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Biomedical subjects

T Dohi

Publications and source records attributed to T Dohi.

At least 55 records · Page 3Linked to original sources
PubMed1998

Augmented reality visualization system for intravascular neurosurgery.

We aimed to construct an augmented reality-based visualization system to support intravascular neurosurgery and evaluate it in clinical environments. Three-dimensional (3D) vascular models are overlaid on motion pictures from X-ray fluoroscopy by 2D/3D registration using fiducial markers. The models are reconstructed from 3D data obtained from X-ray computed tomographic angiography or from magnetic resonance angiography using the marching-cube algorithm. Intraoperative X-ray images are mapped as texture patterns on a screen object which is displayed with the vascular models. Distortion of X-ray fluoroscopy is eliminated by a new technique of screen mesh deformation. A quantity called reprojection distance was introduced to evaluate the reliability of the displayed images. It predicts the maximum registration error around the registered objects. Analyses of reprojection distances were performed using synthetic data consisting of marker coordinates with 2D or 3D errors. The tolerance of reprojection distance for the clinical environment was determined to be 3.0 mm. The system was tested in two clinical cases in which reprojection distances of 2.6 and 2.09 mm were obtained. Construction and evaluation of our prototype system were successfully carried out. Further development is planned employing a range sensor to permit markerless registration.

Computer Graphics↗
PubMed1998

Inhibition of Na+,K(+)-ATPase by platelet-activating factor in dog submandibular glands.

Physiological stimulation of dog submandibular gland has been shown to generate platelet-activating factor (PAF). However, PAF is not released from cells in the tissue. To assess its intracellular activity, the effect of PAF on Na+,K(+)-ATPase was examined in dog submandibular gland cells. PAF inhibited Na+,K(+)-ATPase in membrane preparations, and the inhibitory effect was dependent on the protein concentration in the enzyme preparation. The inhibitory effect of a low concentration of PAF was antagonized by a PAF-receptor antagonist, BN 50,739, but at high concentrations, PAF was not antagonized. Kinetic analysis of PAF inhibition of Na+,K(+)-ATPase suggests that the inhibition of Na+,K(+)-ATPase by PAF is not due to competition by PAF at K(+)- or Na(+)-binding sites on the enzyme, but by complex inhibitory mechanisms. These results suggest that PAF may interact with specific and nonspecific site of action resulting in the inhibition of Na+,K(+)-ATPase. Ouabain increased mucin release from dog submandibular gland cells. Because Na+,K(+)-ATPase and ion exchange pathways are important in the secretory responses of acinar cells, PAF may regulate intracellularly the secretory function of acinar cells by modulating Na+,K(+)-ATPase and ionic homeostasis.

Animals↗
PubMed1998

Tyrosine-533 of rat dopamine transporter: involvement in interactions with 1-methyl-4-phenylpyridinium and cocaine.

To improve our understanding of structure-function relationships for neurotransmitter transporters, we performed site-directed mutagenesis of the rat dopamine transporter (DAT) and assessed the functions of the mutants in transiently-expressing COS cells. Tyrosine-533 of rat DAT lies in the 11th transmembrane region, where the corresponding amino acid of human DAT is phenylalanine. Alanine substitution of tyrosine-533 (Y533A) conferred an increased affinity for 1-methyl-4-phenylpyridinium (MPP+). Phenylalanine substitution of tyrosine-533 (Y533F) increased the velocity of MPP+ uptake but decreased DAT's affinity for MPP+. Cocaine's potency in inhibiting dopamine uptake was unchanged with Y533A, but increased with Y533F. Differences in the uptake kinetics and inhibitory potency of cocaine between rat and human DATs were similar to the differences observed between the wild-type and Y533F mutants DATs. Tyrosine-533 may be important for the DAT function and for species differences in transporter functions, including differential sensitivities to cocaine and 1-methyl-1,2,3,6-tetrahydropyridine (MPTP) in humans and rats.

1-Methyl-4-phenylpyridinium↗
PubMed1998

Case report: rupture of a gastric varix in liver cirrhosis associated with glycogen storage disease type III.

