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ABSTRACT: Beta-amyloid (Abeta) enables Alzheimer's disease (AD) plaque and neurofibrillary pathogenesis. Soluble Abeta promotes intraneuronal Abeta aggregates and tau phosphorylation by interacting with alpha7 nicotinic receptors (alpha7nAChRs). The current study assessed whether the novel alpha7nAChR partial agonist 2-(2-(4-bromophenyl)-2-oxoethyl)-1-methyl pyridinium (S 24795) could reduce AD-like pathologies by interfering with Abeta-alpha7nAChR interaction.
We compared the in vitro effect of S 24795, memantine, galantamine, and Abeta(12-28) on Abeta(42)-alpha7nAChR interaction in rat hippocampal synaptosomes. We further evaluated the effect of S 24795 on Abeta(42)-induced tau phosphorylation with rat hippocampal synaptosomes in vitro. Effects of S 24795 on Abeta(42) immunostaining, Abeta(42)-alpha7nAChR interaction, and/or Abeta(42)-mediated reduction of calcium (Ca(2+)) influx through alpha7nAChR and N-methyl-d-aspartate receptor (NMDAR) were assessed in Abeta(42)-incubated organotypic brain slices and intracerebroventricularly (ICV) Abeta(42)-injected mouse brain.
Preincubation with S 24795 in vitro reduces Abeta(42)-alpha7nAChR interaction and Abeta(42)-induced tau phosphorylation. In organotypic brain slice cultures and in an ICV Abeta(42) injection in vivo model, S 24795 reduces Abeta(42)-alpha7nAChR association and Abeta(42) immunostaining. S 24795 also normalizes Ca(2+) fluxes through both alpha7nAChR and NMDAR channels in Abeta(42)-infused mouse brains and Abeta(42)-exposed organotypic cortical slices. Unlike S 24795 and Abeta(12-28), galantamine or memantine minimally affect Abeta(42)-alpha7nAChR coupling and Abeta(42)-mediated reduction of alpha7nAChR- and NMDAR-mediated Ca(2+) influx.
Drugs like S 24795 that disrupt Abeta(42)-alpha7nAChR interaction might alleviate Abeta(42)-mediated synaptic dysfunction and block AD-like pathologies.
Biological psychiatry 11/2009; 67(6):522-30. · 8.93 Impact Factor
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ABSTRACT: Alzheimer's disease (AD) is characterized by synaptic dysfunction and cardinal neuropathological features including amyloid plaques and neurofibrillary tangles. Soluble amyloid-beta (Abeta) can suppress synaptic activities by interacting with alpha7 nicotinic acetylcholine receptors (alpha7nAChRs). Here, we show that alpha7nAChR and NMDA glutamatergic receptor (NMDAR) activities are severely compromised in synaptosomes prepared from AD and Abeta(1-42) (Abeta42)-exposed control frontal cortex slices from postmortem tissue. Whereas Abeta(12-28) prevents Abeta42 from binding to alpha7nAChRs, 2-[2-(4-bromophenyl)-2-oxoethyl]-1-methyl pyridinium (S 24795), a novel alpha7nAChR partial agonist, facilitates release of Abeta42 from Abeta42-alpha7nAChR and -Abeta42 complexes. S 24795 interacts with alpha7nAChR and Abeta(15-20) region of the Abeta42 to enable partial recovery of the alpha7nAChR and NMDAR channel function. These findings suggest that the Abeta-alpha7nAChR interaction may be an upstream pathogenic event in AD and demonstrate that some recovery of neuronal channel activities may be achieved in AD brains by removing Abeta from alpha7nAChRs.
Journal of Neuroscience 10/2009; 29(35):10961-73. · 7.11 Impact Factor
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ABSTRACT: We studied by immunocytochemistry and Western blots the identity and cellular distribution of voltage-gated calcium channels within dopaminergic neurons of the rat retina. The aim was to associate particular calcium channel subtypes with known activities of the neuron (e.g., transmitter release from axon terminals). Five voltage-gated calcium channels were identified: alpha1A, alpha1B, alpha1E, alpha1F, and alpha1H. All of these, except the alpha1B subtype, were found within dopaminergic perikarya. The alpha1B channels were concentrated at axon terminal rings, together with alpha1A calcium channels. In contrast, alpha1H calcium channels were most abundant in the dendrites, and alpha1F calcium channels were restricted to the perikaryon. The alpha1E calcium channel was present at such a low density that its cellular distribution beyond the perikaryon could not be determined. Our findings are consistent with the available pharmacological data indicating that alpha1A and alpha1B calcium channels control the major fraction of dopamine release in the rat retina.
