Biomedical subjects

M Ichikawa

Publications and source records attributed to M Ichikawa.

At least 109 records · Page 6Linked to original sources

PubMed1998

Excitatory amino acids act on the median eminence nerve terminals to induce gonadotropin-releasing hormone release in female rats.

The present study is designed to examine the terminal regulation of gonadotropin-releasing hormone (GnRH) release by excitatory amino acids in the median eminence of ovariectomized (OVX) rats. In in vitro experiments, median eminence tissues were superfused in the medium containing glutamate or excitatory amino acid agonists, such as N-methyl-d,l-aspartate or kainate. These drugs induced a Ca2+-dependent GnRH release from median eminence fragments. The agonists also stimulated GnRH release from superfused synaptosome prepared from the median eminence tissues in a Ca2+-dependent manner. In the immunocytochemical study, immunoreactivity for glutamate or its ionotropic receptor subtypes, such as NR1, GluR1, GluR2/3, GluR6/7, and KA2, was examined in the median eminence of OVX rats under electron microscopy. Immunoreactivities for glutamate or its receptor subtypes were observed on the nerve terminals, most of which were located in close proximity to the other nerve terminals without forming synaptic contacts. In addition, quite a few synaptic contacts which were immunopositive for GluR1, GluR2/3, KA2, or glutamate were found in this area. The present results indicate that excitatory amino acids stimulate GnRH release by acting at the nerve terminals of the median eminence in a Ca2+-dependent manner in the absence of gonadal steroid. The effect of excitatory amino acids in this area might be mediated by glutamate receptors mainly in nonsynaptic fashion, such as by volume transmission.

Animals↗

PubMed1998

Water-absorbent polymer as a carrier for a discrete deposit of antisense oligodeoxynucleotides in the central nervous system.

One of the problems of introducing antisense oligodeoxynucleotides (ODN) into the central nervous system (CNS) is their rapid disappearance from the target site due to their dispersion and diffusion, which results in poor uptake and/or retention in cells (M. Morris, A.B. Lucion, Antisense oligonucleotides in the study of neuroendocrine systems, J. Neuroendocrinol. 7 (1995) 493-500; S. Ogawa, H.E. Brown, H.J. Okano, D.W. Pfaff, Cellular uptake of intracerebrally administrated oligodeoxynucleotides in mouse brain, Regul. Pept. 59 (1995) 143-149) [2,5]. Recently, we adapted a new method using water-absorbent polymer (WAP; internally cross-linked starch-grafted-polyacrylates) as a carrier for antisense ODN. The polymer forms a hydro-gel after absorbing water which is chemically and biologically inert. In these studies, the polymer (powder-form) is fully swollen by physiological saline containing antisense ODN (0.2 micromol/ml) to make 80-fold volume gel. Hydro-gel (1 microliter) is injected into the target site, and water solutes are assumed to be diffused stoichiometrically into CNS from the surface of the gel. Histological studies indicate that 24 h after the injection, antisense ODN (5'biotinylated-S-oligos of 15 mer) are distributed to within 800 micrometer from the edge of the area where the gel is located and then gradually disappear from this area within days, but still remain within 300-micrometer distance 7 days later. Antisense ODN are effectively incorporated by all the cell types examined, i.e., neurons, astrocytes and microglias, and suppress the synthesis of the target protein. This method can be adapted to slow delivery of antisense ODN and other water soluble substances into the CNS.

Absorption↗

PubMed1998

Atomic force microscopy of histological sections using a new electron beam etching method.

