RESUMEN
Migraine is a debilitating condition that affects hundreds of millions of people worldwide. A subset of these patients experience chronic migraine, resulting in long-term disability and a severely lowered quality of life. The development of novel migraine therapies has been slow, partially due to the small number of predictive animal models. We have recently developed a novel model of chronic migraine-associated pain, using the known human migraine trigger, nitroglycerin. Injection of nitroglycerin evokes an acute mechanical hyperalgesia, which is sensitive to the acute migraine therapy sumatriptan. In addition, chronic administration of nitroglycerin produces a progressive and sustained decrease in basal mechanical responses, and this hypersensitivity is blocked by migraine preventatives such as topiramate. This mouse model of chronic migraine can be used to study the mechanisms underlying progression of migraine from an episodic to a chronic disorder, and for identifying and screening novel acute and preventive migraine therapies. © 2017 by John Wiley & Sons, Inc.
Asunto(s)
Dolor Crónico/inducido químicamente , Modelos Animales de Enfermedad , Trastornos Migrañosos/inducido químicamente , Nitroglicerina/toxicidad , Vasodilatadores/toxicidad , Animales , Aprendizaje por Asociación/efectos de los fármacos , Dolor Crónico/complicaciones , Femenino , Hiperalgesia/inducido químicamente , Hiperalgesia/fisiopatología , Ratones , Ratones Endogámicos C57BL , Trastornos Migrañosos/complicaciones , Dimensión del Dolor , Umbral del Dolor/efectos de los fármacos , Factores de TiempoRESUMEN
Mechanisms of opioid tolerance have focused on adaptive modifications within cells containing opioid receptors, defined here as cellular allostasis, emphasizing regulation of the opioid receptor signalosome. We review additional regulatory and opponent processes involved in behavioral tolerance, and include mechanistic differences both between agonists (agonist bias), and between µ- and δ-opioid receptors. In a process we will refer to as pass-forward allostasis, cells modified directly by opioid drugs impute allostatic changes to downstream circuitry. Because of the broad distribution of opioid systems, every brain cell may be touched by pass-forward allostasis in the opioid-dependent/tolerant state. We will implicate neurons and microglia as interactive contributors to the cumulative allostatic processes creating analgesic and hedonic tolerance to opioid drugs.
Asunto(s)
Alostasis/fisiología , Analgésicos Opioides/farmacología , Tolerancia a Medicamentos/fisiología , Analgésicos Opioides/administración & dosificación , Animales , Encéfalo/efectos de los fármacos , Encéfalo/metabolismo , Regulación hacia Abajo/fisiología , Humanos , Receptores Opioides/efectos de los fármacos , Receptores Opioides/metabolismo , Receptores Opioides delta/efectos de los fármacos , Receptores Opioides delta/metabolismo , Receptores Opioides mu/efectos de los fármacos , Receptores Opioides mu/metabolismoRESUMEN
Opioid dependence is accompanied by neuroplastic changes in reward circuitry leading to a negative affective state contributing to addictive behaviors and risk of relapse. The current study presents a neuroimmune mechanism through which chronic opioids disrupt the ventral tegmental area (VTA) dopaminergic circuitry that contributes to impaired reward behavior. Opioid dependence was induced in rodents by treatment with escalating doses of morphine. Microglial activation was observed in the VTA following spontaneous withdrawal from chronic morphine treatment. Opioid-induced microglial activation resulted in an increase in brain-derived neurotrophic factor (BDNF) expression and a reduction in the expression and function of the K(+)Cl(-) co-transporter KCC2 within VTA GABAergic neurons. Inhibition of microglial activation or interfering with BDNF signaling prevented the loss of Cl(-) extrusion capacity and restored the rewarding effects of cocaine in opioid-dependent animals. Consistent with a microglial-derived BDNF-induced disruption of reward, intra-VTA injection of BDNF or a KCC2 inhibitor resulted in a loss of cocaine-induced place preference in opioid-naïve animals. The loss of the extracellular Cl(-) gradient undermines GABAA-mediated inhibition, and represents a mechanism by which chronic opioid treatments can result in blunted reward circuitry. This study directly implicates microglial-derived BDNF as a negative regulator of reward in opioid-dependent states, identifying new therapeutic targets for opiate addictive behaviors.
