Akitoshi Seiyama

Removal of the skin blood flow artifact in functional near-infrared spectroscopic imaging data through independent component analysis.

We investigate whether the functional near-infrared spectroscopic (fNIRS) signal includes a signal from the changing skin blood flow. During a locomotor task on a treadmill, changes in the hemodynamic response in the front-parietal area of healthy human subjects are simultaneously recorded using an fNIRS imaging system and a laser Doppler tissue blood flow meter. Independent component analysis (ICA) for fNIRS signals is performed. The skin blood flow changes during locomotor tasks on a treadmill. The activated spatial distribution of one of the components separated by ICA reveals an overall increase in fNIRS channels. To evaluate the uniformity of the activated spatial distribution, we define a new statistical value-the coefficient of spatial uniformity (CSU). The CSU value is a highly discriminating value (e.g., 2.82) compared with values of other components (e.g., 1.41, 1.10, 0.96, 0.61, and 0.58). In addition, the independent component signal corresponding to the activated spatial distribution is similar to changes in skin blood flow measured with the laser Doppler tissue blood flow meter. The coefficient of correlation indicates strong correlation. Localized activation areas around the premotor and medial somatosensory cortices are shown more clearly by eliminating the extracted component.

Effects of NG-nitro-l-arginine and/or l-arginine on experimental pulmonary metastasis in mice

Effects of NG-nitro-L-arginine methyl ester (L-NAME; an inhibitor of nitric oxide (NO) synthase) and/or L-arginine (substrate of NO synthase) on pulmonary metastasis of murine melanoma and Lewis lung carcinoma cells were investigated. L-NAME, L-arginine or both L-NAME and L-arginine was injected i.p. into mice 5, 3, and 1 h before and 1, 3, 5, and 7 h after the injection of tumor cells into mice via a tail vein. The administration of L-NAME (9.3 mumol/mouse) alone or L-arginine alone (46.5 or 186 mumol/mouse) potentiated pulmonary metastasis of highly and poorly metastatic B16 melanoma cells. L-NAME alone also increased the number of pulmonary metastasis of Lewis lung carcinoma cells, but L-arginine (185 mumol/mouse) did not. However, the combination of L-NAME and L-arginine increased the number of pulmonary metastasis of both the melanoma and Lewis lung carcinoma cells synergistically. L-NAME or L-arginine administration enhanced the retention of B16 melanoma cells in the lungs examined 24 h after the tumor cell injection. Synergistic effect of L-NAME and L-arginine was also seen in the tumor cell retention. The present results suggest that the metastatic potentials of the tumor cells do not simply correlate to NO production in vivo.

Endothelin A-Receptor Blockade Worsens Endotoxin-Induced Hepatic Microcirculatory Changes and Necrosis

BACKGROUND & AIMSnEndothelin 1 is considered to be an important regulator of sinusoidal blood flow and increases during endotoxemia. The purpose of this study was to investigate the role of endothelin 1 in hepatic microcirculation, oxygen transport, and liver injury during endotoxemia.nnnMETHODSnMale Sprague-Dawley rats were continuously infused with 2.5 mL/h of saline, 0.8 mg . kg-1 . h-1 of lipopolysaccharide (LPS), 3 mg . kg-1 . h-1 of BQ-485, an endothelin A-receptor antagonist, or LPS plus BQ-485 for 7 hours.nnnRESULTSnBQ-485 infusion had no significant effect on hepatic microcirculation and liver injury. LPS increased the plasma levels of aspartate aminotransferase (AST) and total bilirubin and decreased the hepatic adenosine triphosphate (ATP) level and bile flow rate. LPS + BQ-485 infusion further increased the plasma levels of AST and total bilirubin and decreased the bile flow rate and the hepatic ATP level. Dual-spot microspectroscopy revealed mild decreases in sinusoidal erythrocyte velocity and oxygen transport in the LPS group and profound decreases in these parameters in the LPS + BQ-485 group. Histological examinations revealed massive necrotic changes in the pericentral regions of the LPS + BQ-485 group.nnnCONCLUSIONSnThese results suggest that blockade of endothelin A receptors disturbs hepatic microcirculation and oxygen transport and aggravates the necrotic injury induced by endotoxin.

Increase in experimental pulmonary metastasis in mice by L‐arginine under inhibition of nitric oxide production by NG‐nitro‐L‐arginine methyl ester

