RESUMO
Serotonin (5-HT) has been recognized as a neurotransmitter in the vertebrate retina, restricted mainly to amacrine and bipolar cells. It is involved with synaptic processing and possibly as a mitogenic factor. We confirm that chick retina amacrine and bipolar cells are, respectively, heavily and faintly immunolabeled for 5-HT. Amacrine serotonergic cells also co-express tyrosine hydroxylase (TH), a marker of dopaminergic cells in the retina. Previous reports demonstrated that serotonin transport can be modulated by neurotransmitter receptor activation. As 5-HT is diffusely released as a neuromodulator and co-localized with other transmitters, we evaluated if 5-HT uptake or release is modulated by several mediators in the avian retina. The role of different glutamate receptors on serotonin transport and release in vitro and in vivo was also studied. We show that L-glutamate induces an inhibitory effect on [3H]5-HT uptake and this effect was specific to kainate receptor activation. Kainate-induced decrease in [3H]5-HT uptake was blocked by CNQX, an AMPA/kainate receptor antagonist, but not by MK-801, a NMDA receptor antagonist. [3H]5-HT uptake was not observed in the presence of AMPA, thus suggesting that the decrease in serotonin uptake is mediated by kainate. 5-HT (10-50 µM) had no intrinsic activity in raising intracellular Ca2+, but addition of 10 µM 5-HT decreased Ca2+ shifts induced by KCl in retinal neurons. Moreover, kainate decreased the number of bipolar and amacrine cells labeled to serotonin in chick retina. In conclusion, our data suggest a highly selective effect of kainate receptors in the regulation of serotonin functions in the retinal cells.
Assuntos
Ácido Caínico/farmacologia , Retina/metabolismo , Serotonina/metabolismo , Animais , Cálcio/metabolismo , Células Cultivadas , Embrião de Galinha , Agonistas de Aminoácidos Excitatórios/farmacologia , Antagonistas de Aminoácidos Excitatórios/farmacologia , Neurotransmissores/metabolismo , Receptores de Glutamato/metabolismo , Receptores de Ácido Caínico/metabolismo , Retina/citologia , Retina/efeitos dos fármacos , Retina/embriologia , Neurônios Retinianos/efeitos dos fármacos , Neurônios Retinianos/metabolismo , Trítio/metabolismoRESUMO
Retinal bipolar cells (BCs) divide photoreceptor output into different channels for the parallel extraction of temporal and chromatic stimulus properties. In rodents, five types of OFF BCs have been differentiated, based on morphological and functional criteria, but their electrophysiological characterization remains incomplete. This study analyzed OFF BCs with the patch clamp technique in acute slices of rat retina. Their specific voltage-dependent currents and glutamate responses are shown to represent individual fingerprints which define the signal processing and filtering properties of each cell type and allow their unequivocal identification. Two additions to the rat BC repertoire are presented: OFF BC-2', a variation of BC-2 with wider axonal arbours and prominent Na(+) currents, is described for the first time in rodents, and OFF BC-3b, previously identified in mouse, is electrophysiologically characterized in rat. Moreover, the glutamate responses of rat OFF BCs are shown to be differentially sensitive to AMPA- and kainate-receptor blockers and to modulation by nitric oxide (NO) through a cGMP-dependent mechanism. These results contribute to our understanding of the diversity and function of bipolar cells in mammals.
