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K Ikemoto

Publications and source records attributed to K Ikemoto.

At least 19 recordsLinked to original sources
PubMed2001

Expression of GTP cyclohydrolase I in murine locus ceruleus is enhanced by peripheral administration of lipopolysaccharide.

Among the enzymes involved in the system for catecholamine biosynthesis, GTP cyclohydrolase I (GCH) contributes to the system as the first and rate-limiting enzyme for the de novo biosynthesis of tetrahydrobiopterin (BH4), which is the cofactor for tyrosine hydroxylase (TH). Therefore, we investigated whether the endotoxemia caused by an intraperitoneal (i.p.) injection of lipopolysaccharide (LPS) can modulate BH4 production in the norepinephrine nuclei, i.e. the locus ceruleus (LC; A6) and central caudal pons (A5), in C3H/HeN mice and whether such a change in BH4, if any, can result in the modification of norepinephrine production in these nuclei. After a 5-microg i.p. injection of LPS, the protein expression of GCH and TH in both nuclei was examined by immunohistochemistry. The staining intensity of GCH-positive cells increased at 6 h, whereas no significant change in the staining intensity of TH-positive cells was detected. Next, we measured the contents of BH4, norepinephrine, and its metabolites 4-hydroxy-3-methoxyphenylglycol (MHPG) and DL-4-hydroxy-3-methoxymandelic acid (VMA) in these nuclei after LPS i.p. injection. The BH4 content increased to a statistically significant level at 2 and 4 h after the injection. The contents of MHPG and VMA also showed a time-course similar to that of BH4. These data can be rationalized to indicate that an increased supply of BH4 in the LC increased TH activity and resulted in an increase in norepinephrine production rate at the site. This is the first report that sheds light on BH4 as a molecule that intervenes during endotoxemia to increase norepinephrine production rate in the LC.

Animals↗
PubMed2001

Establishment of the transformants expressing human cytochrome P450 subtypes in HepG2, and their applications on drug metabolism and toxicology.

Transformants with stable expression of a series of human cytochrome P450 (CYP) subtypes in the human hepatic cell line, HepG2, were established. These transformants are designated Hepc/1A1.4, Hepc/1A2.9, Hepc/2A6L.14, Hepc/2B6.68, Hepc/2C8.46, Hepc/2C9.1, Hepc/2C19.12, Hepc/2D6.39, Hepc/2E1.3-8 and Hepc/3A4.2-30, which stably expressed human CYP1A1, CYP1A2, CYP2A6, CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2D6, CYP2E1 and CYP3A4, respectively. The expression of the CYP subtypes in the transformants was confirmed by both determination of enzyme activities and the reverse transcriptase polymerase chain reaction (RT-PCR) procedure. The apparent K(m) values of the expressed CYP subtypes for their specific substrates were close to those of human liver microsomes. In addition to their CYP activities, these transformants retained glucuronide- and sulfate-conjugating activities. Furthermore, the activities of CYP2C9, CYP2D6 and CYP3A4 were inhibited by their specific inhibitors. The cytotoxicity of acetaminophen (APAP), cyclophosphamide (CPA) and benz[a]anthracene (BA) were analyzed by CYP-expressing transformants. The cytotoxicity depended on the expression of CYP subtypes and increased in a dose-dependent manner. These results show the metabolic activation of APAP, CPA and BA by the specific CYP subtypes expressed in the transformants and demonstrate the usefulness of these transformants for in vitro metabolic and toxicological studies in human liver.

Acetaminophen↗
PubMed2001

Exon 3 of tyrosine hydroxylase gene: lack of association with Japanese schizophrenic patients.