In order to examine histological sections of the rat vomeronasal epithelium with the atomic force microscope (AFM), we developed an electron beam etching method that improves the resolution of AFM images. This method results in AFM images comparable to those obtained with the transmission electron microscope (TEM). Ultrathin tissue sections embedded in epoxy resin were observed before and after the treatment with electron beam radiation. Before electron beam treatment, epithelial structures such as the microvilli surface, dendritic processes, the supporting cell layers and the neuronal cell layers were all visible using the AFM. However, only a few subcellular structures could also be resolved. The AFM images were not as clear as those obtained with the TEM. After electron beam treatment, however, the resolution of AFM images was greatly improved. Most of the subcellular structures observed in TEM images, including the inner membrane of mitochondria, ciliary-structure precursor body, junctional complexes between the neurons and supporting cells, and individual microvilli were now visible in the AFM images. The electron beam treatment appeared to melt the embedding resin, bringing subcellular structures into high relief. The result of this study suggests that electron beam etching of histological samples may provide a new method for the study of subcellular structure using the AFM.

Animals↗

PubMed1998

Replacement of receptor cells in the hamster vomeronasal epithelium after nerve transection.

Chemoreceptor cells in the vomeronasal and olfactory epithelium are replaced following experimentally induced degeneration. This study analyzes quantitatively the time course and degree of vomeronasal receptor cell replacement. Unilateral transection of the vomeronasal nerves in adult hamster was used to induce a retrograde degeneration of receptor cells in the vomeronasal organ. Histological measurement of both number of receptor cells and epithelial thickness were made for recovery times from 0 to 60 days. After nerve transection, there was a gradual degeneration of receptor cells, the number decreasing to 50% of control by day 2 and 16% by day 6. During days 7-15 maximum receptor cell replacement was observed. Cell number increased rapidly and reached a peak on day 15. At recovery times of 40-60 days, cell number returned to the control level. Epithelial thickness, however, decreased to 60-70% during the degeneration period (days 4-6) and did not return to control levels. After 40-60 days epithelial thickness remained at 70% of control. These results demonstrate that vomeronasal receptor cells are replaced following degeneration, but epithelial thickness does not return to control levels. These findings suggest that the number of replacement cells is not limited by the reduced thickness of the epithelium, and that recovery mechanisms may function to restore an optimum number of receptor cells.

Animals↗

PubMed1998

The native form and maturation process of hepatitis C virus core protein.

The maturation and subcellular localization of hepatitis C virus (HCV) core protein were investigated with both a vaccinia virus expression system and CHO cell lines stably transformed with HCV cDNA. Two HCV core proteins, with molecular sizes of 21 kDa (p21) and 23 kDa (p23), were identified. The C-terminal end of p23 is amino acid 191 of the HCV polyprotein, and p21 is produced as a result of processing between amino acids 174 and 191. The subcellular localization of the HCV core protein was examined by confocal laser scanning microscopy. Although HCV core protein resided predominantly in the cytoplasm, it was also found in the nucleus and had the same molecular size as p21 in both locations, as determined by subcellular fractionation. The HCV core proteins had different immunoreactivities to a panel of monoclonal antibodies. Antibody 5E3 stained core protein in both the cytoplasm and the nucleus, C7-50 stained core protein only in the cytoplasm, and 499S stained core protein only in the nucleus. These results clearly indicate that the p23 form of HCV core protein is processed to p21 in the cytoplasm and that the core protein in the nucleus has a higher-order structure different from that of p21 in the cytoplasm. HCV core protein in sera of patients with HCV infection was analyzed in order to determine the molecular size of genuinely processed HCV core protein. HCV core protein in sera was found to have exactly the same molecular weight as the p21 protein. These results suggest that p21 core protein is a component of native viral particles.

Animals↗

PubMed1998

Spontaneous regression of localized neuroblastoma detected by mass screening.

