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Biomedical subjects

N Miki

Publications and source records attributed to N Miki.

At least 19 recordsLinked to original sources
PubMed1995

Thyroid hormone regulation of gene expression of the pituitary growth hormone-releasing factor receptor.

To examine thyroid hormone regulation of the pituitary receptor for hypothalamic growth hormone (GH)-releasing factor (GRF), we studied effects of hypothyroidism on the pituitary GRF receptor (GRF-R) mRNA and its related parameters in rats. Thyroidectomy (Tx) induced a 61-65% reduction in GRF-R mRNA levels, which was significantly reversed with thyroxine (T4) replacement for 5 days at a dose of 1 microgram/100 g/day. Pituitary GH contents changed parallel to GRF-R mRNA levels following the Tx and T4 replacement. In contrast, Tx enhanced GRF release > 2 fold, which was not reversed with the regime of T4 replacement. These results indicate that thyroid hormone promotes pituitary GRF-R gene expression, not by modulating GRF secretion, but by acting on the pituitary directly. The decline in GRF receptor expression would contribute to somatotroph failure by rendering the pituitary refractory to the increased GRF signal in hypothyroidism.

Animals↗
PubMed1995

Expression and functional analysis of a novel isoform of gicerin, an immunoglobulin superfamily cell adhesion molecule.

We have cloned a novel cDNA of gicerin, a cell adhesion molecule belonging to the immunoglobulin superfamily. Both gicerin isoforms share the same extracellular domain, which has five immunoglobulin-like loop structures and a transmembrane domain as s-gicerin, but differ in the cytoplasmic tail domain. As the newly identified form has a larger cytoplasmic domain than the previously reported form, we refer to them as l-gicerin and s-gicerin, respectively. l-gicerin is transcribed from a distinct mRNA containing an inserted sequence not found in s-gicerin mRNA which caused a frameshift for the coding region for a cytoplasmic domain. Previous studies demonstrated that gicerin showed a doublet band of 82 and 90 kDa in chicken gizzard smooth muscle. We report that the 82-kDa protein corresponds to s-gicerin and the 90-kDa protein to l-gicerin. We also found that the two gicerin isoforms are expressed differentially in the developing nervous system. Functional analysis of these gicerin isoforms in stable transfectants revealed that they had differ in their homophilic adhesion properties, as well as in heterophilic cell adhesion assayed with neurite outgrowth factor. In addition, these isoforms have neurite-promoting activity by their homophilic adhesion, but differ in their ability to promote neurite outgrowth.

Amino Acid Sequence↗
PubMed1995

Sexually dimorphic expression of pituitary growth hormone-releasing factor receptor in the rat.

Secretion of growth hormone (GH) exhibits marked sexual dimorphism in the rat. To examine the underlying mechanism that involves hypothalamic GH-releasing factor (GRF), we determined pituitary GRF receptor mRNA levels in male and female rats and compared their in vitro abilities to release GRF, an endogenous ligand for GRF receptor. Female rats expressed GRF receptor mRNA at a level of only 15% (P < 0.001) of that of male rats. Female rats also showed a 33% lower (P < 0.01) ability to release GRF than male rats. These results indicate that the GRF secretion and action system of female rats is characterized by the combined reduction in GRF receptor expression and GRF-releasing capacity compared with that of male rats. This could explain the in vivo finding that spontaneous, GRF-triggered GH pulses are of much lower amplitude in the female than in the male rat.

Actins↗
PubMed1995

Cortical field potentials preceding vocalization and influences of cerebellar hemispherectomy upon them in monkeys.

