Biomedical subjects

Akemichi Baba

Publications and source records attributed to Akemichi Baba.

At least 73 records · Page 4Linked to original sources

PubMed2003

Protective effects of SEA0400, a novel and selective inhibitor of the Na+/Ca2+ exchanger, on myocardial ischemia-reperfusion injuries.

The Na(+)/Ca(2+) exchanger (NCX) is involved in myocardial ischemia-reperfusion injuries. We examined the effects of 2-[4-[(2,5-difluorophenyl)methoxy]phenoxy]-5-ethoxyaniline (SEA0400), a potent and selective inhibitor of NCX, on myocardial ischemia-reperfusion injury models. In canine cardiac sarcolemmal vesicles and rat cardiomyocytes, SEA0400 potently inhibited the Na(+)-dependent 45Ca(2+) uptake with an IC(50) value of 90 and 92 nM, compared with 2-[2-[4-(4-nitrobenzyloxy)phenyl]isothiourea (KB-R7943, 7.0 and 9.5 microM), respectively. In rat cardiomyocytes, SEA0400 (1 and 3 microM) attenuated the Ca(2+) paradox-induced cell death. In isolated rat Langendorff hearts, SEA0400 (0.3 and 1 microM) improved the cardiac dysfunction induced by low-pressure perfusion followed by normal perfusion. In anesthetized rats, SEA0400 (0.3 and 1 mg/kg, i.v.) reduced the incidence of ventricular fibrillation and mortality induced by occlusion of the left anterior descending coronary artery followed by reperfusion. These results suggest that SEA0400 is a most potent NCX inhibitor in the heart and that it has protective effects against myocardial ischemia-reperfusion injuries.

Aniline Compounds↗

PubMed2003

The 5-HT1A receptor agonist MKC-242 increases the exploratory activity of mice in the elevated plus-maze.

The effect of (S)-5-[3-[(1,4-benzodioxan-2-ylmethyl)amino]propoxy]-1,3-benzodioxole HCl (MKC-242), a 5-HT(1A) receptor agonist, on mouse behavior was examined in the elevated plus-maze. MKC-242 significantly increased the percentage of open-arm entries and the percentage of open-arm time, indices of anxiety reduction, while it did not increase the enclosed-arm entries and time spent in enclosed arms. The effect of MKC-242 was antagonized by a low dose of the 5-HT(1A) receptor antagonist N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-pyridinyl)cyclohexanecarboxamide which alone did not affect the behavior. These findings suggest that MKC-242 increases the exploratory activity of mice in the elevated plus-maze via activation of 5-HT(1A) receptors, probably the presynaptic autoreceptors.

Animals↗

PubMed2003

Focal adhesion kinase is required for endothelin-induced cell cycle progression of cultured astrocytes.

When the brain is damaged, astrocytes often cause hyperplasia resulting in glial scar formation at the injured sites. Endothelins (ETs) have been shown to be involved in the pathophysiologic responses of astrocytes, including proliferation. In this study, we examined the mechanisms underlying the ET-induced astrocytic G1/S-phase cell cycle transition by focusing on focal adhesion kinase (FAK). A transient transfection with wild-type FAK was followed by an increase in bromodeoxyuridine (BrdU) incorporation into cultured rat astrocytes. The increases in BrdU incorporation induced by 100 nM ET-1 were not found in astrocytes transfected with dominant-negative FAK mutants (FRNK and dC14-FAK). The increases in BrdU incorporation induced by 10 nM phorbol 12-myristate 13-acetate (PMA) were not affected by the FAK mutants. Wild-type FAK did not induce stress fiber formation in cultured astrocytes. The dominant negative FAK mutant dC14-FAK did not prevent ET-induced astrocytic stress fiber formation. These results suggest that FAK mediated the astrocytic G1/S cell cycle transition induced by ET-1 downstream of the cytoskeletal actin reorganization.

Actins↗

PubMed2003

Regulation by 5-HT1A receptors of the in vivo release of 5-HT and DA in mouse frontal cortex.