Tyrosine hydroxylase (TH) is the rate-limiting enzyme in dopamine (DA) biosynthesis. Exon 3 of the human TH gene encodes the sequence from Ser31 to Glu104 of type 1 enzyme, which contains the critical parts for regulation of the catalytic activity. The amino acid residues Gly36-Arg37-Arg38 were identified as a key sequence for DA to exert its inhibitory effect on catalytic activity. Therefore, we screened the nucleotide sequences of exon 3 from 201 Japanese patients with schizophrenia to explain the elevation in the synaptic or presynaptic DA concentrations in the schizophrenic brain, based on the hypothesis that any mutation changing the amino acid sequence Gly36-Arg37-Arg38 would result in the elevation of DA synthesis, due to a reduced inhibitory effect of DA on the catalytic activity. However, no mutated sequences of exon 3 and both exon-intron boundaries were detected in any of the patients examined. Polymorphisms generating Val81 and Met81 were compared of the distributions of genotype and allele between the patients and 175 Japanese healthy controls, which did not suggest an association between the polymorphism and schizophrenia. These results indicate that exon 3 of the human TH gene lacks association with schizophrenia in Japanese patients.

Adult↗
PubMed2000

Human midbrain dopamine neurons express serotonin 2A receptor: an immunohistochemical demonstration.

We demonstrated intense serotonin (5-HT) 2A receptor immunoreactivity in the human ventral tegmental area (VTA) using by a recently raised antibody against 5-HT2A receptor. The substantia nigra (SN) neurons also showed 5-HT2A receptor immunoreactivity. Double immunohistochemistry of 5-HT2A receptor and tyrosine hydroxylase (TH) revealed many neurons doubly labeled by 5-HT2A receptor and TH in the VTA and SN. It is suggested that activity of human midbrain dopaminergic neurons might be strongly regulated via 5-HT2A receptors at the level of their originating nuclei.

Adult↗
PubMed2000

The carbohydrate deposits detected by histochemical methods in the molecular layer of the dentate gyrus in the hippocampal formation of patients with schizophrenia, Down's syndrome and dementia, and aged person.

Post-mortem brain tissue was obtained from 28 patients with brain disorders, of which 15 had clinically diagnosed schizophrenia, 6 Alzheimer type dementia, 5 dementia with tangles and 2 cases of Down's syndrome. The controls were 22 cases from autopsies without brain disorders or with no known episodes of brain disorder. The tissues were stained for the detection of carbohydrate deposits in the hippocampal formation, using lectin, immunohistochemical and conventional staining methods. The staining revealed the existence of spherical deposits in the inner and middle molecular layers of the dentate gyrus in the hippocampal formation which contained fucose, galactose, N-acetyl galactosamine, N-acetyl glucosamine, sialic acid, mannose and chondroitin sulfate. The number of the deposits was higher in patients with brain disorder such as schizophrenia, Alzheimer type dementia, dementia with tangles or Down's syndrome, and in some aged individuals, in comparison to those in younger individuals. No deposits were detected in a few younger or aged individuals. Spherical deposits 3-10 microm in diameter may be an immature form of the corpora amylacea, since they were similar in the histochemical characteristics with lectin, immunohistochemical and conventional staining methods. However, differing staining ability by hematoxylin, periodic acid Schiff's reagent and antibodies against the intracellular degraded proteins such as ubiquitin and tau-protein was observed. The antibodies against ubiquitin and tau-protein showed clear reactivity with the corpora amylacea and no reactivity with spherical deposits, indicating that the corpora amylacea has an intracellular origin and spherical deposits an extracellular matrix origin. The results obtained in this study indicate that not only neuronal degeneration but also unusual glycometabolism in neurons may disturb the neuronal function and cause brain disorders, and that spherical deposits may cause dysfunction of the neuronal network in the dentate gyrus of the hippocampus which is closely linked with recognition and memory functions.

Adult↗
PubMed1999

Cholinergic neurons with monoamine oxidase type B (MAOB)-activity in the laterodorsal tegmental nucleus of the mouse.

No neurons in the laterodorsal tegmental nucleus (LDTg) show monoamine oxidase (MAO) activity in the rat or monkey. However, in our recent study, many LDTg neurons with MAO type B (MAOB)-activity were found in MAOA-deficient mice that were derived from C3H mouse line. In the present study, LDTg neurons with MAOB-activity were found not only in normal C3H mouse but also in BALB/C and C57BL/6 mouse lines: MAO histochemistry revealed LDTg neurons with MAO-activity even after pharmacological suppression of MAOA-activity with clorgyline, a specific MAOA inhibitor, but not after pharmacological suppression of MAOB-activity with deprenyl, a specific MAOB inhibitor. LDTg neurons with MAOB-activity also showed NADPH-diaphorase-activity, a marker of cholinergic neurons.