As we have previously reported, intraperitoneal injections of NG‐nitro‐L‐arginine methyl ester [L‐NAME; a competitive inhibitor of nitric oxide (NO) synthase] before and after the injection of B16 melanoma cells through a tail vein increased experimental pulmonary metastasis, while simultaneous injections of L‐arginine (a substrate of NO synthase) at a 20‐fold higher dose synergistically increased pulmonary metastasis. Our present study was intended to elucidate the mechanisms by which L‐NAME alone or together with L‐arginine increases metastasis. Injections of L‐NAME decreased the serum concentration of nitrite plus nitrate (metabolites of NO) by about 50%, which was not reversed by simultaneous injections of L‐arginine. Injections of L‐NAME also decreased the diameter of arterioles and venules by 20–30%, while simultaneous injections of L‐arginine did not show any significant effect. When collagen‐ or ADP‐induced platelet aggregation was examined using platelet‐rich plasma, injections of L‐NAME showed little effects on platelet aggregation, while simultaneous injections of L‐arginine rather suppressed platelet aggregation. B16 melanoma cells produced NO in culture, and L‐NAME (0.2 mM) decreased NO production without effects on viability. Our results suggest that the increased experimental pulmonary metastasis induced by L‐NAME can be ascribed partly to the contraction of arterioles and venules, which is induced by the inhibition of endogenous NO production by L‐NAME, and that the synergistic effect of L‐arginine on metastasis is related to the inhibition of endogenous NO production through unknown mechanisms. Int. J. Cancer 75:140–144, 1998.© 1998 Wiley‐Liss, Inc.

A Near-Infrared Spectroscopic Study of Cerebral Ischemia and Ischemic Tolerance in Gerbils

BACKGROUND AND PURPOSEnTo explore the physiological mechanism of ischemic tolerance, we studied intracerebral oxygenation states noninvasively using near-infrared spectroscopy after bilateral common carotid artery occlusion (BCO) in gerbils with and without ischemic pretreatment.nnnMETHODSnUnder ether anesthesia, gerbils with sham operation (S group, n = 8) and those with pretreatment consisting of BCO for 2 minutes, twice at 3 days and 2 days earlier (T group, n = 8), were again subjected to BCO for 5 minutes. Changes in oxyhemoglobin (HbO2), deoxyhemoglobin (Hb), and total hemoglobin (HbT) as well as reduction in cytochrome oxidase (cyt.aa3) were calculated from the absorbance changes of the light transmitted through the brain. Seven days after the ischemic study, immunohistochemical examination was performed with an antiserum against microtubule-associated proteins.nnnRESULTSnIn both groups, the increase of Hb and decrease of HbO2 and HbT proceeded rapidly after BCO, and the maximal deoxygenation of hemoglobin occurred within 2.5 minutes. Reduction of cyt.aa3 also ensued rapidly and reached the maximal reduction within 3 minutes in both groups. In the T group, however, both deoxygenation of hemoglobin and reduction of cyt.aa3 progressed more slowly than in the S group. The time (seconds) necessary for a maximal change for cyt.aa3 was significantly longer in the T group (203.8 +/- 34.0 [mean +/- SD]; P < .01) than in the S group (68.0 +/- 14.7). The time necessary for a half-maximal change was also significantly longer in the T group than in the S group for both Hb (22.0 +/- 7.5 and 13.5 +/- 4.0, respectively; P < .05) and cyt.aa3 (23.9 +/- 5.7 and 11.6 +/- 4.3; P < .01). After recirculation for 7 days, all gerbils in the S group were found to have neuronal death in the hippocampus, while those in the T group did not.nnnCONCLUSIONSnThe present study indicated that mild ischemic stress can induce improvement in oxygen metabolism during subsequent ischemia, which might be causally related to the phenomenon known as ischemic tolerance, in which a protective effect toward ischemic/postischemic injury is induced by earlier mild ischemic pretreatment.

Changes in regional cerebral blood volume in frontal cortex during mental work with and without caffeine intake: functional monitoring using near-infrared spectroscopy

Near-infrared spectroscopy (NIRS) was used to measure frontal regional cerebral blood volume (rCBV) in a person whose brain was under the influence of pharmacological agents while the person was performing a complex task. Fourteen healthy participants were administered Uchida-Kraepelin psychodiagnostic (UKP) tests before and after caffeine intake, and the concentration of caffeine in the urine was measured. The average number of answers and the average number of correct answers given by the participants improved significantly following caffeine intake. During the UKP testing, changes in the rCBV in the inferior frontal cortex were continuously measured using NIRS. The volume during the rest periods decreased as a result of caffeine-induced constriction of the cerebral arteriola. The volume increased during the mental work, but the degree of the increase was the same before and after caffeine intake. Although the performance of the mental work improved following caffeine intake, the improvement was not reflected in the rCBV in the inferior frontal cerebral cortex. These results suggest that caffeine helps to protect the brain from excessive hyperemia in addition to activating the neurons in the prefrontal cortex.

Optical coherence tomography reveals in vivo cortical plasticity of adult mice in response to peripheral neuropathic pain.

We examined neural plasticity in mice in vivo using optical coherence tomography (OCT) of primary somatosensory (S1) and motor (M1) cortices of mice under the influence of sciatic nerve chronic constriction injury (CCI), a model of neuropathic pain widely utilized in rats. The OCT system used in this study provided cross-sectional images of the cortical tissue of mice up to a depth of about 1mm with longitudinal resolution up to 11 microm. This is the first study to evaluate neural plasticity in vivo using OCT. CCI mice exhibited cold allodynia and spontaneous pain behaviors, which are signs of neuropathic pain, 30 days after sciatic nerve ligation, when OCT observation of S1 and M1 cortices was carried out. The scattering intensity of near-infrared light within the hind paw area of S1 and M1 regions in the contralateral hemisphere was significantly higher than in the ipsilateral hemisphere. These CCI-induced increases in scattering intensity within cortical regions associated with the hind paw probably reflect elevated neural activity associated with neuropathic pain. Synapses and mitochondria are believed to have high light scattering coefficients, since they contain remarkably high concentrations of proteins and complicated membrane structure. Number densities of mitochondria and synapses are known to increase in parallel with increases in neural activity. Our findings thus suggest that neuropathic pain gives rise to neural plasticity within the hind paw area of S1 and M1 contralateral to the ligated sciatic nerve.