This study examines the effects of serotonin (5-HT)1A receptor ligands on the in vivo release of 5-HT and dopamine (DA) in the prefrontal cortex of mice. Oral MKC-242 and 8-OH-DPAT, selective 5-HT1A receptor agonists, decreased cortical 5-HT release at low and high doses, while the receptor agonists increased cortical DA release only at a high dose. Local application of the selective 5-HT1A receptor antagonist, WAY100635, via a dialysis probe, antagonized oral MKC-242-induced increase in cortical DA release, but did not affect the decrease in cortical 5-HT release. Local application of 8-OH-DPAT at 100 and 300 nM via a dialysis probe increased cortical DA release, but did not affect cortical 5-HT release. The effects of oral MKC-242 and 8-OH-DPAT on 5-HT release were blocked by low and high doses of WAY100635, while blocking the agonist-induced increase in DA release required a high dose of WAY100635. These results suggest that 5-HT release and DA release in the frontal cortex of mice are regulated by pre- and postsynaptic 5-HT1A receptors, respectively, and that the presynaptic 5-HT1A receptor-mediated response is more sensitive to inhibition by WAY100635 than the postsynaptic 5-HT1A receptor-mediated response in mice.

Animals↗

PubMed2003

Roles of cathepsins in reperfusion-induced apoptosis in cultured astrocytes.

Astrocytic apoptosis may play a role in the central nervous system injury. We previously showed that reperfusion of cultured astrocytes with normal medium after exposure to hydrogen peroxide (H(2)O(2))-containing medium causes apoptosis. This study examines the involvement of the lysosomal enzymes cathepsins B and D in the astrocytic apoptosis. Reperfusion after exposure to H(2)O(2) caused a marked increase in caspase-3 and cathepsin D activities and a marked decrease in cathepsin B activity. Pepstatin A, an inhibitor of cathepsin D, and acetyl-L-aspartyl-L-methionyl-L-glutaminyl-L-aspart-1-aldehyde (Ac-DMQD-CHO), a specific inhibitor of caspase-3, blocked the H(2)O(2)-induced decrease in cell viability and DNA ladder formation in cultured rat astrocytes. The (L-3-trans-(propylcarbamoyl)oxirane-2-carbonyl)-L-isoleucyl-L-proline methyl ester (CA074 Me), a specific inhibitor of cathepsin B, did not affect the H(2)O(2)-induced cell injury. On the other hand, CA074 Me decreased cell viability with DNA ladder formation when cultured in the presence of Ac-DMQD-CHO. This caspase-independent apoptosis was attenuated by the addition of the cathepsin D inhibitor pepstatin A. Caspase-3 like activity was markedly inhibited by Ac-DMQD-CHO and partially by pepstatin A. Pepstatin A and CA074 Me inhibited cathepsin B and cathepsin D activities, respectively, in the presence and absence of Ac-DMQD-CHO. These results suggest that cathepsins B and D are involved in astrocytic apoptosis: cathepsin D acts as a death-inducing factor upstream of caspase-3 and the caspase-independent apoptosis is regulated antagonistically by cathepsins B and D.

Animals↗

PubMed2003

T-588, a cognitive enhancer, stimulates in vivo phosphorylation of extracellular signal-regulated kinases in the hippocampus.

Administration of (1R)-1-benzo[b]thiophen-5-yl-2-[2-(diethylamino)ethoxy]ethan-1-ol hydrochloride (T-588), a cognitive enhancer, like the acetylcholine esterase inhibitors physostigmine and tacrine, stimulated phosphorylation of extracellular signal-regulated kinases (ERK) in the mouse hippocampus. The effect of T-588 on ERK phosphorylation was persistent from 2 to 6 h after injection. Immunohistochemical study showed that T-588 stimulated neuronal ERK phosphorylation in rat hippocampal CA1 pyramidal subfield. These findings suggest that systemic T-588 stimulates the ERK kinase pathway in the hippocampal neurons.

Animals↗

PubMed2003

Possible involvement of astrocytes in neuroprotection by the cognitive enhancer T-588.

