Biomedical subjects

Hirotaka Ishii

Publications and source records attributed to Hirotaka Ishii.

5 recordsLinked to original sources

PubMed2006

Local neurosteroid production in the hippocampus: influence on synaptic plasticity of memory.

In neuroendocrinology, it is believed that steroid hormones are synthesized in the gonads and/or adrenal glands, and reach the brain via the blood circulation. In contrast to this view, we are in progress of demonstrating that estrogens and androgens are also synthesized locally by cytochrome P450s in the hippocampus, and that these steroids act rapidly to modulate neuronal synaptic plasticity. We demonstrated that estrogens were locally synthesized in the adult hippocampal neurons. In the pathway of steroidogenesis, cholesterol is converted to pregnenolone (by P450scc), dehydroepiandrosterone [by P450(17alpha)], androstenediol (by 17beta-hydroxysteroid dehydrogenase, 17beta-HSD), testosterone (by 3beta-HSD) and finally to estradiol (by P450arom) and dihydrotestosterone (by 5alpha-reductase). The basal concentration of estradiol in the hippocampus was approximately 1 nM, which was greater than that in blood plasma. Significant expression of mRNA for P450scc, P450(17alpha), P450arom, 17beta-HSD, 3beta-HSD and 5alpha-reductase was demonstrated by RT-PCR. Their mRNA levels in the hippocampus were 1/200-1/5,000 of those in the endocrine organs. Localization of P450(17alpha) and P450arom was observed in synapses in addition to endoplasmic reticulum of principal neurons using immunoelectron microscopy. Different from slow action of gonadal estradiol which reaches the brain via the blood circulation, hippocampal neuron-derived estradiol may act locally and rapidly within the neurons. For example, 1 nM 17beta-estradiol rapidly enhanced the long-term depression (LTD) not only in CA1 but also in CA3 and dentate gyrus. The density of thin spines was selectively increased within 2 h upon application of 1 nM estradiol in CA1 pyramidal neurons. Only ERalpha agonist propyl-pyrazole-trinyl-phenol induced the same enhancing effect as estradiol on both LTD and spinogenesis in the CA1. ERbeta agonist hydroxyphenyl-propionitrile suppressed LTD and did not affect spinogenesis. Localization of estrogen receptor ERalpha in spines in addition to nuclei of principal neurons implies that synaptic ERalpha can drive rapid modulation of synaptic plasticity by endogenous estradiol.

Androgens↗

PubMed2006

[Insulinoma].

Explore the source record for details and available documents.

Antibiotics, Antineoplastic↗

PubMed2006

Enhancement of nitric oxide production by association of nitric oxide synthase with N-methyl-D-aspartate receptors via postsynaptic density 95 in genetically engineered Chinese hamster ovary cells: real-time fluorescence imaging using nitric oxide sensitive dye.

The current quantitative study demonstrates that the recruitment of neuronal nitric oxide synthase (nNOS) beneath N-methyl-D-aspartate (NMDA) receptors, via postsynaptic density 95 (PSD-95) proteins significantly enhances nitric oxide (NO) production. Real-time single-cell fluorescence imaging was applied to measure both NO production and Ca(2+) influx in Chinese hamster ovary (CHO) cells expressing recombinant NMDA receptors (NMDA-R), nNOS, and PSD-95. We examined the relationship between the rate of NO production and Ca(2+) influx via NMDA receptors using the NO-reactive fluorescent dye, diaminofluorescein-FM (DAF-FM) and the Ca(2+)-sensitive yellow cameleon 3.1 (YC3.1), conjugated with PSD-95 (PSD-95-YC3.1). The presence of PSD-95 enhanced the rate of NO production by 2.3-fold upon stimulation with 100 microm NMDA in CHO1(+) cells (expressing NMDA-R, nNOS and PSD-95) when compared with CHO1(-) cells (expressing NMDA-R and nNOS lacking PSD-95). The presence of nNOS inhibitor or NMDA-R blocker almost completely suppressed this NMDA-stimulated NO production. The Ca(2+) concentration beneath the NMDA-R, [Ca(2+)](NR), was determined to be 5.4 microm by stimulating CHO2 cells (expressing NMDA-R and PSD-95-YC3.1) with 100 microm NMDA. By completely permealizing CHO1 cells with ionomycin, a general relationship curve of the rate of NO production versus the Ca(2+) concentration around nNOS, [Ca(2+)](NOS), was obtained over the wide range of [Ca(2+)](NOS). This sigmoidal curve had an EC(50) of approximately 1.2 microm of [Ca(2+)](NOS), implying that [Ca(2+)](NR) = 5.4 microm can activate nNOS effectively.

Animals↗

PubMed2003

Hippocampal cytochrome P450s synthesize brain neurosteroids which are paracrine neuromodulators of synaptic signal transduction.

Hippocampal pyramidal neurons and granule neurons of adult male rats are equipped with a complete machinery for the synthesis of pregnenolone, dehydroepiandrosterone, 17beta-estradiol and testosterone as well as their sulfate esters. These brain neurosteroids are synthesized by cytochrome P450s (P450scc, P45017alpha and P450arom) from endogenous cholesterol. Synthesis is acutely dependent on the Ca(2+) influx attendant upon neuron-neuron communication via N-methyl-D-aspartate (NMDA) receptors. Pregnenolone sulfate, estradiol and corticosterone rapidly modulate neuronal signal transduction and the induction of long-term potentiation via NMDA receptors and putative membrane steroid receptors. Brain neurosteroids are therefore promising neuromodulators that may either activate or inactivate neuron-neuron communication, thereby mediating learning and memory in the hippocampus.

Animals↗

PubMedDate not supplied

Clinical characteristics of nateglinide response as assessed by insulinogenic indices: preliminary study to determine an optimal indication for nateglinide.

Insulin secretion dynamics and response to nateglinide were studied in patients with type 2 diabetes and reduced early-phase insulin secretion. On day 1, 24 patients underwent a 75-g oral glucose tolerance test without taking nateglinide. On day 2, they were given oral nateglinide 90 mg immediately before the oral glucose tolerance test. After glucose loading, insulin levels increased significantly at 30, 60, 90, and 120 minutes after the patients took nateglinide, along with insulinogenic indices, the total area under the insulin curve, the area under the 0- to 90-minute insulin curve, and the area under the 90- to 180-minute insulin curve. Both the plasma glucose level at 60, 90, 120, and 180 minutes and the total area under the glucose curve were significantly reduced following nateglinide administration. Compared with the low responders (n=13), the high responders (n=11) had a significantly shorter duration of disease, significantly higher insulinogenic indices in the absence of nateglinide administration, and a higher homeostasis model assessment-beta cell performance. Nateglinide demonstrated a rapid-onset and rapid-offset insulin secretion-stimulating effect in this study population. A single dose of nateglinide may be indicated for patients with a relatively high homeostasis model assessment-beta cell performance, a short duration of disease, and relatively high insulinogenic indices prior to nateglinide administration.

Administration, Oral↗