Assuntos
Fenômenos Eletrofisiológicos , Retina/fisiopatologia , Células Bipolares da Retina/fisiologia , Animais , Axônios/metabolismo , Axônios/fisiologia , Técnicas de Patch-Clamp , Estimulação Luminosa , Células Fotorreceptoras/metabolismo , Células Fotorreceptoras/fisiologia , Ratos , Receptores de Ácido Caínico/metabolismo , Células Bipolares da Retina/metabolismo , Células Fotorreceptoras Retinianas ConesRESUMO
Ligand-gated ion channels (LGICs) are cell surface integral proteins that mediate the fast neurotransmission in the nervous system. LGICs require auxiliary subunits for their trafficking, assembly and pharmacological modulation. Auxiliary subunits do not form functional homomeric receptors, but are reported to assemble with the principal subunits in order to modulate their pharmacological profiles. For example, nACh receptors are built at least by co-assemble of α and ß subunits, and the neuronal auxiliary subunits ß3 and α5 and muscle type ß, δ, γ, and ϵ determine the agonist affinity of these receptors. Serotonergic 5-HT3B, 5-HT3C, 5-HT3D and 5-HT3E are reported to assemble with the 5-HT3A subunit to modulate its pharmacological profile. Functional studies evaluating the role of γ2 and δ auxiliary subunits of GABAA receptors have made important advances in the understanding of the action of benzodiazepines, ethanol and neurosteroids. Glycine receptors are composed principally by α1-3 subunits and the auxiliary subunit ß determines their synaptic location and their pharmacological response to propofol and ethanol. NMDA receptors appear to be functional as heterotetrameric channels. So far, the existence of NMDA auxiliary subunits is controversial. On the other hand, Kainate receptors are modulated by NETO 1 and 2. AMPA receptors are modulated by TARPs, Shisa 9, CKAMP44, CNIH2-3 auxiliary proteins reported that controls their trafficking, conductance and gating of channels. P2X receptors are able to associate with auxiliary Pannexin-1 protein to modulate P2X7 receptors. Considering the pharmacological relevance of different LGICs auxiliary subunits in the present work we will highlight the therapeutic potential of these modulator proteins.
Assuntos
Canais Iônicos de Abertura Ativada por Ligante/efeitos dos fármacos , Animais , Humanos , Ativação do Canal Iônico/efeitos dos fármacos , Canais Iônicos de Abertura Ativada por Ligante/química , Canais Iônicos de Abertura Ativada por Ligante/metabolismo , Modelos Moleculares , Subunidades Proteicas , Receptores de AMPA/química , Receptores de AMPA/efeitos dos fármacos , Receptores de AMPA/metabolismo , Receptores de GABA-A/química , Receptores de GABA-A/efeitos dos fármacos , Receptores de GABA-A/metabolismo , Receptores de Glutamato/química , Receptores de Glutamato/efeitos dos fármacos , Receptores de Glutamato/metabolismo , Receptores de Glicina/química , Receptores de Glicina/efeitos dos fármacos , Receptores de Glicina/metabolismo , Receptores de Ácido Caínico/química , Receptores de Ácido Caínico/efeitos dos fármacos , Receptores de Ácido Caínico/metabolismo , Receptores de N-Metil-D-Aspartato/química , Receptores de N-Metil-D-Aspartato/efeitos dos fármacos , Receptores de N-Metil-D-Aspartato/metabolismo , Receptores Nicotínicos/química , Receptores Nicotínicos/efeitos dos fármacos , Receptores Nicotínicos/metabolismo , Receptores Purinérgicos P2X/química , Receptores Purinérgicos P2X/efeitos dos fármacos , Receptores Purinérgicos P2X/metabolismo , Receptores 5-HT3 de Serotonina/química , Receptores 5-HT3 de Serotonina/efeitos dos fármacos , Receptores 5-HT3 de Serotonina/metabolismoRESUMO
Eugenol is utilized together with zinc oxide in odontological clinical for the cementation of temporary prostheses and the temporary restoration of teeth and cavities. This work explored the antinociceptive effects of the eugenol in different models of acute pain in mice and investigated its possible modulation of the inhibitory (opioid) and excitatory (glutamatergic and pro-inflammatory cytokines) pathways of nociceptive signaling. The administration of eugenol (3-300 mg/kg, p.o., 60 min or i.p., 30 min) inhibited 82 ± 10% and 90 ± 6% of the acetic acid-induced nociception, with ID50 values of 51.3 and 50.2 mg/kg, respectively. In the glutamate test, eugenol (0.3-100 mg/kg, i.p.) reduced the response behavior by 62 ± 5% with an ID50 of 5.6 mg/kg. In addition, the antinociceptive effect of eugenol (10 mg/kg, i.p.) in the glutamate test was prevented by the i.p. treatment for mice with naloxone. The pretreatment of mice with eugenol (10 mg/kg, i.p.) was able to inhibit the nociception induced by the intrathecal (i.t.) injection of glutamate (37 ± 9%), kainic (acid kainite) (41 ± 12%), α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) (55 ± 5%), and substance P (SP) (39 ± 8%). Furthermore, eugenol (10 mg/kg, i.p.) also inhibited biting induced by tumor necrosis factor alpha (TNF-α, 65 ± 8%). These results extend our current knowledge of eugenol and confirm that it promotes significant antinociception against different mouse models of acute pain. The mechanism of action appears to involve the modulation of the opioid system and glutamatergic receptors (i.e., kainate and AMPA), and the inhibition of TNF-α. Thus, eugenol could represent an important compound in the treatment for acute pain.
