RESUMO
AIMS: Glycine receptors (GlyRs) are potentiated by physiologically relevant concentrations of ethanol, and mutations in the intracellular loop of α1 and α2 subunits reduced the effect of the drug. Knock-in (KI) mice having these individual mutations revealed that α1 and α2 subunits played a role in ethanol-induced sedation and ethanol intake. In this study, we wanted to examine if the effects of stacking both mutations in a 2xKI mouse model (α1/α2) generated by a selective breeding strategy further impacted cellular and behavioral responses to ethanol. MAIN METHODS: We used electrophysiological recordings to examine ethanol's effect on GlyRs and evaluated ethanol-induced neuronal activation using c-Fos immunoreactivity and the genetically encoded calcium indicator GCaMP6s in the nucleus accumbens (nAc). We also examined ethanol-induced behavior using open field, loss of the righting response, and drinking in the dark (DID) paradigm. KEY FINDINGS: Ethanol did not potentiate GlyRs nor affect neuronal excitability in the nAc from 2xKI. Moreover, ethanol decreased the Ca2+ signal in WT mice, whereas there were no changes in the signal in 2xKI mice. Interestingly, there was an increase in c-Fos baseline in the 2xKI mice in the absence of ethanol. Behavioral assays showed that 2xKI mice recovered faster from a sedative dose of ethanol and had higher ethanol intake on the first test day of the DID test than WT mice. Interestingly, an open-field assay showed that 2xKI mice displayed less anxiety-like behavior than WT mice. SIGNIFICANCE: The results indicate that α1 and α2 subunits are biologically relevant targets for regulating sedative effects and ethanol consumption.
Assuntos
Etanol , Técnicas de Introdução de Genes , Receptores de Glicina , Animais , Etanol/farmacologia , Receptores de Glicina/genética , Receptores de Glicina/metabolismo , Camundongos , Masculino , Núcleo Accumbens/metabolismo , Núcleo Accumbens/efeitos dos fármacos , Consumo de Bebidas Alcoólicas/genética , Consumo de Bebidas Alcoólicas/metabolismo , Proteínas Proto-Oncogênicas c-fos/metabolismo , Proteínas Proto-Oncogênicas c-fos/genética , Camundongos Endogâmicos C57BL , Neurônios/metabolismo , Neurônios/efeitos dos fármacos , Camundongos Transgênicos , Receptores de GABA-ARESUMO
In the spinal cord, attenuation of the inhibitory action of glycine is related to an increase in both inflammatory and diabetic neuropathic pain; however, the glycine receptor involvement in diabetic neuropathy has not been reported. We determined the expression of the glycine receptor subunits (α1-α3 and ß) in streptozotocin-induced diabetic Long-Evans rats by qPCR and Western blot. The total mRNA and protein expression (whole spinal cord homogenate) of the α1, α3, and ß subunits did not change during diabetes; however, the α2 subunit mRNA, but not the protein, was overexpressed 45 days after diabetes induction. By contrast, the synaptic expression of the α1 and α2 subunits decreased in all the studied stages of diabetes, but that of the α3 subunit increased on day 45 after diabetes induction. Intradermal capsaicin produced higher paw-licking behavior in the streptozotocin-induced diabetic rats than in the control animals. In addition, the nocifensive response was higher at 45 days than at 20 days. During diabetes, the expression of the glycine receptor was altered in the spinal cord, which strongly suggests its involvement in diabetic neuropathy.
Assuntos
Diabetes Mellitus Experimental , Neuropatias Diabéticas , Ratos , Animais , Glicina/metabolismo , Receptores de Glicina/genética , Receptores de Glicina/metabolismo , Estreptozocina/toxicidade , Neuropatias Diabéticas/metabolismo , Diabetes Mellitus Experimental/induzido quimicamente , Diabetes Mellitus Experimental/metabolismo , Ratos Long-Evans , Medula Espinal/metabolismo , RNA Mensageiro/metabolismoRESUMO
The nucleus accumbens (nAc) is a critical region in the brain reward system since it integrates abundant synaptic inputs contributing to the control of neuronal excitability in the circuit. The presence of inhibitory α1 glycine receptor (GlyRs) subunits, sensitive to ethanol, has been recently reported in accumbal neurons suggesting that they are protective against excessive binge consumption. In the present study, we used viral vectors (AAV) to overexpress mutant and WT α1 subunits in accumbal neurons in D1 Cre and α1 KI mice. Injection of a Cre-inducible AAV carrying an ethanol insensitive α1 subunit in D1 Cre neurons was unable to affect sensitivity to ethanol in GlyRs or affect ethanol drinking. On the other hand, using an AAV that transduced WT α1 GlyRs in GABAergic neurons in the nAc of high-ethanol consuming mice caused a reduction in ethanol intake as reflected by lowered drinking in the dark and reduced blood ethanol concentration. As expected, the AAV increased the glycine current density by 5-fold without changing the expression of GABAA receptors. Examination of the ethanol sensitivity in isolated accumbal neurons indicated that the GlyRs phenotype changed from an ethanol resistant to an ethanol sensitive type. These results support the conclusion that increased inhibition in the nAc can control excessive ethanol consumption and that selective targeting of GlyRs by pharmacotherapy might provide a mechanistic procedure to reduce ethanol binge.
