RESUMO
A number of studies have suggested that the glutamatergic and cholinergic systems are both involved in learning and memory processes and that they interact in order to facilitate these processes. However, the role of M1-muscarinic receptors in mediating this interaction has not been elucidated. The aim of this study was to determine whether the concomitant administration of MK-801 (non-competitive NMDA antagonist) and dicyclomine (M1-muscarinic antagonist--DIC) in sub-effective doses impairs contextual fear conditioning (hippocampal-dependent task) and tone fear conditioning tasks (hippocampal-independent task). The results showed that concomitant pre-training administration of DIC (8.0 mg/kg) and MK-801 (0.07 mg/kg)--two sub-effectives doses for the contextual fear conditioning task--does impair the performance of animals on this task (as measured by freezing behavior time). Tone fear conditioning tasks were not affected by the drugs either administered separately or concurrently. The pre-training administration of sub-effective doses of MK-801 and DIC in combination impairs performance on contextual fear conditioning task (hippocampal-dependent), but not on tone fear conditioning task (hippocampal-independent). These data support the hypothesis that the interaction between glutamatergic and cholinergic systems in hippocampus-dependent learning and memory processes probably occurs through M1 receptor.
Assuntos
Condicionamento Clássico , Diciclomina/farmacologia , Maleato de Dizocilpina/farmacologia , Antagonistas de Aminoácidos Excitatórios/farmacologia , Medo , Antagonistas Muscarínicos/farmacologia , Animais , Comportamento Animal/efeitos dos fármacos , Condicionamento Clássico/efeitos dos fármacos , Condicionamento Clássico/fisiologia , Diciclomina/metabolismo , Maleato de Dizocilpina/metabolismo , Antagonistas de Aminoácidos Excitatórios/metabolismo , Medo/efeitos dos fármacos , Medo/fisiologia , Ácido Glutâmico/metabolismo , Hipocampo/metabolismo , Masculino , Antagonistas Muscarínicos/metabolismo , N-Metilaspartato/metabolismo , Ratos , Ratos Wistar , Receptor Muscarínico M1/metabolismo , Receptores de N-Metil-D-Aspartato/metabolismoRESUMO
Glutamate, the major excitatory neurotransmitter, can cause the death of neurons by a mechanism known as excitotoxicity. This is a calcium-dependent process and activation of the NMDA receptor subtype contributes mainly to neuronal damage, due to its high permeability to calcium. Activation of calpain, a calcium-dependent cysteine protease, has been implicated in necrotic excitotoxic neuronal death. We have investigated the contribution of NMDA and non-NMDA ionotropic receptors to calpain activation and neuronal death induced by the acute administration of glutamate into the rat striatum. Calpain activity was assessed by the cleavage of the cytoskeletal protein, alpha-spectrin. Caspase-3 activity was also studied because glutamate can also lead to apoptosis. Results show no caspase-3 activity, but a strong calpain activation involving both NMDA and non-NMDA receptors. Although neuronal damage is mediated mainly by the NMDA receptor subtype, it can not be attributed solely to calpain activity.
Assuntos
Calpaína/metabolismo , Corpo Estriado/metabolismo , Neurônios/metabolismo , Neurônios/patologia , Receptores de Glutamato/metabolismo , Receptores de N-Metil-D-Aspartato/metabolismo , Animais , Calpaína/antagonistas & inibidores , Caspase 3/metabolismo , Corpo Estriado/citologia , Corpo Estriado/patologia , Inibidores de Cisteína Proteinase/metabolismo , Dipeptídeos/metabolismo , Maleato de Dizocilpina/metabolismo , Ativação Enzimática , Antagonistas de Aminoácidos Excitatórios/metabolismo , Masculino , Neurônios/citologia , Fármacos Neuroprotetores/metabolismo , Quinoxalinas/metabolismo , Ratos , Ratos Wistar , Espectrina/metabolismoRESUMO
Medium spiny projection neurons (MSNs) are the main neuronal population in the neostriatum. MSNs are inhibitory and GABAergic. MSNs connect with other MSNs via local axon collaterals that produce lateral inhibition, which is thought to select cell assemblies for motor action. MSNs also receive inhibitory inputs from GABAergic local interneurons. This work shows, through the use of the paired pulse protocol, that somatostatin (SST) acts presynaptically to regulate GABA release from the terminals interconnecting MSNs. This SST action is reversible and not mediated through the release of dopamine. It is blocked by the SST receptor (SSTR) antagonist ciclosomatostatin (cicloSST). In contrast, SST does not regulate inhibition coming from interneurons. Because, SST is released by a class of local interneuron, it is concluded that this neuron helps to regulate the selection of motor acts.
