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Chuzo Tanaka

Publications and source records attributed to Chuzo Tanaka.

10 recordsLinked to original sources
PubMed2006

Toward a common circle: interhemispheric contextual modulation in human early visual areas.

Humans can readily and effortlessly perceive a rich, stable, and unified visual world from a complex visual scene. Yet our internal representation of a visual object appears to be sparse and fragmented. How and where in the brain are such fragmented representations organized into a whole percept? Recent studies have accumulated evidence that some global feature integration is mediated at the early stage of visual processing. However, the spatial operating range of the integration still remains unclear. The present human functional magnetic resonance imaging study provides support that the global integration process in early visual areas, including even the primary visual area V1, is mediated beyond the separated projection of visual hemifields from right and left sides of the fixation to the visual cortex of the contralateral cerebral hemisphere. Retinotopic neural responses corresponding to a visual target were significantly enhanced when another target was simultaneously presented at the point-symmetrical position in the nonassociated visual field quadrant. The result makes a convincing case that the contextual effects involve feedback from higher areas, because there are no direct callosal connections that allow such interhemispheric contextual modulation. This enhancement from the ipsilateral hemifield may help rapid position-and-size-invariant detection of a circular pattern, which may be special among visual structures because of its ubiquity in natural scenes. Early visual areas as well as higher ones may play a more essential role in perceiving the unity of the real world than previously thought.

Adult↗
PubMed2006

Cell labeling for magnetic resonance imaging with the T1 agent manganese chloride.

There is growing interest in using MRI to track cellular migration. To date, most work in this area has been performed using ultra-small particles of iron oxide. Immune cells are difficult to label with iron oxide particles. The ability of adoptively infused tumor specific T cells and N cells to traffic to the tumor microenvironment may be a critical determinant of their therapeutic efficacy. We tested the hypothesis that lymphocytes and B cells would label with MnCl2 to a level that would allow their detection by T1-weighted MRI. Significant signal enhancement was observed in human lymphocytes after a 1 h incubation with 0.05-1.0 mM MnCl2. A flow cytometry-based evaluation using propidium iodide and Annexin V staining showed that lymphocytes did not undergo apoptosis or necrosis immediately after and 24 h following a 1 h incubation with up to 1.0 mM MnCl2. Importantly, NK cells and cytotoxic T cells maintained their in vitro killing capacity after being incubated with up to 0.5 mM MnCl2. This is the first report to describe the use of MnCl2 to label lymphocytes. Our data suggests MnCl2 might be an alternative to iron oxide cell labeling for MRI-based cell migration studies.

Cell Movement↗
PubMed2004

Neuroprotective effects of an immunosuppressant agent on diffusion/perfusion mismatch in transient focal ischemia.

The immunosuppressant FK506 (tacrolimus) exerts potent neuroprotection following focal ischemia in animals; however, the separate effects of FK506 on the ischemic core and penumbra have not been reported. The ischemic penumbra is clinically defined as the difference between a large abnormal area on perfusion-weighted imaging (PWI) and a smaller lesion on diffusion-weighted imaging (DWI). The goal of this study was to determine the effect of FK506 on DWI/PWI match and mismatch areas in transient focal ischemia in rats. Twelve rats were subjected to 1 hr of transient middle cerebral artery (MCA) occlusion, and given an intravenous injection of a placebo (N = 6) or 1 mg/kg FK506 (N = 6) immediately before reperfusion. Magnetic resonance imaging (MRI) was performed during MCA occlusion, and 0.5, 1, and 24 hr after reperfusion. FK506 significantly protected the ischemic brain only in the mismatch cortex where the initial apparent diffusion coefficient (ADC) was normal and there was a mild reduction of cerebral blood flow (CBF). This is the first report to describe the protective effects of FK506 on ischemic penumbra, as measured by DWI/PWI mismatch. The findings provide direct evidence for the utility of DWI/PWI mismatch as a guideline for therapeutic intervention with FK506.

Animals↗
PubMed2004

Manganese-enhanced magnetic resonance imaging (MEMRI) of brain activity and applications to early detection of brain ischemia.

