Biomedical subjects

Yukihisa Suzuki

Publications and source records attributed to Yukihisa Suzuki.

10 recordsLinked to original sources

PubMed2006

Effects of 2.45 GHz electromagnetic fields with a wide range of SARs on bacterial and HPRT gene mutations.

Present day use of mobile phones is ubiquitous. This causes some concern for human health due to exposure to high-frequency electromagnetic fields (HFEMF) from mobile phones. Consequently, we have examined the effects of 2.45 GHz electromagnetic fields on bacterial mutations and the hypoxanthine-guanine phosphoribosyl transferase (HPRT) gene mutations. Using the Ames test, bacteria were exposed to HFEMF for 30 min at specific absorption rates (SARs) from 5 to 200 W/kg. In all strains, there was no significant difference in the frequency of revertant colonies between sham exposure and HFEMF-exposed groups. In examination of mutations of the HPRT gene, Chinese hamster ovary (CHO)-K1 cells were exposed to HFEMF for 2 h at SARs from 5 to 200 W/kg. We detected a combination effect of simultaneous exposure to HFEMF and bleomycin at the respective SARs. A statistically significant difference was observed between the cells exposed to HFEMF at the SAR of 200 W/kg. Cells treated with the combination of HFEMF at SARs from 50 to 200 W/kg and bleomycin exhibited increased HPRT mutations. As the exposure to HFEMF induced an increase in temperature, these increases of mutation frequency may be a result of activation of bleomycin by heat. We consider that the increase of mutation frequency may be due to a thermal effect.

Animals↗

PubMed2006

Effects of continuous and intermittent exposure to RF fields with a wide range of SARs on cell growth, survival, and cell cycle distribution.

To examine the biological effects of radio frequency (RF) electromagnetic fields in vitro, we have examined the fundamental cellular responses, such as cell growth, survival, and cell cycle distribution, following exposure to a wide range of specific absorption rates (SAR). Furthermore, we compared the effects of continuous and intermittent exposure at high SARs. An RF electromagnetic field exposure unit operating at a frequency of 2.45 GHz was used to expose cells to SARs from 0.05 to 1500 W/kg. When cells were exposed to a continuous RF field at SARs from 0.05 to 100 W/kg for 2 h, cellular growth rate, survival, and cell cycle distribution were not affected. At 200 W/kg, the cell growth rate was suppressed and cell survival decreased. When the cells were exposed to an intermittent RF field at 300 W/kg(pk), 900 W/kg(pk) and 1500 W/kg(pk) (100 W/kg(mean)), no significant differences were observed between these conditions and intermittent wave exposure at 100 W/kg. When cells were exposed to a SAR of 50 W/kg for 2 h, the temperature of the medium around cells rose to 39.1 degrees C, 100 W/kg exposure increased the temperature to 41.0 degrees C, and 200 W/kg exposure increased the temperature to 44.1 degrees C. Exposure to RF radiation results in heating of the medium, and the thermal effect depends on the mean SAR. Hence, these results suggest that the proliferation disorder is caused by the thermal effect.

Animals↗

PubMed2005

Effect of high-frequency electromagnetic fields with a wide range of SARs on chromosomal aberrations in murine m5S cells.

To investigate the induction of chromosomal aberrations in mouse m5S cells after exposure to high-frequency electromagnetic fields (HFEMFs) at 2.45 GHz, cells were exposed for 2 h at average specific absorption rates (SARs) of 5, 10, 20, 50 and 100 W/kg with continuous wave-form (CW), or at a mean SAR of 100 W/kg (with a maximum of 900 W/kg) with pulse wave-form (PW). The effects of HFEMF exposure were compared with those in sham-exposed controls and with mitomycin C (MMC) or X-ray treatment as positive controls. We examined all structural, chromatid-type and chromosome-type changes after HFEMF exposures and treatments with MMC and X-rays. No significant differences were observed following exposure to HFEMFs at SARs from 5 to 100 W/kg CW and at a mean SAR of 100 W/kg PW (a maximum SAR of 900 W/kg) compared with sham-exposed controls, whereas treatments with MMC and X-rays increased the frequency of chromatid-type and chromosome-type aberrations. In summary, HFEMF exposures at 2.45 GHz for 2 h with up to 100 W/kg SAR CW and an average 100 W/kg PW (a maximum SAR of 900 W/kg) do not induce chromosomal aberrations in m5S cells. Furthermore, there was no difference between exposures to CW and PW HFEMFs.