Asunto(s)
Cocaína/administración & dosificación , Neuronas GABAérgicas/metabolismo , Microglía/metabolismo , Morfina/administración & dosificación , Síndrome de Abstinencia a Sustancias/inmunología , Núcleos Talámicos Ventrales/metabolismo , Animales , Factor Neurotrófico Derivado del Encéfalo/metabolismo , Neuronas GABAérgicas/efectos de los fármacos , Masculino , Ratones , Ratones Endogámicos C57BL , Microglía/efectos de los fármacos , Modelos Neurológicos , Neuroinmunomodulación , Recompensa , Simportadores/metabolismo , Núcleos Talámicos Ventrales/efectos de los fármacos , Cotransportadores de K ClRESUMEN
δ-Opioid receptors are G-protein-coupled receptors that regulate nociceptive and emotional responses. It has been well established that distinct agonists acting at the same G-protein-coupled receptor can engage different signaling or regulatory responses. This concept, known as biased agonism, has important biological and therapeutic implications. Ligand-biased responses are well described in cellular models, however, demonstrating the physiological relevance of biased agonism in vivo remains a major challenge. The aim of this study was to investigate the long-term consequences of ligand-biased trafficking of the δ-opioid receptor, at both the cellular and behavioral level. We used δ agonists with similar binding and analgesic properties, but high [SNC80 ((+)-4-[(αR)-α-((2S,5R)-4-allyl-2,5-dimethyl-1-piperazinyl)-3-methoxybenzyl]-N,N-diethylbenzamide)]- or low [ARM390 (N,N-diethyl-4-(phenyl-piperidin-4-ylidenemethyl)-benzamide)]-internalization potencies. As we found previously, a single SNC80-but not ARM390-administration triggered acute desensitization of the analgesic response in mice. However, daily injections of either compound over 5 d produced full analgesic tolerance. SNC80-tolerant animals showed widespread receptor downregulation, and tolerance to analgesic, locomotor and anxiolytic effects of the agonist. Hence, internalization-dependent tolerance developed, as a result of generalized receptor degradation. In contrast, ARM390-tolerant mice showed intact receptor expression, but δ-opioid receptor coupling to Ca²+ channels was abolished in dorsal root ganglia. Concomitantly, tolerance developed for agonist-induced analgesia, but not locomotor or anxiolytic responses. Therefore, internalization-independent tolerance was produced by anatomically restricted adaptations leading to pain-specific tolerance. Hence, ligand-directed receptor trafficking of the δ-opioid receptor engages distinct adaptive responses, and this study reveals a novel aspect of biased agonism in vivo.
Asunto(s)
Analgésicos/farmacología , Tolerancia a Medicamentos/fisiología , Ligandos , Umbral del Dolor/fisiología , Receptores Opioides delta/metabolismo , Analgésicos/uso terapéutico , Animales , Benzamidas/farmacología , Benzamidas/uso terapéutico , Encéfalo/ultraestructura , Calcio/metabolismo , Membrana Celular/efectos de los fármacos , Membrana Celular/genética , Modelos Animales de Enfermedad , Interacciones Farmacológicas , Tolerancia a Medicamentos/genética , Femenino , Adyuvante de Freund , Ganglios Espinales/citología , Proteínas Fluorescentes Verdes/genética , Guanosina 5'-O-(3-Tiotrifosfato)/metabolismo , Hiperalgesia/tratamiento farmacológico , Hiperalgesia/fisiopatología , Inflamación/inducido químicamente , Inflamación/complicaciones , Locomoción/efectos de los fármacos , Locomoción/genética , Masculino , Aprendizaje por Laberinto/efectos de los fármacos , Potenciales de la Membrana/efectos de los fármacos , Ratones , Ratones Endogámicos C57BL , Ratones Transgénicos , Dolor/tratamiento farmacológico , Dolor/etiología , Umbral del Dolor/efectos de los fármacos , Técnicas de Placa-Clamp/métodos , Piperazinas/farmacología , Piperazinas/uso terapéutico , Piperidinas/farmacología , Piperidinas/uso terapéutico , Unión Proteica/efectos de los fármacos , Transporte de Proteínas/genética , Transporte de Proteínas/fisiología , Receptores Opioides delta/agonistas , Receptores Opioides delta/genética , Células Receptoras Sensoriales/efectos de los fármacos , Médula Espinal/ultraestructura , Estadísticas no Paramétricas , Isótopos de Azufre/metabolismo , Factores de TiempoRESUMEN