Assuntos
Corpo Estriado/metabolismo , Potenciais Pós-Sinápticos Inibidores/fisiologia , Neurônios/metabolismo , Terminações Pré-Sinápticas/metabolismo , Somatostatina/metabolismo , 6-Ciano-7-nitroquinoxalina-2,3-diona/metabolismo , Potenciais de Ação/fisiologia , Animais , Corpo Estriado/citologia , Agonistas de Aminoácidos Excitatórios/metabolismo , Antagonistas de Aminoácidos Excitatórios/metabolismo , N-Metilaspartato/metabolismo , Neurônios/citologia , Técnicas de Patch-Clamp , Ratos , Ratos Wistar , Valina/análogos & derivados , Valina/metabolismo , Ácido alfa-Amino-3-hidroxi-5-metil-4-isoxazol Propiônico/metabolismoRESUMO
The N-methyl-D-aspartate type of glutamate receptor (NMDAR) plays a major role in the vertebrate retina. Expression of NR1 splice-variants and NR2 subunits in the retina differs from that in the brain, suggesting a tissue-specific heteromeric assembly of NMDARs. We previously demonstrated that serum alters retinal glutamate receptor properties. In order to relate this effect to NMDAR subunit composition, we here studied the effect of serum on the expression of NMDAR subunits and splice-variants in chick retinal neurons in primary culture. Our results show that mRNA and protein expression of NR1 alternative splice-variants and NR2 subunits are differentially modified by glutamate contained in serum. Such alteration suggests that NMDAR structure is reversed to embryonic heteromeric composition, through the control of subunit availability. The present findings could be relevant for the understanding of the lack of effect in the retina, of drugs which have been shown to protect cortical neurons from glutamate-induced excitotoxicity in those pathological or clinical conditions in which the retina is exposed to serum.
Assuntos
Neurônios/metabolismo , Biossíntese de Proteínas , Subunidades Proteicas/metabolismo , Receptores de N-Metil-D-Aspartato/metabolismo , Retina/citologia , Soro/metabolismo , Transcrição Gênica , Animais , Embrião de Galinha , Antagonistas de Aminoácidos Excitatórios/metabolismo , Genisteína/metabolismo , Glicina/análogos & derivados , Glicina/metabolismo , Neurônios/citologia , Isoformas de Proteínas/genética , Isoformas de Proteínas/metabolismo , Inibidores de Proteínas Quinases/metabolismo , Subunidades Proteicas/genética , Quinoxalinas/metabolismo , Receptor trkA/genética , Receptor trkA/metabolismo , Receptores de N-Metil-D-Aspartato/genética , Retina/metabolismoRESUMO
Ionotropic glutamate receptors are major excitatory receptors in the central nervous system and also have a far reaching influence in other areas of the body. Their modular nature has allowed for the isolation of the ligand-binding domain and for subsequent structural studies using a variety of spectroscopic techniques. This review will discuss the role of specific ligand:protein interactions in mediating activation in the a-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid subtype of glutamate receptors as established by various spectroscopic investigations of the GluR2 and GluR4 subunits of this receptor. Specifically, this review will provide an introduction to the insight gained from X-ray crystallography and nuclear magnetic resonance investigations and then go on to focus on studies utilizing vibrational spectroscopy and fluorescence resonance energy transfer to study the behavior of the isolated ligand-binding domain in solution and discuss the importance of specific ligand:protein interactions in the mechanism of receptor activation.