Animals↗
PubMed1999

Tyrosine hydroxylase and aromatic L-amino acid decarboxylase do not coexist in neurons in the human anterior cingulate cortex.

Immunoreactivity for aromatic L-amino acid decarboxylase (AADC), the second step dopamine-synthesizing enzyme, was found immunohistochemically in neurons of the human anterior cingulate cortex (ACC). Most of these neurons were located in layers V and VI and subcortical white matter; a small number were occasionally found in layer III. Double immunohistochemistry for tyrosine hydroxylase (TH: the first step dopamine-synthesizing enzyme) and AADC revealed that no neuronal cell bodies in the ACC were doubly immunostained for TH and AADC, suggesting that these TH-only- or AADC-only-immunoreactive neurons were not dopaminergic. AADC neurons in the human ACC might transform L-DOPA to dopamine, droxidopa to noradrenaline, and/or 5-hydroxytryptophan to serotonin.

Adult↗
PubMed1999

A comparison of tau protein in cerebrospinal fluid between corticobasal degeneration and progressive supranuclear palsy.

Many clinical and pathological discussions have been focused on the difficulty of differential diagnosis between corticobasal degeneration (CBD) and progressive supranuclear palsy (PSP) in recent years. This study was conducted to evaluate the usefulness of tau proteins in cerebrospinal fluid (CSF) for the differentiation of these two diseases. Subjects consisted of 10 patients with CBD (four males and six females with a mean age of 67.9+/-5.8 years), 12 patients with PSP (eight males and four females with a mean age of 62.6+/-5.8 years) and 36 control subjects (CTL) (16 males and 20 females with a mean age of 65.8+/-9.9 years). The CBD group included patients with probable CBD, while all the patients in the PSP group satisfied the diagnostic criteria developed by the National Institute of Neurological Disorders and Stroke and Society for PSP (NINDS-SPSP). CSF tau proteins were measured with the sandwich ELISA method (Innogenetics, Belgium). The CSF tau protein level was 320.1+/-86.5 pg/ml in the CBD group, 151.5+/-52.7 pg/ml in the PSP group and 128.7+/-91.7 pg/ml in the CTL group. Significant differences were noted in tau protein levels between the CBD group and both the PSP group (P<0.001) and the CTL group (P<0.005). We suggested that the measurement of CSF tau proteins may be useful for the differentiation between CBD and PSP.

Aged↗
PubMed1999

Specific localization of the guanosine triphosphate (GTP) cyclohydrolase I-immunoreactivity in the human brain.

Guanosine triphosphate (GTP) cyclohydrolase I (GCH) is the first and rate-limiting enzyme for biosynthesis of tetrahydrobiopterin, the cofactor of tyrosine hydroxylase (TH). Our previous study reported the presence of GCH in several neuronal groups in animal brains using a newly raised anti-GCH antibody. The present study aims at elucidating whether GCH and TH coexist in the same neurons of the human brain with the aid of immunohistochemical dual labeling. GCH-immunoreactivity was observed in the cell bodies and fibers of monoaminergic neurons of the human brain. Neurons which contain both enzymes are seen in the human substantia nigra, ventral tegmental area, locus coeruleus, dorsal raphe, and zona incerta. In these regions, almost all the cells also show immunoreactivity for aromatic L-amino acid decarboxylase (AADC), the second step enzyme for catecholamine synthesis, indicating that these neurons are catecholaminergic. However, some neurons in the dorsal and dorsomedial hypothalamic nuclei are stained only for GCH or TH. They appear to constitute an independent cell group in the human brain. The present observation suggests that L-dopa is not produced in the cells immunoreactive for TH but not for GCH, and that TH in these cells which lack GCH may have an unidentified role other than dopa synthesis.

Aromatic-L-Amino-Acid Decarboxylases↗
PubMed1999

Effects of NTE-122, a novel acyl-CoA:cholesterol acyltransferase inhibitor, on cholesterol esterification and high-density lipoprotein-induced cholesterol efflux in macrophages.