We have previously shown that the cognition enhancer (1R)-1-benzo[b]thiophen-5-yl-2-[2-(diethylamino)ethoxy]ethan-1-ol hydrochloride (T-588) protects astrocytes against hydrogen peroxide (H2O2) injury via activation of extracellular signal-regulated kinase (ERK) pathway. The present study examines whether the effect of T-588 on astrocytes contributes to neuroprotection in neuronal injury models. Astrocyte-conditioned medium (ACM) protected against neuronal injury induced by amyloid-beta protein (A beta) in cultured cortical neurons. The effect of ACM on A beta-induced injury was blocked by the ERK kinase inhibitor 2'-amino-3'-methoxyflavone. ACM stimulated ERK phosphorylation in cultured neurons. ACM derived from astrocytes exposed to H2O2 lost the activities to stimulate ERK phosphorylation and protect against neuronal injury. T-588 blocked the H2O2-induced loss of the activities of ACM. These results suggest that ACM protects against neuronal injury by an ERK-dependent mechanism, and the effect of T-588 on astrocytic injury results in neuroprotection.

Animals↗

PubMed2003

Intracerebroventricular administration of an endothelin ETB receptor agonist increases expressions of GDNF and BDNF in rat brain.

Endothelins (ETs) are suggested to be involved in functional alterations of astrocytes after brain injury, including proliferation, hypertrophy and production of neurotrophic factors. In this study, effects of Ala1,3,11,15-endothelin-1 (Ala1,3,11,15-ET-1), an ETB receptor selective agonist, on neurotrophic factor production were examined in rat brain. A continuous intracerebroventricular administration of Ala1,3,11,15-ET-1 (500 pmol/day for 7 days) increased the numbers of GFAP- and vimentin-positive astrocytes in the hippocampus, caudate putamen and cerebrum. Ala1,3,11,15-ET-1 did not induce neuronal degeneration and activation of microglia/macrophage in these brain regions. The intracerebroventricular administration of Ala1,3,11,15-ET-1 for 7 days caused two- to three-fold increases in glial cell line-derived neurotrophic factors (GDNF) mRNA in the hippocampus and cerebrum. The mRNA levels of brain-derived neurotrophic factors (BDNF) in caudate putamen were increased by Ala1,3,11,15-ET-1. Expressions of nerve growth factor (NGF) and basic fibroblast growth factor (bFGF) mRNA in these regions were not largely affected by Ala1,3,11,15-ET-1, except cerebral NGF mRNA level was increased. The Ala1,3,11,15-ET-1-induced increases in GDNF and BDNF mRNA levels were accompanied by increases in immunoreactive GDNF and BDNF. Immunohistochemical observations showed that GFAP-positive astrocytes expressed GDNF and BDNF in the brain regions of Ala1,3,11,15-ET-1-infused rats. In cultured rat astrocytes, Ala1,3,11,15-ET-1 (100 nm) increased mRNA levels of GDNF and BDNF. These results suggest that activation of brain ETB receptors induced GDNF and BDNF expression in astrocytes.

Animals↗

PubMed2003

Protective effect of T-588 on toxic damage by serum deprivation and amyloid-beta protein in cultured neurons.

The present study examines the effect of the cognition enhancer (1R)-1-benzo[b]thiophen-5-yl-2-[2-(diethylamino)ethoxy]ethan-1-ol hydrochloride (T-588) on neuronal injury induced by serum deprivation or amyloid-beta protein (A beta). T-588 protected partially against neuronal injury induced by serum deprivation or A beta in cultured cortical neurons. T-588 did not affect the phosphorylation of extracellular signal-regulated kinase (ERK) in cortical neurons and SH-SY5Y cells. These results suggest that T-588 has a protective effect in neuronal injury models and the effect is not mediated by an ERK signal pathway.

Amyloid beta-Peptides↗

PubMed2003

Pituitary adenylate cyclase-activating polypeptide does not colocalize with vasoactive intestinal polypeptide in the hypothalamic magnocellular nuclei and posterior pituitary of cats and rats.