Glycogen storage disease type III, or Cori's disease, is caused by a deficiency of amylo-1,6-glucosidase (debranching enzyme), which leads to the storage of an abnormal glycogen in the liver and in skeletal and heart muscle. Glycogen storage disease type III is usually characterized by hepatic symptoms, growth failure and myopathy. Even though liver cirrhosis is reported, portal hypertension is a rare complication of this disease. We describe the case of a glycogen storage disease type III patient who was diagnosed at 3 years of age and developed complications (liver cirrhosis and rupture of a gastric varix) at 31 years of age. We discuss the histological progression to cirrhosis of the liver and describe the liver enzyme profile at 3 and 31 years of age.

Adult↗
PubMed1998

Cyclic ADP-ribose induces Ca2+ release from caffeine-insensitive Ca2+ pools in canine salivary gland cells.

Cyclic ADP-ribose (cADPR), a novel putative messenger of the ryanodine receptor, was examined regarding its ability to mobilize Ca2+ from intracellular Ca2+ stores in isolated cells of parotid and submandibular glands of the dog. cADPR induced a rapid and transient Ca2+ release in the digitonin-permeabilized cells of salivary glands. cADPR-induced Ca2+ release was inhibited by ryanodine receptor antagonists ruthenium red, ryanodine, benzocaine, and imperatoxin inhibitor but not by the inositol 1,4,5-trisphosphate (IP3)-receptor antagonist heparin. Thapsigargin, at a concentration of 3 to 30 microM, inhibited IP3-induced Ca2+ release, while higher concentrations were required to inhibit cADPR-induced Ca2+ release. Cross-potentiation was observed between cADPR and ryanodine or SrCl2, suggesting that cADPR sensitizes the Ca2+-induced Ca2+ release mechanism. Cyclic AMP plays a stimulatory role on cADPR- and IP3-induced Ca2+ release in digitonin-permeabilized cells. Calmodulin also potentiated cADPR-induced Ca2+ release, but inhibited IP3-induced Ca2+ release. Acetylcholine and ryanodine caused the rise in intracellular free Ca2+ concentration ([Ca2+]i) in intact submandibular and parotid cells. Caffeine did not produce any increase in Ca2+ release or [Ca2+]i rise in any preparation. ADP-ribosyl cyclase activity was found in the centrifuged particulate fractions of the salivary glands. These results suggest that cADPR serves as an endogenous modulator of Ca2+ release from Ca2+ pools through a caffeine-insensitive ryanodine receptor channel, which are different from IP3-sensitive pools in canine salivary gland cells. This system is positively regulated by cyclic AMP and calmodulin.

ADP-ribosyl Cyclase↗
PubMed1998

[Dysregulation of mucosal immunity and inflammatory bowel diseases].

Normal mucosal immunity is regulated in a delicate balance between up- and down-regulatory responses to dietal or bacterial antigens. Recent studies demonstrated that pathogenesis of inflammatory bowel disease could be dysregulation of the balance of mucosal immunity. Recent advances in animal models of inflammatory bowel disease, pathogenic roles of mucosal immunoregulatory T cells, cytokines and intestinal flora are reviewed.

Animals↗
PubMed1998

[Evaluation of the cystic duct and cysticohepatic junction with MR cholangiography: comparison of various techniques and clinical evaluation with respiratory-triggered three-dimensional multislab technique].

The purpose of this study was to evaluate depiction of the cystic duct and cysticohepatic junction by MR cholangiography (MRC). In 10 volunteers, MR cholangiograms were obtained by breath-hold two-dimensional (2D), respiratory-triggered 2D, respiratory-triggered three-dimensional (3D) single slab, and 3D multislab techniques. The images then were compared qualitatively. MRC using the respiratory-triggered 3D multislab techniques was evaluated as better than the other techniques, and was performed in 35 patients. Depiction of the anatomy of the cystic duct and cysticohepatic junction were evaluated. In 8 of 35 patients, MRC images were compared with those obtained by endoscopic retrograde cholangiography (ERC). The cystic duct and cysticohepatic junction were visualized adequately in 93% of volunteers and patients by the respiratory-triggered 3D multislab technique. Anatomic variations in the cystic duct and cysticohepatic junction were evaluated. The frequency of anatomic variations was the same as previously reported. The anatomic evaluations obtained by MRC were correlated closely with those obtained by ERC in 8 patients. In conclusion, MRC with the respiratory-triggered 3D multislab techniques is useful in evaluation of the cystic duct and cysticohepatic junction.

Adult↗
PubMed1997

Stimulation of cyclic ADP-ribose synthesis by acetylcholine and its role in catecholamine release in bovine adrenal chromaffin cells.