We investigated the effects of a novel acyl-CoA:cholesterol acyltransferase (ACAT) inhibitor, NTE-122 (trans-1,4-bis[[1-cyclohexyl-3-(4-dimethylamino phenyl)ureido]methyl]cyclohexane), on ACAT activities in macrophages originating from several species and high-density lipoprotein (HDL)-induced cholesterol efflux in phorbol 12-myristate 13-acetate (PMA)-treated THP-1 cells. NTE-122 inhibited cell-free ACAT activities in human PMA-treated THP-1 cells and mouse J774.1 cells with IC50 values of 0.88 and 360 nM, respectively. NTE-122 competively inhibited the ACAT activity in PMA-treated THP-1 cells. NTE-122 also inhibited cellular ACAT activities in PMA-treated THP-1 cells, rat peritoneal macrophages and J774.1 cells with IC50 values of 3.5, 84 and 6800 nM, respectively. Furthermore, NTE-122 prevented cholesterol accumulation in PMA-treated THP-1 cells incubated with acetylated low density lipoprotein, simultaneously with HDL, while it caused accumulation of a significant amount of free cholesterol in the absence and even in the presence of HDL. NTE-122 also enhanced HDL-induced cholesterol efflux from established foam cells converted from PMA-treated THP-1 cells. These results suggest that NTE-122, capable of inhibiting macrophage ACAT activity in humans more strongly than those in the other species, exhibits anti-atherogenic effects by preventing the foam cell formation and enhancing the foam cell regression in humans.

Aniline Compounds↗
PubMed1999

Injection of 6-hydroxydopamine into the ventral tegmental area suppresses the increase in arterial pressure during REM sleep in the rat.

We have examined the effect of injection of 6-hydroxydopamine (6-OHDA) into the ventral tegmental area (VTA) on the changes in arterial blood pressure (AP) and heart rate (HR) during the transition from non-rapid eye movement (NREM) sleep to REM sleep. The 6-OHDA-treated rats showed suppression of the increase of AP and HR during REM sleep and of theta frequency in the cortical electroencephalogram (EEG) during wakefulness (W) and REM sleep. It is suggested that midbrain dopaminergic neurons are involved in the control of AP and HR during REM sleep and in the EEG theta activity.

Analysis of Variance↗
PubMed1998

Do all of human midbrain tyrosine hydroxylase neurons synthesize dopamine?

We examined whether all of human midbrain tyrosine hydroxylase (TH) neurons substantially synthesize dopamine (DA) using dual labeling immunohistochemical technique of TH and aromatic L-amino acid decarboxylase (AADC). In the substantia nigra, besides many neurons doubly stained for TH and AADC, neurons stained only for TH and only for AADC (D-neurons [C.B. Jaeger, D.A. Ruggiero, V.R. Albert, T.H. Joh, D.J. Reis, Immunocytochemical localization of aromatic l-amino acid decarboxylase, in: A. Björklund, T. Hökfelt (Eds.), Handbook of Chemical Neuroanatomy, Classical Transmitters in the CNS, Vol. 2, Part 1, Elsevier, Amsterdam, 1984, pp. 387-408.]) were identified. In the ventral tegmental area, dually labeled neurons and TH-only-positive neurons were found. It is indicated that the number of midbrain TH neurons does not reflect the exact number of DA neurons.

Adult↗
PubMed1998

Does tyrosinase exist in neuromelanin-pigmented neurons in the human substantia nigra?

It is controversial whether tyrosinase is involved in the neuromelanin-biosynthetic pathway. We examined tyrosinase-immunoreactivity in human substantia nigra neurons which contain neuromelanin pigments, using antibodies against human tyrosinase and human tyrosine hydroxylase. In human melanoma, the antibody to tyrosinase showed intense immunoreactivity while there was no immunoreactivity with antibody to tyrosine hydroxylase. In the human midbrain pigmented neurons, however, we could detect no tyrosinase-immunoreactivity while the neurons were strongly immunoreactive to tyrosine hydroxylase. The present results suggest that tyrosinase is not involved in the main pathway of neuromelanin biosynthesis.