Pituitary adenylate cyclase-activating polypeptide (PACAP) and vasoactive intestinal polypeptide (VIP) immunoreactive cells were demonstrated in the hypothalamic magnocellular nuclei in cats and rats. In cats these immunoreactive cells were stained without any treatment or intervention; however, in rats we had to use the pituitary stalk section to enhance the amount of PACAP and VIP for successful immunostaining. In both species the regions occupied by PACAP and VIP immunoreactive cells partially overlap each other in the paraventricular and supraoptic nuclei. Nevertheless, in either cats or rats PACAP and VIP immunoreactivities do not colocalize in the same cells studied by double labeling immunohistochemistry (IHC) or by the combination of immunohistochemistry and in situ hybridization. As was expected, PACAP and VIP immunoreactive materials were stored in different fibers of the posterior pituitary where the distribution of PACAP and VIP fibers also showed different patterns: PACAP fibers form a dense plexus at the periphery of the posterior lobe, in the vicinity of the intermediate lobe; however, the VIP fibers were evenly distributed mainly in the center of the posterior lobe. In spite of the high sequence homology of PACAP and VIP, the two peptides are synthesized in different subpopulations of hypothalamic neurons. This different distribution correlates well with the different role of the hypothalamic PACAP and VIP in the biologic clock and in the functions of the anterior and posterior pituitary.

Animals↗

PubMed2003

Overexpression of PACAP in transgenic mouse pancreatic beta-cells enhances insulin secretion and ameliorates streptozotocin-induced diabetes.

Pituitary adenylate cyclase-activating polypeptide (PACAP), a member of the vasoactive intestinal peptide/secretin/glucagon family, stimulates insulin secretion from islets in a glucose-dependent manner at femtomolar concentrations. To assess PACAP's pancreatic function in vivo, we generated transgenic mice overexpressing PACAP in the pancreas under the control of human insulin promoter. Northern blot and immunohistochemical analyses showed that PACAP is overexpressed in pancreatic islets, specifically in transgenic mice. Plasma glucose and glucagon levels during a glucose tolerance test were not different between PACAP transgenic mice and nontransgenic littermates. However, plasma insulin levels in transgenic mice were higher after glucose loading. Also, increases of streptozotocin-induced plasma glucose were attenuated in transgenic compared with nontransgenic mice. Notably, an increase in 5-bromo-2-deoxyuridine-positive beta-cells in the streptozotocin-treated transgenic mice was observed but without differences in the staining patterns by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling. Morphometric analysis revealed that total islet mass tends to increase in 12-month-old transgenic mice but showed no difference between 12-week-old transgenic and nontransgenic littermates. This is the first time that PACAP has been observed to play an important role in the proliferation of beta-cells.

Animals↗

PubMed2003

[Altered behavioral response to centrally acting drugs in mice lacking PACAP].

Mice lacking PACAP (PACAP-KO) exhibits altered psychomotor behaviors, including impaired habituation to a novel environment and perseverative jumping, with a slightly reduced levels of the serotonin metabolite, 5-HIAA, in the brain. We have recently demonstrated that PACAP-KO exhibits abnormalities in sensorimotor gating as measured by prepulse inhibition (PPI) of the acoustic startle. In the present study, behavioral responses to centrally acting drugs (amphetamine, haloperidol, risperidone, fluoxetine, and 8-OH-DPAT) were examined in PACAP-KO. Surprisingly, a psychostimulant amphetamine effectively normalized the deficit in PPI as well as hyperactivity and jumping behavior. These results implied phenotypic and pharmacological similarity between PACAP-KO and attention deficit hyperactivity disorder (ADHD). Although a potent dopamine D2-like receptor antagonist, haloperidol, ameliorated the hyperactivity and jumping behavior, it had no effect on the deficit in PPI. In contrast, a prototype of serotonin-dopamine antagonist (SDA), risperidone, effectively normalized the deficit in PPI as well as hyperactivity, and jumping behavior. A selective serotonin reuptake inhibitor (SSRI), fluoxetine, also suppressed the hyperactivity and jumping behavior. A 5-HT1A receptor agonist, 8-OH-DPAT, significantly lowered rectal temperature in wild-type mice, while it had only a small effect in PACAP-KO. These results suggest the involvement of dopaminergic and serotonergic dysfunction in phenotypic changes observed in PACAP-KO.

Amphetamine↗

PubMed2002

Defects in reproductive functions in PACAP-deficient female mice.

