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Suguru Kawato

Publications and source records attributed to Suguru Kawato.

At least 19 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

Comparison between basal and apical dendritic spines in estrogen-induced rapid spinogenesis of CA1 principal neurons in the adult hippocampus.

Modulation of hippocampal synaptic plasticity by estrogen has been attracting much attention. Here, we demonstrated the rapid effect of 17beta-estradiol on the density and morphology of spines in the stratum oriens (s.o., basal side) and in the stratum lacunosum-moleculare (s.l.m., apical side) by imaging Lucifer Yellow-injected CA1 neurons in adult male rat hippocampal slices, because spines in s.o. and s.l.m. have been poorly understood as compared with spines in the stratum radiatum. The application of 1nM estradiol-induced a rapid increase in the density of spines of pyramidal neurons within 2h. This increase by estradiol was blocked by Erk MAP kinase inhibitor and estrogen receptor inhibitor in both regions. Effect of blockade by agonists of AMPA receptors and NMDA receptors was different between s.o. and s.l.m. In both regions, ERalpha agonist PPT induced the same enhancing effect of spinogenesis as that induced by estradiol.

6-Cyano-7-nitroquinoxaline-2,3-dione↗
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↗
PubMed2006

Role of cytochrome p450 in synaptocrinology: endogenous estrogen synthesis in the brain hippocampus.

In the hippocampus, the center for learning and memory, cytochrome P450s (P450scc, P450(17alpha), and P450arom) as well as 17beta-, 3beta-hydroxysteroid dehydrogenases, and 5alpha-reductase participate in the synthesis of brain steroids from endogenous cholesterol. These brain steroids include pregnenolone, dehydroepiandrosterone, testosterone, dihydrotestosterone, and 17beta-estradiol. Both estrogens and androgens are synthesized in the adult male hippocampal neurons. Although the expression levels of steroidogenic enzymes are as low as 1/200 to 1/50,000 of those in testis or ovary, the levels of synthesized steroids are sufficient for the local usage within small neurons (i.e., intracrine system). This intracrine system contrasts with the endocrine system in which high expression levels of steroidogenic enzymes are necessary in endocrine organs in order to supply steroids to many other organs via blood circulation. Endogenous synthesis of sex steroids in the hypothalamus is also discussed. Rapid modulation by estrogens and xenoestrogens is discussed concerning synaptic plasticity such as the long-term potentiation, the long-term depression, or spinogenesis. Synaptic expression of P450(17alpha), P450arom, and estrogen receptors suggests "synaptocrine" mechanisms of brain steroids, which are synthesized at synapses and act as synaptic modulators.

Animals↗
PubMed2005

Estrogen induces rapid decrease in dendritic thorns of CA3 pyramidal neurons in adult male rat hippocampus.

Modulation of hippocampal synaptic plasticity by estrogen has been attracting much attention. Thorns of thorny excrescences of CA3 hippocampal neurons are post-synaptic regions whose presynaptic partners are mossy fiber terminals. Here we demonstrated the rapid effect of estradiol on the density of thorns of thorny excrescences, by imaging Lucifer Yellow-injected CA3 neurons in adult male rat hippocampal slices. The application of 1nM estradiol induced rapid decrease in the density of thorns on pyramidal neurons within 2h. The estradiol-mediated decrease in the density of thorns was blocked by CNQX (AMPA receptor antagonist) and PD98059 (MAP kinase inhibitor), but not by MK-801 (NMDA receptor antagonist). ERalpha agonist PPT induced the same suppressive effect as that induced by estradiol on the density of thorns, but ERbeta agonist DPN did not affect the density of thorns. Note that a 1nM estradiol treatment did not affect the density of spines in the stratum radiatum and stratum oriens. A search for synaptic ERalpha was performed using purified RC-19 antibody. The localization of ERalpha (67kDa) in the CA3 mossy fiber terminals and thorns was demonstrated using immunogold electron microscopy. These results imply that estradiol drives the signaling pathway including ERalpha and MAP kinase.