Adult↗
PubMed1998

Phenylethanolamine-N-methyltransferase - immunoreactive nerve terminals afferent to the mouse substantia nigra.

In the substantia nigra pars compacta, many phenylethanolamine-N-methyltransferase immunoreactive (PNMT-ir) terminals as well as serotonin-ir terminals were observed for the first time to be very closely situated to the tyrosine hydroxylase (TH)-ir, aromatic L-amino acid decarboxylase-ir, and GTP cyclohydrolase I (GCH)-ir dopaminergic cells [Nagatsu, I., Arai, R., Sakai, M., Yamawaki, Y., Takeuchi, T., Karasawa, N. and Nagatsu, T., Neurosci. Lett., 224 (1997) 185-188]. Immunohistochemical colocalization of TH with GCH or PNMT in the somata and dendrites of TH-positive neurons in the rostral ventrolateral reticular formation of the medulla oblongata (C1 region, [Hokfelt, T., Fuxe, K., Goldstein, M. and Johansson, O., Brain Res., 66 (1974) 235-251]) was proved by a double-labeling immunofluorescence method with a confocal laser-scanning microscope, indicating that the neurons are adrenergic. These results suggest that dopaminergic neurons in the substantia nigra receive PNMT-ir, adrenergic afferents from the C1 region of the medulla oblongata.

Animals↗
PubMed1998

Dopamine synthesizing enzymes in paraventricular hypothalamic neurons of the human and monkey (Macaca fuscata).

Using immunohistochemistry, we demonstrated that paraventricular hypothalamic neurons immunoreactive for tyrosine hydroxylase (TH) were not immunopositive for the second step catecholamine synthesizing enzyme L-amino acid decarboxylase (AADC) in the human and monkey Macaca fuscata. In the latter species, they were not immunoreactive for dopamine. It is most likely that primate paraventricular TH-containing neurons do not synthesize dopamine.

Adult↗
PubMed1998

A dopamine-synthesizing cell group demonstrated in the human basal forebrain by dual labeling immunohistochemical technique of tyrosine hydroxylase and aromatic L-amino acid decarboxylase.

The human basal forebrain has been known to contain many neurons immunoreactive (ir) to tyrosine hydroxylase (TH; the first dopamine-synthesizing enzyme). We examined whether these neurons might contain aromatic L-amino acid decarboxylase (AADC; the second step dopamine-synthesizing enzyme) by dual labeling immunohistochemistry and confocal laser-scanning microscopy. Neurons dually-labeled for TH and AADC were found in the anterior olfactory nucleus, olfactory tubercle and the ventral margin of the rostral nucleus accumbens. The examination in the basal forebrain of the macaque monkey also gave substantially the same results. These neurons appear to constitute an independent dopaminergic cell group in the primate basal forebrain.

Adult↗
PubMed1998

Aromatic L-amino acid decarboxylase- and tyrosine hydroxylase-immunohistochemistry in the adult human hypothalamus.

The distribution of cell bodies immunoreactive for tyrosine hydroxylase and aromatic L-amino acid decarboxylase was studied in the adult human hypothalamus. Many neurons in the posterior (A11) and caudal dorsal hypothalamic areas (A13) as well as in the arcuate (A12) and periventricular (A14) zone were immunoreactive for the two enzymes, suggesting that they were dopaminergic. Numerous tyrosine hydroxylase-immunoreactive neurons, which were not immunoreactive for aromatic L-amino acid decarboxylase, could be seen in the paraventricular, supraoptic and accessory nuclei (A15) as well as in the rostral dorsal hypothalamic area. These were considered to be non-dopaminergic. Conversely, large numbers of small neurons immunoreactive for aromatic L-amino acid decarboxylase but not for tyrosine hydroxylase, were identified in the premammillary nucleus (D8), zona incerta (D10), lateral hypothalamic area (D11), anterior portion of the dorsomedial nucleus (D12), suprachiasmatic nucleus (D13), medial preoptic area and bed nucleus of the stria terminalis (D14). In the human hypothalamus, besides dopaminergic cell bodies, there exists a large number of tyrosine hydroxylase-only and aromatic L-amino acid decarboxylase-only neurons, whose physiological roles remain to be determined.

Aged↗