Biomedical subjects

Akemichi Baba

Publications and source records attributed to Akemichi Baba.

At least 37 records · Page 2Linked to original sources

PubMed2005

T-817MA, a novel neurotrophic agent, improves sodium nitroprusside-induced mitochondrial dysfunction in cortical neurons.

1-{3-[2-(1-Benzothiophen-5-yl)ethoxy]propyl}-3-azetidinol maleate (T-817MA), a novel neurotrophic agent, protects against amyloid-beta peptide- or hydrogen peroxide-induced neuronal death. The exact mechanism of the neuroprotection is not known. This study examines the effects of T-817MA on oxidative stress-induced cytotoxicity in primary rat cortical neurons. Treatment with the NO donor sodium nitoroprusside (SNP) at 300microM decreased cell viability and induced apoptotic cell death. SNP-induced neuronal toxicity was accompanied by a decrease in mitochondrial transmembrane potential without an increase in the expression of CHOP and GRP78 mRNAs, endoplasmic reticulum stress makers. T-817MA at 0.1 and 1microM attenuated the neurotoxicity in a dose-dependent way and the protective effect required pretreatment for more than 8h. T-817MA attenuated SNP-induced decrease in mitochondrial transmembrane potential. In addition, the agent reduced SNP-induced increase in mitochondrial reactive oxygen species (ROS) production. The effects of T-817MA on SNP-induced decrease in cell viability and SNP-induced increase in mitochondrial ROS production were blocked by cycloheximide. These results suggest that T-817MA improves SNP-induced mitochondrial dysfunction in cortical neurons in a newly synthesized protein-mediated mechanism and this effect contributes to its neuroprotective effect.

Animals↗

PubMed2005

Antidepressant-like effect of coadministration of sulpiride and fluvoxamine in mice.

We have recently reported that coadministration of sulpiride, an antipsychotic drug, and fluvoxamine, a selective serotonin (5-HT) reuptake inhibitor, selectively increases in vivo dopamine release in the prefrontal cortex. This study examined the effects of coadministration of these drugs on duration of immobility in the tail suspension test using mice. Neither sulpiride (3 or 10 mg/kg) nor fluvoxamine (10 or 20 mg/kg) alone affected immobility time, whereas coadministration significantly reduced immobility time. WAY 100635, a 5-HT(1A) receptor antagonist, did not affect the effects of sulpiride and fluvoxamine coadministration, but reduced immobility time in combination with fluvoxamine (20 mg/kg). A high dose of fluvoxamine alone (60 mg/kg) also reduced immobility time. These results suggest that the antidepressant-like effects of fluvoxamine in combination with sulpiride or WAY 100635 in the tail suspension test are mediated by the activation of dopamine or 5-HT systems, respectively.

Animals↗

PubMed2005

Endothelin increases expression of exon III- and exon IV-containing brain-derived neurotrophic factor transcripts in cultured astrocytes and rat brain.

The effects of endothelins (ETs) on brain-derived neurotrophic factor (BDNF) production in astrocytes were investigated. ET-1 (100 nM) increased the mRNA level and extracellular release of BDNF in cultured astrocytes. RT-PCR analyses using primer pairs that amplified exon-specific BDNF transcripts revealed that exon III- and exon IV-containing BDNF transcripts existed in cultured astrocytes, whereas exon I- and exon II-containing BDNF transcripts did not. ET-1 and Ala(1,3,11,15)-ET-1, an ET(B) receptor agonist, increased the expressions of the exon III and exon IV transcripts in cultured astrocytes. Intracerebroventricular administration of 500 pmol/day of Ala(1,3,11,15)-ET-1 increased exon III and exon IV BDNF transcripts in the rat striatum. In cultured astrocytes, Ca(2+)-chelation, W-7 (a calmodulin inhibitor), and KN93 (a Ca(2+)/calmodulin kinase inhibitor) inhibited the increases in exon IV BDNF mRNA and CCAAT enhancer-binding protein beta (C/EBPbeta) levels induced by ET-1. The ET-induced increases in exon III BDNF mRNA expression and phosphorylation of cAMP response element binding protein (CREB) were reduced by Ca(2+) chelation, W-7, KN93, PD98059 (a MEK inhibitor), and wortmannin (a phosphatidylinositol 3-kinase inhibitor). These results suggest that ETs stimulate the expressions of exon III and exon IV BDNF transcripts in astrocytes through CREB and C/EBPbeta-mediated mechanisms, respectively.

