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Biomedical subjects

A Akaike

Publications and source records attributed to A Akaike.

At least 55 records · Page 3Linked to original sources
PubMed1999

Effects of nicotinic receptor agonists on beta-amyloid beta-sheet formation.

Previously we demonstrated that nicotinic acetylcholine receptor stimulation protects neurons against beta-amyloid (Abeta)-induced cytotoxicity. In the present study, the effects of nicotinic receptor agonists on the beta-sheet formation were investigated using a thioflavin T (ThT)-based fluorescence assay. Nicotine, cytisine (an alpha4beta2 agonist), and 3-(2,4)-dimethoxybenzylidene anabaseine (DMXB, an alpha7 agonist) did not reduce fluorescence intensity when these agents were added to the beta-sheet-formed Abeta. Simultaneous incubation of Abeta with nicotinic agonists also did not cause a reduction in fluorescence intensity. This data suggests that nicotinic receptor agonists do not influence the formation of the beta-sheet structure.

Alkaloids↗
PubMed1999

Receptor-mediated modulation of voltage-dependent Ca2+ channels via heterotrimeric G-proteins in neurons.

The activity of voltage-dependent Ca2+ channels is highly regulated by neurotransmitter receptors coupled to heterotrimeric G-proteins. In the expression studies using cloned Ca2+ channel subunits, it has been clarified that the main mechanism of the inhibition of N-type channel current is mediated directly by G-protein betagamma subunits in a membrane-delimited and voltage-sensitive manner. In addition, recent studies have also clarified that N-type channels are modulated by several G-protein alpha subunits in different ways. Among them, G(alpha o) mediates a voltage-resistant inhibition of N-type current by neurotransmitters. This type of inhibition is more apparent in the case of P/Q-type channels in both native cells and expression systems. Moreover, other G-protein subunits, such as G(alpha q) and G(alpha s), also seem to regulate N-type channels in a membrane-delimited manner. The fine tunings of Ca2+ channel activity by intracellular proteins have physiological and pathological meanings in the regulation of Ca2+ influx into excitable cells by neurotransmitters and pharmacological implications as novel drug targets for controlling Ca2+ influx.

Animals↗
PubMed1998

Estradiol protects mesencephalic dopaminergic neurons from oxidative stress-induced neuronal death.

Oxidative stress is important in the process of dopaminergic neuronal degeneration in Parkinson's disease. Recent studies suggest that estrogens have neuroprotective effects in neurodegenerative disorders, including Alzheimer's disease. In the present study, we investigated neuroprotection against oxidative stress afforded by estradiol using primary neuronal culture of the rat ventral mesencephalon. Oxidative stress induced by glutamate, superoxide anions, and hydrogen peroxide caused significant neuronal death. Although simultaneous administration of 17beta-estradiol and glutamate did not show any significant effects, preincubation with 17beta-estradiol provided significant neuroprotection against glutamate-induced neurotoxicity (ED50 was 50 microM for dopaminergic and 15 microM for nondopaminergic neurons). Neuroprotection occurred even after a brief preincubation with 17beta-estradiol and was not significantly blocked by either an estrogen receptor antagonist or a protein synthesis inhibitor. These findings indicate that the neuroprotection against glutamate neurotoxicity is mediated by neither estrogen receptors nor activation of genome transcription. Other steroids (corticosterone, testosterone, and cholesterol) did not provide significant neuroprotection against glutamate-induced neurotoxicity. Furthermore, preincubation with 17beta-estradiol provided neuroprotection against neuronal death induced by both superoxide anions and hydrogen peroxide. Dichlorofluorescin diacetate, a marker of oxygen radicals, revealed that preincubation with 17beta-estradiol suppressed intracellular oxygen radicals induced by hydrogen peroxide. The biologically inactive stereoisomer of estradiol, 17alpha-estradiol, provided neuroprotection against glutamate-induced toxicity in dopaminergic neurons, as well as the 17beta isoform. 17Alpha-estradiol may be a potential therapeutic agent used to prevent dopaminergic neuronal death induced by oxidative stress in Parkinson's disease.

Animals↗
PubMed1998

Localization of fractalkine and CX3CR1 mRNAs in rat brain: does fractalkine play a role in signaling from neuron to microglia?