PURPOSE: To clarify whether and when neuroblastomas identified through screening do regress, and to ascertain how to treat them appropriately, we observed screened patients who had localized tumors, without any therapeutic intervention. PATIENTS AND METHODS: The criteria for the observation program were as follows: disease stage I or II; tumor less than 5 cm in diameter; no invasion to the intraspinal canal or growth to the great vessels; urinary vanillylmandelic acid (VMA) and homovanillic acid (HVA) less than 50 microg/mg creatinine; and informed consent. Of 25 patients identified through screening for 6-month-old infants in Saitama Prefecture, Japan between April 1994 and March 1996, 11 patients who met the criteria and one other patient with stage III tumor were enrolled onto the program. They were examined by abdominal ultrasonography (US) and their urinary VMA and HVA levels were assessed approximately once per month. The observation periods ranged from 4 to 27 months. RESULTS: The 11 tumors decreased in size, although one of these 11 tumors initially enlarged until the patient was 12 months of age and decreased in size thereafter. One other tumor slightly increased in size. Urinary VMA levels decreased in all patients. None of the tumors had completely disappeared by the last observation day. CONCLUSION: Our results suggest that regression of screened neuroblastoma is not a rare phenomenon. At present, it seems reasonable to adopt a wait-and-see strategy, with careful observation, for selected stage I or II tumors identified in infants screened at 6 months of age.

Homovanillic Acid↗

PubMed1998

Evidence for terminal regulation of GnRH release by excitatory amino acids in the median eminence in female rats: a dual immunoelectron microscopic study.

The present study was designed to determine whether excitatory amino acids directly act on the gonadotropin-releasing hormone (GnRH) nerve terminals to release the peptide. The median eminence taken from ovariectomized rats was dual immunostained with GnRH and ionotropic glutamate receptor subtypes (NR1, GIuR1, GluR2/3, GluR6/7 and KA2), and their colocalization was examined under electron microscopy. The connection of fibers immunopositive for GnRH and glutamate was also examined. Of the glutamate receptor subtypes, NR1- and KA2-immunoreactivities were colocalized with GnRH-immunoreactivity in nerve terminals of the median eminence. In addition, some glutamate-immunopositive nerve terminals were shown to abut the many GnRH-immunopositive nerve terminals. No synaptic contacts were observed on these immunopositive nerve terminals. These results suggest that GnRH release is regulated at the GnRH nerve terminals by excitatory amino acids in a non-synaptic manner in the median eminence.

Animals↗

PubMed1998

Inhibitory effect of glucocorticoid for osteoblast apoptosis induced by activated peripheral blood mononuclear cells.

Recent studies suggest a protective effect of glucocorticoid against progression of bone erosion and periarticular osteoporosis in patients with rheumatoid arthritis (RA), although this steroid hormone itself is believed to increase bone loss. To understand the antagonistic effect of glucocorticoid for osteopenic process in RA patients, we examined the effect of dexamethasone on Fas-mediated apoptosis of cultured human osteoblasts induced by either anti-Fas IgM or activated peripheral blood mononuclear cells (PBMC). Human osteoblastic cell line MG63 and primary osteoblast-like cells obtained from biopsy specimens were used in this study. PBMC isolated from healthy donors were cultured with or without recombinant interleukin-2 (rIL-2) followed by 12-O-tetradecanoyl-phorbol 13-acetate (PMA) with ionomycin in the presence or absence of dexamethasone. Fas was functionally expressed on MG63 and primary osteoblast-like cells, and treatment of these cells with dexamethasone affected neither Fas expression nor anti-Fas IgM-induced apoptosis. Activated PBMC expressing membrane-type Fas ligand (mFasL) efficiently killed both MG63 and primary osteoblasts-like cells, and the addition of human Fas chimeric protein (hFas-Fc) significantly diminished the cytotoxicity, indicating that interactions between mFasL of activated PBMC and Fas on human osteoblasts induce apoptosis of the latter. Although dexamethasone did not affect apoptosis of MG63 and primary osteoblast-like cells induced by anti-Fas IgM, treatment of activated PBMC with dexamethasone markedly inhibited both mFasL expression and cytotoxicity of these cells against human osteoblasts, suggesting that dexamethasone preferentially acts not on osteoblasts but PBMC. Cultured supernatants from activated PBMC induced apoptosis of human osteoblasts and the addition of hFas-Fc also inhibited the cytotoxicity of the supernatants. In addition, soluble form FasL (sFasL) was detected in the supernatants of activated PBMC. Furthermore, both the cytotoxicity and sFasL concentration of cultured supernatants of activated PBMC incubated with dexamethasone was significantly lower than that in the absence of dexamethasone. Our data suggest that glucocorticoid suppresses the apoptotic process of osteoblasts by inhibiting the expression of both mFasL and sFasL derived from activated PBMC, mediating a protective effect against periarticular bone loss and bone erosion in inflammatory arthritis such as RA.