Cyclic ADP-ribose (cADPR) is suggested to be a novel messenger of ryanodine receptors in various cellular systems. However, the regulation of its synthesis in response to cell stimulation and its functional roles are still unclear. We examined the physiological relevance of cADPR to the messenger role in stimulation-secretion coupling in cultured bovine adrenal chromaffin cells. Sensitization of Ca2+-induced Ca2+ release (CICR) and stimulation of catecholamine release by cADPR in permeabilized cells were demonstrated along with the contribution of CICR to intracellular Ca2+ dynamics and secretory response during stimulation of intact chromaffin cells. ADP-ribosyl cyclase was activated in the membrane preparation from chromaffin cells stimulated with acetylcholine (ACh), excess KCl depolarization, and 8-bromo-cyclic-AMP. ACh-induced activation of ADP-ribosyl cyclase was dependent on the influx of Ca2+ into cells and on the activation of cyclic AMP-dependent protein kinase. These and previous findings that ACh activates adenylate cyclase by Ca2+ influx in chromaffin cells suggested that ACh induces activation of ADP-ribosyl cyclase through Ca2+ influx and cyclic AMP-mediated pathways. These results provide evidence that the synthesis of cADPR is regulated by cell stimulation, and the cADPR/CICR pathway forms a significant signal transduction for secretion.

ADP-ribosyl Cyclase↗
PubMed1997

Increased sialyl Lewis A expression and fucosyltransferase activity with acquisition of a high metastatic capacity in a colon cancer cell line.

A human colon cancer cell line, OCUC-LM1(LM), was established from a liver metastasis in our laboratory. Intrasplenic injection of LM into nude mice was repeated three and five times, and the daughter cell lines were designated as LM-H3 and LM-H5 respectively. The level of sialyl Lewis A (SLA) in the supernatant of LM-H3 and LM-H5 was 3 and 4.5 times higher than that of LM respectively. Flow cytometric analysis of SLA expression showed that the peak channel for LM was 113; for LM-H3, 126; and for LM-H5, 146. The mean fluorescence intensity of LM was 102.3 +/- 43.5; for LM-H3, 126.2 +/- 28.4; and for LM-H5, 144.8 +/- 23.4. In endothelial cell adhesion assays, the percentages of adherent LM-H3 and LM-H5 cells were significantly higher than for LM. The activity of alpha1-->4 fucosyltransferase was higher in LM-H3 and LM-H5 than in LM, but there was no difference in alpha2-->3 sialyltransferase activities for type 1 chain among the cell lines. Our results suggest that SLA expression is associated with acquisition of a high capacity for liver metastasis of colon cancer; increased SLA expression is due mainly to increased fucosyltransferase activity.

Animals↗
PubMed1997

Development of a frameless and armless stereotactic neuronavigation system with ultrasonographic registration.

OBJECTIVE: We have developed a frameless stereotactic neuronavigation system that allows navigation during neurosurgical procedures through an image formed from integrating ultrasonography and preoperative magnetic resonance (MR) imaging and/or x-ray computed tomography. METHODS: The system consists of a ultrasound imaging scanner, a workstation with an image capture board, and an ultrasonic tracking sensor with a 5-MHz ultrasonographic transducer. The ultrasonic tracking sensor measures the position and orientation of the ultrasonographic transducer. The oblique plane of the MR/computed tomographic image corresponding to the ultrasound image is then displayed on the workstation monitor. A three-dimensional computer graphic representation of the integrated image is also reported as a preliminary test. For the patient-image registration, the coordinates of digitized and imaged markers on a specifically developed reference frame are used. The reference frame is noninvasive because it is not bolted but only fastened to the patient's head with silicon. RESULTS: Based on the findings from the clinical application of the system in three cases, the system was advantageous because of the surgical procedures could be controlled by intraoperative ultrasonography as well as by preoperative MR/computed tomographic images. Missing parts in the ultrasonogram were supplemented with preoperative MR/computed tomographic images. At other times, spatial positioning and visualization by ultrasonography were useful for identifying anatomical objects in the image. CONCLUSION: This preliminary study of the frameless integration of ultrasonography into stereotactic space demonstrated its clinical usefulness. We believe that the concept of pre- and intraoperative image-guided surgery presented here will find increasing use in the future.