Animals↗

PubMed2005

Neuroprotective action of endogenous PACAP in cultured rat cortical neurons.

Pituitary adenylate cyclase-activating polypeptide (PACAP) exerts neurotrophic effects both in vitro and in vivo. Here we demonstrate the upregulation of PACAP mRNA expression in cultured rat cortical neurons after excitotoxic glutamate exposure, and the exacerbating effect of the PACAP receptor antagonist, PACAP(6-38), on neuronal viability. PACAP mRNA levels were increased up to 3.5-fold 8 h after glutamate exposure. PACAP(6-38) decreased the viability of cortical neurons, irrespective of whether the cells were exposed to glutamate or not. PACAP(6-38) also inhibited glutamate-induced expression of PACAP mRNA, suggesting that PACAP acts via an autocrine or paracrine mechanism to enhance PACAP expression itself. Glutamate exposure is known to increase brain-derived neurotrophic factor (BDNF) mRNA expression. This increased expression was markedly suppressed by PACAP(6-38). Our previous study has shown that PACAP stimulates the PACAP gene transcription in PC12 cells. Taken together, these data may suggest that endogenous PACAP regulates the expression of PACAP itself and BDNF. Although it may also be possible that PACAP(6-38)-induced death of PACAP and BDNF mRNA-expressing cells, per se, results in reduced levels of these mRNAs, the present results support the idea that endogenous PACAP has a neuroprotective action.

Animals↗

PubMed2005

Differential expression of mRNAs for PACAP and its receptors during neural differentiation of embryonic stem cells.

The expressions of mRNAs for pituitary adenylate cyclase-activating polypeptide (PACAP), vasoactive intestinal peptide (VIP), and their receptors (PAC1, VPAC1 and VPAC2) were examined in the five steps of the in vitro neuronal culture model of embryonic stem (ES) cell differentiation. mRNAs for PACAP, VIP, PAC1 receptor, and VPAC2 receptor were moderately expressed in neural stem cell-enriched cultures, while VPAC1 receptor mRNA was most prominently expressed in embryoid bodies (EBs). The expression of PAC1 receptor mRNA was further upregulated after terminal differentiation into neurons. In contrast, the expressions of PAC1 receptor and PACAP mRNAs were markedly decreased after glial differentiation. These results suggest that this in vitro neuronal culture system will be a useful model for future studies on the functional role of the PACAPergic system during different stages of neuronal development.

Animals↗

PubMed2005

Monoaminergic neuronal development is not affected in PACAP-gene-deficient mice.

Pituitary adenylate cyclase-activating polypeptide (PACAP) has been implicated in several physiological functions. Several lines of evidence from in vitro studies have shown that PACAP plays some important roles in development of nervous system such as neural proliferation and differentiation. Recently, mice lacking PACAP have been reported to show a higher mortality shortly after birth, impaired thermal adaptation, and altered psychomotor behaviors. Inasmuch as monoaminergic nervous systems are implicated in these phenotypes and a quite few data have been reported on the role of this peptide in nervous development in vitro, we studied early development [embryonic days 10.5 (E10.5) and 12.5 (E12.5)] of monoaminergic nervous systems in mice lacking PACAP. The fetuses lacking PACAP showed immunoreactivities (IRs) for tyrosine hydroxylase (TH) and serotonin (5-HT) similarly to the wild type. We observed TH-IR in the forebrain [striatal differentiating zone (dz) and hypothalamic dz], midbrain, hindbrain, neural-crest-derived sympathetic ganglionic primordia, ventral spinal cord dz, and bowel at E10.5 in both PACAP null and wild type with no difference. At E12.5, in the wild-type- and PACAP-gene-deficient mice, no differences of 5-HT- and TH-IRs were observed in several brain regions, including brainstem (midbrain and pons). Thus, the depletion of PACAP does not affect monoaminergic nervous systems in the early development.

Animals↗

PubMed2005

Functional proteins involved in regulation of intracellular Ca(2+) for drug development: pharmacology of SEA0400, a specific inhibitor of the Na(+)-Ca(2+) exchanger.

