RESUMO
The dopamine transporter (DAT) is the main target of methylphenidate (MPH), which remains the number one drug prescribed worldwide for the treatment of Attention-Deficit Hyperactivity Disorder (ADHD). In addition, abnormalities of the DAT have been widely associated with ADHD. Based on clinical and preclinical studies, the direction of DAT abnormalities in ADHD are, however, still unclear. Moreover, chronic treatment of MPH has been shown to increase brain DAT expression in both animals and ADHD patients, suggesting that findings of overexpressed levels of DAT in ADHD patients are possibly attributable to the effects of long-term MPH treatment rather than the pathology of the condition itself. In this chapter, we will discuss some of the effects exerted by MPH, which are related to its actions on catecholamine protein targets and brain metabolites, together with genes and proteins mediating neuronal plasticity. For this purpose, we present data from biochemical, proton nuclear magnetic resonance spectroscopy (1H-NMR) and gene/protein expression studies. Overall, results of the studies discussed in this chapter show that MPH has a complex biological/pharmacological action well beyond the DAT.
Assuntos
Transtorno do Deficit de Atenção com Hiperatividade , Estimulantes do Sistema Nervoso Central , Metilfenidato , Animais , Transtorno do Deficit de Atenção com Hiperatividade/tratamento farmacológico , Encéfalo/metabolismo , Estimulantes do Sistema Nervoso Central/farmacologia , Estimulantes do Sistema Nervoso Central/uso terapêutico , Proteínas da Membrana Plasmática de Transporte de Dopamina/metabolismo , Metilfenidato/farmacologia , Metilfenidato/uso terapêuticoRESUMO
Psychostimulant drugs are widely used in children for the treatment of attention-deficit/hyperactivity disorder. Recent animal studies have suggested that exposure to these agents in early life could be detrimental to brain development. Here, for the first time, the effect of methylphenidate (MPH) and D-amphetamine (AMPH) on the expression of two key genes for neuronal development and plasticity, brain-derived neurotrophic factor (bdnf) and the effector immediate early gene activity-regulated, cytoskeletal-associated protein (Arc), was examined in both juvenile and adult rats. Both MPH [2 mg/kg, intraperitoneal (i.p.)] and AMPH (0.5 mg/kg, i.p.) induced marked decreases of bdnf mRNA in hippocampal and cortical brain regions of juveniles, whereas effects in adults were significantly less (hippocampus) or opposite (frontal cortex). In comparison, Arc mRNA was decreased (hippocampus and parietal cortex), largely unaffected (frontal cortex) or increased (striatum) in juveniles, whereas in adults, Arc mRNA increased in most brain regions. MPH-induced locomotion was also measured, and showed a much smaller increase in juveniles than in adults. In summary, our data show that the effects of MPH and AMPH on expression of the neurodevelopmentally important genes, bdnf and Arc, differ markedly in juvenile and adult rats, with juveniles showing evidence of brain region-specific decreases in both genes. These age-dependent effects on gene expression may be linked with the reported long-term harmful effects of psychostimulants in animal models.
Assuntos
Fator Neurotrófico Derivado do Encéfalo/genética , Encéfalo/efeitos dos fármacos , Estimulantes do Sistema Nervoso Central/farmacologia , Proteínas do Citoesqueleto/genética , Regulação da Expressão Gênica/efeitos dos fármacos , Genes Precoces/efeitos dos fármacos , Proteínas do Tecido Nervoso/genética , Envelhecimento/genética , Envelhecimento/metabolismo , Anfetamina/farmacologia , Animais , Encéfalo/crescimento & desenvolvimento , Encéfalo/metabolismo , Regulação para Baixo/efeitos dos fármacos , Regulação para Baixo/genética , Regulação da Expressão Gênica/genética , Genes Precoces/genética , Masculino , Metanfetamina/farmacologia , Ratos , Ratos Sprague-DawleyRESUMO
The psychostimulant methylphenidate (MPH) is the primary drug treatment for attention deficit hyperactivity disorder (ADHD) in children. MPH is well known to acutely block the dopamine (DAT) and noradrenaline (NET) transporters. Its effect on additional catecholamine targets is however less known. This study was aimed at comparing the effects of acute (2â¯mg/kg, i.p.) and chronic (2â¯mg/kg twice daily for 2 weeks) MPH treatment to young rats on key catecholamine protein targets in brain regions implicated in the symptoms and treatment of ADHD. For this purpose, the density of DAT, NET, the vesicular monoamine transporter 2 (VMAT2), the rate limiting enzyme for catecholamine synthesis tyrosine hydroxylase (TH) and the dopamine D1 receptor were measured in frontal (FC), parietal cortex (PCx) and the dorsal (DS) and ventral (VS) striatum. The data demonstrate that the effects of MPH depend on duration of treatment and brain region investigated. With the exception of DAT in the VS our results indicate that chronic but not acute administration of MPH increases levels of DAT, NET, TH, VMAT2 and D1. These effects were further more prominent in the VS over DS and in the PCx compared to the FC. In addition, chronic MPH enhanced DAT levels in the left DS but not in right side. To summarize, this study shows new evidence that chronic MPH to young rats preferentially alters catecholamine targets in PCx and VS over DS and FC. The effect of chronic MPH to increase levels of DAT, NET and VMAT2 suggests that the drug might long-term loose some of its acute action to increase extracellular levels of dopamine and noradrenaline. In conclusion, these findings provide novel insights into the mechanism of action by MPH in the treatment of ADHD and further suggest that the long-term effectiveness of the stimulant drug could be limited.