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a highly conserved neuropeptide and widely expressed in both brain and peripheral tissues, including several reproductive organs (e.g., testis and ovary). PACAP stimulates syntheses of several sexual hormones and steroids, suggesting it has possible roles in reproductive function. In this study, the role of PACAP in female reproductive functions such as fertility, mating behavior and maternal behaviors were investigated by using mice lacking PACAP (PACAP(-/-)). PACAP(-/-) females showed reduced fertility (the number of parturitions relative to the number of pairings). Mating experiments using vasectomized males revealed that mating frequency and its intervals in some PACAP(-/-) females were quite different (zero to eight times/4 weeks), whereas the frequency was relatively constant (two to three times/4 weeks) in wild-type females. In PACAP(-/-) females, maternal crouching behavior tended to decrease compared to wild-type females, although the influence of litter size on maternal behavior needs to be considered. These data suggest a role for endogenous PACAP in female reproductive processes.

Animals↗

PubMed2002

Involvement of intracellular Ca2+ elevation but not cyclic AMP in PACAP-induced p38 MAP kinase activation in PC12 cells.

We have recently shown that in PC12 cells, pituitary adenylate cyclase-activating polypeptide (PACAP) and NGF synergistically stimulate PACAP mRNA expression primarily via a mechanism involving a p38 mitogen-activated protein kinase (MAPK)-dependent pathway. Here we have analyzed p38 MAPK activation by PACAP and the mechanism underlying this action of PACAP in PC12 cells. PACAP increased phosphorylation of p38 MAPK with a bell-shaped dose-response relationship and a maximal effect was obtained at 10(-8) M. PACAP (10(-8) M)-induced p38 MAPK phosphorylation was already evident at 2.5 min, maximal at 5 min, and rapidly declined thereafter. PACAP-induced p38 MAPK phosphorylation was potently inhibited by depletion of Ca(2+) stores with thapsigargin and partially inhibited by the phospholipase C inhibitor U-73122, L-type voltage-dependent calcium channel inhibitors nifedipine and nimodipine, and the Ca(2+) chelator EGTA, whereas the protein kinase C inhibitor calphostin C, the protein kinase A inhibitor H-89, the cAMP antagonist Rp-cAMP, and the nonselective cation channel blocker SKF96365 had no effect. These results indicate that PACAP activates p38 MAPK in PC12 cells through activation of a phospholipase C, mobilization of intracellular Ca(2+) stores, and Ca(2+) influx through voltage-dependent Ca(2+) channels, but not cyclic AMP-dependent mechanisms.

Animals↗

PubMed2002

Higher brain functions of PACAP and a homologous Drosophila memory gene amnesiac: insights from knockouts and mutants.

Neuropeptides usually exert a long-lived modulatory effect on the small-molecule neurotransmitters with which they colocalize via regulation of the response times of second messenger systems. Pituitary adenylate cyclase-activating polypeptide (PACAP) functions as a neuromodulator and neurotransmitter and regulates a variety of physiological processes. PACAP is structurally highly conserved during evolution, implying its vital importance. In Drosophila, loss-of-function mutations in a PACAP-like neuropeptide gene, amnesiac (amn), affect both memory retention and ethanol sensitivity. The amnesiac gene is expressed in neurons innervating the mushroom body lobes, the olfactory associative learning center. Conditional genetic ablation of neurotransmitter release from these neurons mimics the amnesiac memory phenotypes, suggesting an acute role for amnesiac in memory. However, genetic rescue experiments also suggest developmental defects in amnesiac mutants, implying a role in neuronal development. There is a parallel between memory formation in Drosophila and mammals. PACAP-specific (PAC(1)) receptor-deficient mice show a deficit in hippocampus-dependent associative learning and mossy fiber long-term potentiation (LTP). Meanwhile, PACAP-deficient mice display a high early mortality rate and additional CNS phenotypes including behavioral and psychological phenotypes (e.g., hyperlocomotion, intense novelty-seeking behavior, and explosive jumping). A functional comparison between PACAP and amnesiac underlines phylogenetically conserved functions across phyla and may provide insights into the possible mechanisms of action and evolution of this neuropeptidergic system.