BACKGROUND: GPCRs regulate a remarkable diversity of biological functions, and are thus often targeted for drug therapies. Stimulation of a GPCR by an extracellular ligand triggers receptor signaling via G proteins, and this process is highly regulated. Receptor activation is typically accompanied by desensitization of receptor signaling, a complex feedback regulatory process of which receptor internalization is postulated as a key event. The in vivo significance of GPCR internalization is poorly understood. In fact, the majority of studies have been performed in transfected cell systems, which do not adequately model physiological environments and the complexity of integrated responses observed in the whole animal. METHODS AND FINDINGS: In this study, we used knock-in mice expressing functional fluorescent delta opioid receptors (DOR-eGFP) in place of the native receptor to correlate receptor localization in neurons with behavioral responses. We analyzed the pain-relieving effects of two delta receptor agonists with similar signaling potencies and efficacies, but distinct internalizing properties. An initial treatment with the high (SNC80) or low (AR-M100390) internalizing agonist equally reduced CFA-induced inflammatory pain. However, subsequent drug treatment produced highly distinct responses. Animals initially treated with SNC80 showed no analgesic response to a second dose of either delta receptor agonist. Concomitant receptor internalization and G-protein uncoupling were observed throughout the nervous system. This loss of function was temporary, since full DOR-eGFP receptor responses were restored 24 hours after SNC80 administration. In contrast, treatment with AR-M100390 resulted in retained analgesic response to a subsequent agonist injection, and ex vivo analysis showed that DOR-eGFP receptor remained G protein-coupled on the cell surface. Finally SNC80 but not AR-M100390 produced DOR-eGFP phosphorylation, suggesting that the two agonists produce distinct active receptor conformations in vivo which likely lead to differential receptor trafficking. CONCLUSIONS: Together our data show that delta agonists retain full analgesic efficacy when receptors remain on the cell surface. In contrast, delta agonist-induced analgesia is abolished following receptor internalization, and complete behavioral desensitization is observed. Overall these results establish that, in the context of pain control, receptor localization fully controls receptor function in vivo. This finding has both fundamental and therapeutic implications for slow-recycling GPCRs.
Asunto(s)
Conducta Animal/efectos de los fármacos , Conducta Animal/fisiología , Receptores Opioides delta/agonistas , Receptores Opioides delta/fisiología , Animales , Benzamidas/farmacología , Transporte Biológico Activo/efectos de los fármacos , Membrana Celular/metabolismo , Células Cultivadas , Proteínas Fluorescentes Verdes/química , Proteínas Fluorescentes Verdes/genética , Proteínas Fluorescentes Verdes/metabolismo , Técnicas In Vitro , Ligandos , Ratones , Ratones Transgénicos , Neuronas/efectos de los fármacos , Neuronas/fisiología , Dolor/tratamiento farmacológico , Dolor/fisiopatología , Fosforilación , Piperazinas/farmacología , Piperidinas/farmacología , Conformación Proteica , Receptores Opioides delta/química , Receptores Opioides delta/genética , Proteínas Recombinantes de Fusión/química , Proteínas Recombinantes de Fusión/genética , Proteínas Recombinantes de Fusión/metabolismoRESUMEN
The goal of this study was to determine the neuroanatomical extent of mu opioid receptor knockdown in central nervous system (CNS) following intracerebroventricular (i.c.v.) administration of peptide nucleic acid antisense. Rats received subchronic i.c.v. injections of anti-mu opioid receptor antisense, mismatch or vehicle, and were tested for paw pressure latency following i.c.v. mu opioid receptor agonist ([D-Ala2, N-Me-Phe4, Gly-ol5]-enkephalin; DAMGO) or delta opioid receptor agonist ((+)-4-[(aR)-a-((2S,5R)-4-allyl-2,5-dimethyl-1-piperazinyl)-3-methoxybenzyl]-N,N-diethylbenzamide; SNC80). The anti-mu opioid receptor antisense (but not mismatch) sequence abolished DAMGO-induced antinociception with no reduction in the delta opioid receptor-mediated response. In contrast, postmortem receptor autoradiographic analysis of CNS areas revealed no change in mu opioid receptor functional response ([35S]GTPgammaS assay) or receptor labelling ([125I]FK-33824 and mu opioid receptor immunoautoradiography). These results provide further evidence for antisense-induced knockdown at the behavioural level in the absence of clear changes at the tissue level.