Assuntos
Consumo Excessivo de Bebidas Alcoólicas , Glicina , Animais , Camundongos , Consumo Excessivo de Bebidas Alcoólicas/genética , Consumo Excessivo de Bebidas Alcoólicas/metabolismo , Etanol/farmacologia , Neurônios GABAérgicos/metabolismo , Glicina/farmacologia , Glicina/metabolismo , Núcleo Accumbens/metabolismo , Receptores de Glicina/genética , Receptores de Glicina/metabolismoRESUMO
OBJECTIVE: To determine the involvement of TNF-α and glycine receptors in the inhibition of pro-inflammatory adipokines in 3T3-L1 cells. METHODS: RT-PCR evidenced glycine receptors in 3T3-L1 adipocytes. 3T3-L1 cells were transfected with siRNA for the glycine (Glrb) and TNF1a (Tnfrsf1a) receptors and confirmed by confocal microscopy. Transfected cells were treated with glycine (10 mM). The expressions of TNF-α and IL-6 mRNA were measured by qRT-PCR, while concentrations were quantified by ELISA. RESULTS: Glycine decreased the expression and concentration of TNF-α and IL-6; this effect did not occur in the absence of TNF-α receptor due to siRNA. In contrast, glycine produced only slight changes in the expression of TNF-α and IL-6 in the absence of the glycine receptor due to siRNA. A docking analysis confirmed the possibility of binding glycine to the TNF-α1a receptor. CONCLUSION: These findings support the idea that glycine could partially inhibit the binding of TNF-α to its receptor and provide clues about the mechanisms by which glycine inhibits the secretion of pro-inflammatory adipokines in adipocytes through the TNF-α receptor.
Assuntos
Adipócitos/metabolismo , Citocinas/metabolismo , Glicina/farmacologia , Receptores Tipo II do Fator de Necrose Tumoral/antagonistas & inibidores , Receptores Tipo I de Fatores de Necrose Tumoral/antagonistas & inibidores , Células 3T3-L1 , Adiponectina/genética , Animais , Citocinas/genética , Expressão Gênica , Camundongos , NF-kappa B/antagonistas & inibidores , NF-kappa B/metabolismo , RNA Mensageiro/metabolismo , RNA Interferente Pequeno/genética , Receptores de Glicina/genética , Receptores Tipo I de Fatores de Necrose Tumoral/genética , Receptores Tipo II do Fator de Necrose Tumoral/genéticaRESUMO
BACKGROUND AND PURPOSE: The precise mechanism/s of action of ethanol, although studied for many years, are not well understood. Like other drugs of abuse, ethanol affects dopamine levels in the nucleus accumbens (nAc), an important region of the mesolimbic system, causing a reinforcing effect. It has been shown that glycine receptors (GlyRs) present in the nAc are potentiated by clinically relevant concentrations of ethanol, where α1 and α2 are the predominant subunits expressed. EXPERIMENTAL APPROACH: Using a combination of electrophysiology and behavioural assays, we studied the involvement of GlyR α2 subunits on the effects of low and high doses of ethanol, as well as on consumption using mice lacking the GlyR α2 subunit (male Glra2-/Y and female Glra2-/- ). KEY RESULTS: GlyR α2 subunits exist in accumbal neurons, since the glycine-evoked currents and glycinergic miniature inhibitory postsynaptic currents (mIPSCs) in Glra2-/Y mice were drastically decreased. In behavioural studies, differences in ethanol consumption and sedation were observed between wild-type (WT) and Glra2 knockout (KO) mice. Using the drinking in the dark (DID) paradigm, we found that Glra2-/Y mice presented a binge-like drinking behaviour immediately when exposed to ethanol rather than the gradual consumption seen in WT animals. Interestingly, the effect of knocking out Glra2 in female (Glra2-/- ) mice was less evident, since WT female mice already showed higher DID. CONCLUSION AND IMPLICATIONS: The differences in ethanol consumption between WT and KO mice provide additional evidence supporting the conclusion that GlyRs are biologically relevant targets for the sedative and rewarding properties of ethanol.