Apoptosis↗

PubMed1998

Change in erythrocyte shape induced by cyclosporine administration.

In order to estimate the effect of the long term administration of cyclosporine (CsA) on the shape change of erythrocytes, erythrocyte shapes which are observed with a scanning electron microscope were classified according to the nomenclature of Bessis for stomatocyte-echinocyte shape transformation. As a result of observing the erythrocyte shape of fifty-six patients with kidney transplantation treated with CsA, the morphological index of the erythrocytes of patients significantly increased to 0.0835+/-0.0085*** in comparison with 0.0004+/-0.0051 of those from healthy volunteers (control) (***: p<0.001, ANOVA). Such transformations had no relation to the subjects' sex or age. On the other hand, the erythrocytes of patients administered more than 100 ng/ml of CsA and posttransplanted within less than two years were transformed by CsA from the state of discocyte to echinocyte. In rats, the morphological index of erythrocytes of rats treated with 3 mg/kg/d or 5 mg/kg/d of CsA significantly increased in comparison with rats treated with saline (control). Furthermore, the erythrocytes of two patients were observed in terms of shape before the treatment with CsA. In both patients, the echinocyte type of erythrocyte increased by treatment with CsA. In vitro, the morphological index of the erythrocytes incubated with plasma containing CsA significantly increased, to 0.459+/-0.066*** in comparison with 0.064+/-0.029 of the control. It is suggested from these results that CsA treatment induces the echinocyte type of erythrocyte.

Adult↗

PubMed1998

Disappearance of diurnal rhythm of energy expenditure in genetically diabetic obese rats.

The daily profile of energy expenditures was examined in the new animal model of genetically diabetic obese rats. The diurnal rhythm was observed at 8 weeks of age, with highest and lowest values for energy consumption per hour observed in the dark and light periods, respectively. However, at 24 weeks of age after the manifestation of noninsulin-dependent diabetes mellitus, the rhythm completely disappeared, but it did not in the control rats.

Animals↗

PubMed1998

Induction of a multiple sclerosis-like disease in mice with an immunodominant epitope of myelin oligodendrocyte glycoprotein.

Myelin oligodendrocyte glycoprotein (MOG) is postulated to be a target autoantigen in multiple sclerosis (MS). Here we investigated the encephalitogenicity of an immunodominant epitope of MOG, peptide 35-55, in various strains of mice. An MS-like disease was induced in NOD/Lt mice (H-2g7) and C57BL/6 mice (H-2b) by a single injection of MOG35-55 in CFA. The disease followed a relapsing-remitting course in NOD/Lt mice, whereas C57BL/6 mice developed a chronic paralytic disease. Histologically, the disease in both strains was characterized by cellular infiltration and multifocal demyelination in the CNS. Significant DTH type reactions to MOG35-55 were only seen in MOG-susceptible animals, with the NOD/Lt mice showing the strongest responses. Susceptible mice also showed specific antibody responses to MOG35-55 but not to a panel of other MOG peptides. These results provide further evidence for the role of MOG as a highly autoantigenic molecule capable of inducing severe demyelinating disease.

Animals↗

PubMed1998

[MRI, SPECT and MRS findings in a case of acute hemiplegia syndrome with a marked hemispheric brain edema].