Assuntos
Dor Aguda/prevenção & controle , Analgésicos Opioides/uso terapêutico , Modelos Animais de Doenças , Eugenol/uso terapêutico , Neurônios GABAérgicos/efeitos dos fármacos , Transdução de Sinais/efeitos dos fármacos , Fator de Necrose Tumoral alfa/antagonistas & inibidores , Dor Aguda/metabolismo , Analgésicos Opioides/administração & dosagem , Analgésicos Opioides/antagonistas & inibidores , Animais , Anti-Inflamatórios não Esteroides/administração & dosagem , Anti-Inflamatórios não Esteroides/antagonistas & inibidores , Anti-Inflamatórios não Esteroides/uso terapêutico , Comportamento Animal/efeitos dos fármacos , Relação Dose-Resposta a Droga , Eugenol/administração & dosagem , Eugenol/antagonistas & inibidores , Antagonistas de Aminoácidos Excitatórios/administração & dosagem , Antagonistas de Aminoácidos Excitatórios/química , Antagonistas de Aminoácidos Excitatórios/uso terapêutico , Neurônios GABAérgicos/metabolismo , Hipnóticos e Sedativos/administração & dosagem , Hipnóticos e Sedativos/antagonistas & inibidores , Hipnóticos e Sedativos/uso terapêutico , Masculino , Camundongos , Atividade Motora/efeitos dos fármacos , Naloxona/farmacologia , Antagonistas de Entorpecentes/farmacologia , Receptores de Glutamato/química , Receptores de Glutamato/metabolismo , Receptores de Ácido Caínico/antagonistas & inibidores , Receptores de Ácido Caínico/metabolismo , Fator de Necrose Tumoral alfa/metabolismoRESUMO
It is well known that excitatory amino acids induce unconditioned fear responses when locally injected into the dorsal periaqueductal gray matter (dPAG). However, there are only few studies about the involvement of excitatory amino acids mediation in dPAG in the expression of conditioned fear. The present series of experiments evaluates the participation of AMPA/Kainate and NMDA glutamatergic receptors of dPAG in the expression of conditioned fear, assessed by the fear-potentiated startle (FPS) and conditioned freezing responses. Wistar rats were subjected to fear conditioning to light. Twenty-four hours later, they received intra-dPAG injections of kainic acid or NMDA (AMPA/Kainate and NMDA agonists) and 1,2,3,4-Tetrahydro-6-nitro-2,3-dioxo-benzo[f]quinoxaline-7-sulfonamide disodium salt hydrate (NBQX) or D(-)-2-Amino-7-phosphonoheptanoic acid (AP7) (AMPA/Kainate and NMDA antagonists) and were submitted to the FPS test. Conditioned freezing response was simultaneously measured. Effects of drug treatment on motor activity were evaluated in the open-field test. Intra-dPAG injections of glutamatergic agonists enhanced conditioned freezing and promoted pro-aversive effects in the FPS. Lower doses of the agonists had no effect or enhanced FPS whereas higher doses disrupted FPS, indicating a non-monotonic relationship between fear and FPS. The antagonist NBQX had no significant effects while AP7 decreased conditioned freezing but did not affect FPS. Both antagonists reduced the effects of the agonists. The obtained results cannot be attributed to motor deficits. The results suggest an important role of the AMPA/Kainate and NMDA mechanisms of the dPAG in the expression of conditioned freezing and FPS.