The Journal of Comparative Neurology 08/2006; 497(3):384-96. · 3.81 Impact Factor
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ABSTRACT: The mitogen-activated protein kinases (MAPKs) are a family of signal transduction mediators that regulate a host of cellular activities, including cell growth and proliferation, and differentiation and survival, via sequential phosphorylation and activation of a cassette of three protein kinases. MAPKs are also recruited when the brain undergoes synaptic plasticity and remodeling (e.g., during induction of long-term potentiation, learning and memory consolidation). The activities of some of these kinases are altered in response to various acute stimuli such as ischemic insult, visceral pain and electroconvulsive shock. In the present study we used immunoblotting techniques to examine the effects of acute and repeated restraint stress on the phosphorylation state of three MAPKs, the extracellular signal-regulated kinase Erk1/2, c-Jun-N-terminal kinase/stress-activated protein kinase (JNK/SAPK) and p38 MAPK, in different brain regions. A single exposure to 30 min of restraint stress-elevated phospho-Erk1/2 (P-Erk1/2) levels in all three brain regions examined (hippocampus, medial prefrontal cortex and cingulate cortex), but did not alter the phosphorylation pattern of the other two MAPKs in any region. In marked contrast, exposure to restraint for 11 days (30 min/day) reduced the levels of all three MAPKs, but only in the prefrontal cortex. The results are compared to the reported effects of acute and chronic stress on other biochemical and functional measures.
Brain Research 08/2003; 979(1-2):57-64. · 2.73 Impact Factor
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ABSTRACT: Mitogen-activated protein kinases (MAPKs), a family of signal transduction mediators important in a host of cellular activities, include the extracellular signal-regulated kinases Erk1 and Erk2. We determined whether 5-HT(1A) receptors activate Erk1/2 in rat brain in vivo, as they do in recombinant cell lines. In contrast to the effect in cells, the 5-HT(1A) receptor agonist 8-hydroxy-N,N-diproylaminotetralin (8-OH-DPAT) dose- and time-dependently decreased basal levels of phosphorylated Erk1/2 (phospho-Erk1/2) in rat hippocampus (ED(50) approximately 0.1 mg/kg, maximum approximately 90%) without altering total Erk1/2. The effects were kinase-specific, as 8-OH-DPAT did not modify phosphorylated or total levels of the MAPKs c-Jun-N-terminal kinase/stress-activated protein kinase (JNK/SAPK) and p38 MAPK. Moreover, 8-OH-DPAT did not modify phospho-Erk1/2 in striatum or frontal cortex. The effect of 8-OH-DPAT was blocked by pretreatment with the selective 5-HT(1A) receptor antagonists N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-2-pyridinylcyclohexanecarboxamide (WAY 100635), 1-(2-methoxyphenyl)-4-(4-[2-phthalimido]butyl)piperazine (NAN-190) and 4-fluoro-N-(2-[4-(2-methoxyphenyl)1-piperazinyl]ethyl)-N-(2-pyridinyl)benzamide dihydrochloride (p-MPPF), but not by the weak partial agonist/antagonist 8-(2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl)-8-azaspiro(4.5)decane-7,9-dione dihydrochloride (BMY 7378). Other 5-HT(1A) receptor agonists (buspirone, gepirone and ipsapirone) also reduced phospho-Erk1/2 levels in hippocampus. 8-OH-DPAT also reduced the levels of the upstream activator of Erk1/2, phosphorylated extracellular signal-regulated kinase kinase (phospho-MEK1/2), and at least one potential downstream target, the nuclear transcription factor phospho-Elk-1. The region- and kinase-specific effects suggest that the Erk1/2 signal transduction cascade is likely an important differential mediator of 5-HT(1A) receptor-regulated events in the central nervous system.
European Journal of Pharmacology 11/2002; 452(2):155-62. · 2.52 Impact Factor
