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Biomedical subjects

J Yamada

Publications and source records attributed to J Yamada.

At least 181 records · Page 10Linked to original sources
PubMed1996

In vitro maturation and transmission electron microscopic observation of horse oocytes after vitrification.

The study was designed to examine the suitability of immature horse oocytes for vitrification. Immature oocytes derived from slaughtered horse ovaries were transferred to a vitrification solution (EFS; 40% ethylene glycol, 18% Ficoll, and 0.3 M sucrose in modified phosphate-buffered saline) directly (Groups 1 and 4) or were first exposed to 20% ethylene glycol solution for 10 min (Groups 2 and 5) or 20 min (Groups 3 and 6). Oocytes were handled at 20 degrees C (Groups 1, 2, and 3) or 30 degrees C (Groups 4, 5, and 6). After vitrification and warming, their viability was assessed by maturation culture for 32 h. The percentages of oocytes reaching the metaphase II stage after the in vitro maturation in Groups 2, 3, 5, and 6 (16.0, 16.7, 10.0. and 8.2%, respectively) were higher than those in Groups 1 and 4 (2.2 and 1.9%, respectively). In untreated control oocytes, 55.6% completed meiosis in vitro. Transmission electron microscopy was used to compare the fine structure of vitrified oocytes (treated as Group 2) with those of untreated control oocytes and EFS-exposed, nonvitrified oocytes (n = 10 each). The viability of EFS-exposed oocytes, assessed by in vitro maturation, was 27.7%. Vitrification induced some ultrastructural changes, such as the swelling of mitochondria together with reduced matrix density, the destruction of communication between oocytes and their surrounding cumulus cells, and the presence of vacuoles located in the periphery of the ooplasm. However, these changes were not always observed. Exposure of the oocytes to EFS solution induced similar ultrastructural changes in mitochondria and cell-cell communication but to a lesser extent. However, the exposure to EFS induced vacuoles in the periphery of the ooplasm to the same extent as did the vitrification. Thus, immature horse oocytes can be cryopreserved by vitrification with EFS solution. Reduced viability of EFS-exposed and/or vitrified horse oocytes may relate to morphological changes such as destruction of the intercellular communications between cumulus cells and oocytes.

Animals↗
PubMed1996

Topiramate reduces abnormally high extracellular levels of glutamate and aspartate in the hippocampus of spontaneously epileptic rats (SER).

The spontaneously epileptic rat (SER), a double mutant, manifests both tonic and absence-like seizures. The effect of topiramate, a novel antiepileptic drug, on the extracellular levels of excitatory amino acids (EAA) in the hippocampus of SER was investigated using in vivo microdialysis. The basal levels of glutamate and aspartate in dialysates of hippocampus in SER were 2- to 3-fold higher than those in normal Wistar rats. Both the dose-response relationship and the time course of the suppression of tonic seizures by topiramate were similar to the attenuation of glutamate level in SER. Topiramate (40 mg/kg i.p.) significantly (P < 0.05) reduced both glutamate and aspartate levels in SER while showing no effect on normal Wistar rats. These findings suggest that topiramate reduces abnormally high extracellular levels of glutamate and aspartate in the hippocampus of SER. This effect may, at least in part, be related to the anticonvulsant activity of topiramate.

Animals↗
PubMed1996

Canine H(+)-K(+)-ATPase alpha-subunit gene promoter: studies with canine parietal cells in primary culture.

H(+)-K(+)-adenosinetriphosphatase (H(+)-K(+)-ATPase) is the principal enzyme responsible for the process of gastric acid secretion. This enzyme is expressed in a cell-type-specific manner in gastric parietal cells. To explore the mechanisms regulating its expression, we transfected differentiated canine parietal cells in primary culture with H(+)-K(+)-ATPase-luciferase reporter genes and assessed transcriptional activities. Deletional analysis of the 5'-flanking region of this gene demonstrated a remarkable increment in transcriptional activity associated with a segment between bases -54 to -45 (5' GCTCCGCCTC 3') relative to the transcriptional initiation site. Gel shift assays with competition and supershift analysis demonstrated that this segment is specifically bound by the transcription factor Sp1. A point mutation, eliminating Sp1 binding, diminished basal transcriptional activity by 80%, indicating that this Sp1 binding site is important for constitutive transcriptional activity. Although these studies indicate that Sp1 is required to maintain a high concentration of the H(+)-K(+)-ATPase gene in the parietal cell, its cell-type-specific expression must rely on other elements because Sp1 is a ubiquitously expressed transcription factor.