The Na(+)-Ca(2+) exchanger (NCX) is involved in regulation of intracellular Ca(2+) concentration. A specific inhibitor of NCX has been required for clarification of the physiological and pathological roles of NCX. We have developed 2-[4-[(2,5-difluorophenyl)methoxy]phenoxy]-5-ethoxyaniline (SEA0400), a highly potent and selective inhibitor of NCX. SEA0400 in the concentration range that inhibits NCX exhibits negligible affinities for the Ca(2+) channels, Na(+) channels, K(+) channels, noradrenaline transporter, and 14 receptors; and it does not affect the activities of the store-operated Ca(2+) channel, Na(+)-H(+) exchanger, and several enzymes including Na(+),K(+)-ATPase and Ca(2+)-ATPase. Furthermore, recent studies show that SEA0400 attenuates ischemia-reperfusion injury in the brain, heart, and kidney and radiofrequency lesion-induced edema in rat brain. These findings suggest that NCX plays a key role in ischemia-reperfusion injury and may be a target molecule for treatment of reperfusion injury-related diseases.

Aniline Compounds↗

PubMed2005

SEA0400, a specific inhibitor of the Na+-Ca2+ exchanger, attenuates sodium nitroprusside-induced apoptosis in cultured rat microglia.

1. Using SEA0400, a potent and selective inhibitor of the Na+-Ca2+ exchanger (NCX), we examined whether NCX is involved in nitric oxide (NO)-induced disturbance of endoplasmic reticulum (ER) Ca2+ homeostasis followed by apoptosis in cultured rat microglia. 2. Sodium nitroprusside (SNP), an NO donor, decreased cell viability in a dose- and time-dependent manner with apoptotic cell death in cultured microglia. 3. Treatment with SNP decreased the ER Ca2+ levels as evaluated by measuring the increase in cytosolic Ca2+ level induced by exposing cells to thapsigargin, an irreversible inhibitor of ER Ca2+-ATPase. 4. The treatment with SNP also increased mRNA expression of CHOP and GPR78, makers of ER stress. 5. SEA0400 at 0.3-1.0 microM protected microglia against SNP-induced apoptosis. 6. SEA0400 blocked not only the SNP-induced decrease in ER Ca2+ levels but also SNP-induced increase in CHOP and GRP78 mRNAs. 7. SEA0400 did not affect capacitative Ca2+ entry in the presence and absence of SNP. 8. SNP increased Na+-dependent 45Ca2+ uptake and this increase was blocked by SEA0400. 9. These results suggest that SNP induces apoptosis via the ER stress pathway and SEA0400 attenuates SNP-induced apoptosis via suppression of the ER stress in cultured microglia. Our findings imply that NCX plays a role in ER Ca2+ depletion under pathological conditions.

Aniline Compounds↗

PubMed2005

Sulpiride in combination with fluvoxamine increases in vivo dopamine release selectively in rat prefrontal cortex.

Coadministration of atypical antipsychotics and selective serotonin reuptake inhibitors (SSRIs) enhances the release of monoamines such as dopamine (DA), norepinephrine (NE), and serotonin (5-HT) in the prefrontal cortex. To clarify the role of DA-D2/3 receptors in the combination effect, we examined the effects of coadministration of the selective DA-D2/3 antagonist sulpiride and the SSRI fluvoxamine on amine neurotransmitter release in rat prefrontal cortex. Sulpiride (10 mg/kg, i.p.) and fluvoxamine (10 mg/kg, i.p.) alone did not affect extracellular DA levels, while their coadministration caused a significant increase in DA levels. Sulpiride alone did not affect extracellular levels of 5-HT and NE in the prefrontal cortex, while fluvoxamine alone caused a marked increase in 5-HT levels and a slight increase in NE levels. Sulpiride did not affect the fluvoxamine-induced increases in extracellular levels of 5-HT and NE. The DA-D2/3 antagonist haloperidol (0.1 mg/kg) in combination with fluvoxamine also caused a selective increase in extracellular DA levels in the cortex. Coadministration of sulpiride and fluvoxamine did not affect extracellular DA levels in the striatum. Combination of systemic sulpiride and local fluvoxamine did not increase the DA levels, but that of systemic fluvoxamine with local sulpiride increased. The combination effect in increasing prefrontal DA levels was antagonized systemically, but not locally, by the 5-HT1A antagonist WAY100635 at a low dose. These findings suggest that the combination of prefrontal DA-D2/3 receptor blockade and 5-HT1A receptor activation in regions other than the cortex plays an important role in sulpiride and fluvoxamine-induced increase in prefrontal DA release.