Localization of the mRNAs for fractalkine, a CX3C chemokine, and for its receptor CX3CR1 was investigated in the rat brain. In situ hybridization study revealed that fractalkine mRNA was dominantly expressed in neuronal cells particularly in the olfactory bulb, cerebral cortex, hippocampus, caudate putamen and nucleus accumbens. In vitro study using enriched neuronal or glial culture supported the dominant expression of fractalkine mRNA in neurons. On the other hand, CX3CR1 mRNA was dominantly expressed in glial cells throughout the whole brain. The in vitro study suggested the cells expressing CX3CR1 mRNA are microglia, not astrocytes or neurons. Fractalkine appears to function as a signal molecule from neuron to microglia.

Amino Acid Sequence↗
PubMed1998

Intracellular Ca2+ store-operated influx of Ca2+ through TRP-R, a rat homolog of TRP, expressed in Xenopus oocytes.

To elucidate whether rat transient receptor potential (TRP-R), a rat TRP4 homolog, functions as a store-operated Ca2+ channel (SOC), we have measured the Ca2+ entry after thapsigargin treatment in Xenopus oocytes injected with mRNA for TRP-R. While non-injected oocytes elicited an SOC response, significantly larger responses were observed in the oocytes expressing TRP-R. The oocyte-native SOC response was inhibited by injection of antisense oligodeoxyribonucleotide for mammalian TRP1. When Ca2+ concentration-SOC response curve was examined, the EC50 value was much smaller in oocytes expressing TRP-R than that of non-injected oocytes. These results suggest that TRP-R functions as SOC having higher sensitivity to external Ca2+ than amphibian TRP1 channel.

Animals↗
PubMed1998

Inhibition of NMDA receptors and nitric oxide synthase reduces ischemic injury of the retina.

This study was performed to examine the roles of body temperature, NMDA receptors and nitric oxide (NO) synthase in post-ischemic retinal injury in rats. Cell loss in the ganglion cell layer and thinning of the inner plexiform layer were observed 7 days after ischemia. Cell loss in the ganglion cell layer but not thinning of the inner plexiform layer was reduced by hypothermia during ischemia. Intravenous injection of dizocilpine (MK-801) or Nomega-nitro-L-arginine methyl ester (L-NAME) prior to ischemia ameliorated retinal injury. These results suggest that activation of NO synthase following NMDA receptor stimulation is involved in ischemia-induced retinal injury.

Animals↗
PubMed1998

Stimulation of alpha4beta2 nicotinic acetylcholine receptors inhibits beta-amyloid toxicity.

We examined the effects of nicotinic receptor agonists against beta amyloid (Abeta) cytotoxicity to rat cortical neurons. Administration of nicotine protected against Abeta-induced neuronal death. This neuroprotection was blocked by dihydro-beta-erythroidine, an alpha4beta2 nicotinic receptor antagonist. Furthermore, incubation with cytisine, a selective alpha4beta2 nicotinic receptor agonist, inhibited Abeta cytotoxicity. These results suggest that alpha4beta2 nicotinic receptor activation plays an important role in neuroprotection against Abeta cytotoxicity.

Alkaloids↗
PubMed1998

Effect of SA4503, a novel sigma1 receptor agonist, against glutamate neurotoxicity in cultured rat retinal neurons.

We examined the effects of sigma1 receptor agonists against glutamate-induced neurotoxicity in cultured retinal neurons. Primary cultures obtained from fetal rat retinas (16-19 d gestation) were used. The neurotoxic effect of glutamate was quantitatively assessed using the trypan blue exclusion method. A brief exposure of retinal cultures to glutamate (500 microM) led to delayed neuronal cell death. The glutamate-induced neurotoxicity was inhibited by (5R,10S)-(+)-5-methyl-10,11-dihydro-5H-dibenzo-[a,b]-cyclohepten-5 ,10-imine hydrogen maleate (MK-801). The sigma1 receptor agonists, 1-(3,4-dimethoxyphenethyl)-4-(3-phenylpropyl)-piperazine dihydrochloride (SA4503) and (+)-pentazocine at a concentration range of 0.1 approximately 100 microM reduced the glutamate-induced neurotoxicity in a dose-dependent manner. In addition, the neuroprotective effects of both SA4503 and (+)-pentazocine were antagonized by co-treatment with N,N-dipropyl-2-[4-methoxy-3-(2-phenylethoxy)phenyl]ethylamine monohydrochloride (NE-100), a putative sigma1 receptor antagonist. These findings suggest that sigma1 receptor agonists protect retinal cells against glutamate-induced neurotoxicity.