Amino Acid Sequence↗

PubMed2002

Heat shock inhibits hydrogen peroxide-induced apoptosis in cultured astrocytes.

Heat shock proteins (HSPs) have been shown to act as inhibitors of apoptosis, but this anti-apoptotic effect is not known in the central nervous system. Prior heat shock has been demonstrated to protect astrocytes from cell death in a model of reperfusion injury (Brain Res. 735 (1996) 265). The present study examines the mechanism underlying the protective effect of the heat shock. Preincubation of astrocytes at 40 degrees C for 10 min attenuated the hydrogen peroxide (H(2)O(2))-induced decrease in cell viability, DNA ladder formation and nuclear condensation, and these effects were blocked by the protein synthesis inhibitor cycloheximide. The thermal stress inhibited the H(2)O(2)-induced increase in caspase-3 like protease activity, but it did not affect the H(2)O(2)-induced loss of mitochondrial membrane potential. The cytosol prepared from preheated cells did not affect Ca(2+)-induced swelling of mitochondria, a marker of the permeable transition pore. The protective effect of the thermal stress on the H(2)O(2)-induced decrease in cell viability was not affected by the mitogen-activated protein/extracellular signal-regulated kinase kinase inhibitor 2'-amino-3'-methoxyflavone, the phosphatidylinositol-3 kinase inhibitor wortmannin and the NF-kappaB inhibitor pyrrolidinedithiocarbamate. These findings suggest that HSPs inhibit apoptosis via an inhibition of caspase-3 activation without effect on mitochondrial dysfunction.

Animals↗

PubMed2002

Sodium tanshinone IIA sulfonate derived from Danshen (Salvia miltiorrhiza) attenuates hypertrophy induced by angiotensin II in cultured neonatal rat cardiac cells.

Sodium tanshinone IIA sulfonate (STS), a derivative of tanshinone IIA, is isolated from the root of Salvia miltiorrhiza known as "Danshen." Although injection of S. miltiorrhiza extract and STS is used widely and successfully in clinics in China for treating cardiovascular diseases, the exact mechanism for its therapeutic basis is poorly understood. The present study was undertaken to characterize the effect of STS on angiotensin II-induced hypertrophy on cultured myocytes and cardiac fibroblasts (nonmyocytes) prepared from neonatal rat hearts. Angiotensin II (1nM) increased protein synthesis and surface area in myocytes, and DNA synthesis and cell number in nonmyocytes, respectively. Exposure of the myocytes to STS (5-80 microM) for 24hr produced no cytotoxicity as evaluated by the 3-[4,5-dimethylthiazol-2-yl]-3,5-diphenylformazan (MTT) assay. Although STS (10 microM) alone showed no effect on the growth of cultured cardiac cells, it markedly suppressed angiotensin II-induced enlargement of cells and [3H]phenylalanine incorporation, proceeding from the induction of immediate early gene (c-jun) expression in myocytes. Furthermore, STS prevented the rise in [Ca(2+)](i) mediated by angiotensin II in myocytes. In contrast, STS (10 microM) was without effect on hyperplasia and c-jun expression induced by angiotensin II in nonmyocytes. The present in vitro findings support the interpretation that STS is a substance that may be beneficial in protecting the myocardium against hypertrophy.

Angiotensin II↗

PubMed2002

Knockout mice for pharmacological screening: testing the specificity of Na+-Ca2+ exchange inhibitors.

The role of the Na+-Ca2+ exchanger as a major determinant of cell Ca2+ is well defined in cardiac tissue, and there has been much effort to develop specific inhibitors of the exchanger. We use a novel system to test the specificity of two putative specific inhibitors, KB-R7943 and SEA0400. The drugs are applied to electrically stimulated heart tubes from control mouse embryos or embryos with the Na+-Ca2+ exchanger knocked out. We monitored effects of the drugs on Ca2+ transients. Both drugs depress the Ca2+ transients at low concentrations even in the absence of any Na+-Ca2+ exchanger. KB-R7943 and SEA0400 are not completely specific and should be used with caution as Na+-Ca2+ exchange inhibitors.

Aniline Compounds↗