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Kokichi Yamamoto

Publications and source records attributed to Kokichi Yamamoto.

8 recordsLinked to original sources
PubMed2006

Prefrontal hemodynamic activity predicts false memory--a near-infrared spectroscopy study.

Evidence from lesion studies suggests an important role of the prefrontal cortex (PFC) in the reconstructive processes of episodic memory or memory distortion. Results from functional imaging studies imply PFC involvement during the illusionary recollection of non-experienced events. Here, we used a two-channel near-infrared spectroscopy (NIRS) system and conducted real-time monitoring of PFC hemodynamics, while subjects studied word lists and subsequently recognized unstudied items (false recognition). Bilateral increases in the oxygenated hemoglobin concentration ([oxy-Hb]) were observed during false recognition compared to true recognition, and a left PFC dominant increase of [oxy-Hb] was observed during encoding phases where subjects later claimed that they recognized unstudied words. Traces of semantic processing, reflected primarily in the left PFC activity, could eventually predict whether subjects falsely recognize non-experienced events.

Adult↗
PubMed2005

Prefrontal activation during verbal fluency tests in schizophrenia--a near-infrared spectroscopy (NIRS) study.

Letter- or semantically-cued verbal fluency tests (VFT) induce different, but overlapping activities in the prefrontal cortex (PFC) in healthy subjects. Functional differences between letter and semantic VFT may be important in elucidating the nature of language-related problems in schizophrenia since more profound impairment in semantically-cued retrieval may be suggestive of semantic system dysfunction specific to this disorder. However, the functional differences between the letter vs. semantic VFT on prefrontal metabolism in the subjects with schizophrenia have not been described. In the present study, we used near-infrared spectroscopy (NIRS) to assess hemoglobin concentration changes in the bilateral PFCs in subjects and controls. Sixteen subjects with schizophrenia and 19 healthy controls performed letter and semantic VFTs. Prefrontal hemodynamic changes were simultaneously monitored by NIRS. While healthy subjects performed both tasks equivalently, the subjects with schizophrenia showed more compromised performance in the semantic VFTs compared to the letter VFTs. NIRS measurement revealed that the pattern of PFC activation was greater during the letter VFT when compared to the semantic VFT in the healthy subjects, suggesting more prominent PFC involvement in letter-cued retrieval. In contrast, the subjects with schizophrenia showed the opposite pattern of activation, implying that the semantic mode of lexical access might impose greater cognitive demands on the PFC. The present study is the first to detect abnormal patterns of PFC activation in adults with schizophrenia in response to the distinct cognitive demands associated with letter and semantic VFT.

Adult↗
PubMed2005

Nitric oxide derived from human umbilical vein endothelial cells inhibits transendothelial migration of neutrophils.

We evaluated the roles of nitric oxide (NO) derived from endothelial cells in neutrophil transendothelial migration (TEM). Pretreatment of human umbilical vein endothelial cells (HUVECs) with NG-nitro-L-arginine methyl ester hydrochloride (L-NAME) or NG-monomethyl L-arginine (L-NMMA), which are inhibitors of NO synthases, enhanced neutrophil TEM. Similar augmentation of TEM was observed in the presence of an NO scavenger, 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (carboxy PTIO). Neutrophil TEM across L-NAME- or L-NMMA-treated HUVECs was inhibited by continuous NO supply by NO donors. These findings support the suggestion that continuous production of NO by endothelial cells suppresses neutrophil TEM. Flow cytometric analyses revealed that NO accumulates in neutrophils co-cultured with NO-producing HUVECs. A decreased amount of NO was detected in neutrophils co-cultured with L-NAME-treated HUVECs compared with neutrophils co-cultured with untreated HUVECs. Soluble guanylyl cyclase (sGC) is known as one of the most important targets of NO in neutrophils. 3-(53-Hydroxymethyl-23furyl)-1-benzyl indazole (YC-1), an activator of sGC, inhibited L-NAME-induced neutrophil TEM. It was interesting that inhibition of neutrophil sGC with 1-H[1,2,4-]oxadiazolo[4,3-a]quinoxalin-1-1 (ODQ) was sufficient to enhance TEM. These results suggest that NO derived from HUVECs acts on neutrophils to inhibit TEM, at least in part by activating sGC. Our findings imply the role of NO constitutively generated by HUVECs in protection against excessive neutrophil extravasation and unnecessary tissue damage under physiological conditions.

Cell Movement↗
PubMed2004

Hemodynamic differences in the activation of the prefrontal cortex: attention vs. higher cognitive processing.