Magnetic resonance imaging (MRI), single photon emission computed tomography (SPECT) and magnetic resonance spectroscopy (MRS) were successively recorded in a 3-year-old girl with the acute hemiplegia syndrome. She was admitted to our hospital with complaints of fever, loss of consciousness and right side dominant clonic convulsions evolving into status epilepticus, and then recovered with sequelae of aphasia and right hemiparesis. Electroencephalography showed a generalized slow rhythm at the onset, and very low activities on the left hemisphere in the follow-up records. Brain CT and MRI revealed edema of the left hemisphere initially, followed by left side dominant brain atrophy. No cerebral vascular lesion was detected by magnetic resonance angiography. N-Isopropyl-[123I]-iodoamphetamine SPECT showed marked hypoperfusion of the left hemisphere accompanied by crossed cerebellar diaschisis. MRS at the initial stage detected decreased N-acetyl-aspartic acid and increased lactic acid signals in the bilateral hemisphere, which subsequently normalized only on the right side. These findings suggested brain damage and neural cell death in the left cerebral hemisphere, caused by acute encephalopathy. SPECT and MRS are useful new techniques to study the pathophysiology of the acute hemiplegia syndrome.

Acute Disease↗

PubMed1998

[Clinical evaluation of fundic gland polyps and hyperplastic polyps].

We performed a retrospective review of 477 cases of fundic gland polyps compared with 562 cases of hyperplastic polyps, which were detected endoscopically during the past 8 years between January, 1989 and December, 1996. All lesions were histologically confirmed by endoscopic biopsy or the examination of polypectomy specimens. Fundic gland polyps were more prevalent in middle aged-female, and were not associated with gastric adenomas and gastric cancers. These results suggested that the background mucosa of patients with fundic gland polyp was different from that of patients with hyperplastic polyp. Fundic gland polyps in 55 patients were followed up. No change was observed in the polyps of the about half subjects, the polyps of 12 cases (21.8%) decreased in size and number or resolved completely. Cases decreased in size and number or resolved completely were much more in fundic gland polyps than hyperplastic polyps. There were no malignant transformation of fundic gland polyps. We claimed that fundic gland polyps were benign and distinct from hyperplastic polyps which had a possibility of malignant transformation.

Aged↗

PubMed1998

[Continuous arterial infusion of protease inhibitor with supplementary therapy for the patients with severe acute pancreatitis--clinical effect of arterial injection of ulinastatin].

We treated five patients with severe acute pancreatitis by continuous arterial infusion (CAI) of protease inhibitor, nafamostat mesilate. Arterial injection (AI) of ulinastatin was performed in four cases and AI of antibiotics (IPM/CS) was done in one case, as supplemental therapies of CAI. Abdominal pain disappeared in 7.9 hours on the average, abdominal tenderness disappeared in 5.0 days and laboratory data lately recovered. All five cases treated by these therapies were cured without hemodialysis or surgical treatment in acute phase. AI of ulinastatin through arterial infusion catheter is pharmacokinetically more effective, because it yields a relatively high concentration of the drug at the acting site when compared with that of intravenous injection. Furthermore ulinastatin inhibits different types of protease from nafamostat mesilate. Therefore the clinical effect of CAI of nafamostat mesilate is enhanced by the combined therapy with AI of ulinastatin. It is also suggested that arterial injection of ulinastatin might be effective for the control of abdominal pain and that arterial injection of antibiotics might have an advantage on prevention of infectious pancreatic necrosis.

Acute Disease↗

PubMed1997

Synaptic plasticity in olfactory memory formation in female mice.

Female mice develop a long-lasting olfactory recognition memory of a partner male at the first relay in the vomeronasal system. In this study the synaptic plasticity relevant to this phenomenon was examined at reciprocal dendrodendritic synapses in the accessory olfactory bulb of female mice by electron microscopy. The size of asymmetrical excitatory synapses (mitral/tufted to granule cells) of the reciprocal synapses was significantly larger in the group of female mice which were subjected to a treatment intended to induce olfactory memory formation than in the control group. It is suggested that olfactory memory formation is associated with a conformational change at the level of synaptic structure of the accessory olfactory bulb.