Analgesics, Opioid↗
PubMed1998

Increase in nitric oxide in the hypoxic-ischemic neonatal rat brain and suppression by 7-nitroindazole and aminoguanidine.

We measured the changes in nitric oxide (NO) metabolites in the brains of neonatal rats with hypoxic-ischemic damage. There were two peaks of NO metabolites in the lesioned side of the cortex without treatment: one during hypoxia and the other during the re-oxygenation period. Prehypoxic treatment with 7-nitroindazole, a selective neuronal NO synthase inhibitor, suppressed both peaks of NO metabolites, whereas prehypoxic treatment with aminoguanidine, a selective inducible NO synthase inhibitor, partially suppressed only the peak in the re-oxygenation period. These data suggest different roles of neuronal and inducible NO synthases in the pathogenesis of hypoxic-ischemic encephalopathy.

Animals↗
PubMed1998

Dopamine D2-type agonists protect mesencephalic neurons from glutamate neurotoxicity: mechanisms of neuroprotective treatment against oxidative stress.

Oxidative stress, a process in which neurotoxic oxygen free radicals cause dopaminergic neuronal degeneration, has been implicated in the degenerative process in Parkinson's disease. Glutamate-induced neurotoxicity is a model of oxidative stress. We demonstrated that preincubation with D2-type dopamine agonists bromocriptine and quinpirole provides neuroprotection against glutamate-induced neurotoxicity in cultured rat mesencephalic neurons. Simultaneous administration of D2 agonists, however, did not provide neuroprotection. The protective effects were dependent on the duration of preincubation and were blocked by a D2 antagonist and a protein synthesis inhibitor. Furthermore, preincubation with D2 agonists provided neuroprotection against toxicity induced by calcium overload and exposure to superoxide anions. Confocal microscopic analysis, using 2,7-dichlorofluorescin diacetate, revealed that bromocriptine preincubation suppressed the action of radicals on neurons. These findings indicate that dopamine D2 agonists provide protection mediated not only by the inhibition of dopamine turnover but also via D2-type dopamine receptor stimulation and the subsequent synthesis of proteins that scavenge free radicals.

Animals↗
PubMed1998

Mechanism of selective motor neuronal death after exposure of spinal cord to glutamate: involvement of glutamate-induced nitric oxide in motor neuron toxicity and nonmotor neuron protection.

In this study, we analyzed the mechanism of selective motor neuronal death, a characteristic of amyotrophic lateral sclerosis, using embryonic rat spinal cord culture. When dissociated cultures were exposed to low-level glutamate (Glu) coadministered with the Glu transporter inhibitor L-trans-pyrrolidine-2,4-decarboxylate (PDC) for 24 hours, motor neurons were selectively injured through N-methyl-D-aspartate (NMDA) and alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA)/kainate receptors. Nitric oxide synthase (NOS) inhibitors attenuated this toxicity, and long-acting nitric oxide (NO) donors damaged motor neurons selectively. Nonmotor neurons survived after exposure to low-dose Glu/PDC, but Glu-induced toxicity was potentiated by coadministration of an NO-dependent guanylyl cyclase inhibitor. In addition, 8-bromo-cyclic GMP, a soluble cyclic GMP analogue, rescued nonmotor neurons, but not motor neurons, exposed to high-dose Glu/PDC. Twenty-four hours' incubation with PDC elevated the number of neuronal NOS-immunoreactive neurons by about twofold compared with controls, and a double-staining study, using the motor neuron marker SMI32, revealed that most of them were nonmotor neurons. These findings suggest that selective motor neuronal death caused by chronic low-level exposure to Glu is mediated by the formation of NO in nonmotor neurons, which inversely protects nonmotor neurons through the guanylyl cyclase-cyclic GMP cascade. Induction of neuronal NOS in nonmotor neurons might enhance both the toxicity of motor neurons and the protection of nonmotor neurons, which could explain the pathology of amyotrophic lateral sclerosis.

Amyotrophic Lateral Sclerosis↗
PubMed1998

Mechanism of the pathogenesis of glutamate neurotoxicity in retinal ischemia.