Assuntos
Receptores de Glicina , Transmissão Sináptica , Animais , Etanol , Feminino , Glicina , Masculino , Camundongos , Camundongos Knockout , Receptores de Glicina/genética , Receptores de Glicina/metabolismoRESUMO
Diabetes mellitus is a metabolic disease that leads to several complications which include retinopathy. Neuronal abnormalities have been reported to appear before microvasculature alterations. We analyzed the expression levels of GlyR subunits in the retina at 7, 20, and 45 days after streptozotocin-induced diabetes to gain insight into the pathogenesis of diabetic retinopathy. We determined the mRNA and protein expression by qPCR and western blot, respectively. The mRNA and protein expression of the α1 subunit was not altered over the study period; however, they were slightly reduced in α2 yet statistically significant. While protein expression of α3 subunit was only reduced at 45 days diabetes. The mRNA and protein expression of the α4 subunit was remarkably decreased since day 7 of diabetes, remaining only â¼20% on day 45 of diabetes. Surprisingly, the mRNA of the ß subunit was highly increased, while its protein levels were not changed. The decrease in GlyR α subunits expression in the retina from diabetic animals suggest a perturbation in the inhibitory glycine signaling pathway, which might be related to the visual alterations observed in diabetes.
Assuntos
Diabetes Mellitus Experimental/metabolismo , Receptores de Glicina/metabolismo , Retina/metabolismo , Animais , Progressão da Doença , Feminino , Regulação da Expressão Gênica , Neurônios/metabolismo , Ratos , Ratos Long-Evans , Receptores de Glicina/genética , Transmissão Sináptica/fisiologiaRESUMO
The small ventral lateral neurons (sLNvs) constitute a central circadian pacemaker in the Drosophila brain. They organize daily locomotor activity, partly through the release of the neuropeptide pigment-dispersing factor (PDF), coordinating the action of the remaining clusters required for network synchronization. Despite extensive efforts, the basic principles underlying communication among circadian clusters remain obscure. We identified classical neurotransmitters released by sLNvs through disruption of specific transporters. Adult-specific RNAi-mediated downregulation of the glycine transporter or impairment of glycine synthesis in LNv neurons increased period length by nearly an hour without affecting rhythmicity of locomotor activity. Electrophysiological recordings showed that glycine reduces spiking frequency in circadian neurons. Interestingly, downregulation of glycine receptor subunits in specific sLNv targets impaired rhythmicity, revealing involvement of glycine in information processing within the network. These data identify glycinergic inhibition of specific targets as a cue that contributes to the synchronization of the circadian network.
Assuntos
Ritmo Circadiano/fisiologia , Proteínas da Membrana Plasmática de Transporte de Glicina/metabolismo , Glicina/metabolismo , Receptores de Glicina/metabolismo , Transmissão Sináptica , Animais , Animais Geneticamente Modificados , Encéfalo/metabolismo , Regulação para Baixo , Proteínas de Drosophila/metabolismo , Drosophila melanogaster/metabolismo , Proteínas da Membrana Plasmática de Transporte de Glicina/genética , Humanos , Neurônios/metabolismo , Neuropeptídeos/metabolismo , Neurotransmissores/metabolismo , Interferência de RNA , Receptores de Glicina/genéticaRESUMO
It is well accepted that ethanol is able to produce major health and economic problems associated to its abuse. Because of its intoxicating and addictive properties, it is necessary to analyze its effect in the central nervous system. However, we are only now learning about the mechanisms controlling the modification of important membrane proteins such as ligand-activated ion channels by ethanol. Furthermore, only recently are these effects being correlated to behavioral changes. Current studies show that the glycine receptor (GlyR) is a susceptible target for low concentrations of ethanol (5-40mM). GlyRs are relevant for the effects of ethanol because they are found in the spinal cord and brain stem where they primarily express the α1 subunit. More recently, the presence of GlyRs was described in higher regions, such as the hippocampus and nucleus accumbens, with a prevalence of α2/α3 subunits. Here, we review data on the following aspects of ethanol effects on GlyRs: (1) direct interaction of ethanol with amino acids in the extracellular or transmembrane domains, and indirect mechanisms through the activation of signal transduction pathways; (2) analysis of α2 and α3 subunits having different sensitivities to ethanol which allows the identification of structural requirements for ethanol modulation present in the intracellular domain and C-terminal region; (3) Genetically modified knock-in mice for α1 GlyRs that have an impaired interaction with G protein and demonstrate reduced ethanol sensitivity without changes in glycinergic transmission; and (4) GlyRs as potential therapeutic targets.