Animals↗

PubMed2004

Overexpression of PACAP in the pancreas failed to rescue early postnatal mortality in PACAP-null mice.

PACAP exerts multiple activities as a hormone and neurotransmitter, and has been proposed to play vital roles in a variety of neuronal functions. PACAP is also involved in insulin secretion from pancreatic beta-cells. Recently, we and other groups demonstrated that PACAP-deficient mice (PACAP(-/-)) are viable, but suffer from increased postnatal mortality. To ascertain whether this high mortality is rescued by overexpression of PACAP in peripheral tissue (such as pancreas), we performed a genetic cross between PACAP(-/-) and our recently developed transgenic mice overexpressing PACAP in pancreatic beta-cells; and then examined the survival rate of their F2 progeny. PACAP(-/-) mice were segregated into two groups based on mortality as well as body weight gain: PACAP(-/-) that survived >20 days of age with normal weight gain and PACAP(-/-) that died before 20 days with a marked weight loss. Kaplan-Meier survival analysis demonstrated that PACAP(-/-) mice and those carrying the PACAP transgene have similarly lower survival probability compared with their heterozygous littermates that served as positive controls. Further study using additional tissue-specific transgenic or knockout mouse models will be required to determine the causative defects underlying the high mortality of PACAP(-/-) mice.

Animals↗

PubMed2004

Reduced hypothermic and hypnotic responses to ethanol in PACAP-deficient mice.

Using pituitary adenylate cyclase-activating polypeptide (PACAP)-deficient mice, we investigated whether PACAP is involved in the intoxicating effects of ethanol. The structure of PACAP is highly conserved during evolution, and in Drosophila, loss-of-function mutations in a PACAP-like neuropeptide gene, amnesiac, result in impairment of memory retention and increased sensitivity to ethanol. In mice, PACAP deficiency is associated with impaired memory performance and hippocampal long-term potentiation (LTP), however, sensitivity to ethanol has not been well investigated. Here, we addressed this issue in our recently developed PACAP-deficient mice. Sleep time (duration of the loss of righting reflex) was markedly shortened in PACAP-deficient mice compared with wild-type, although latency to the loss of righting reflex was not different between the two groups. Ethanol-induced hypothermia in wild-type control mice was significantly reduced in PACAP-deficient mice. Blood ethanol levels were not different between the two groups, excluding the possibility of increased ethanol metabolism. Thus, in contrast to that in Drosophila, PACAP deficiency in mammals caused a reduced sensitivity to ethanol. However, in both cases, PACAP or amnesiac products are likely to play significant roles in modifying the intoxicating effects of ethanol.

Animals↗

PubMed2004

Apelin is a novel angiogenic factor in retinal endothelial cells.

There has been much focus recently on the possible functions of apelin, an endogenous ligand for the orphan G-protein-coupled receptor APJ, in cardiovascular and central nervous systems. We report a new function of apelin as a novel angiogenic factor in retinal endothelial cells. The retinal endothelial cell line RF/6A highly expressed both apelin and APJ transcripts, while human umbilical venous endothelial cells (HUVECs) only expressed apelin mRNA. In accordance with these observations, apelin at concentrations of 1 pM-1 microM significantly enhanced migration, proliferation, and capillary-like tube formation of RF/6A cells, but not those of HUVECs, whereas VEGF stimulates those parameters of both cell types. In vivo Matrigel plug assay for angiogenesis, the inclusion of 1 nM apelin in the Matrigel resulted in clear capillary-like formations with an increase of hemoglobin content in the plug. This is the first report showing that apelin is an angiogenic factor in retinal endothelial cells.

Adipokines↗

PubMed2004

Effects of SEA0400, a novel inhibitor of the Na+/Ca2+ exchanger, on myocardial stunning in anesthetized dogs.