Adsorption↗

PubMed2005

Differential activation of cerebral blood flow by stimulating amblyopic and fellow eye.

PURPOSE: Positron emission tomography (PET), the blood flow response in the primary visual cortex (V1) to two visual stimuli, low temporal frequency (6 Hz) to activate the parvocellular system, and high temporal frequency (25 Hz) to activate the magnocellular system were used to investigate pathophysiologic mechanism of amblyopia. METHODS: Five women and one man who were aged between 26 and 60 years, who were ophthalmologically normal except for amblyopia, and who had corrected visual acuity in the amblyopic eye of 0.6 or worse were examined. An intravenous injection of the H(2)(15)O was given, and the regional cerebral blood flow was measured by PET during full-field stimulation with either 6 Hz or 25 Hz flicker to the amblyopic or the sound eye. RESULT: The activation of blood flow in the contra-lateral area V1 by the 6-Hz stimulation of the sound eye was greater than that during the stimulation of the amblyopic eye (P<0.05, small volume correction, n=6). With 25-Hz stimulation of the sound and amblyopic eyes, the blood flow in the contra-lateral and ipsi-lateral areas V1 was not significantly different. CONCLUSION: The decreased activation of blood flow in the contra-lateral V1 by low temporal frequency stimuli supports the hypothesis that the parvocellular pathway in amblyopic eyes is depressed.

Adult↗

PubMed2005

Effects of 2450 MHz electromagnetic fields with a wide range of SARs on methylcholanthrene-induced transformation in C3H10T1/2 cells.

This study examined whether 2450 MHz continuous wave high frequency electromagnetic fields (HFEMF) could induce cancer-like changes in mouse C3H10T1/2 cells, and whether HFEMF could initiate malignant or synergistic transformation. Transformed foci, Type II and Type III, were independently counted as the experiment endpoint. The cells were exposed to HFEMF alone at a wide range of specific absorption rates (SARs) of 5 to 200 W/kg for 2 h and/or were treated with a known initiating chemical, methylcholanthrene (MC) (2.5 microg/ml). No significant differences were observed in the malignant transformation (Type II + Type III) frequency between the controls and HFEMF with or without 12-O-tetradecanoylphorbol-13-acetate (TPA) (0.5 ng/ml), a tumor promoter that could enhance transformation frequency initiated by MC in multistage carcinogenesis. However, the transformation frequency for HFEMF at SAR of more than 100 W/kg with MC or MC plus TPA was increased compared with MC alone or MC plus TPA. On the other hand, the corresponding heat groups (heat alone, heat + MC, and heat + MC + TPA) did not increase transformation compared with each control level in C3H10T1/2 cells. This result suggests that 2450 MHz HFEMF could not contribute to the initiation stage of tumor formation, but it may contribute to the promotion stage at the extremely high SAR (100 W/kg).

Animals↗

PubMed2003

Glucose hypometabolism in medial frontal cortex of patients with apraxia of lid opening.

PURPOSE: To determine whether regional cerebral functional abnormalities exist in patients with apraxia of lid opening (ALO). METHODS: Cerebral glucose metabolism was examined by positron emission tomography (PET) in 11 patients (8 women and 3 men, age 48-69 years); 10 with ALO accompanied by blepharospasm and 1 patient with pure ALO. Eleven normal volunteers (6 women and 5 men, age 45-66 years) were examined as controls. A comprehensive ophthalmological examination, magnetic resonance imaging (MRI), and PET were performed. The cerebral glucose metabolism was evaluated by the relative uptake of [fluorine-18]fluorodeoxyglucose by PET. The mean +/- two standard deviations of the normal controls was defined as the normal range for cerebral glucose metabolism. RESULTS: MRI revealed no particular lesion except for an infarction in the unilateral basal ganglia in two patients. Decreased glucose metabolism was observed in a wide area of the medial frontal lobe (six cases) and primary visual cortex (PVC) (four cases). Group multiple comparisons revealed a significant decrease ( P<0.0035) in the bilateral anterior cingulate gyrus, left supplementary motor area (SMA), and bilateral PVC. CONCLUSION: The results support the hypothesis that ALO is associated with hypofunction in the SMA and/or anterior cingulate gyrus.

Aged↗

PubMed2002

Detection of visual activation of lateral geniculate nucleus by positron emission tomography.