Assuntos
Comportamento/efeitos dos fármacos , Etanol/farmacologia , Receptores de Glicina/efeitos dos fármacos , Transmissão Sináptica/efeitos dos fármacos , Anestésicos Gerais/farmacologia , Animais , Comportamento/fisiologia , Etanol/toxicidade , Humanos , Camundongos , Camundongos Mutantes , Modelos Neurológicos , Receptores de Glicina/química , Receptores de Glicina/genética , Receptores de Glicina/metabolismo , Transdução de Sinais/efeitos dos fármacos , Transmissão Sináptica/fisiologiaRESUMO
Previous studies have shown that the effect of ethanol onglycine receptors (GlyRs) containing the a1 subunit is affected by interaction with heterotrimeric G proteins (Gßγ). GlyRs containing the α3 subunit are involved in inflammatory pain sensitization and rhythmic breathing and have received much recent attention. For example, it is unknown whether ethanol affects the function of this important GlyR subtype. Electrophysiologic experiments showed that GlyR α3 subunits were not potentiated by pharmacologic concentrations of ethanol or by Gßγ. Thus, we studied GlyR α1α3 chimeras and mutants to determine the molecular properties that confer ethanol insensitivity. Mutation of corresponding glycine 254 in transmembrane domain 2 (TM2) found in a1 in the α3(A254G) α1 chimera induced a glycine-evoked current that displayed potentiation during application of ethanol (46 ± 5%, 100 mM) and Gßγ activation (80 ± 17%). Interestingly,insertion of the intracellular α3L splice cassette into GlyR α1 abolished the enhancement of the glycine-activated current by ethanol (5 ± 6%) and activation by Gßγ (21 6 7%). In corporation of the GlyR α1 C terminus into the ethanol-resistant α3S(A254G) mutant produced a construct that displayed potentiation of the glycine-activated current with 100 mM ethanol (40 ± 6%)together with a current enhancement after G protein activation (68 ± 25%). Taken together, these data demonstrate that GlyRα3 subunits are not modulated by ethanol. Residue A254 in TM2, the α3L splice cassette, and the C-terminal domain of α3GlyRs are determinants for low ethanol sensitivity and form the molecular basis of subtype-selective modulation of GlyRs by alcohol.
Assuntos
Etanol/farmacologia , Receptores de Glicina/metabolismo , Processamento Alternativo , Sequência de Aminoácidos , Animais , Subunidades beta da Proteína de Ligação ao GTP/metabolismo , Subunidades gama da Proteína de Ligação ao GTP/metabolismo , Células HEK293 , Humanos , Modelos Moleculares , Dados de Sequência Molecular , Mutação , Estrutura Terciária de Proteína , Ratos , Receptores de Glicina/genéticaRESUMO
Alcohol abuse and alcoholism are major health problems and one of the leading preventable causes of death. Before achieving better treatments for alcoholism, it is necessary to understand the critical actions of alcohol on membrane proteins that regulate fundamental functions in the central nervous system. After generating a genetically modified knock-in (KI) mouse having a glycine receptor (GlyR) with phenotypical silent mutations at KK385/386AA, we studied its cellular and in vivo ethanol sensitivity. Analyses with western blotting and immunocytochemistry indicated that the expression of α1 GlyRs in nervous tissues and spinal cord neurons (SCNs) were similar between WT and KI mice. The analysis of synaptic currents recorded from KI mice showed that the glycinergic synaptic transmission had normal properties, but the sensitivity to ethanol was significantly reduced. Furthermore, the glycine-evoked current in SCNs from KI was resistant to ethanol and G-protein activation by GTP-γ-S. In behavioral studies, KI mice did not display the foot-clasping behavior upon lifting by the tail and lacked an enhanced startle reflex response that are characteristic of other glycine KI mouse lines with markedly impaired glycine receptor function. The most notable characteristic of the KI mice was their significant lower sensitivity to ethanol (â¼40%), expressed by shorter times in loss of righting reflex (LORR) in response to a sedative dose of ethanol (3.5 g/Kg). These data provide the first evidence to link a molecular site in the GlyR with the sedative effects produced by intoxicating doses of ethanol.