Both simple attention tasks (e.g. letter cancellation) and most tasks of higher cognitive processing (e.g. word generation) are known to activate the dorsolateral prefrontal cortex (PFC). While attention and higher cognitive processing differ phenomenologically, with attention tasks requiring great subjective effort despite their simplicity, possible physiological differences in the activation of the PFC between the two types of cognitive processing have remained uninvestigated. Hemodynamic changes in the PFC during activation due to tasks of attention and those of higher cognitive processing were examined using near-infrared spectroscopy in 10 Japanese and 10 American healthy adults. In tasks of higher cognitive processing, which included both verbal and non-verbal tasks, the concentration of oxygenated hemoglobin ([HbO2]) increased, and that of deoxygenated hemoglobin ([HbR]) decreased, with an increase in the tissue hemoglobin saturation (THS). In tasks of attention, which consisted of the letter cancellation and continuous performance test, both [HbO2] and [HbR] increased, with no significant changes in the THS observed. The distinctive patterns of hemodynamic changes were not affected by the factors of task difficulty or language. The change in [HbR] may be a physiological marker of the prefrontal lobe activation that discriminates between attention and higher cognitive processing. The increase in [HbR] suggests increased oxygen consumption of the PFC during tasks of attention, which might be related to the disproportionately great subjective effort associated with sustained attention. The physiological alteration in hemodynamic patterns according to changes in cognition needs to be examined in subjects with prefrontal lobe dysfunction, such as schizophrenia and mood disorder.

Adolescent↗
PubMed2004

Successful allogeneic bone marrow transplantation for acute myelogenous leukemia after drug-induced cardiomyopathy.

Anthracycline derivatives often induce cardiomyopathy. Patients with seriously decreased cardiac function due to chemotherapeutic drugs cannot usually receive allogeneic hematopoietic stem cell transplantation (SCT) for hematologic disorders. We successfully performed allogeneic bone marrow transplantation (BMT) in a patient with severe cardiomyopathy. An 18-year-old woman with relapsed acute myelogenous leukemia had cardiomyopathy due to previous anthracycline administration. She underwent allogeneic BMT from her HLA-identical brother. Her preconditioning regimen was cytosine arabinoside, etoposide, total body irradiation, and high-dose cyclophosphamide. Congestive heart failure (CHF) was not present before BMT. Right heart pressures were monitored by a pulmonary arterial balloon catheter system (Swan-Ganz catheter). After BMT, she had severe CHF, which was controlled using pimobendan and amrinone. Patients with cardiomyopathy can receive allogeneic SCT under strict hemodynamic management.

Adolescent↗
PubMed2002

Calpain-mediated X-linked inhibitor of apoptosis degradation in neutrophil apoptosis and its impairment in chronic neutrophilic leukemia.

The number of neutrophils in the blood and tissues is controlled by constitutive apoptotic programmed cell death and clearance by phagocytes such as macrophages. Here, we found that calpains cleave the X-linked inhibitor of apoptosis (XIAP) in vitro, producing fragments that are unable to inhibit caspase-3. These fragments were detected in normal neutrophils but were unstable and rapidly degraded. Calpain inhibition delayed tumor necrosis factor-alpha-induced apoptosis of normal neutrophils, consistent with a role for calpains in regulating the onset of apoptosis. Interestingly, neutrophils from three patients with chronic neutrophilic leukemia, a rare syndrome characterized by accumulation of mature neutrophils, exhibited decreased mu-calpain expression, diminished calpain activity, and impaired XIAP degradation. Neutrophils from these patients displayed a delay in spontaneous, Fas-stimulated, and tumor necrosis factor-alpha-induced apoptosis. These observations suggest that calpain-mediated XIAP degradation contributes to initiation of apoptosis in normal neutrophils and dysfunction of this regulatory pathway can lead to pathological neutrophil accumulation.

Aged↗
PubMed2002

A lack of self-consciousness in autism.

OBJECTIVE: This study investigated self-consciousness in autism. METHOD: An incidental memory task was conducted on 18 adults with high-functioning autism and 18 normal comparison subjects. Three kinds of orienting questions (phonological, semantic, and self-referent, i.e., "Does the word describe you?") were asked about target words (adjectives for personality traits) in order to induce different types of processing. This was followed by an unexpected recognition test. RESULTS: While semantic processing resulted in better memory than phonological processing in both groups, self-referent processing yielded better memory performance than semantic processing in the comparison group but not in the autistic group. CONCLUSIONS: The results suggest deficits in self-consciousness in individuals with autism.

Adult↗