Activation of the Na+/Ca2+ exchanger may contribute to Ca2+ overload during reperfusion after transient ischemia. We examined the effects of 2-[4-[(2,5-difluorophenyl) methoxy]phenoxy]-5-ethoxyaniline (SEA0400), a selective inhibitor of Na+/Ca2+ exchange, on a canine model of ischemia/reperfusion injury (myocardial stunning). Myocardial stunning was induced by a 15-min occlusion of the left anterior descending coronary artery followed by a 4-h reperfusion in anesthetized open-chest dogs. Reperfusion gradually restored myocardial percent segment shortening but remained depressed during a 4-h reperfusion period. A bolus intravenous injection of SEA0400 (0.3 or 1.0 mg/kg), given 1 min before reperfusion, improved significantly the recovery of percent segment shortening in the ischemic/reperfused myocardium. SEA0400 did not affect the hemodynamics and electrocardiogram parameters. In addition, SEA0400 did not affect reperfusion-induced change in coronary blood flow. These results suggest that the Na+/Ca2+ exchanger is involved in the stunned myocardium of dogs after reperfusion, and that SEA0400 has a protective effect against myocardial stunning in dogs.

Anesthesia↗

PubMed2004

PACAP deficient mice display reduced carbohydrate intake and PACAP activates NPY-containing neurons in the rat hypothalamic arcuate nucleus.

Pituitary adenylate cyclase-activating polypeptide (PACAP) potentiates both insulin release from islets and insulin action in adipocytes. Therefore, this peptide is considered a regulator of glucose homeostasis. PACAP and its receptors are localized not only in the peripheral tissues but in the central nervous system. The present study examined whether PACAP regulates the feeding behavior and the activity of neurons in the hypothalamic arcuate nucleus (ARC), a feeding center. Food intake was measured in the PACAP knock-out mice. Cytosolic Ca2+ concentration ([Ca2+]i) in single neurons isolated from the ARC of rats was measured by fura-2 microfluorometry, followed by immunocytochemical staining with anti-NPY antiserum. PACAP knock-out mice showed a decrease in the intake of high carbohydrate, but not high fat, food. PACAP increased [Ca2+]i in NPY neurons of the ARC that are implicated in the feeding, particularly the carbohydrate ingestion. Agonists of PACAP receptors, PAC1-R and VPAC2-R, also increased [Ca2+]i. The present study, by demonstrating that PACAP directly reacts with the ARC NPY neurons to increase [Ca2+]i and that ingestion of the carbohydrate-rich food is reduced in PACAP-deficiency, suggests a facilitative role for PACAP in the carbohydrate intake.

Animals↗

PubMed2004

Pituitary adenylate cyclase-activating polypeptide is required for the development of spinal sensitization and induction of neuropathic pain.

The prolonged sensitization of pain transmission after nerve injury by increasing excitability of spinal neurons and thereby promoting repair is an adaptive response of the body. The neuropeptide pituitary adenylate cyclase-activating polypeptide (PACAP) is widely distributed in the nervous system and implicated in neurotransmission, neural plasticity, and neurotrophic actions. Although PACAP is distributed in the spinal cord and dorsal root ganglia, a role of PACAP in pain responses remains essentially unknown. Here we show that mice lacking the PACAP gene (PACAP-/-) did not exhibit inflammatory pain induced by intraplantar injection of carrageenan or neuropathic pain induced by L5 spinal nerve transection, whereas they did retain normal nociceptive responses. Intrathecal administration of NMDA induced mechanical allodynia in wild-type mice, but not in PACAP-/- mice. The NMDA-induced allodynia in PACAP-/- mice was reproduced by simultaneous intrathecal injection of PACAP with NMDA. Concomitant with the increase in PACAP immunoreactivity after nerve injury, NADPH-dependent nitric oxide synthase (NOS) activity visualized by NADPH diaphorase histochemistry markedly increased in the superficial layer of the spinal cord of wild-type mice, which was not observed in PACAP-/- mice. Simultaneous addition of PACAP and NMDA caused translocation of neuronal NOS from the cytosol to the membrane and stimulated NO production in vitro. These results demonstrate that PACAP might promote the functional coupling of neuronal NOS to NMDA receptors for both inflammatory and neuropathic pain to occur.

Animals↗

PubMed2004

Increase by FK960, a novel cognitive enhancer, in glial cell line-derived neurotrophic factor production in cultured rat astrocytes.