Field potentials preceding vocalization were recorded with electrodes chronically implanted on the surface and at 2.0-3.0 mm depth in various cortical areas in three monkeys. Surface-negative, depth-positive (s-N, d-P) slow potentials prior to vocalization were recorded in the premotor (including the Broca's homology), motor and somatosensory cortices in both hemispheres, and the supplementary motor area in the cerebral hemisphere. Such premovement potentials were recorded also in the cingulate and prefrontal cortices when a monkey uttered with intense motivation for reward. Cerebellar hemispherectomy on the right side eliminated the s-N, d-P premovement potentials in the motor cortex and in the posterior bank of inferior limb of the arcuate sulcus (homolog of Broca's area) in the left hemisphere. Vocal tone contained less components in different frequencies, and its duration became more variable than before the operation. These facts suggest that the neocortical area homologous to the human speech area takes part in generation and control of monkey vocalization together with the cerebellum, possibly through cerebro-cerebellar interactions, against ideas so far offered on nonhuman primate vocalization.

Action Potentials↗
PubMed1995

Determination of a necdin cis-acting element required for neuron specific expression by using zebra fish.

To determine cis-acting elements required for neuron specific expression of a necdin gene, we tried to use zebra fish assay system in vivo instead of cell lines in vitro. Various expression vectors carrying upstream sequences of necdin gene fused to MEKA (lacZ) gene as a reporter were injected into fertilized zebra fish embryos and then the expression of the reporter gene was analyzed by the whole mount immunochemical method. No promoter activity was obtained with a construct carrying sequence from -63 to +63 of the necdin gene, while promoter activity with preferential skin expression was obtained with a construct having sequence from -86 to +28. Further upstream sequence from -173 to +28 exhibited neuron specific expression as well as that from -845 to +63. These results indicate that a cis-acting element responsible for neuron specific expression is located in an 87bp sequence from -173 to -87 of necdin gene.

Animals↗
PubMed1995

Field potential change in the prefrontal cortex of the left hemisphere during learning processes of reaction time hand movement with complex tone in the monkey.

Field potentials were recorded with electrodes implanted in various cortical areas while a naive monkey was learning reaction time hand movements with complex tone. When cortical surface-negative, depth-positive potential (at a latency of about 80 ms after a stimulus onset) appeared in the rostral bank of the inferior limb of the arcuate sulcus of the left cerebral hemisphere, and became gradually larger, the monkey began to respond to the stimulus with the movement. As the potential in the prefrontal (prearcuate) cortex and the cerebellar-mediated potential in the motor cortex gradually increased with further training, the movement became quicker and more skillful. Three naive monkeys achieved the movement with complex tone in shorter training days than the movement with pure tone; the movement with pure tone was not accompanied by any significant potential in the prefrontal cortex. It is deduced from the present study, and previous studies on visuo-initiated movements, that the prefrontal area, especially in the left hemisphere, plays a significant role for a monkey to associate a stimulus with appropriate motor execution.

Acoustic Stimulation↗
PubMed1995

Decrease in CRE binding activity by chronic morphine administration in mouse brain.

Recent studies have suggested that opiate addiction is associated with transcriptional changes. We developed a novel method, in situ DNA-protein binding (ISDB), for investigating the distribution and changes of DNA binding activity of transcription factors in the brain. Using this method, we found that cAMP response element (CRE) binding activity was decreased by chronic morphine treatment in specific regions including the amygdala complex, thalamus, cerebral cortex and hypothalamus in mouse brain. This effect persisted for at least 14 days after the cessation of morphine. These data suggest that chronic morphine treatment elicits a long-term change in cAMP-mediated gene expression in the brain.

Animals↗
PubMed1995

TMP-153, a novel ACAT inhibitor, inhibits cholesterol absorption and lowers plasma cholesterol in rats and hamsters.