Animals↗
PubMed1996

The effects of peripheral serotonin2 (5-HT2) and serotonin3 (5-HT3) receptor agonists on blood glucose levels in rats.

The involvement of the peripheral serotonin2A (5-HT2A) receptor in alpha-methyl-5-HT-induced hyperglycemia was examined in rats. The 5-HT2A receptor antagonist, ketanserin, significantly inhibited alpha-methyl-5-HT-elicited hyperglycemia. Taken together with a previous report that 5-HT-induced hyperglycemia was prevented by ketanserin, it is suggested that the peripheral 5-HT2A receptor participates in glucose regulation. As alpha-methyl-5-HT increased serum insulin but did not affect glucagon levels, it is indicated that these pancreatic hormones are probably not related to alpha-methyl-5-HT-induced hyperglycemia. Moreover, the peripheral 5-HT3 receptor agonist, 2-methyl-5-HT, did not affect blood glucose, insulin or glucagon levels. Our results therefore suggest that the peripheral 5-HT3 receptor is not involved in glucose regulation.

Animals↗
PubMed1996

Transcriptional induction of Acyl-CoA oxidase by dehydroepiandrosterone sulfate in cultured rat hepatocytes.

To elucidate the molecular basis of the induction of peroxisomal enzymes, transcriptional regulation of the acyl-CoA oxidase (AOX) gene by dehydroepiandrosterone sulfate (DHEAS) was examined using primary cultures of rat hepatocytes. Incubation of the hepatocytes with 0.1 mM DHEAS resulted in a progressive increase in the cellular AOX mRNA level, which after 24 h reached a 5.6-fold higher level than that in the control cells treated with vehicle alone. However, this mRNA induction was completely inhibited by alpha-amanitin, an RNA polymerase II inhibitor. When examined by the nuclear run-on transcription assay, the rate of de novo synthesis of AOX mRNA was 3- to 4-fold higher in the hepatocytes exposed to DHEAS than in the control cells, even after 3h. These results indicate that DHEAS acts directly on hepatocytes to activate the transcription of the AOX gene, which leads to the marked induction of AOX in the cell.

Acyl-CoA Oxidase↗
PubMed1996

Antimutagenic activity of caffeic acid and related compounds.

Effects of caffeic acid and chlorogenic acid on mutagenicity were studied using the Salmonella typhimurium system. These compounds had inhibitory effects on the mutagenicity of Trp-P-1 and Glu-P-2. Caffeic acid completely eliminated the mutagenicity induced by activated Glu-P-2. Some compounds analogous to caffeic acid, such as cinnamic acid, coumaric acid, and ferulic acid, also significantly decreased the mutagenicity of Glu-P-2.

Antimutagenic Agents↗
PubMed1996

Immunohistochemically-determined changes in the distribution of insulin-like growth factor-I (IGF-I) and epidermal growth factor (EGF) in the bovine endometrium during the estrous cycle.

The aims of this study were to investigate whether there are cell-specific distributions of insulin-like growth factor I (IGF-I) and epidermal growth factor (EGF) in the endometrium, and to determine whether or not the expression of these factors varies with the stage of the estrous cycle. Fifty-four endometrial biopsy specimens were collected from normal cycle Holstein-Friesian heifers. The endometrial specimens were divided into nine groups (at least five different animals per group) corresponding to the following days of the cycle: days 20-0, 1-3, 4-5, 6-7, 8-10, 11-13, 14-15, 16-17, and 18-19 (day 0 = estrus). IGF-I and EGF were localized by immunohistochemistry in the intact heifer endometrium throughout the estrous cycle. Throughout the estrous cycle, IGF-I was localized in the luminal epithelium and stroma with a little staining in the glandular epithelium (P < 0.01). In the luminal epithelium, the number of IGF-I-positive cells increased on days 1-3, 6-7, 11-13, and 16-17. In the stroma, the number of IGF-I-positive cells increased on days 8-10 and 20-3. The number of positively stained cells in the glandular epithelium increased around the estrous period. EGF stained intensely in the stroma but very little in the luminal and glandular epithelia (P < 0.01). In the stroma, three peaks in the number of EGF-positive cells were observed: on days 1-3, 6-7, and 11-13. These results demonstrate cyclical changes in the endometrial cell types localization of IGF-I and EGF.