Recovery of blood flow and oxygen transport after temporary ischemia of rat liver

Hepatic tissue perfusion and O2 supply after ischemia are indispensable for recovery of cellular functions, but few studies have been performed regarding the recovery of tissue blood flow and O2 transport. After 5, 15, and 30 min of ischemia of rat livers, hepatic tissue perfusion, hepatic arterial and portal blood flow, plasma PO2, and O2 transport parameters were measured. Hepatic tissue blood flow and erythrocyte velocity in the sinusoids showed biphasic recoveries after temporal ischemia for 5, 15, and 30 min. The first peak in the flow appeared at 3-4 min after the initiation of tissue perfusion, and the second peak appeared at approximately 20 min, irrespective of the ischemic period. Hepatic blood flow during the initial increase contained relatively low O2-saturated blood compared with that in the second increase. Livers that had been subjected to a prior hepatic artery ligation only showed the first peak at approximately 4 min. The first increase in hepatic blood flow corresponded to the peak in the portal venous flow, and the second increase corresponded to that of the hepatic artery. These results suggested that hepatic microcirculation after temporary hepatic ischemia showed biphasic recoveries because of different restoration patterns of the portal vein and hepatic artery.Hepatic tissue perfusion and O2 supply after ischemia are indispensable for recovery of cellular functions, but few studies have been performed regarding the recovery of tissue blood flow and O2 transport. After 5, 15, and 30 min of ischemia of rat livers, hepatic tissue perfusion, hepatic arterial and portal blood flow, plasma[Formula: see text], and O2 transport parameters were measured. Hepatic tissue blood flow and erythrocyte velocity in the sinusoids showed biphasic recoveries after temporal ischemia for 5, 15, and 30 min. The first peak in the flow appeared at 3-4 min after the initiation of tissue perfusion, and the second peak appeared at ∼20 min, irrespective of the ischemic period. Hepatic blood flow during the initial increase contained relatively low O2-saturated blood compared with that in the second increase. Livers that had been subjected to a prior hepatic artery ligation only showed the first peak at ∼4 min. The first increase in hepatic blood flow corresponded to the peak in the portal venous flow, and the second increase corresponded to that of the hepatic artery. These results suggested that hepatic microcirculation after temporary hepatic ischemia showed biphasic recoveries because of different restoration patterns of the portal vein and hepatic artery.

Multichannel optical mapping: investigation of depth information

Near infrared (NIR) light has become a powerful tool for non-invasive imaging of human brain activity. Many systems have been developed to capture the changes in regional brain blood flow and hemoglobin oxygenation, which occur in the human cortex in response to neural activity. We have developed a multi-channel reflectance imaging system, which can be used as a `mapping device and also as a `multi-channel spectrophotometer. In the present study, we visualized changes in the hemodynamics of the human occipital region in multiple ways. (1) Stimulating left and right primary visual cortex independently by showing sector shaped checkerboards sequentially over the contralateral visual field, resulted in corresponding changes in the hemodynamics observed by `mapping measurement. (2) Simultaneous measurement of functional-MRI and NIR (changes in total hemoglobin) during visual stimulation showed good spatial and temporal correlation with each other. (3) Placing multiple channels densely over the occipital region demonstrated spatial patterns more precisely, and depth information was also acquired by placing each pair of illumination and detection fibers at various distances. These results indicate that optical method can provide data for 3D analysis of human brain functions.

Increased Oxygen Dissociation by Nitric Oxide from RBC

Endogenous carbon monoxide (CO), a product of heme oxygenase, is thought to share several biological actions with NO (Zhuo et al., 1993). Hemoglobin (Hb) tetramer in circulating erythrocytes traps the molecules so generated. CO increases the relative affinity of other heme sites for oxygen, thus shifting the remaining oxygen dissociation curve to the left, i.e., CO decreases oxygen (O2) supply to tissues (Douglas et al. 1912). Exceedingly high concentration of NO also shifted the O2 dissociation curve to the left (Kon et al., 1977). This may be because of the extremely high affinity of NO for Hb than CO. However, endogenous NO generated by stimuli (Green et al., 1981, Stuehr and Marietta, 1985, Hibbs et al., 1987) will not increase tissue hypoxia, because NO generated in vivo by cytokines or by nitrovasodilators (Kurz et al., 1993) is bound to the a subunit of eryth- rocyte Hb tetramer (Hb α-NO), composed of a and b subunits, and the Hb tetramer binding NO yields only less than 4% of total Hb tetramer in the circulating blood (Kosaka et al., 1994). Furthermore the present study shows that the small amount of NO decreases O2 affinity of erythrocytes under low O2 pressure (pO2) and the effect is also observed in vivo.