RESUMO
Nicotinic acetylcholine receptor (nAChR)-mediated neuroprotection has been implicated in the treatment of neurodegenerative disorders such as Alzheimer's and Parkinson's diseases and hypoxic ischemic events as well as other diseases hallmarked by excitotoxic and apoptotic neuronal death. Several modalities of nicotinic neuroprotection have been reported. However, although this process generally involves α4ß2 and α7 subtypes, the underlying mechanisms are largely unknown. Interestingly, both activation and inhibition of α7 nAChRs have been reported to be neuroprotective. We have shown that inhibition of α7 nAChRs protects the function of acute hippocampal slices against excitotoxicity in an α4ß2-dependent manner. Neuroprotection was assessed as the prevention of the N-methyl-D-aspartate-dependent loss of the area of population spikes (PSs) in the CA1 area of acute hippocampal slices. Our results support a model in which α7 AChRs control the release of γ-aminobutyric acid (GABA). Blocking either α7 or GABA(A) receptors reduces the inhibitory tone on cholinergic terminals, thereby promoting α4ß2 activation, which in turn mediates neuroprotection. These results shed light on how α7 nAChR inhibition can be neuroprotective through a mechanism mediated by activation of α4ß2 nAChRs.
Assuntos
Antagonistas GABAérgicos/farmacologia , Fármacos Neuroprotetores/metabolismo , Fármacos Neuroprotetores/farmacologia , Antagonistas Nicotínicos/farmacologia , Receptores Nicotínicos/metabolismo , Potenciais de Ação/efeitos dos fármacos , Potenciais de Ação/fisiologia , Animais , Região CA1 Hipocampal/efeitos dos fármacos , Região CA1 Hipocampal/fisiologia , Humanos , Masculino , Técnicas de Cultura de Órgãos , Ratos , Ratos Sprague-Dawley , Receptores Nicotínicos/fisiologia , Receptor Nicotínico de Acetilcolina alfa7RESUMO
The goal of this study was to characterize acute neuronal injury in a novel nonhuman primate (NHP) ischemic stroke model by using multiple outcome measures. Silk sutures were inserted into the M1 segment of the middle cerebral artery of rhesus macaques to achieve permanent occlusion of the vessel. The sutures were introduced via the femoral artery by using endovascular microcatheterization techniques. Within hours after middle cerebral artery occlusion (MCAO), infarction was detectable by using diffusion-weighted MRI imaging. The infarcts expanded by 24 h after MCAO and then were detectable on T2-weighted images. The infarcts seen by MRI were consistent with neuronal injury demonstrated histologically. Neurobehavioral function after MCAO was determined by using 2 neurologic testing scales. Neurologic assessments indicated that impairment after ischemia was limited to motor function in the contralateral arm; other neurologic and behavioral parameters were largely unaffected. We also used microarrays to examine gene expression profiles in peripheral blood mononuclear cells after MCAO-induced ischemia. Several genes were altered in a time-dependent manner after MCAO, suggesting that this ischemia model may be suitable for identifying blood biomarkers associated with the presence and severity of ischemia. This NHP stroke model likely will facilitate the elucidation of mechanisms associated with acute neuronal injury after ischemia. In addition, the ability to identify candidate blood biomarkers in NHP after ischemia may prompt the development of new strategies for the diagnosis and treatment of ischemic stroke in humans.