PURPOSE: This study was carried out to examine the involvement of glutamate and nitric oxide neurotoxicity in ischemia/reperfusion-induced retinal injury in vivo. METHODS: We monitored glutamate release from in vivo cat retina during and after pressure-induced ischemia using a microdialysis technique. Morphometric studies were performed to study the effects of MK-801 (dizocilpine), L-NAME (N omega-nitro-L-arginine methyl ester), and D-NAME (N omega-nitro-D-arginine methyl ester) on the histological changes in the rat retina induced by ischemia or intravitreal injection of NMDA (N-methyl-D-aspartate; 200 nmol). RESULTS: A large release of glutamate occurred during ischemia, followed by a marked release after reperfusion. Histological changes occurred selectively in the inner part of the retina after ischemia as well as intravitreal injection of NMDA. Pretreatment with intravenous injection of MK-801 or L-NAME significantly inhibited the ischemic injury of the inner retina. Intravitreal injection of L-NAME inhibited NMDA-induced neurotoxicity in the retina. CONCLUSION: These findings indicate that nitric oxide mediates neurotoxic actions of glutamate which are responsible for ischemic injury in the retina.

Animals↗
PubMed1998

Differential regulation of N- and Q-type Ca2+ channels by cyclic nucleotides and G-proteins.

Voltage-dependent Ca2+ channels play a central role in controlling neurotransmitter release at the synapse. They can be inhibited by certain G-protein-coupled receptors, acting by a pathway delimited to the membrane. In addition, modulation of Ca2+ channel activity by protein kinases also contributes to the dynamic regulation of neuronal physiology. Recently, differences in these modulations between Ca2+ channel subtypes have been shown in several neuronal preparations. Here we show that two types of presynaptic Ca2+ channel (N-type and Q-type) are differentially regulated by cAMP and G-proteins using a Xenopus oocyte expression system. Treatment to increase cytosolic cAMP concentration with forskolin and 3-isobutyl-1-methylxanthine (IBMX) markedly potentiated Q-type channel current, and the enhancement was reversed by protein kinase A inhibitors. Much smaller enhancement was observed in N-type channel current after the cAMP elevation. When large depolarizing prepulse was applied to the oocytes for evaluation of the tonic inhibition of Ca2+ channels by intrinsic G-protein activity, N-type channel current elicited a large prepulse facilitation but Q-type channels did not. The tonic inhibition of N-type channels was abolished by an intracellular perfusion with a 'cut-open' recording configuration, or by co-expression with G(alpha o). When kappa opioid receptors were co-expressed and stimulated with agonists, depolarization-resistant inhibition was more apparent in Q-type channels than in N-type channels. These results suggest that Q-type channels are more susceptible to the protein kinase A-mediated facilitation than N-type channels, and that activity of N-type channels can be more highly regulated in a voltage-dependent manner by G(betagamma) than that of Q-type channels. These differences may account for the selective regulation of neurotransmitter release by these Ca2+ channels.

1-Methyl-3-isobutylxanthine↗
PubMed1998

Endogenously occurring beta-carboline induces parkinsonism in nonprimate animals: a possible causative protoxin in idiopathic Parkinson's disease.

To examine whether simple beta-carbolines induce parkinsonian-like symptoms in vivo via N-methylation, the simple beta-carbolines norharman (NH), 2-mono-N-methylated norharmanium cation (2-MeNH+), and 9-mono-N'-methylnorharman (9-MeNH) were systematically administered to C57BL/6 mice for 7 days. These substances induced bradykinesia with reduction of locomotion activity. NH or 2-MeNH+ decreased dopamine (DA) contents to 50-70% of values in controls in the striatum and midbrain. 9-MeNH potently decreased not only DA but also serotonin content in various regions. Immunohistochemical examination revealed that the numbers of tyrosine hydroxylase (TH)-positive cells in the substantia nigra pars compacta of NH- and 9-MeNH-treated mice were diminished to 76 and 66% of values in control mice, respectively. The formation of a toxic metabolite, 2,9-di-N,N'-methylated norharmanium cation (2,9-Me2NH+), was 14 and eight times higher in the brain of mice receiving 9-MeNH than that in NH- and 2-MeNH+-treated mice, respectively. In cultured mesencephalic cells from rat embryo, 2,9-Me2NH+ selectively killed TH-positive neurons only at a lower dose but was toxic to all neurons at higher doses. Thus, the excess formation of 2,9-Me2NH+ would induce nonspecific neurotoxicity. These results indicated that 9-indole nitrogen methylation should be the limiting step in the development of the toxicity. NH, a selective dopaminergic toxin precursor, is sequentially methylated to form 2,9-Me2NH+, which could be an underlying factor in idiopathic Parkinson's disease.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1998

[Techniques for evaluating neuronal death of the retina in vitro and in vivo].