Aging↗
PubMed2005

Rapid spinogenesis of pyramidal neurons induced by activation of glucocorticoid receptors in adult male rat hippocampus.

Modulation of hippocampal synaptic plasticity by glucocorticoids has been attracting much attention, due to its importance in stress responses. Dendritic spines are essential for memory storage processes. Here, we investigated the effect of dexamethasone (DEX), a specific agonist of glucocorticoid receptor (GR), on density and morphology of dendritic spines in adult male rat hippocampus by imaging of Lucifer Yellow-injected spines in slices. The application of 100 nM DEX (stressful high concentration) induced rapid modulation of the density and morphology of dendritic spines in CA1 pyramidal neurons within 1h. The total spine density increased from 0.88 spines/microm (control) to 1.36 spines/microm (DEX-treated). DEX significantly increased the density of thin and mushroom type spines, however only a slight increase was observed for stubby and filopodium type spines. Because the presence of 10 microM cycloheximide, an inhibitor of protein synthesis, did not suppress the DEX effect, these responses are probably non-genomic. Western immunoblot analysis demonstrated the localization of classical type GR in Triton-insoluble synaptosomal fractions (enriched in postsynaptic membranes) from hippocampal slices, suggesting a possible action site of DEX at spines.

Animals↗
PubMed2005

Acquisition of ischemic tolerance by repetitive transcranial magnetic stimulation in the rat hippocampus.

We investigated the acquisition of ischemic tolerance in the rat hippocampus using repetitive transcranial magnetic stimulation (rTMS). Rats received 1000 pulses/day for 7 days, and the field excitatory postsynaptic potentials were measured in the hippocampal CA1. After slices were exposed to ischemic conditions, long-term potentiation (LTP) was induced. The LTP of the stimulated group was enhanced compared with the LTP of the sham control group in each ischemic condition, suggesting that rTMS has the potential to protect hippocampal function from ischemia.

Animals↗
PubMed2005

Spatiotemporal analysis of NO production upon NMDA and tetanic stimulation of the hippocampus.

Nitric oxide (NO) is a gaseous neuromessenger. Although increasing evidence reveals significant physiological effects of NO in the hippocampal synaptic plasticity, the spatial distribution of NO production has remained largely uncharacterized due to the poor development of techniques for real-time NO imaging. In this work, using a NO-reactive fluorescent dye, diaminorhodamine-4M (DAR-4M), time-dependent heterogeneous NO production is demonstrated in hippocampal slices upon N-methyl-D-aspartate (NMDA) stimulation or tetanic stimulation. NMDA-induced DAR fluorescence increase in the CA1 was found to be twice that in the CA3 and the dentate gyrus (DG). Intracellular Ca(2+) concentration was also investigated. NMDA induced similar Ca(2+) responses both in the CA1 and DG, which were approx. 13% greater than that in the CA3. Subsequently, spatial distribution of NO production in the CA1 upon a tetanic stimulation of Schaffer collateral was investigated, because there are contradictory reports on the effect of NO on long-term potentiation (LTP), and that NO is known to exert various physiological effects depending on its concentration. In the stratum radiatum (sr), DAR fluorescence increase upon tetanus was largest at the vicinity of a stimulating electrode and decreased as a function of increasing distance from the stimulating electrode, suggesting the possibility that the effect of NO in LTP is dependent on the distance between stimulating and recording electrodes. The tetanus-induced Ca(2+) response observed in the sr showed the same but weak distant dependence from the stimulating electrode. Taken together, the observed heterogeneity in the distribution of NO production is suggestive of region-specific effects of NO in the hippocampus.

Animals↗
PubMed2004

Acute effect of corticosterone on N-methyl-D-aspartate receptor-mediated Ca2+ elevation in mouse hippocampal slices.