Assuntos
Humanos , Receptores de Glutamato/química , Transferência de Energia , Antagonistas de Aminoácidos Excitatórios/química , Antagonistas de Aminoácidos Excitatórios/metabolismo , Ligantes , Espectroscopia de Ressonância Magnética , Ligação Proteica , Conformação Proteica , Receptores de Glutamato/metabolismo , Espectroscopia de Infravermelho com Transformada de Fourier , Relação Estrutura-Atividade , /química , /metabolismoRESUMO
Ionotropic glutamate receptors are major excitatory receptors in the central nervous system and also have a far reaching influence in other areas of the body. Their modular nature has allowed for the isolation of the ligand-binding domain and for subsequent structural studies using a variety of spectroscopic techniques. This review will discuss the role of specific ligand:protein interactions in mediating activation in the a-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid subtype of glutamate receptors as established by various spectroscopic investigations of the GluR2 and GluR4 subunits of this receptor. Specifically, this review will provide an introduction to the insight gained from X-ray crystallography and nuclear magnetic resonance investigations and then go on to focus on studies utilizing vibrational spectroscopy and fluorescence resonance energy transfer to study the behavior of the isolated ligand-binding domain in solution and discuss the importance of specific ligand:protein interactions in the mechanism of receptor activation.
Assuntos
Receptores de Glutamato/química , Transferência de Energia , Antagonistas de Aminoácidos Excitatórios/química , Antagonistas de Aminoácidos Excitatórios/metabolismo , Humanos , Ligantes , Espectroscopia de Ressonância Magnética , Ligação Proteica , Conformação Proteica , Receptores de Glutamato/metabolismo , Espectroscopia de Infravermelho com Transformada de Fourier , Relação Estrutura-Atividade , Ácido alfa-Amino-3-hidroxi-5-metil-4-isoxazol Propiônico/química , Ácido alfa-Amino-3-hidroxi-5-metil-4-isoxazol Propiônico/metabolismoRESUMO
Bradykinin is one of the most potent endogenous algesic substances and its role in pain transmission has been intensively studied in the periphery. However, the action of this peptide in central structures involved in pain transmission remains unclear. Administration of bradykinin (0.25 nmol/site) into the right amygdala of adult male Wistar rats induced thermal hyperalgesia, evaluated in the paw-flick test. Bradykinin-induced hyperalgesia was abolished by co-administration with the B(2) receptor antagonist Hoe 140 (5 pmol/site), the NMDA antagonist MK-801 (5 nmol/site), the cyclooxygenase inhibitor indomethacin (10 nmol/site) and the glial metabolic inhibitor fluorocitrate (1 nmol/site). Since the intra-amygdala administration of bradykinin did not alter spontaneous locomotion in the open-field test, it is unlikely that the current described hyperalgesic effect of bradykinin is due to an unspecific action on motor activity. These findings provide evidence that bradykinin, through activation of amygdalar B(2) receptors induces hyperalgesia and that glutamatergic- and prostanoid-mediated mechanisms are involved in such effect.
Assuntos
Tonsila do Cerebelo/efeitos dos fármacos , Bradicinina/farmacologia , Hiperalgesia/induzido quimicamente , Tonsila do Cerebelo/metabolismo , Animais , Comportamento Animal/efeitos dos fármacos , Comportamento Animal/fisiologia , Bradicinina/administração & dosagem , Bradicinina/análogos & derivados , Bradicinina/metabolismo , Antagonistas dos Receptores da Bradicinina , Citratos/metabolismo , Inibidores de Ciclo-Oxigenase/metabolismo , Maleato de Dizocilpina/metabolismo , Antagonistas de Aminoácidos Excitatórios/metabolismo , Indometacina/metabolismo , Masculino , Atividade Motora/efeitos dos fármacos , Atividade Motora/fisiologia , Neuroglia/metabolismo , Medição da Dor , Ratos , Ratos WistarRESUMO
Male Wistar rats received bilateral infusions of vehicle (VEH) or aminophosphonopentanoic acid (AP5), an N-metil-D-aspartate (NMDA) receptor antagonist, into the dorsal hippocampus immediately after inhibitory avoidance (IA) training. Intrahippocampal infusion of AP5 blocked 24 h IA retention. In the second experiment, animals were preexposed to the IA training context 24 h prior to training and received an infusion of either VEH or AP5 immediately after the preexposure trial and a second infusion of VEH or AP5 immediately after IA training. AP5 did not affect retention in animals preexposed to the IA box and given VEH after preexposure, but blocked retention when given after both preexposure and training. AP5 impaired retention in rats preexposed to an environment distinct from the IA box. These results suggest that NMDA receptors in the dorsal hippocampus mediate the formation of a contextual representation of the task environment.