Assuntos
Medo/fisiologia , Reação de Congelamento Cataléptica/fisiologia , Substância Cinzenta Periaquedutal/metabolismo , Receptores de Glutamato/metabolismo , Reflexo de Sobressalto/fisiologia , Animais , Condicionamento Clássico/fisiologia , Aminoácidos Excitatórios/metabolismo , Ácido Glutâmico/metabolismo , Masculino , Ratos , Ratos Wistar , Receptores de AMPA/metabolismo , Receptores de Ácido Caínico/metabolismo , Receptores de N-Metil-D-Aspartato/metabolismoRESUMO
The present study was designed to investigate further the mechanisms involved in the antinociception caused by bis-selenide in behavioral model of pain in mice. Bis-selenide (5-50 mg/kg), given orally, produced significant inhibition of the antinociceptive behavior induced by intrathecal (i.t.) injection of glutamate (175 nmol/site), kainate (110 pmol/site) and (+/-)-1-aminocyclopentane-trans-1,3-dicarboxylic acid (trans-ACPD; 50 nmol/site) and the maximal inhibitions observed were 57+/-5, 46+/-7 and 73+/-3%, respectively. Bis-selenide failed to affect the nociception induced by alpha-amino-3-hydroxy-5-mehtyl-4-isoxazolepropionic acid (AMPA; 135 pmol/site) and N-methyl-d-aspartate (NMDA; 450 pmol/site). This compound also reduced the nociceptive response induced by tumor necrosis factor-alpha (TNF-alpha; 0.1 pg/site), interleukin-1beta (IL-1beta; 1 pg/site), substance P (SP) (135 ng/site, i.t.) and capsaicin (30 ng/site) and the inhibitions observed were 81+/-3%, 88+/-1%, 77+/-3 and 67+/-3, respectively. The oral administration of bis-selenide (25-50 mg/kg) in mice caused a significant increase in the reaction time to thermal stimuli in the hot plate test and the mean ID(50) value (and the 95% confidence limits) was 20.37 (15.00-25.74) mg/kg. The antinociceptive effect caused by bis-selenide (50 mg/kg, p.o.) on the hot plate test in mice was reversed by intrathecal (i.t.) injection of some K(+) channel blockers such as tetraethylammonium (TEA, non-selective voltage-dependent K(+) channel inhibitor) and glibenclamide (ATP-sensitive K(+) channel inhibitor), but not apamin and charybdotoxin (large- and small-conductance Ca(2+)-activated K(+) channel inhibitors, respectively). Together, these results indicate that bis-selenide produces antinociception at spinal sites through the activation of ATP-sensitive and voltage-gated K(+) channels and interaction with kainate and trans-ACDP receptors as well as vanilloid and neuropeptide receptors and pro-inflammatory cytokines.
Assuntos
Nociceptores/efeitos dos fármacos , Compostos Organosselênicos/farmacologia , Dor/tratamento farmacológico , Medula Espinal/efeitos dos fármacos , Administração Oral , Analgésicos/química , Analgésicos/farmacologia , Animais , Capsaicina/antagonistas & inibidores , Citocinas/antagonistas & inibidores , Relação Dose-Resposta a Droga , Agonistas de Aminoácidos Excitatórios/farmacologia , Feminino , Injeções Espinhais , Camundongos , Estrutura Molecular , Nociceptores/metabolismo , Dor/induzido quimicamente , Dor/fisiopatologia , Limiar da Dor/efeitos dos fármacos , Limiar da Dor/fisiologia , Bloqueadores dos Canais de Potássio/farmacologia , Canais de Potássio/efeitos dos fármacos , Canais de Potássio/metabolismo , Tempo de Reação/efeitos dos fármacos , Tempo de Reação/fisiologia , Receptores de Ácido Caínico/efeitos dos fármacos , Receptores de Ácido Caínico/metabolismo , Receptores de Glutamato Metabotrópico/efeitos dos fármacos , Receptores de Glutamato Metabotrópico/metabolismo , Medula Espinal/metabolismo , Medula Espinal/fisiopatologiaRESUMO
Kainic acid receptor (KA-R) subunits are differentially expressed during brain development, and they modulate both neural growth and survival. High concentrations of glutamate in the brain can induce neuronal injury through these receptors, altering normal development. However, it is unclear whether KAR subunit expression itself is also modified by neonatal exposure to high glutamate. To analyze this, monosodium glutamate (4mg/g of body weight) was subcutaneously administered on postnatal days 1, 3, 5 and 7, and the expression of GluR5, GluR6, KA1 and KA2, as well as [(3)H]-kainic acid (KA-R) binding, was evaluated on postnatal days 14, 21, 30 and 60 in different regions of rat brain. As a result, high