PURPOSE: Although activation of the lateral geniculate nucleus (LGN) has been shown by functional magnetic resonance imaging, a quantitative evaluation of the activity has not been reported by positron emission tomography (PET). The purpose of this study was to quantify the degree of activation of the LGN and other vision-related structures by visual stimuli as detected by PET. METHODS: PET activation was induced by a bolus injection of 15O-labelled water (H2(15)O) in six normal volunteers. The regional cerebral blood flow (rCBF) was measured under three conditions: eyes closed, binocular flickering light stimulation, and binocular viewing of a video movie. Single-subject analysis, group analysis, and correlation analysis were performed. RESULTS: Although single-subject analysis did not show significant changes, group analysis revealed a significant increase in rCBF in the left LGN induced by flickering light stimulation ( P<0.01) and video stimulation ( P<0.05). Localization of the activation foci in the LGN agreed with the retinotopic organization of the LGN. CONCLUSION: Although the LGN is relatively small compared with the resolution of the PET image, visually activated blood flow changes could be determined by H2(15)O PET:

Adult↗

PubMedDate not supplied

Oscillopsia associated with dysfunction of visual cortex.

PURPOSE: To investigate the cause of oscillopsia without nystagmus or vestibular dysfunction in a 31-year-old man with no past history of serious illness. METHODS: The changes in the regional cerebral blood flow elicited by visual stimuli were studied by positron emission tomography (PET) in the patient and were compared with changes in normal subjects. The primary visual cortex (PVC) and area V5 were defined on Talairach coordinates, as shown in previous PET studies, and were confirmed with their activation patterns in our subjects. RESULTS: Flicker stimulation (8 Hz) and a stationary random dot pattern activated area V5 in the patient, but not in the six normal controls. A moving random dot pattern activated both the PVC and the extra-striate cortex in both the patient and the controls. CONCLUSIONS: Oscillopsia in this case is associated with dysfunction of the visual cortices and may be caused by it.

Adult↗

PubMedDate not supplied

A case of multiple sclerosis with homonymous hemianopia examined by positron emission tomography.

BACKGROUND: To demonstrate the efficacy of positron emission tomography (PET) for examining multiple sclerosis (MS) patients with hemianopia. CASE: A 20-year-old man visited us with a complaint of left homonymous hemianopia and headache. OBSERVATIONS: The patient's visual acuity was 1.2 (n.c.) OD and 0.9 (1.0) OS. Magnetic resonance imaging (MRI) showed a mass in the temporoparietal lobe. A pathological diagnosis of MS was made by brain biopsy. Low glucose metabolism in the lesion and visual cortex was observed by PET with (18)F-fluorodeoxy glucose. PET with (11)C-flumazenyl revealed a reduction of (11)C-uptake in the demyelinated optic radiation, and only a slight reduction of (11)C-uptake in the primary visual cortex. The results of (11)C-flumazenyl PET suggested a slight reduction of neuronal density. In 2 years, the visual field recovered to the normal state. CONCLUSION: PET can be a useful tool for estimating the visual outcome of patients with hemianopia in MS.

Adult↗

PubMedDate not supplied

Neuroimaging analysis of a case with left homonymous hemianopia and left hemispatial neglect.

PURPOSE: To correlate the neuro-ophthalmological observations with the magnetic resonance images (MRI) and positron emission tomographic (PET) findings in a case with left homonymous hemianopia and left hemispatial neglect. CASE: A 57-year-old woman underwent surgery for a ruptured anterior communicating artery aneurysm. After she recovered consciousness, it was found that she had left homonymous hemianopia and left hemispatial neglect. Although the hemispatial neglect slowly improved, the homonymous hemianopia persisted. MRI and measurements of cerebral glucose metabolism by 2-fluoro-2-deoxy-D-glucose(FDG)-PET were performed 1 year later. RESULTS: MRI revealed infarctions on the medial surface of the frontal lobe, on the right medial surface of the occipital lobe, and global atrophy of the right cortical hemisphere. FDG-PET disclosed severe glucose hypometabolism in the entire right hemisphere. Glucose metabolism in the right occipital cortex was 61.1% of that in the homologous region on the left side, 62.8% in the right anterior cingulate gyrus, and 93.8% in the temporal-parietal-occipital junction. CONCLUSIONS: The low glucose metabolism in the right visual cortex explains the persistent left hemianopia, and that in the right anterior cingulate gyrus and the right temporal-parietal-occipital junction may be responsible for the left hemispatial neglect. The relatively mild damage in the right temporal-parietal-occipital junction explained the recovery of the neglect symptom. Measurements of regional cerebral glucose metabolism by PET are useful for determining the cause of cerebral visual dysfunction and its prognosis after a cerebral lesion.

Aneurysm, Ruptured↗