBVw ...fMRI is unknown. In this study, we measured the laminar spread of the CBVw fMRI evoked response in the external plexiform layer (EPL, 265 ± 65 μm anatomical thickness, mean ± SD, n = 30 locations from 5 rats) of the rat olfactory bulb during electrical stimulation of the lateral olfactory tract and examined its potential vascular source. First, we obtained the evoked CBVw fMRI responses with a 55 × 55 μm2 in-plane resolution and a 500-μm thickness at 9.4 T, and found that the fMRI signal peaked predominantly in the inner half of EPL (136 ± 54 μm anatomical thickness). The mean full-width at half-maximum of these fMRI peaks was 347 ± 102 μm and the functional spread was approximately 100 or 200 μm when the effects of the laminar thicknesses of EPL or inner EPL were removed, respectively. Second, we visualized the vascular architecture of EPL from a different rat using a Clear Lipid-exchanged Anatomically Rigid Imaging/immunostaining-compatible Tissue hYdrogel (CLARITY)-based tissue preparation method and confocal microscopy. Microvascular segments with an outer diameter of <11 μm accounted for 64.3% of the total vascular volume within EPL and had a mean segment length of 55 ± 40 μm (n = 472). Additionally, vessels that crossed the EPL border had a mean segment length outside of EPL equal to 73 ± 61 μm (n = 28), which is comparable to half of the functional spread (50–100 μm). Therefore, we conclude that dilation of these microvessels, including capillaries, likely dominate the CBVw fMRI response and that the biological limit of the fMRI spatial resolution is approximately the average length of 1–2 microvessel segments, which may be sufficient for examining sublaminar circuits.
•Compared layer-specific fMRI to vasoarchitecture using CLARITY in a single layer.•Contrast-enhanced fMRI spread was measured at a 55 × 55 μm2 in-plane resolution.•Mean fMRI spread approximately the mean length of 1–2 microvessels (50–100 μm).•Ultrahigh-resolution fMRI may be sufficient to examine laminar neurophysiology.
Stem cell-based therapeutics is a rapidly developing field associated with a number of clinical challenges. One such challenge lies in the implementation of methods to track stem cells and stem ...cell-derived cells in experimental animal models and in the living patient. Here, we provide an overview of cell tracking in the context of cardiac and neurological disease, focusing on the use of iron oxide-based particles (IOPs) visualized
in vivo
using magnetic resonance imaging (MRI). We discuss the types of IOPs available for such tracking, their advantages and limitations, approaches for labeling cells with IOPs, biological interactions and effects of IOPs at the molecular and cellular levels, and MRI-based and associated approaches for
in vivo
and histological visualization. We conclude with reviews of the literature on IOP-based cell tracking in cardiac and neurological disease, covering both preclinical and clinical studies.
After lesions of the somatosensory dorsal column (DC) pathway, the cortical hand representation can become unresponsive to tactile stimuli, but considerable responsiveness returns over weeks of ...post-lesion recovery. The reactivation suggests that preserved subthreshold sensory inputs become potentiated and axon sprouting occurs over time to mediate recovery. Here, we studied the recovery process in 3 squirrel monkeys, using high-resolution cerebral blood volume-based functional magnetic resonance imaging (CBV-fMRI) mapping of contralateral somatosensory cortex responsiveness to stimulation of distal finger pads with low and high level electrocutaneous stimulation (ES) before and 2, 4, and 6weeks after a mid-cervical level contralateral DC lesion. Both low and high intensity ES of digits revealed the expected somatotopy of the area 3b hand representation in pre-lesion monkeys, while in areas 1 and 3a, high intensity stimulation was more effective in activating somatotopic patterns. Six weeks post-lesion, and irrespective of the severity of loss of direct DC inputs (98%, 79%, 40%), somatosensory cortical area 3b of all three animals showed near complete recovery in terms of somatotopy and responsiveness to low and high intensity ES. However there was significant variability in the patterns and amplitudes of reactivation of individual digit territories within and between animals, reflecting differences in the degree of permanent and/or transient silencing of primary DC and secondary inputs 2weeks post-lesion, and their spatio-temporal trajectories of recovery between 2 and 6weeks. Similar variations in the silencing and recovery of somatotopy and responsiveness to high intensity ES in areas 3a and 1 are consistent with individual differences in damage to and recovery of DC and spinocuneate pathways, and possibly the potentiation of spinothalamic pathways. Thus, cortical deactivation and subsequent reactivation depends not only on the degree of DC lesion, but also on the severity and duration of loss of secondary as well as primary inputs revealed by low and high intensity ES.