We examined the effect of N-(4-acetyl-1-piperazinyl)-p-fluorobenzamide monohydrate (FK960), a novel anti-dementia drug, on neurotrophic factor production in cultured rat astrocytes. FK960 (100nM) increased mRNA and protein levels of glial cell line-derived neurotrophic factor (GDNF). FK960 did not affect mRNA levels of neurotrophic factors other than GDNF. The effect of FK960 was not affected by antagonists of dopamine and alpha7-nicotinic acetylcholine receptors. FK960 stimulated phosphorylation of mitogen-activated protein/extracellular signal-regulated kinase (ERK) without any effect on phosphoryolation of p38 and c-Jun N-terminal kinase. FK960 increased the levels of c-Fos and phosphorylation of cAMP responsive element binding protein (CREB). The effect of FK960 on c-Fos was inhibited by PD98059 (10microM), an ERK kinase inhibitor, and cycloheximide (1microg/ml), a transcription inhibitor, and the effect of FK960 on CREB phosphorylation was blocked by PD98059. The effect of FK960 on GDNF mRNA expression was attenuated by PD98059, curcumin (10microM), an activator protein-1 inhibitor, cycloheximide and actinomycin D (10microg/ml). These results suggest that FK960 stimulates GDNF production in c-Fos- and CREB-dependent mechanisms in cultured astrocytes and that ERK signal is responsible for both c-Fos expression and CREB phosphorylation in the cascades.

Animals↗

PubMed2004

Inhibitory profile of SEA0400 [2-[4-[(2,5-difluorophenyl)methoxy]phenoxy]-5-ethoxyaniline] assessed on the cardiac Na+-Ca2+ exchanger, NCX1.1.

SEA0400 (2-[4-[(2,5-difluorophenyl)methoxy]phenoxy]-5-ethoxyaniline) has recently been described as a potent and selective inhibitor of Na(+)-Ca(2+) exchange in cardiac, neuronal, and renal preparations. The inhibitory effects of SEA0400 were investigated on the cloned cardiac Na(+)-Ca(2+) exchanger, NCX1.1, expressed in Xenopus laevis oocytes to gain insight into its inhibitory mechanism. Na(+)-Ca(2+) exchange currents were measured using the giant excised patch technique using conditions to evaluate both inward and outward currents. SEA0400 inhibited outward Na(+)-Ca(2+) exchange currents with high affinity (IC(50) = 78 +/- 15 and 23 +/- 4 nM for peak and steady-state currents, respectively). Considerably less inhibitory potency (i.e., micromolar) was observed for inward currents. The inhibitory profile was reexamined after proteolytic treatment of excised patches with alpha-chymotrypsin, a procedure that eliminates ionic regulatory mechanisms. After this treatment, an IC(50) value of 1.2 +/- 0.6 microM was estimated for outward currents, whereas inward currents became almost insensitive to SEA0400. The inhibitory effects of SEA0400 on outward exchange currents were evident at both high and low concentrations of regulatory Ca(2+), although distinct features were noted. SEA0400 accelerated the inactivation rate of outward currents. Based on paired pulse experiments, SEA0400 altered the recovery of exchangers from the Na(+)(i)-dependent inactive state, particularly at higher regulatory Ca(2+)(i) concentrations. Finally, the inhibitory potency of SEA0400 was strongly dependent on the intracellular Na(+) concentration. Our data confirm that SEA0400 is the most potent inhibitor of the cardiac Na(+)-Ca(2+) exchanger described to date and provide a reasonable explanation for its apparent transport mode selectivity.

Aniline Compounds↗

PubMed2004

The selective Na+-Ca2+ exchange inhibitor attenuates brain edema after radiofrequency lesion in rats.

2-[4-[(2,5-Difluorophenyl)methoxy]phenoxy]-5-ethoxyaniline (SEA0400), a specific inhibitor of the Na+-Ca2+ exchanger, exerts cytoprotective action and reduces brain infarct volume after cerebral ischemia. We examined the effect of SEA0400 on vasogenic brain edema in rats. Histological observations showed that radiofrequency current caused brain infarct and extravasation of endogenous albumin in the brain. SEA0400 (3 and 10 mg/kg, i.v.) significantly suppressed the increase in brain water content with attenuation of Evans blue dye and sodium fluorescein extravasation after radiofrequency lesion. The findings suggest that the Na+-Ca2+ exchanger plays a role in vasogenic edema formation after radiofrequency lesion.

Aniline Compounds↗