Assuntos
Catecolaminas/metabolismo , Estimulantes do Sistema Nervoso Central/administração & dosagem , Metilfenidato/administração & dosagem , Lobo Parietal/efeitos dos fármacos , Estriado Ventral/efeitos dos fármacos , Animais , Catecolaminas/antagonistas & inibidores , Proteínas da Membrana Plasmática de Transporte de Dopamina/antagonistas & inibidores , Proteínas da Membrana Plasmática de Transporte de Dopamina/metabolismo , Esquema de Medicação , Masculino , Proteínas da Membrana Plasmática de Transporte de Norepinefrina/antagonistas & inibidores , Proteínas da Membrana Plasmática de Transporte de Norepinefrina/metabolismo , Lobo Parietal/metabolismo , Ratos , Ratos Sprague-Dawley , Receptores de Dopamina D1/antagonistas & inibidores , Receptores de Dopamina D1/metabolismo , Estriado Ventral/metabolismo , Proteínas Vesiculares de Transporte de Monoamina/antagonistas & inibidores , Proteínas Vesiculares de Transporte de Monoamina/metabolismoRESUMO
Abnormalities in the cerebellar circuitry have been suggested to contribute to some of the symptoms associated with attention deficit hyperactivity disorder (ADHD). The psychostimulant methylphenidate (MPH) is the major drug for treating this condition. Here, the effects of acute (2.0â¯mg/kg and 5.0â¯mg/kg) and chronic (2.0â¯mg/kg, twice daily for 15 days) MPH treatments were investigated in adolescent (35-40 days old) rats on monoaminergic and metabolic markers in the cerebellum. Data acquired indicates that acute MPH treatment (2.0â¯mg/kg) decreased cerebellar vesicular monoamine transporter (VMAT2) density, while chronic treatment caused an increase. In contrast, protein levels of tyrosine hydroxylase (TH) and the dopamine D1 receptor were not significantly altered by neither acute nor chronic MPH treatment. In addition, while chronic but not acute MPH treatment significantly enhanced dopamine turnover (DOPAC/dopamine) in the cerebellum, levels of dopamine and homovanillic acid (HVA) were not altered. Acute MPH (5.0â¯mg/kg) significantly modified levels of a range of cerebellar metabolites with similar trends also detected for the lower dose (2.0â¯mg/kg). In this regard, acute MPH tended to decrease cerebellar metabolites associated with energy consumption and excitatory neurotransmission including glutamate, glutamine, N-acetyl aspartate, and inosine. Conversely, levels of some metabolites associated with inhibitory neurotransmission, including GABA and glycine were reduced by acute (5.0â¯mg/kg) MPH, together with acetate, aspartate and hypoxanthine. In conclusion, this study demonstrated that MPH alters cerebellar biochemistry, and that this effect depends on both dose and duration of treatment. The therapeutic significance of these results requires further investigation.
Assuntos
Estimulantes do Sistema Nervoso Central/farmacologia , Cerebelo/efeitos dos fármacos , Cerebelo/crescimento & desenvolvimento , Metilfenidato/farmacologia , Animais , Monoaminas Biogênicas/metabolismo , Cerebelo/metabolismo , Relação Dose-Resposta a Droga , Masculino , Distribuição Aleatória , Ratos Sprague-Dawley , Maturidade SexualRESUMO
Methylphenidate (MPH) is the front-line psychostimulant medication prescribed for alleviating the symptoms associated with attention deficit hyperactivity disorder (ADHD) in children. Here, we investigated the effects of chronic MPH (2.0mg/kg, twice daily for 15days) exposure to young rats (20-25days old at start of treatment) on the expression of genes and proteins associated with neuroplasticity, such as activity regulated cytoskeleton-associated protein (Arc), insulin receptor substrate protein 53 (IRSp53), cell division control protein 42 (Cdc42), and actin-related protein 2 (Arp2). Chronic MPH increased Arc expression in areas of the cerebrum including, the striatum, nucleus accumbens and hippocampus. In addition, chronic MPH also increased the expression of IRSp53 in the striatum, while Cdc42 and Arp2 were specifically increased in the nucleus accumbens. Conversely, chronic MPH decreased Arc and IRSp53 protein expression in the cerebellum, indicating differential effects of the drug in cerebral areas relative to the cerebellum. Overall, our results indicate that chronic MPH treatment increases expression of genes and proteins associated with dendritic spine formation and neuronal plasticity in target areas of the cerebrum while it decreases the expression in the cerebellum.