levels of GluR5 expression associated with strong [(3)H]-kainic acid binding were observed on postnatal days 30 and 60 in the cerebral cortex of rats exposed to glutamate. Similarly, the changes induced by glutamate administration in the expression of the KA1 and KA2 subunits were paralleled by those of [(3)H]-kainic acid binding in the striatum at postnatal days 21 and 30. In contrast, while KAR subunits were over expressed in the hippocampus, no changes were observed in [(3)H]-kainic acid binding in adult rats that had been exposed to glutamate. Therefore, glutamate modifies both the expression of kainic acid receptor subunits and kainic acid binding in a determined spatial and temporal manner, which may be indicative of a regional susceptibility to glutamate neurotoxicity.
Assuntos
Encéfalo , Regulação da Expressão Gênica no Desenvolvimento/efeitos dos fármacos , Ácido Glutâmico/toxicidade , Receptores de Ácido Caínico/metabolismo , Fatores Etários , Animais , Animais Recém-Nascidos , Encéfalo/anatomia & histologia , Encéfalo/efeitos dos fármacos , Encéfalo/crescimento & desenvolvimento , Ligação Proteica/efeitos dos fármacos , Ratos , Ratos Wistar , Receptores de Ácido Caínico/genética , Trítio/farmacocinéticaRESUMO
O sistema glutamatérgico, um dos mais extensos do sistema nervoso central, é formado por neurônios, vias e receptores específicos. O agonista natural corresponde a um aminoácido excitador de constituição relativamente simples, o glutamato. Este atua em uma ampla gama de subtipos de receptores, ionotrópicos e metabotrópicos, que oferecem a possibilidade de uma variada atividade sináptica, desde a neurotransmissão rápida até às respostas lentas que induzem modificações sinápticas de longa duração. Essa ampla distribuição dos receptores influencia neurônios que transmitem com o mesmo ou com outros neurotransmissores. Os receptores ionotrópicos, os mais bem estudados, apresentam funções diferenciadas, sendo que o do tipo AMPA é responsável pela maior parte das transmissões sinápticas excitadoras rápidas, a do tipo KA contribui nas respostas pós-sinápticas nas sinapses excitadoras, podendo ainda modular a liberação pré-sináptica do transmissor em determinadas sinapses, enquanto o receptor NMDA é fundamental na indução de formas específicas de plasticidade sináptica. Os variados receptores metabotrópicos também contribuem de modo importante em diversas dessas atividades. Dessa maneira, o sistema glutamatérgico encontra-se relacionado a diversas funções normais, como a plasticidade neural, subjacente a processos cognitivos, assim como a situações patológicas, responsáveis por diversas desordens neuropsiquiátricas agudas e crônicas. O conhecimento detalhado do sistema glutamatérgico, portanto, é essencial para a compreensão de variados processos normais e patológicos, assim como das possibilidades de intervenção farmacológica com objetivos terapêuticas
Assuntos
Humanos , Ácido alfa-Amino-3-hidroxi-5-metil-4-isoxazol Propiônico , Aminoácidos Excitatórios/metabolismo , Doenças do Sistema Nervoso Central/etiologia , Glutamina , Plasticidade Neuronal , Receptores de Ácido Caínico/metabolismo , Receptores de Glutamato , Receptores de N-Metil-D-Aspartato , Cérebro/metabolismo , Cérebro/patologia , Cognição/fisiologiaRESUMO
In this study we investigated the effects of alpha-ketoisocaproic acid (KIC), the main keto acid accumulating in the inherited neurometabolic disorder maple syrup urine disease (MSUD), on the in vitro incorporation of 32P into intermediate filament (IF) proteins from cerebral cortex of rats during development. KIC decreased the in vitro incorporation of 32P into the IF proteins studied up to day 12, had no effect on day 15, and increased this phosphorylation in cortical slices of 17- and 21-day-old rats. A similar effect on IF phosphorylation was achieved along development by incubating cortical slices with glutamate. Furthermore, the altered phosphorylation caused by the presence of KIC in the incubation medium was mediated by the ionotropic receptors NMDA, AMPA and kainate up to day 12 and by NMDA and AMPA in tissue slices from 17- and 21-day-old rats. The results suggest that alterations of IF phosphorylation may be associated with the neuropathology of MSUD.