Effects of TMP-153, N-[4-(2-chlorophenyl)-6,7-dimethyl-3-quinolyl]-N'-(2,4-difluorophe nyl)urea, on intestinal and hepatic acyl-CoA:cholesterol acyltransferase (ACAT) activities, cholesterol absorption and plasma cholesterol level in rats and hamsters were studied. TMP-153 has IC50 values of around 5-10 nM for the hepatic and intestinal ACAT from various animals. The most potent inhibition was observed in the intestinal ACAT from Golden hamsters (IC50 = 2.3 nM). The inhibition mode of TMP-153 was non-competitive for rat intestinal ACAT. TMP-153 inhibited cholesterol esterification both in human colonic adenocarcinoma cells, LS180, and in human hepatoma cells, HepG2 (IC50 = 150 nM and 330 nM, respectively). [14C]cholesterol and cold cholesterol absorption from the small intestine was markedly inhibited by oral administration of TMP-153 (1 mg/kg) without affecting lymph flow and triglyceride absorption. When the compound was given as a dietary admixture, plasma cholesterol was reduced in rats fed a cholesterol diet (ED50 = 0.25 mg/kg/day), but not in those fed a stock diet. On the other hand, TMP-153 showed more prominent hypocholesterolemic effect in Golden hamsters fed the stock diet (ED50 = 0.81 mg/kg/day) than in those fed the cholesterol diet (ED50 = 8.01 mg/kg/day). In hamsters fed the stock diet, TMP-153 markedly decreased the hepatic unesterified cholesterol in addition to esterified cholesterol content, but did not affect bile flow and the biliary secretion of bile acid and lipids. Different mechanisms for plasma cholesterol lowering by TMP-153 between rats and hamsters was discussed.

Adenocarcinoma↗
PubMed1995

Expression of gicerin in development, oncogenesis and regeneration of the chick kidney.

Neurite outgrowth factor, which promotes neurite extension from neuronal cells, is an extracellular matrix glycoprotein belonging to the laminin family. Gicerin is a protein that binds neurite outgrowth factor. Its cDNA cloning has revealed that it is a novel cell adhesion molecule belonging to the immunoglobulin super-family. Functional analysis demonstrates that gicerin possesses homophilic binding activity as well as heterophilic binding activity with neurite outgrowth factor. We examined the role and expression of neurite outgrowth factor and gicerin in chick kidney during development. In the embryonic kidney, gicerin was found to be highly expressed both on ureteric bud cells and metanephrogenic mesenchymal cells, when the mesenchymal cells become condensed to be converted into polarized epithelial cells. In the adult kidney, the expression of gicerin was decreased and restricted to the glomerulus, proximal tubule and medullary loop. On the other hand, neurite outgrowth factor was constitutively expressed in the basement membranes of tubules and the matrices of glomeruli during development. As some molecules which are expressed during embryogenesis and suppressed after maturation are re-expressed in tumor cells or tissues during regeneration, we also examined the expression of gicerin in chicken Wilms' tumor and regenerating kidney in interstitial nephritis. Gicerin was remarkably upregulated in Wilms' tumor and re-expressed in collecting ducts recovering from interstitial nephritis. These findings suggest that gicerin could play a role not only in normal renal development but also in oncogenesis and regeneration.

Animals↗
PubMed1995

Low concentration of oxidized low-density lipoprotein and lysophosphatidylcholine upregulate constitutive nitric oxide synthase mRNA expression in bovine aortic endothelial cells.

Endothelium-dependent relaxation is markedly reduced in atherosclerotic arteries. Recently, the endothelium-dependent relaxing factor has been identified as nitric oxide (NO). We used RNase protection assay and immunoblotting to elucidate the effect of atherogenic lipoprotein on the expression of constitutive NO synthase (cNOS) mRNA and protein levels in bovine aortic endothelial cells. Twenty-four-hour exposure to a low concentration of oxidized low-density lipoprotein (10 micrograms protein/mL) upregulated cNOS mRNA levels (2.4 +/- 0.4-fold, P < .01). However, native low-density lipoprotein and high-density lipoprotein did not have any effect on cNOS mRNA levels. Furthermore, 5 micrograms/mL of lysophosphatidylcholine (LPC) also upregulated cNOS mRNA levels (2.6 +/- 0.5-fold, P < .01) at 8 hours. This action of LPC was abolished with cycloheximide but not with staurosporine. We concluded that atherogenic lipoproteins upregulate cNOS mRNA and protein levels in bovine aortic endothelial cells. This observation supports the hypothesis that an impairment of endothelium-dependent vasodilatation in atherosclerotic vessels may not be due to a decrease in cNOS expression. Moreover, the LPC action on cNOS mRNA levels requires new protein synthesis.