Assuntos
Encéfalo/efeitos dos fármacos , Estimulantes do Sistema Nervoso Central/farmacologia , Metilfenidato/farmacologia , Plasticidade Neuronal/efeitos dos fármacos , Animais , Regulação da Expressão Gênica/efeitos dos fármacos , Masculino , Ratos , Ratos Sprague-DawleyRESUMO
The psychostimulant methylphenidate (MPH) is increasingly used in the treatment of attention deficit hyperactivity disorder (ADHD). While there is little evidence for common brain pathology in ADHD, some studies suggest a right hemisphere dysfunction among people diagnosed with the condition. However, in spite of the high usage of MPH in children and adolescents, its mechanism of action is poorly understood. Given that MPH blocks the neuronal transporters for dopamine and noradrenaline, most research into the effects of MPH on the brain has largely focused on these two monoamine neurotransmitter systems. Interestingly, recent studies have demonstrated metabolic changes in the brain of ADHD patients, but the impact of MPH on endogenous brain metabolites remains unclear. In this study, a proton nuclear magnetic resonance (1H NMR)-based metabolomics approach was employed to investigate the effects of MPH on brain biomolecules. Adolescent male Sprague Dawley rats were injected intraperitoneally with MPH (5.0 mg/kg) or saline (1.0 ml/kg), and cerebral extracts from the left and right hemispheres were analysed. A total of 22 variables (representing 13 distinct metabolites) were significantly increased in the MPH-treated samples relative to the saline-treated controls. The upregulated metabolites included: amino acid neurotransmitters such as GABA, glutamate and aspartate; large neutral amino acids (LNAA), including the aromatic amino acids (AAA) tyrosine and phenylalanine, both of which are involved in the metabolism of dopamine and noradrenaline; and metabolites associated with energy and cell membrane dynamics, such as creatine and myo-inositol. No significant differences in metabolite concentrations were found between the left and right cerebral hemispheres. These findings provide new insights into the mechanisms of action of the anti-ADHD drug MPH.
Assuntos
Química Encefálica/efeitos dos fármacos , Encéfalo/metabolismo , Estimulantes do Sistema Nervoso Central/administração & dosagem , Espectroscopia de Ressonância Magnética/métodos , Metabolômica/métodos , Metilfenidato/administração & dosagem , Fatores Etários , Animais , Transtorno do Deficit de Atenção com Hiperatividade/tratamento farmacológico , Transtorno do Deficit de Atenção com Hiperatividade/metabolismo , Encéfalo/efeitos dos fármacos , Química Encefálica/fisiologia , Estimulantes do Sistema Nervoso Central/toxicidade , Masculino , Metilfenidato/toxicidade , Prótons , Ratos , Ratos Sprague-DawleyRESUMO
RATIONALE: 3,4-Methylenedioxymethamphetamine (MDMA) administration to rats produces an acute hyperthermic response and induces localised neuronal activation, which can be visualised via expression of immediate-early genes. The pharmacological and anatomical basis of these effects are unclear. At high doses, MDMA also causes selective neurotoxicity at serotonergic nerve terminals. OBJECTIVE: We investigated the effect of 5-hydroxytryptamine (5-HT) depletion on the acute hyperthermic response to MDMA and the pattern of neuronal excitation indicated by Arc (activity-regulated cytoskeleton associated gene) in naive rats and following administration of MDMA at a neurotoxic dose. METHODS: Expression of Arc mRNA was investigated by in situ hybridisation histochemistry using 35S-labelled oligonucleotide probe. RESULTS: MDMA induced a significant hyperthermia together with increased Arc mRNA expression in cortical regions, caudate-putamen and CA1 hippocampus but not hypothalamus. At 21 days after a neurotoxic dose of MDMA, brain 5-HT and 5-HIAA levels were significantly reduced by 21-32%. In these animals, both the hyperthermic response and the pattern and extent of Arc mRNA expression induced by a subsequent dose of MDMA were unaltered. However, basal Arc expression was significantly increased in cortical regions and CA1 hippocampus. CONCLUSION: We conclude that the acute hyperthermic response induced by MDMA is not attenuated by moderate depletion of 5-HT, further questioning mediation via a serotonergic mechanism. Arc mRNA induction by MDMA exhibits highly localised expression, which is not altered following 5-HT depletion. However, following a neurotoxic dose of MDMA, basal expression of Arc is increased, particularly in cortex and CA1, suggesting that mechanisms underlying synaptic plasticity might also be modified.