Assuntos
Modelos Animais de Doenças , Infarto da Artéria Cerebral Média/sangue , Infarto da Artéria Cerebral Média/complicações , Infarto da Artéria Cerebral Média/patologia , Transtornos Psicomotores/patologia , Acidente Vascular Cerebral/patologia , Animais , Western Blotting , Cateterismo , Citocinas/metabolismo , Técnicas de Diagnóstico Neurológico , Ensaio de Imunoadsorção Enzimática , Perfilação da Expressão Gênica , Técnicas Histológicas , Leucócitos Mononucleares/metabolismo , Macaca mulatta , Imageamento por Ressonância Magnética , Análise em Microsséries , Neurônios/patologia , Transtornos Psicomotores/etiologia , Acidente Vascular Cerebral/sangueRESUMO
BACKGROUND: Kinins, with bradykinin and des-Arg(9)-bradykinin being the most important ones, are pro-inflammatory peptides released after tissue injury including stroke. Although the actions of bradykinin are in general well characterized; it remains controversial whether the effects of bradykinin are beneficial or not. Kinin-B2 receptor activation participates in various physiological processes including hypotension, neurotransmission and neuronal differentiation. The bradykinin metabolite des-Arg(9)-bradykinin as well as Lys-des-Arg(9)-bradykinin activates the kinin-B1 receptor known to be expressed under inflammatory conditions. We have investigated the effects of kinin-B1 and B2 receptor activation on N-methyl-D-aspartate (NMDA)-induced excitotoxicity measured as decreased capacity to produce synaptically evoked population spikes in the CA1 area of rat hippocampal slices. PRINCIPAL FINDINGS: Bradykinin at 10 nM and 1 µM concentrations triggered a neuroprotective cascade via kinin-B2 receptor activation which conferred protection against NMDA-induced excitotoxicity. Recovery of population spikes induced by 10 nM bradykinin was completely abolished when the peptide was co-applied with the selective kinin-B2 receptor antagonist HOE-140. Kinin-B2 receptor activation promoted survival of hippocampal neurons via phosphatidylinositol 3-kinase, while MEK/MAPK signaling was not involved in protection against NMDA-evoked excitotoxic effects. However, 100 nM Lys-des-Arg(9)-bradykinin, a potent kinin-B1 receptor agonist, reversed bradykinin-induced population spike recovery. The inhibition of population spikes recovery was reversed by PD98059, showing that MEK/MAPK was involved in the induction of apoptosis mediated by the B1 receptor. CONCLUSIONS: Bradykinin exerted protection against NMDA-induced excitotoxicity which is reversed in the presence of a kinin-B1 receptor agonist. As bradykinin is converted to the kinin-B1 receptor metabolite des-Arg(9)-bradykinin by carboxypeptidases, present in different areas including in brain, our results provide a mechanism for the neuroprotective effect in vitro despite of the deleterious effect observed in vivo.
Assuntos
Bradicinina/toxicidade , N-Metilaspartato , Receptor B1 da Bradicinina/agonistas , Receptor B2 da Bradicinina/fisiologia , Animais , Bradicinina/administração & dosagem , Bradicinina/análogos & derivados , Química Encefálica , Região CA1 Hipocampal , Carboxipeptidases/metabolismo , Fármacos Neuroprotetores , Ratos , Receptor B1 da Bradicinina/fisiologiaRESUMO
Nicotinic acetylcholine receptors (nAChR) exert pivotal roles in synaptic transmission, neuroprotection and differentiation. Particularly, homomeric alpha7 receptors participate in neurite outgrowth, presynaptic control of neurotransmitter release and Ca2+ influx. However, the study of recombinant alpha7 nAChRs in transfected cell lines is difficult due to low expression of functional receptor channels. We show that PC12 pheochromocytoma cells induced to differentiation into neurons are an adequate model for studying differential nAChR gene expression and receptor activity. Whole-cell current recording indicated that receptor responses increased during the course of differentiation. Transcription of mRNAs coding for alpha3, alpha5, alpha7, beta2 and beta4 subunits was present during the course of differentiation, while mRNAs coding for alpha2, alpha4 and beta3 subunits were not expressed in PC12 cells. alpha7 subunit expression was highest following 1 day of induction to differentiation. Activity of alpha7 nAChRs, however, was most elevated on day 2 as revealed by inhibition experiments in the presence of 10 nM methyllycaconitine, rapid current decay and receptor responsiveness to the alpha7 agonist choline. Increased alpha7 receptor activity was noted when PC12 were induced to differentiation in the presence of choline, confirming that chronic agonist treatment augments nAChR activity. In summary, PC12 cells are an adequate model to study the role and pharmacological properties of this receptor during neuronal differentiation.