Amino Acid Oxidoreductases↗
PubMed1995

Inhibition of growth hormone-releasing factor production in mouse placenta by cytokines using gp130 as a signal transducer.

The aim of this study was to investigate whether mouse placenta produces mature mouse GHRF (mGHRF) and whether cytokines regulate placental mGHRF production. Using Sephadex G-50 gel filtration chromatography and reverse phase HPLC, we identified immunoreactive mGHRF in acid-ethanol extract of placental tissues, which had chromatographic characteristics identical to those of hypothalamic mature mGHRF peptide. The major peak of immunoreactive GHRF in the medium from cultured placental cells was resolved by HPLC at a fraction identical to hypothalamic mature mGHRF. Interleukin-6 (IL-6), IL-11, leukemia inhibitory factor (LIF), and oncostatin-M, which all use gp130 as a signal transducer, significantly inhibited mGHRF secretion by cultured placental cells. However, IL-1 alpha and tumor necrosis factor-alpha had no effect on mGHRF secretion. Antibodies to IL-6 or IL-6 receptor completely blocked the inhibitory effect of IL-6 on mGHRF secretion. Anti-LIF, and oncostatin-M inhibited the expression of mGHRF messenger RNA. These results suggest that mouse placenta produces and releases the mature mGHRF, which is indistinguishable by chromatographic criteria from that produced by the hypothalamus, and that signals through gp130 lead to the inhibition of mGHRF production and release in the mouse placenta.

Animals↗
PubMed1995

Fast oscillations of the electro-oculogram in a series of normal subjects.

Using a newly devised automated electro-oculograph, Nidek EOG-2, the fast oscillations (FOs) of the electro-oculogram were recorded in the 120 eyes of 60 normal subjects. We evaluated the normal means and variability of FO parameters, namely the "Rf" value, which is the average ratio in percentage of the maximum amplitude in the dark period (AD)/the minimum amplitude in the light period (AL), and the "df" value, which is the average difference between AD and AL during the FO measurement. No correlation with age was noted in the "Rf" value, although the lowest mean value of the "df" was detected in the twenties. Regarding sex, the mean levels of the "Rf" and "df" for female subjects were statistically higher than those for male subjects in the younger and global age groups. Some hormonal factor which can stimulate the metabolic activity of the retinal pigment epithelium might have caused this sexual difference.

Adult↗
PubMed1994

Transforming growth factor-beta 1 post-transcriptionally inhibits mouse growth hormone releasing factor secretion in placenta.

The aim of this study was to investigate whether TGF-beta 1 regulates mouse GHRF secretion by primary cultures of placental cells from day 12 of pregnancy. Ten ng/ml TGF-beta 1 significantly inhibited mouse GHRF secretion by the third day of culture. The lowest concentration of TGF-beta 1 that significantly inhibited mouse GHRF secretion was 1 ng/ml. The inhibitory effect of TGF-beta 1 on mouse GHRF secretion was completely eliminated by addition of an anti-TGF-beta 1 antibody. Steady-state levels of mouse GHRF mRNA as assessed by Northern analysis was not reduced by incubation of placental cells from day 12 of pregnancy with 10 ng/ml TGF-beta 1 for 5 days. Both placenta and decidua expressed TGF-beta 1 mRNA, and the level of TGF-beta 1 mRNA in decidua increased during gestation while the level of TGF-beta 1 mRNA was constant throughout gestation. These findings suggest that TGF-beta 1 is one of the potent regulators of mouse GHRF secretion and that TGF-beta 1 regulates mouse GHRF secretion in an autocrine or paracrine manner in the mouse placenta in vivo.

Animals↗
PubMed1994

Tyrosine phosphorylation of a 58 kDa protein induced by morphine in SK-N-SH cells.