Assuntos
Encéfalo/metabolismo , Febre/metabolismo , Proteínas Imediatamente Precoces/biossíntese , N-Metil-3,4-Metilenodioxianfetamina/toxicidade , Proteínas do Tecido Nervoso/biossíntese , RNA Mensageiro/biossíntese , Antagonistas da Serotonina/toxicidade , Serotonina/metabolismo , Animais , Proteínas do Citoesqueleto , Febre/induzido quimicamente , Proteínas Imediatamente Precoces/genética , Hibridização In Situ , Masculino , N-Metil-3,4-Metilenodioxianfetamina/administração & dosagem , Proteínas do Tecido Nervoso/genética , Ratos , Antagonistas da Serotonina/administração & dosagemRESUMO
OBJECTIVES: The study aims to investigate the role of 5-hydroxytryptamine receptor subtypes in mediating the inhibitory effect of the selective serotonin reuptake inhibitor (fluoxetine on brain-derived neurotrophic factor gene (bdnf) expression in rat hippocampus. METHODS: In situ hybridization was used for regional determination of bdnf expression levels in hippocampal brain slices from normal, lesioned (5-hydroxytryptamine or noradrenaline) or adrenalectomized rats; treated with fluoxetine and/or 5-hydroxytryptamine selective ligands. KEY FINDINGS: Our study shows that the transient fluoxetine-induced down-regulation of bdnf gene expression depends on an intact 5-hydroxytryptamine but not noradrenaline system or circulating glucocorticoids. Pretreatment with the 5-hydroxytryptamine4 antagonist SB-204070 blocked the overall fluoxetine-induced inhibition of bdnf levels in hippocampus, while pretreatment with the 5-hydroxytryptamine2 antagonists ketanserin had an effect in the CA3 but not in the dentate gyrus sub-region of hippocampus. The 5-hydroxytryptamine1A antagonist WAY-100635 and the 5-hydroxytryptamine3 antagonist granisetron were both ineffective. CONCLUSIONS: Our study found strong support for a primary effect of 5-hydroxytryptamine but not noradrenaline or circulating glucocorticoids in the mediation of fluoxetine-induced down-regulation of bdnf expression. More specifically, we also show that 5-hydroxytryptamine4 receptor-stimulation seems to play a pivotal role in this effect.
Assuntos
Fator Neurotrófico Derivado do Encéfalo/genética , Expressão Gênica/genética , Receptores de Serotonina/metabolismo , Animais , Fator Neurotrófico Derivado do Encéfalo/metabolismo , Fluoxetina/farmacologia , Expressão Gênica/efeitos dos fármacos , Glucocorticoides/metabolismo , Hipocampo/efeitos dos fármacos , Hipocampo/metabolismo , Masculino , Norepinefrina/farmacologia , Ratos , Ratos Sprague-Dawley , Receptores de Serotonina/genética , Serotonina/metabolismo , Inibidores Seletivos de Recaptação de Serotonina/farmacologiaRESUMO
Brain-derived neurotrophic factor (BDNF) has been suggested as a target for antidepressant treatment and chronic antidepressant drug administration shows a 'biphasic effect' on BDNF mRNA in rat hippocampus (transient decrease followed by an increase). In comparison, following acute administration only, an inhibitory action on BDNF gene expression is detected. The present study aimed to understand the mechanism behind the acute inhibitory action on BDNF gene expression by investigating the possible involvement of γ-aminobutyric acid (GABA) receptors in mediating this effect. Rats were injected with either saline, the GABA(A) selective compound 4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3-ol (THIP), the benzodiazepine flunitrazepam or the GABA(B) selective compound baclofen. BDNF mRNA levels were measured 4h later using in-situ hybridization. Baclofen (10mg/kg, i.p.), but not THIP (10mg/kg, i.p.) or flunitrazepam (10mg/kg, i.p.), administration resulted in significant inhibition of BDNF mRNA expression in the cornu ammonis 3 and dentate gyrus but not in the cornu ammonis 1 region of the hippocampus. The inhibitory effect of baclofen on hippocampal BDNF mRNA expression was significantly attenuated by pre-treatment the selective GABA(B) antagonists, CGP 46381 and CGP 55845 (10mg/kg, i.p.). The inhibitory action by the selective serotonin re-uptake inhibitor (SSRI) paroxetine on hippocampal BDNF mRNA was also attenuated by CGP 46381. Our findings suggest a role for GABA(B), but not GABA(A), receptor-mediated mechanisms in the inhibitory regulation of basal hippocampal BDNF gene expression. Our results indicate that GABA(B) receptor activation may play a role in the antidepressant drug-induced inhibition of BDNF gene expression in the hippocampus.