•High-resolution CBV-fMRI responses to ES can track digit-specific cortical reorganization after sensory loss in monkeys.•After a DC lesion, high intensity nociceptive stimulation activates more of the cortical network than innocuous stimuli.•Even after extensive loss of DC inputs, the hand representations in areas 3b and 1 become extensively reactivated.•The spared afferents and second order spinal cord pathways likely contribute to the cortical reactivation after DC lesions.
The spatiotemporal characteristics of cerebral blood volume (CBV) and flow (CBF) responses are important for understanding neurovascular coupling mechanisms and blood oxygenation level-dependent ...(BOLD) signals. For this, cortical layer-dependent BOLD, CBV and CBF responses were measured at the cat visual cortex using fMRI. Major findings are: (
i) the time-dependent fMRI cortical profile is dependent on imaging modality. Overall, the peak across the cortex occurs at the cortical surface for BOLD, but at the middle cortical layer for CBV and CBF. Compared to an initial stimulation period (4–10 s), the spatial specificity of CBV to the middle cortical layer increases significantly at a later time, while the specificity of BOLD and CBF slightly changes. (
ii) The CBV response at the upper cortical area containing large pial vessels has a faster onset time and time to peak than the BOLD response at the same area, and a faster time to peak than CBV at the middle cortical area with microvessels. This suggests that the dilation of microvessels at the middle cortical area follows arterial volume increase at the surface of the cortex. (
iii) For all three modalities, the post-stimulus undershoot was observed with the 60-s stimulation paradigm, indicating that the post-stimulus BOLD undershoot cannot be explained by the delayed venous CBV recovery theory under our experimental conditions. (
iv) The relationship between CBV and CBF responses is both spatially and temporally dependent. Thus, a single power-law scaling constant (gamma value) may not be applicable for high-resolution study.
Functional magnetic resonance imaging (fMRI) techniques are based on the assumption that changes in spike activity are accompanied by modulation in the blood oxygenation level—dependent (BOLD) ...signal. In addition to conventional increases in BOLD signals, sustained negative BOLD signal changes are occasionally observed and are thought to reflect a decrease in neural activity. In this study, the source of the negative BOLD signal was investigated using T2*-weighted BOLD and cerebral blood volume (CBV) techniques in isoflurane-anesthetized cats. A positive BOLD signal change was observed in the primary visual cortex (area 18) during visual stimulation, while a prolonged negative BOLD change was detected in the adjacent suprasylvian gyrus containing higher-order visual areas. However, in both regions neurons are known to increase spike activity during visual stimulation. The positive and negative BOLD amplitudes obtained at six spatial-frequency stimuli were highly correlated, and negative BOLD percent changes were approximately one third of the postitive changes. Area 18 with positive BOLD signals experienced an increase in CBV, while regions exhibiting the prolonged negative BOLD signal underwent a decrease in CBV. The CBV changes in area 18 were faster than the BOLD signals from the same corresponding region and the CBV changes in the suprasylvian gyrus. The results support the notion that reallocation of cortical blood resources could overcome a local demand for increased cerebral blood flow induced by increased neural activity. The findings of this study imply that caution should be taken when interpreting the negative BOLD signals as a decrease in neuronal activity.
A rapid, sensitive, and simple immunosensor has been developed for the detection of Pantoea stewartii subsp. Stewartii (Pss). This immunosensor combines magnetic relaxation switch (MRS) assay with ...polystyrene microparticle-induced immune multivalency enrichment system. Comparing to conventional enzyme-linked immunosorbent assay (ELISA), the immunosensor developed in this study provides higher sensitivity and requires less analysis time. The detection limit of Pss obtained by immunosensor was determined to be 103cfu/mL, 50 times lower than that by ELISA (5×104cfu/mL), while the analysis time required by immunosensor is 30min much shorter than that by ELISA. The average recoveries studied with Pss at various spiking levels ranged from 85.5% to 93.4% with a relative standard deviation (RSD) below 6.0%. No cross-reaction with the other five strains was found, demonstrating a good specificity of Pss detection. The results showed that the MRS immunosensor combined with PS-induced immune multivalency enhancement system is a promising platform for the determination of large biological molecules due to its high sensitivity, specificity, homogeneity, and speed.
► An immunosensor combines magnetic relaxation switch and immune multivalency enrichment system. ► The LOD of this MRS immunosensor was determined to be 50 times lower than that by ELISA. ► The analysis time of MRS immunosensor (30min) was much shorter compared with that of ELISA.
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