Animals↗
PubMed1996

Classification of the cycle of the seminiferous epithelium in the common tree shrew (Tupaia glis).

The classification of the cycle of the seminiferous epithelium was carried out in the common tree shrew (Tupaia glis). The tree shrew captured in Thailand were fixed with Bouin's fixative, embedded in paraffin wax, and stained with PAS-hematoxylin. The cycle was classified into twelve stages on the basis of the acrosomal changes of spermatids. Relative frequencies of stages form I to XII were 11.9, 7.2, 8.9, 22.5, 12.9, 9.7, 8.0, 5.9, 4.0, 3.2, 2.9, and 3.6%, respectively. Different stages did no appear in a cross-sectioned tubule as did in primates. The head of matured spermatid was discoidal in shape and different from that of primates and rodents. Spermatogenesis of the common tree shrew is different from that of primates and rodents according to its morphological features.

Animals↗
PubMed1996

Effect of nicardipine, a calcium antagonist, on induction of peroxisomal enzymes by dehydroepiandrosterone sulfate in cultured rat hepatocytes.

We examined the effect of nicardipine, a calcium antagonist, on the induction of peroxisomal enzymes, such as acyl-CoA oxidase and carnitine acetyltransferase, by dehydroepiandrosterone sulfate (DHEAS) and clofibric acid (CPIB), in primary cultured rat hepatocytes. Peroxisomal beta-oxidation and carnitine acetyltransferase activities were increased 11- and 20-fold, respectively, after 5 days of treatment with DHEAS (40 microM). However, 60 microM nicardipine significantly suppressed the induction of both of these activities by DHEAS to about 2-fold that of the control. This suppression was found to be both dose- and time-dependent. Immunoblot and Northern blot analyses of acyl-CoA oxidase revealed that suppression by nicardipine of the induction of peroxisomal beta-oxidation activity would be responsible for an increase in the amount of mRNA. In addition, the manner in which nicardipine suppressed the induction of peroxisomal beta-oxidation and carnitine acetyltransferase activity, was similar to that of clofibric acid. These findings suggest that in the calcium-dependent pathway, the mechanism for the induction of peroxisomal enzymes by DHEAS is basically the same as that by clofibric acid, a typical peroxisome proliferator. The present results also support our previous hypothesis that calcium may play an important role in the induction of these enzymes by peroxisome proliferators.

Animals↗
PubMed1996

An ultrastructural and lectin-histochemical study on the seminiferous epithelium of the common tree shrew (Tupaia glis).

The seminiferous epithelium of the common tree shrew (Tupaia glis) was investigated using transmission electron microscopy and lectin-histochemistry. It was compared with that of shrews examined in previous studies. Some peculiar structures were detected in the tree shrew spermatid at the electron microscopic level. The most characteristic feature was the disposition of mitochondria in early spermatids. In cap and early acrosome-phase spermatids, mitochondria accumulated in one area of the spermatid cytoplasm and then dispersed in the late acrosome phase. Subsequently they again clustered to form the middle piece of spermatozoa. While the lamellar structure was clearly seen in the caudal region of the spermatid nucleus, it gradually disappeared during the process of elongation. The dilated area in the postacrosomal space of early round spermatids was also characteristic. The dilation was not detected in elongated spermatids. These structures were not recognised in the seminiferous epithelium of shrews. With respect to lectin histochemistry, the binding patterns in the spermatid acrosome of the tree shrew were similar to those of the musk shrew. However, PNA and BPA, which reacted with the Sertoli cell cytoplasm of the musk shrew, showed no reaction in the tree shrew Sertoli cell. Thus, except for some lectin binding patterns in the spermatid acrosome, no close similarity was recognised in the morphology of the seminiferous epithelium between tree shrews and shrews.

Acrosome↗
PubMed1996

Ultrastructural study on the harderian gland of the rabbit (Oryctolagus cuniculus).