A 58 kDa protein which was phosphorylated on tyrosine residues with morphine was found in human neuroblastoma cells (SK-N-SH cells) by immunoblot with monoclonal anti-phosphotyrosine antibody. The tyrosine phosphorylation was induced by morphine in 5 min in a dose-dependent manner and the increment was completely inhibited by naloxone. A Delta (d) agonist, [D-Pen2,Pen5]-enkephalin (DPDPE), but not a m agonist, [D-Ala2,N-Me-Phe,Gly5-ol]-enkephalin (DAGO), stimulated the phosphorylation and treatment of the cells with pertussis toxin inhibited the phosphorylation by morphine. These data suggest that d receptor-stimulation increases tyrosine phosphorylation of the 58 kDa protein through Gi protein in SK-N-SH cells.

Cell Line↗
PubMed1994

Modulation by chronic morphine administration of single-stranded cAMP response element (ssCRE) binding proteins in the mouse cerebellum.

The development of opiate tolerance and dependence are thought to be associated with gene expression. Our previous studies have shown that the binding activity of nuclear factors to a single-stranded oligo-DNA containing cAMP response element (ssCRE) is altered by long term treatment with morphine in cultured neuronal cells. In the present experiments, the effects of acute and chronic treatments with morphine on the binding of nuclear proteins to single- and double-stranded oligo-DNAs of the cAMP response element were studied in the mouse brains by using gel shift assay. The activity of single-stranded CRE binding proteins (ssCRE-BP) was decreased by chronic morphine treatment to about 40% of control in the cerebellum. The effect of chronic morphine treatment on the binding activity persisted for at least 2 weeks after morphine withdrawal. The activity of double-stranded CRE binding proteins was also detected in the cerebellum, but it was insensitive to the morphine treatment. The activity of ssCRE-BP was also decreased by acute morphine treatment in 5 h, but it returned to control level in 24 h. These data suggest that the change of ssCRE-BP can be involved in the development of tolerance and dependence.

Animals↗
PubMed1994

Molecular cloning and functional expression of gicerin, a novel cell adhesion molecule that binds to neurite outgrowth factor.

Gicerin is an integral membrane glycoprotein of about 82 kd that is transiently expressed in the developing CNS. Gicerin was first identified as a binding protein for neurite outgrowth factor (NOF), a member of the laminin family of extracellular matrix proteins. By isolating and sequencing a gicerin cDNA, we have found that this protein is a novel member of the immunoglobulin superfamily. The deduced protein (584 amino acids) consists of five immunoglobulin-like loop structures in an extracellular domain, a single transmembrane region, and a short cytoplasmic tail. Cells transfected stably with gicerin cDNA adhered to NOF and aggregated with each other, indicating that gicerin exhibits both heterophilic and homophilic adhesion activities.

Amino Acid Sequence↗
PubMed1994

Characterization and localization of mouse hypothalamic growth hormone-releasing factor and effect of gold thioglucose-induced hypothalamic lesions.

Hypothalamic growth hormone-releasing factor (GRF) in higher mammals, including human GRF, is a 44 amino acid residue peptide and is highly homologous in structure. By contrast, mouse GRF (mGRF) recently deduced by cDNA cloning consists of only 42 residues and shows relatively low homology to the GRFs of higher mammals and the same rodent species, rat. To characterize and localize the predicted mature mGRF peptide in the hypothalamus, we have generated its antiserum and developed a homologous radioimmunoassay. Immunoreactive mGRF in the acid hypothalamic extract was eluted as a single peak at a position identical to that of synthetic peptide on both gel filtration chromatography and reverse-phase high-performance liquid chromatography (HPLC). Secretion of immunoreactive mGRF from incubated hypothalami increased several fold in response to 50 mM K+, and this rise was abolished in the absence of medium Ca2+. Only a single peak of immunoreactive mGRF that coeluted with synthetic replicate was observed after the K(+)-stimulated medium was extracted on Bond Elut C18 cartridges and applied on reverse-phase HPLC. Immunohistochemistry identified many mGRF-positive cell bodies in the arcuate nucleus and dense bundles of immunoreactive fibers in the median eminence. Treatment of mice with gold thioglucose (GTG), a chemical agent known to cause hypothalamic lesions, markedly depleted both content and in vitro secretion of immunoreactive mGRF. The decline in mGRF secretion was greater in GTG obese than in nonobese mice, whereas somatostatin secretion was not affected by GTG treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