Adolescent↗
PubMed1997

Study of the effect of atrial contraction on mitral prosthetic valve by high speed video camera.

To clarify the effect of atrial contraction on the dynamic behavior of mitral prosthetic valves, a mechanical mock circulatory system has been developed. It is able to simulate the inflow characteristics during diastole. The disc motions of Björk-Shiley Monostrut (BSM29) and CarboMedics (CM29) valves (both with an annulus diameter of 29 mm) were measured and compared with a high speed video camera. After contraction of the artificial atrium (100 ms), there was a delay of 75 ms before the onset of the ventricular contraction. Mitral flow similar to physiological conditions could be achieved. The BSM29 was tested in the anterior position (a) and the posterior position (p). Under the condition of active atrial contraction (AC), we confirmed that the closing motion was initiated and the period during closing motion (PDCM) was prolonged (BSM29[a]: 22.4 +/- 3.4-->63 +/- 3.2; BSM29[p]: 71.2 +/- 38-->94.2 +/- 11; and CM29: 14 +/- 0.0-->28.4 +/- 2.3 [unit: ms]), the prolongation of the PDCM of the CM29 due to the AC being smaller than that of the BSM29. We also confirmed that the closing volume (CV) increased slightly (BSM29 [a]: 7.8 +/- 0.4-->8.5 +/- 0.8; BSM29[p]: 6.9 +/- 0.6-->7.0 +/- 0.5; and CM29: 3.6 +/- 0.6-->4.1 +/- 0.6 [unit: ml]). The CM29 had a shorter PDCM, less prolongation of the PDCM due to the AC, and less CV than the BSM29. Thus, we confirmed that the CM29 produced better response at valve closure than the BSM29.

Atrial Function↗
PubMed1997

Nonsymmetric leaflet motion of St. Jude Medical mitral valves simulated with a computer-controlled hydraulic mock circulator.

Since the introduction of high-performance prosthetic heart valves, particularly bileaflet valves and monoleaflet valves with larger opening angles, we have observed in vivo complex leaflet motion which has not been experimentally confirmed yet. We developed a computer-controlled hydraulic mock circulator to study the motion of in vivo leaflets. A high speed CCD camera recorded the valve movement. In the mitral position, a standard St. Jude Medical valve was tilted to be horizontal or vertical. The test valve was driven with single- or double-peaked flow. The flow rate was set to 5.0 L/min at 70 bpm with a systole/diastole ratio of 0.3. We found the following results: independent of valve orientation, the valve showed a nonsymmetric leaflet motion; the valve showed unpredictable leaflet position during decreasing flow or absence of flow; and the disc closed temporarily at the lower inflow rate between the 2 flow peaks.

Blood Flow Velocity↗
PubMed1997

Volumegraph (overlaid three-dimensional image-guided navigation). Clinical application of augmented reality in neurosurgery.

OBJECTIVE: We have developed an overlaid three-dimensional image (Volumegraph)-guided navigation system that allows navigation during operative procedures. The three-dimensional image is superimposed on the patient's head and body via a semi-transparent mirror. The Volumegraph can display three-dimensional images in the air by a light beam which is based on CT/MRI. METHOD: The system consists of a Volumegraph (thin plate of three-dimensional recorded medium), a Volumegraphscope and an original designed triangular-shaped marker system for registration. The three-dimensional data obtained from CT and MRI before the operation were processed by a computer. Such image data are applied for preoperative investigation to recognize the three-dimensional structure of organs and tumor. These reconstructed three-dimensional images were superimposed and registered at the patient's head according to a fiducial marker (registration). Then the operator can operate with this three-dimensional-image-guided navigation system. RESULTS: Based on clinical application in 7 cases, the system was found to be advantageous because the surgical procedures could be navigated easily by augmented reality in the surgical field. Invisible parts of the surgical field were supplemented with the overlaid three-dimensional images (Volumegraph) as if it were the virtual operative field. At another time, spatial positioning and overlaid visualization by the Volumegraph was useful for identifying anatomical structures and functional location in the image. CONCLUSION: This preliminary study of overlaid three-dimensional-image-guided navigation demonstrated its clinical usefulness. The application of augmented reality in the surgical field makes it possible to do a neurosurgical intervention easily and accurately.

Brain Neoplasms↗
PubMed1997

Stimulation of platelet-activating factor synthesis by neurotransmitters in salivary glands.