We examined the rapid effects of corticosterone (CORT) on N-methyl-D-aspartate (NMDA) receptor-mediated Ca2+ signals in adult mouse hippocampal slices by using Ca2+ imaging technique. Application of NMDA caused a transient elevation of intracellular Ca2+ concentration followed by a decay to a plateau within 150s. The 30min preincubation of CORT induced a significant decrease of the peak amplitude of NMDA-induced Ca2+ elevation in the CA1 region. The rapid effect of CORT was induced at a stress-induced level (0.4-10microM). Because the membrane non-permeable bovine serum albumin-conjugated CORT also induced a similar rapid effect, the rapid effect of CORT might be induced via putative surface CORT receptors. In contrast, CORT induced no significant effects on NMDA-induced Ca2+ elevation in the dentate gyrus. In the CA3 region, CORT effects were not evaluated, because the marked elevation of NMDA-induced Ca2+ signals was not observed there.

Animals↗
PubMed2004

Endocrine disrupters as disrupters of brain function: a neurosteroid viewpoint.

The mechanisms of neurosteroid synthesis in the rat hippocampus were investigated. Metabolism assay demonstrated the pathway of "cholesterol alpha pregnenolone --> dehydroepiandrosterone --> androstenedione --> testosterone --> estradiol." Upon exposure of pups to bisphenol A (BPA) from the embryonic stage until 3 week-old stage, a significant facilitation of the synthesis of estradiol was observed in the hippocampus. The localization of cytochrome P450s (P450scc, P45017alpha, and P450arom) as well as estrogen receptor alpha (ER(alpha)) was observed in pyramidal and granule neurons, using immunohistochemical staining. Furthermore, the synaptic localization of P45017alpha, P450arom and ER(alpha) was demonstrated with immuno-electron microscopic analysis. The acute action of estradiol and endocrine disrupters were then analyzed with an electrophysiological measurement of hippocampal pyramidal neurons. A 30 min preperfusion of diethylstylbesterol (DES) enhanced the induction of long-term potentiation (LTP) by almost an identical magnitude to that obtained by estradiol perfusion. On the other hand, although the application of BPA alone did not affect LTP-induction, the co-perfusion of BPA with estradiol completely suppressed the enhancement effect of LTP by estradiol. The current investigations demonstrate in the hippocampus (1) that locally synthesized estrogen rapidly enhances the synaptic plasticity of neurons, and (2) that BPA and DES modulate the synaptic plasticity as well as the synthesis of estradiol. The probable targets of BPA and DES are ER(alpha) and steroidogenic proteins.

Animals↗
PubMed2003

Adult male rat hippocampus synthesizes estradiol from pregnenolone by cytochromes P45017alpha and P450 aromatase localized in neurons.

In adult mammalian brain, occurrence of the synthesis of estradiol from endogenous cholesterol has been doubted because of the inability to detect dehydroepiandrosterone synthase, P45017alpha. In adult male rat hippocampal formation, significant localization was demonstrated for both cytochromes P45017alpha and P450 aromatase, in pyramidal neurons in the CA1-CA3 regions, as well as in the granule cells in the dentate gyrus, by means of immunohistochemical staining of slices. Only a weak immunoreaction of these P450s was observed in astrocytes and oligodendrocytes. ImmunoGold electron microscopy revealed that P45017alpha and P450 aromatase were localized in pre- and postsynaptic compartments as well as in the endoplasmic reticulum in principal neurons. The expression of these cytochromes was further verified by using Western blot analysis and RT-PCR. Stimulation of hippocampal neurons with N-methyl-d-aspartate induced a significant net production of estradiol. Analysis of radioactive metabolites demonstrated the conversion from [(3)H]pregnenolone to [(3)H]estradiol through dehydroepiandrosterone and testosterone. This activity was abolished by the application of specific inhibitors of cytochrome P450s. Interestingly, estradiol was not significantly converted to other steroid metabolites. Taken together with our previous finding of a P450scc-containing neuronal system for pregnenolone synthesis, these results imply that 17beta-estradiol is synthesized by P45017alpha and P450 aromatase localized in hippocampal neurons from endogenous cholesterol. This synthesis may be regulated by a glutamate-mediated synaptic communication that evokes Ca(2+) signals.