Analysis of Variance↗

PubMed1997

Predominant expression of Brn-2 in the postmitotic neurons of the developing mouse neocortex.

The expression of Brn-2, a central nervous systems (CNS)-specific POU domain transcription factor, in the developing mouse neocortex was examined with an anti-Brn-2 antibody. Brn-2 protein was first detected in CNS on embryonic day (E) 11.5, and remained strong until E15.5. From E11.5 to postnatal day (P) 0, a high level of Brn-2 expression was observed in the subventricular zone, the intermediate zone, and the outer layer of the neocortex, but not in the ventricular zone. In the double-staining experiments, most of the Brn-2 positive cells were also positive for NCAM-H, an adhesion molecule specific to post-mitotic neurons. Furthermore, BrdU-labeling experiments demonstrated the presence of Brn-2 protein exclusively in postmitotic cells. These results indicated that, in the developing neocortex, Brn-2 expression is up-regulated after the final cell division. Therefore, this transcription factor may be involved in the migration and/or maturation process of the immature neuronal cells.

Animals↗

PubMed1997

Differential alteration of hippocampal synaptic strength induced by pituitary adenylate cyclase activating polypeptide-38 (PACAP-38).

We investigated the effect of pituitary adenylate cyclase activating polypeptide-38 (PACAP-38) on synaptic transmission in rat hippocampal slices using extracellular recordings. Brief bath application of PACAP-38 induced a long-lasting depression of transmission at the Schaffer collateral-CA1 synapse while at the same time causing enhancement of the perforant path-granule cell synapse in the dentate gyrus. Depression at the CA1 synapse was not occluded by low frequency-induced long-term depression (LTD), nor was enhancement at the granule cell synapse blocked by previous high frequency-induced long-term potentiation (LTP). Both actions of PACAP-38 could be elicited in the presence of an N-methyl-D-aspartate (NMDA) receptor antagonist, or in the presence of inhibitors of cyclic AMP- or Ca2+-dependent protein kinases, suggesting a novel mechanism of synaptic modulation.

Animals↗

PubMed1997

Plasma level monitoring of nasal salmon calcitonin in the rat by a heterogeneous two-site enzyme immunoassay.

The experimental and clinical effectiveness of nasal salmon calcitonin (SCT) for treatment of osteoporosis in humans has been well established, but none is known yet about the pharmacokinetic property in relation to therapeutic efficacy, especially when used in a therapeutic dose range. This preclinical study was designed to evaluate such a property, first of all in rats, using a novel heterogeneous two-site enzyme immunoassay that has allowed us to evaluate the pharmacokinetic property of parenteral SCT in rats due to the high sensitivity (the detection limit = 2 pg of SCT/ml of plasma). It was found that as early as 10 min after the nasal dosing of 1.25, 5, or 20 U/rat, the SCT immunoactivity became detectable in plasma and thereafter it waned rapidly with time. Hypocalcemia developed in a dose-dependent manner, but with a delay of approximately 20 min from the peak of the immunoactivity and lasted hours. The pharmacokinetic parameters measured for the doses (1.25, 5, and 20 U/rat) were as follows; the AUCs (pg.hr/ml) = 20.8, 89.0, and 189, and the MRTs (min) = 52, 54, and 45, respectively. The results appear to suggest: (1) the unexpected quick transfer of nasal SCT into and from the circulation, (2) a delayed onset of hypocalcemia and possibly its anti-osteopenic action, both of which may last longer, (3) that keeping the plasma SCT above the in vitro anti-osteoclastic level (approximately 1 pM) only for a few hours per 2 days would be enough for inducing the distinct anti-osteopenic effect in rats, and (4) the feasibility of designing the clinical study as to the pharmacokinetics and pharmacodynamics of nasal SCT on humans.

Administration, Intranasal↗