This review describes the techniques to evaluate retinal neurodegeneration induced by excitatory amino acids and transient ischemia. Glutamate-induced neurotoxicity was examined in cultured rat cortical cells. Cultures obtained from the retinas of fetal rats were incubated in Eagle's minimal essential medium supplemented with 10% fetal calf serum or 10% horse serum at 37 degrees C in a humidified 5% CO2 atmosphere for 10-14 days. The neurotoxicity induced by glutamate was quantified by trypan blue exclusion. The viability of cultures was markedly reduced by a 10-min exposure to glutamate followed by incubation with glutamate-free medium for 1 hr. N-methyl-D-aspartate (NMDA)-induced retinal damage was examined in adult rats. Transverse sections of the retinas through the optic disk were stained with hematoxylin and eosin. A single intravitreal injection of NMDA damaged the ganglion cell layer and the inner plexiform layer without affecting the other retinal layers 7 days after injection. Retinal ischemia was induced by elevating the intraocular pressure for 45 min through the needle which was placed in the anterior chamber. Ischemia-induced retinal damage was inhibited by MK-801. These results indicate that the techniques described in this review can be employed to develop new drugs possessing neuroprotective action against neurodegeneration that occurs during retinal ischemia.

Animals↗
PubMed1998

[Regulation of neuronal death by endogenous protective factors].

Glutamate is postulated to play an important role in the pathogenesis of the neuronal cell loss that is associated with neurological disorders in the CNS. Nitric oxide (NO) mediates glutamate neurotoxicity observed in the primary culture derived from the cerebral cortex, substantia nigra and retina. In search of endogenous protective factors that inhibit the neurotoxic action of glutamate and NO, we found that certain neurotransmitters such as nicotinic acetylcholine, dopamine and cholecystokinin prevent glutamate neurotoxicity by suppressing the activity of NO synthase. Neurotrophins such as brain-derived neurotrophic factor (BDNF) also prevented glutamate neurotoxicity via TrkB neurotrophin receptors although prolonged pretreatment was necessary to induce marked neuroprotection. BDNF prevented the neurotoxic actions of NO donors. This evidence indicates that BDNF protects neurons against glutamate cytotoxicity by reducing the radical chain reaction triggered by NO. We also found that the conditioned medium of the striatal cultures reduced glutamate neurotoxicity. Moreover, ether extract of fetal calf serum (FCS), contained in the conditioned medium, also reduced glutamate neurotoxicity. Concomitant application of ether extract of FCS with S-nitrosocysteine (SNOC), a NO donor, markedly reduced SNOC-induced neurotoxicity. These substances may have roles as neuroprotective factors that promote neuron survival under neurological disease states in the CNS.

Animals↗
PubMed1998

[Protective effect of neurotrophin against glutamate neurotoxicity in cortical cultures].

This study was performed to investigate the effects of neurotrophins on glutamate cytotoxicity by using cultured cortical neurons. Primary cultures obtained from the cerebral cortex of fetal rats (17-19 days gestation) were used for experiments. NGF did not elicit tyrosine phosphorylation of Trks whereas BDNF induced Trk tyrosine phosphorylation within 10 min, followed by time-dependent decrease. Brief glutamate exposure to the cell induced delayed cytotoxicity. Similar cytotoxicity was observed with the brief application of a calcium ionophore, ionomycin, and nitric oxide (NO) generating agents, S-nitrosocysteine (SNOC) and SIN-1. Exposure of the cultures to NGF and BDNF for 1 or 24 hr prior to glutamate exposure reduced glutamate-induced cytotoxicity. In contrast, simultaneous addition of NGF and BDNF with glutamate did not affect glutamate-induced cytotoxicity. Ionomycin-induced cytotoxicity was prevented by exposing cultures to NGF and BDNF for 24-hr. Moreover, NGF and BDNF ameliorated cytotoxicity induced by SNOC and SIN-1. These results suggest that neurotrophins prevent NO mediated glutamate cytotoxicity.

Animals↗