Platelet-activating factor (PAF), a phospholipid mediator exhibiting potent biological activities, has been shown to stimulate amylase release from the pancreas and salivary glands. The capacity of salivary glands for PAF biosynthesis in response to stimulation has also been demonstrated. To elucidate the role of PAF in salivary glands, we studied the regulation of platelet-activating factor synthesis by the autonomic nervous system in canine salivary glands. Acetylcholine and ionomycin stimulated PAF production in dispersed cells from parotid, submandibular, and sublingual glands of dogs. Norepinephrine and phenylephrine, but not isoproterenol, also stimulated PAF production in submandibular gland cells. Norepinephrine-induced PAF production was blocked by phentolamine but not by propranolol. Acetylcholine and norepinephrine increased both the PAF production and liberation of [14C]arachidonic acid from cells pre-labeled with [14C]arachidonic acid in the presence of Ca2+ in the medium. These stimulants increased [14C]arachidonic acid liberation without the accompanying production of PAF in Ca(2+)-deprived medium. No activators or inhibitors of protein kinase C produced or affected acetylcholine-induced PAF production. Lyso-PAF:acetyl-CoA acetyltransferase was activated in the cells treated with acetylcholine, norepinephrine, isoproterenol, and 8Br-cyclic AMP. Deprivation of Ca2+ in the medium markedly reduced acetylcholine-induced activation of the transferase, but little affected norepinephrine-, isoproterenol-, and 8Br-cyclic AMP-induced activation. Dithiothreitol-insensitive cholinephosphotransferase activity was also increased by acetylcholine, norepinephrine, isoproterenol, and 8Br-cyclic AMP, and the deprivation of Ca2+ in the medium further increased the activation of the enzyme activity by these agents. These results suggest that PAF synthesis in canine salivary glands is under the control of muscarinic cholinergic and alpha-adrenergic systems via Ca(2+)-dependent remodeling pathways, and that the independent activation of either phospholipase A2 or acetyltransferase is insufficient for PAF production in submandibular gland cells, i.e., the concurrent activation of these enzymes is required.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1996

Suppression of sialyl Lewis X expression and E-selectin-mediated cell adhesion in cultured human lymphoid cells by transfection of antisense cDNA of an alpha1-->3 fucosyltransferase (Fuc-T VII).

The antisense cDNA approach was used to identify the endogenous fucosyltransferase species responsible for synthesis of the sialyl Lewis X (NeuAcalpha2-->3 Galbeta1-->4[Fucalpha1-->3]GlcNAcbeta1-->R) determinant in human lymphoid cells. The cultured human adult T-cell leukemia cell line, ED40515-N, expressed the message of alpha1-->3 fucosyltransferase (Fuc-T) IV and VII, with a low level of the Fuc-T III and VI message, and manifested the sialyl Lewis X as well as Lewis X (Galbeta1-->4 [Fucalpha1-->3]GlcNAcbeta1-->R) determinant at the cell surface. Transfection of this cell line with the pRc/CMV vector containing an antisense human Fuc-T VII construct (pRc/CMV/5'FT7AS) resulted in a significant decrease of endogenous Fuc-T VII message and a marked reduction in the cell surface expression of sialyl Lewis X determinant as well as a reduction in the enzymatic activity of alpha1-->3 fucosyltransferase against sialylated type 2 chain substrate. This was accompanied by diminution of cell adhesive activity toward E-selectin on interleukin-1beta-treated endothelial cells. These results indicated that the synthesis of the sialyl Lewis X determinants that were functionally active as E-selectin ligands was mainly mediated by Fuc-T VII in these lymphoid cells. On the other hand, the message of Fuc-T IV showed no significant change in the transfectant clones, and the surface expression of the Lewis X antigen as well as the enzymatic activity of alpha1-->3 fucosyltransferase against non-sialylated type 2 chain substrate was well preserved. The clear contrast between the diminished expression of sialyl Lewis X and the conserved manifestation of Lewis X in the transfectant clones suggested that the synthesis of sialyl Lewis X and that of Lewis X are independently regulated by different fucosyltransferases in human lymphoid cells. Fuc-T VII must be involved in the synthesis of sialyl Lewis X, while the synthesis of Lewis X is mediated by an enzyme other than Fuc-T VII, most probably Fuc-T IV.

Adult↗