Animals↗
PubMed2003

The effect of repetitive transcranial magnetic stimulation on long-term potentiation in rat hippocampus depends on stimulus intensity.

We investigated the effect of repetitive transcranial magnetic stimulation (rTMS) on long-term potentiation (LTP) in the rat hippocampus. Rats were magnetically stimulated at a rate of 1000 pulses/day for 7 days by a round coil, in which the peak magnetic fields at the center of the coil were 0.75 and 1.00 T. LTP enhancement was observed only in the 0.75-T rTMS group, while no change was observed in the 1.00-T rTMS group. These results suggest that the effect of rTMS on LTP depends on the stimulus intensity.

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↗
PubMed2002

Corticosterone acutely prolonged N-methyl-d-aspartate receptor-mediated Ca2+ elevation in cultured rat hippocampal neurons.

This work reports the first demonstration that corticosterone (CORT) has a rapid and transient effect on NMDA receptor-mediated Ca2+ signaling in cultured rat hippocampal neurons. Using single cell Ca2+ imaging, CORT and agonists of glucocorticoid receptors were observed to modulate the NMDA receptor-mediated Ca2+ signals in a completely different fashion from pregnenolone sulfate. In the absence of steroids, 100 micro m NMDA induced a transient Ca2+ signal that lasted for 30-70 s in 86.1% of the neurons prepared from postnatal rats (3-5 days old). After pre-treatment with 0.1-100 micro m CORT for 10-20 min, NMDA induced extremely prolonged Ca2+ elevation. This prolonged Ca2+ elevation was terminated by the application of MK-801 and followed by washing out of CORT. The proportion of CORT-modulated neurons within the NMDA-responsive cells increased from 25.1 to 95.5% when the concentration of CORT was raised from 0.1 to 50 micro m. Substitution of BSA-conjugated CORT produced essentially the same results. When hippocampal neurons were preincubated with 10 micro m cortisol and 1 micro m dexamethasone for 20 min, a very prolonged Ca2+ elevation was also observed upon NMDA stimulation. The CORT-prolonged Ca2+ elevation caused a long-lasting depolarization of the mitochondrial membrane, as observed with rhodamine 123. In contrast, incubation with 100 micro m pregnenolone sulfate did not considerably alter the time duration of NMDA-induced transient Ca2+ elevation, but caused a significant increase in the peak amplitude of Ca2+ elevation in hippocampal neurons. These results imply that high levels of CORT induce a rapid and non-genomic prolongation of NMDA receptor-mediated Ca2+ elevation, probably via putative membrane surface receptors for CORT in the hippocampal neurons.

Androstanols↗
PubMedDate not supplied

Acute repetitive transcranial magnetic stimulation reactivates dopaminergic system in lesion rats.

Repetitive transcranial magnetic stimulation (rTMS) offers potential benefit as a therapeutic treatment for neurological and psychiatric disorders. However, the mechanism underlying the therapeutic effects of rTMS is still unknown. In this study, we investigated the rescue effects of rTMS in the lesioned rats by administering the neurotoxin MPTP (l-methyl-4-phenyl-l,2,3,6-tetrahydropyridine). The rats received rTMS (10 trains of 25 pulses/s for 8 s) 48 h after MPTP injection, and tyrosine hydroxylase (TH) and NeuN expressions were investigated in the substantia nigra. The functional observational battery-hunched posture score for the MPTP-rTMS group was significantly lower and the number of rearing events was higher compared with the MPTP-sham group, these behavioral parameters revert to control levels. These results suggest that rTMS treatment reactivates the dopaminergic system in lesion rats.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