Divalent manganese ion (Mn2+) has been reported to be a useful contrast agent for functional MRI, through a technique named activity-induced manganese-dependent MRI (AIM). In AIM, signal enhancement is related to functional increases in calcium influx, and therefore AIM is, thus far, the only MRI method able to map brain activation in vivo independently of the surrogate hemodynamic changes used in functional MRI. Because of its high signal-to-noise ratio (SNR) and high sensitivity, AIM allows the use of multi-slice or three-dimensional MRI techniques to map functional activity at high spatial resolution. In the present review, we define AIM as a functional MRI tool based on the administration of divalent ionized manganese through an open or disrupted blood-brain barrier (BBB). The adequacy and efficacy of AIM in detecting neural activation is described in light of supporting experiments on inhibition of calcium channels, FOS expression, and on direct comparison to BOLD- and perfusion-based functional MRI. Two main applications of AIM, mapping brain activation in rat somatosensory cortex, as well stroke research based on the well-established middle cerebral artery occlusion model, are described in detail. Methodological problems associated with a strong dependence on anesthetic conditions, potential corruption due to disruption of the BBB, and unspecific increase of the baseline signal due to acoustical noise are discussed. Finally, recommended preparation methods and experimental protocols for AIM are introduced.

Animals↗
PubMed2003

Interindividual and interspecies variations of the extrastriate visual cortex.

Functional homology between human and macaque visual cortices has provided an important cue to functional subdivisions of the human visual cortex, but it is unclear beyond V1. We estimated the sizes and the visual field eccentricity functions of the extrastriate visual areas of human brains using MRI and fMRI measurements to analyze the interindividual and interspecies variations. We found distinctive features of the area fraction values relative to V1 and the visual field eccentricity functions beyond V2 between the human and the macaque visual cortices. This suggests that selection on color-form and stereoscopic vision, associated with processing and manipulating socio-visual stimuli, may generate variations of the architecture of the extrastriate visual cortex beyond V2.

Adult↗
PubMed2003

Detection of the anoxic depolarization of focal ischemia using manganese-enhanced MRI.

Mismatch between diffusion- and perfusion-weighted MRI was used to indicate a treatable area following focal ischemia, called the penumbra. Activity-induced manganese contrast MRI has been reported as a new visualization method for neural activation using manganese ions as a depolarization-dependent contrast agent. It is well known that energy failure induced by cerebral ischemia produces anoxic depolarization. The purpose of this study was to detect manganese accumulation caused by permanent middle cerebral artery occlusion (MCAO) of rat brain and to compare regional differences between manganese accumulation and decreased apparent diffusion coefficient (ADC). The ratios of signal intensity of manganese-enhanced MRI in the ipsilateral cortex to that in the contralateral cortex were 171.0 +/- 17.5% in MCAO group and 108.4 +/- 13.2% in the sham group. In addition, the enhanced region was much smaller than the area which was detected as having a reduced ADC.

Animals↗
PubMed2003

[3.0T imaging].

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Humans↗
PubMed2002

Dynamic activity-induced manganese-dependent contrast magnetic resonance imaging (DAIM MRI).

Activity-induced manganese-dependent contrast (AIM) MRI is a hemodynamic-independent functional MRI method that used manganese ion as an MR-detectable contrast agent. In AIM, MnCl(2) is infused intra-arterially after the blood-brain barrier (BBB) is opened with a hyperosmolar agent. Upon functional stimulation of the brain, Mn(2+) accumulates in the active region(s) by entering active cells through voltage-gated Ca(2+) channels, causing local signal increases in T(1)-weighted images. The contrast of AIM MRI depends strongly on the depth of anesthesia, and the low levels used in somatosensory stimulation studies can lead to significant nonspecific accumulation of manganese ion throughout the brain. The purpose of this study was to produce an AIM functional map of somatosensory stimulation, which separates the stimulation-specific signal increase from the nonspecific activation due to light anesthesia. A dynamic AIM (DAIM) paradigm was developed, which used sequential MR scans during MnCl(2) infusion, prior to and following functional stimulation of the brain. Stimulation-specific functional maps were produced using time-course analysis. The new method was tested during glutamate administration and electric stimulation of the rat forepaw. It was shown that DAIM maps are better confined to the specific region of brain activated by somatosensory stimulation as compared to AIM MRI.

Analysis of Variance↗
PubMed2002

Functional analysis of human parotid gland in vivo using the (1)H MRS MT effect.

Magnetization transfer (MT) was measured in the parotid gland in vivo by (1)H MR spectroscopy in 10 adult volunteers. A comparison was made of stimulated (excess saliva) and resting parotid gland (SPG and RPG, respectively). Following irradiation at an MT pulse of 150 Hz downfield from the water proton signal, signal reductions in SPG and RPG were 83.8 +/- 4.7 and 91.4 +/- 5.7%, respectively. The larger reduction for SPG indicates that an increase in the amount of water in gland cells for the production of more parotid saliva may lead to greater affinity between the protons adjacent to macromolecules and free water which contributes to the MT effect. Activity in the parotid gland correlates with the effect. This method is useful for diagnosing disorders of parotid gland secretion.

Adult↗