Asunto(s)
Analgésicos Opioides/antagonistas & inhibidores , Oligodesoxirribonucleótidos Antisentido/farmacología , Dimensión del Dolor/efectos de los fármacos , Ácidos Nucleicos de Péptidos/farmacología , Receptores Opioides mu/antagonistas & inhibidores , Analgésicos/antagonistas & inhibidores , Analgésicos/metabolismo , Analgésicos Opioides/metabolismo , Animales , Relación Dosis-Respuesta a Droga , Encefalina Ala(2)-MeFe(4)-Gli(5)/farmacología , Masculino , Dimensión del Dolor/métodos , Ácidos Nucleicos de Péptidos/genética , Ratas , Ratas Sprague-Dawley , Receptores Opioides mu/metabolismoRESUMEN
In rat extended striatum, most nicotinic cholinoceptors are likely to be presynaptic. A previous report suggested that DA and 5-HT afferents each account for at least 30% of nicotinic binding sites in the striatum. To explore this question further, rats received unilateral infusions of the neurotoxins 5,7-dihydroxytryptamine, 6-hydroxydopamine or vehicle into the medial forebrain bundle, and were sacrificed 3 weeks later. Denervation was quantified by [125I]RTI-55 autoradiography, using separate assay conditions that revealed DA and 5-HT transporters (i.e. DAT and SERT). Nicotinic cholinoceptors were quantified by [125I]epibatidine autoradiography. Infusion of 6-hydroxydopamine depleted DAT but not SERT labelling in all striatal areas (i.e. caudate-putamen, nucleus accumbens core and shell, olfactory tubercle). The serotonergic neurotoxin 5,7-dihydroxytryptamine depleted SERT and, to a lesser extent, DAT labelling. Both neurotoxins reduced [125I]epibatidine binding in striatal areas. Multiple linear regression analysis showed that these reductions in [125I]epibatidine binding were entirely associated with loss of DAT rather than SERT. The DAT-associated proportion of total [125I]epibatidine binding was 36+/-2% (caudate-putamen), 28+/-3% (accumbens core), 27+/-4% (accumbens shell) and 44+/-5% (olfactory tubercle). Cortical [125I]epibatidine binding was unaltered by 5,7-dihydroxytryptamine lesions that reduced SERT labelling by 46 to 73%. In all brain areas, even small (3.4 to 8.8%) SERT-associated reductions in [125I]epibatidine binding would have been detected as statistically significant. In conclusion, we report the failure to detect nAChRs on 5-HT terminals in extended striatum or cerebral cortex, using a sensitive [125I]epibatidine autoradiographic assay.
Asunto(s)
Compuestos Bicíclicos Heterocíclicos con Puentes , Corteza Cerebral/química , Cocaína/análogos & derivados , Neostriado/química , Proteínas del Tejido Nervioso , Agonistas Nicotínicos , Piridinas , Receptores Nicotínicos/análisis , 5,7-Dihidroxitriptamina/toxicidad , Vías Aferentes/efectos de los fármacos , Vías Aferentes/lesiones , Animales , Autorradiografía , Proteínas Portadoras/análisis , Cocaína/análisis , Dopamina/metabolismo , Proteínas de Transporte de Dopamina a través de la Membrana Plasmática , Radioisótopos de Yodo , Masculino , Haz Prosencefálico Medial/efectos de los fármacos , Haz Prosencefálico Medial/lesiones , Glicoproteínas de Membrana/análisis , Proteínas de Transporte de Membrana/análisis , Neurotoxinas/toxicidad , Núcleo Accumbens/química , Vías Olfatorias/química , Oxidopamina/toxicidad , Radiofármacos , Ratas , Ratas Sprague-Dawley , Serotonina/metabolismo , Serotoninérgicos/toxicidad , Proteínas de Transporte de Serotonina en la Membrana PlasmáticaRESUMEN
Phosphorothioate (PS)-capped phosphodiester (PE) oligodeoxynucleotides (ODNs) were used to determine whether the dopamine-dependent locomotor-stimulant effect of nicotine is mediated via a4 subunit-containing nicotinic receptors. To this end, rats received direct intraventral tegmental area infusion of a4 antisense via osmotic minipump, and their locomotor response to nicotine (0.2 mg/kg, s.c.) was tested. Eight antisense ODNs were screened, but only one inhibited nicotine-induced locomotion. This inhibition was reversible and selective, insofar as basal (saline) activity was unaffected, and a mismatch ODN was without effect. However, antisense treatment also caused sequence-dependent toxic effects, including neuronal degeneration in the ventral tegmental area, dopaminergic denervation, and weight loss. We conclude that despite previous reports, PS-capped PE-ODNs can cause severe neurotoxicity on chronic infusion into brain tissue. Moreover, sequence dependence and temporal reversibility, two generally accepted criteria of antisense action, may sometimes reflect the occurrence of toxic effects and resultant functional compensation.