Assuntos
Córtex Cerebral/efeitos dos fármacos , Filamentos Intermediários/efeitos dos fármacos , Cetoácidos/metabolismo , Doença da Urina de Xarope de Bordo/metabolismo , Neurônios/efeitos dos fármacos , Animais , Animais Recém-Nascidos , Córtex Cerebral/crescimento & desenvolvimento , Córtex Cerebral/metabolismo , Agonistas de Aminoácidos Excitatórios/farmacologia , Antagonistas de Aminoácidos Excitatórios/farmacologia , Proteína Glial Fibrilar Ácida/efeitos dos fármacos , Proteína Glial Fibrilar Ácida/metabolismo , Ácido Glutâmico/metabolismo , Ácido Glutâmico/farmacologia , Proteínas de Filamentos Intermediários/efeitos dos fármacos , Proteínas de Filamentos Intermediários/metabolismo , Filamentos Intermediários/metabolismo , Cetoácidos/farmacologia , Doença da Urina de Xarope de Bordo/fisiopatologia , Neurônios/metabolismo , Técnicas de Cultura de Órgãos , Fosforilação/efeitos dos fármacos , Ratos , Ratos Wistar , Receptores de AMPA/efeitos dos fármacos , Receptores de AMPA/metabolismo , Receptores de Glutamato/efeitos dos fármacos , Receptores de Glutamato/metabolismo , Receptores de Ácido Caínico/efeitos dos fármacos , Receptores de Ácido Caínico/metabolismo , Receptores de Glutamato Metabotrópico/efeitos dos fármacos , Receptores de Glutamato Metabotrópico/metabolismo , Receptores de N-Metil-D-Aspartato/efeitos dos fármacos , Receptores de N-Metil-D-Aspartato/metabolismo , Transmissão Sináptica/efeitos dos fármacos , Transmissão Sináptica/fisiologia , Vimentina/efeitos dos fármacos , Vimentina/metabolismoRESUMO
1. Previous studies have shown that phorbol esters induce protein kinase C (PKC) mediated phosphorylation of the vesicular acetylcholine transporter (VAChT) and change its interaction with vesamicol. However, it is not clear whether physiological activation of receptors coupled to PKC activation can alter VAChT behavior. 2. Here we tested whether activation of kaianate (KA) receptors alters VAChT. Several studies suggest that the cholinergic amacrine cells display KA/AMPA receptors that mediate excitatory input to these neurons. In addition, KA in the chicken retina can generate intracellular messengers with the potential to regulate cellular functions. 3. In cultured chicken retina (E8C11) KA reduced vesamicol binding to VAChT by 53%. This effect was potentiated by okadaic acid, a protein phosphatase inhibitor, and was totally prevented by BIM, a PKC inhibitor. 4. Phorbol myristate acetate (PMA), but not alpha-PMA, reduced in more than 85% the number of L-[3H]-vesamicol-specific binding sites in chicken retina, confirming that activation of PKC can influence vesamicol binding to chicken VAChT. 5. The data show that activation of glutamatergic receptors reduces [3H]-vesamicol binding sites (VAChT) likely by activating PKC and increasing the phosphorylation of the ACh carrier.