Assuntos
Aprendizagem da Esquiva/fisiologia , Hipocampo/fisiologia , Memória/fisiologia , Receptores de N-Metil-D-Aspartato/metabolismo , 2-Amino-5-fosfonovalerato/metabolismo , Animais , Antagonistas de Aminoácidos Excitatórios/metabolismo , Hipocampo/anatomia & histologia , Masculino , Ratos , Ratos WistarRESUMO
OBJECTIVES: To extend the genotyping analysis of the CYP2D6 gene and further explain variability of CYP2D6 activity in Mexican Americans by genetic factors. METHODS: CYP2D6 gene sequence variations associated with *6, *7, *8, *9, *11, *14, *29, *41, *45, and *46 alleles as well as the 2988G>A SNP were examined in 264 Mexican Americans; 236 had previously been phenotyped with dextromethorphan. All subjects were previously genotyped for CYP2D6*2, *3, *4, *5, *10, *17, and the presence of a gene duplication. Associations between genotype and CYP2D6 activity were determined. RESULTS: Mexican Americans revealed a high frequency of functional alleles (CYP2D6*1 and *2; 73.1%), followed by CYP2D6*4 (non-functional, 10.0%) and the reduced-function allele *41 (9.5%). The frequencies of CYP2D6*5, *6, *9, *10, duplication, and 2988A were 1.7%, 0.4%, 1.1%, 2.8%, 0.8%, and 5.7%, respectively. CYP2D6*3, *17, and *29 were found only in one individual (CYP2D6*2/*3, *1/*17, and *4/*29), while CYP2D6*7, *8, *11, *14, *45, and *46 were absent in this study population. Decreased CYP2D6 activity was more accurately predicted by the presence *41[-1584C] compared to *41[2988A]. One genotype/phenotype discordant subject was resolved by the presence of a CYP2D6*6 allele (*4/*6), while two other cases remained discordant (*41/*41 and *1/*1). CONCLUSIONS: The CYP2D6*4, *5, and *6 null alleles along the reduced function alleles *9, *10, and *41 are the major cause for diminished dextromethorphan oxidative capacity in Mexican Americans. These findings may have implications for the safety and efficacy of CYP2D6 substrates taken by Mexican Americans.
Assuntos
Citocromo P-450 CYP2D6/genética , Genética Populacional , Americanos Mexicanos/genética , Adulto , Alelos , Citocromo P-450 CYP2D6/classificação , Dextrometorfano/metabolismo , Antagonistas de Aminoácidos Excitatórios/metabolismo , Feminino , Genótipo , Humanos , MasculinoRESUMO
Physical activity has been proposed as a behavior intervention that promotes mental health and some of the benefits induced by exercise have been related to the glutamatergic system. Indeed, glutamate is the most abundant excitatory neurotransmitter in brain. Thus, we evaluated if voluntary exercise in mice could modulate glutamatergic synapses at level of postsynaptic density (PSD). Through Western blot, we found that exercise during 1 month increased glutamatergic-related protein content in PSD from cortex of mice. Exercise increased the immunocontent of GluR1 (129%), SAP-97 (179%), GRIP-1 (129%), and in less extent, GluR2/3 (118%) and PSD-95 (112%) proteins. The overall content of NMDA subunits R1, R2A and R2B were not altered in mice that had exercised, however, the phosphorylated NMDA subunits, phospho-NMDAR1 (150%), and phospho-NMDAR2B (183%) showed a strong increase. Because exercise increased the content of phosphorylated forms of NMDA receptors, we evaluated the binding of MK-801, a specific ligand that binds to open NMDA channel. Exercise increased the binding of MK-801 in cortical cellular membranes in 51%. Altogether, our results point to a modulation of glutamatergic synapses by exercise with likely implications in the exercise-induced mental health.