Assuntos
Diferenciação Celular/genética , Regulação da Expressão Gênica no Desenvolvimento/fisiologia , Neurônios/metabolismo , Feocromocitoma/metabolismo , Receptores Nicotínicos/biossíntese , Receptores Nicotínicos/genética , Animais , Diferenciação Celular/efeitos dos fármacos , Neurônios/efeitos dos fármacos , Neurônios/patologia , Células PC12 , Feocromocitoma/patologia , Ratos , Receptores Nicotínicos/efeitos dos fármacos , Receptor Nicotínico de Acetilcolina alfa7RESUMO
In tobacco, there are two types of compounds that interact with neuronal nicotinic acetylcholine receptors (nnAChRs) in the brain. The first is the addictive component of tobacco and an agonist of these receptors, nicotine. The second are cyclic diterpenoids called cembranoids that non-competitively inhibit many types of nnAChRs. Nictotinic receptors composed of alpha4beta2 subunits are the predominant type of nicotinic receptors in the brain. These alpha4beta2 receptors are up-regulated upon chronic exposure to nicotine and have been implicated in nicotine addiction. The present study was designed to determine whether the inhibitory effects of two cembranoids from tobacco [(1S, 2E, 4R, 6R, 7E, 11E)-2,7,11-cembratriene-4,6-diol (4R) and its diastereoisomer (1S, 2E, 4S, 6R, 7E, 11E)-2,7,11-cembratriene-4,6-diol (4S)] were comparable on acetylcholine (ACh) and nicotine-evoked currents through alpha4beta2 nnAChRs. alpha4beta2 nnAChRs from rat brain were expressed in Xenopus oocytes and studied using the two-electrode voltage-clamp technique. The dose-response curves for acetylcholine and nicotine were hyperbolic and bell-shaped, respectively. Although there was no difference in the potency between cembranoids 4R and 4S, both of these cembranoids more potently inhibited nicotine-induced currents than acetylcholine-induced currents. Furthermore, both cembranoids were more potent inhibitors of this receptor when they were preincubated for 1 min prior to application of agonist. The finding that cembranoids preferentially inhibit nicotine-induced currents over those elicited by the natural neurotransmitter acetylcholine may have important implications when developing strategies to prevent nicotine addiction and tobacco use.
Assuntos
Acetilcolina/farmacologia , Diterpenos/farmacologia , Nicotina/farmacologia , Agonistas Nicotínicos/farmacologia , Antagonistas Nicotínicos/farmacologia , Receptores Nicotínicos/fisiologia , Animais , Diterpenos/química , Feminino , Técnicas In Vitro , Oócitos/efeitos dos fármacos , Oócitos/fisiologia , Técnicas de Patch-Clamp , Ratos , Estereoisomerismo , Xenopus laevisRESUMO
This review describes and analyzes the evidence from studies using noncompetitive inhibitors of the nicotinic acetylcholine receptor that the receptor's ion channel is formed by the second transmembrane segment of all five receptor subunits. Inconsistencies in this generally accepted model are also presented and discussed
Assuntos
Animais , Antagonistas Colinérgicos/farmacologia , Canais Iônicos/efeitos dos fármacos , Receptores Colinérgicos/antagonistas & inibidores , Sequência de Aminoácidos , Ativação do Canal Iônico/efeitos dos fármacos , Sítios de Ligação , Canais Iônicos/metabolismo , Cátions/metabolismo , Modelos Químicos , Dados de Sequência Molecular , Neurotoxinas/farmacologia , Conformação Proteica , Receptores Colinérgicos/química , Receptores Colinérgicos/metabolismoRESUMO
Se ha estudiado la conducta de un grupo de Saimiri sciureus en presencia de objetos novedosos, no comestibles. El grupo de 21 animales, de ambos sexos y varias edades, vivía en un corral cubierto ubicado al aire libre. Diez objetos de diversas formas, colores, materiales y tamaños fueron introducidos en el corral y el número de monos que interactuaban con cada objeto se registró usando una técnica de muestreo. También se hicieron observaciones cualitativas sobre el tipo de interacción. Los mismos objetos se volvieron a presentar al día siguiente, repetiendo las determinaciones. Este experimento, con algunas variantes se repitió tres veces durante un período de seis meses. Durante el primer día, la interacción con los objetos fue máxima inmediatamente después de la presentación de los mismos y caía abruptamente por el resto del día. Al segundo día, la habitación era menos notoria y el puntaje total fue similar en ambos días. Las características que influyeron en la cantidad de interacción fueron el material de los objetos y probablemente la complejidad estructural de los mismos. Ni el color ni el peso tuvieron influencia estadísticamente significativa. Aquellos objetos que fueron tocados más frecuentemente despertaban una intensa actividad investigativa y vigoroso juego social. Estos resultados difieren de algunos estudios anteriores que reportaron falta de interês por objetos no comestibles en Saimiris