The ultrastructure of the Harderian gland of the rabbit has been studied. The gland can be divided into two lobes (pink and white) by the naked eye. At the microscopic level, their epithelial cells differ morphologically, the vacuoles in the cells of the pink lobe being large, while those of the white lobe, small. In addition to the pink and white lobes, an intermediate area can be distinguished around the boundary between the two lobes on the basis of epithelial cell compositions. The acini on this area consist of two epithelial cell types, one is similar to that found in the white lobe, the second consists of the same cells as the pink lobe Myoepithelial cells are located between the secretory epithelium and its basal lamina. Mast cells, macrophages and plasma cells are found in the interstitial connective tissue of the Harderian gland.

Animals↗
PubMed1995

Epidermal growth factor induces H+,K+-ATPase alpha-subunit gene expression through an element homologous to the 3' half-site of the c-fos serum response element.

Epidermal growth factor (EGF) acutely inhibits acid secretion; however, prolonged administration of EGF has been reported to increase acid production. We undertook these studies to examine whether the physiological effects of EGF on acid secretion are mediated by regulation of gastric H+,K+-ATPase, the principle enzyme responsible for acid secretion. EGF in concentrations equivalent to those in plasma increased H+,K(+)-ATPase alpha-subunit mRNA levels. Using H+,K(+)-ATPase-luciferase constructs transfected into primary cultured parietal cells, a significant step up in EGF inducibility was observed between bases -162 and -156 (5'-GACATGG-3') relative to the cap site. This EGF response element (ERE) conferred EGF inducibility when linked to homologous and heterologous promoters. The ERE is homologous to the 3' half-site of the c-fos serum response element to which rNFIL-6, rE12, and SRE-ZBP bind. Electrophoretic mobility shift assays using an ERE probe and parietal cell nuclear extracts revealed a specific DNA-protein complex, the formation of which was changed by neither E12 and NFIL-6 consensus oligonucleotides nor antibodies for NFIL-6, SRE-ZBP, and E12. Our studies indicate that EGF induces gastric H+,K(+)-ATPase alpha-subunit gene expression via an interaction between a specific ERE and a novel transcriptional factor and that this may be a physiologic mechanism by which EGF regulates acid secretion.

Aminopyrine↗
PubMed1995

Developmental deep dyslexia in Japanese: a case study.

This report demonstrates the existence of developmental deep dyslexia involving Japanese orthography. When asked to read (or name) isolated kanji, T.S., a sixth grader with a normal IQ and no speech impairment, produced a number of visual, selection, and semantic errors. It is suggested that these errors arise from an interaction between phonological coding impairment and the relative sparing of direct visual processing, which are taken to be characteristic of developmental deep dyslexia. A selection hypothesis is presented to explain selection errors, semantic errors, and some peculiar phenomena observed in acquired dyslexics.

Child↗
PubMed1995

Altered brain contents of neuropeptides in spontaneously epileptic rats (SER) and tremor rats with absence seizures.

Immunoreactive- (IR-) somatostatin (SRIF), neuropeptide Y (NPY) and corticotropin-releasing factor (CRF) contents were investigated in the brain of tremor rats with absence-like seizure and spontaneously epileptic rats (SER), which is a genetically defined double-mutant (zi/zi, tm/tm) obtained by mating zitter homozygote (zi/zi) with tremor heterozygote (tm/+) and shows both absence-like seizure and tonic convulsions. Increased levels of IR-NPY and IR-CRF were observed in several regions including the amygdala and hippocampus in homozygous SER compared to heterozygous SER (zi/zi, tm/+ or +/+). Homozygous tremor rats (tm/tm) showed lower levels of IR-NPY and IR-CRF contents mainly in the hippocampus and mesolimbic system (entorhinal and pyriform cortex and nucleus accumbens) than heterozygous tremor rats. IR-SRIF contents of homozygous SER were higher in frontal cortex than heterozygous SER and in amygdala than homozygous tremor rats. No change of IR-SRIF between groups was noted in the hippocampus among brain structures underlying epileptogenicity. The results suggest that the change of neuropeptide levels, most conspicuous in NPY among three peptides tested, may be involved in the phenotypical manifestation of seizures in SER and tremor rats, and that the development of tonic convulsion and absence seizures may be differently associated with the change of brain neuropeptide levels.

Animals↗