RESUMO
The dynorphin peptides are the endogenous ligands for the kappa opioid receptor (KOR) and regulate food intake. Administration of dynorphin-A1-13 (DYN) in the paraventricular hypothalamic nucleus (PVN) increases palatable food intake, and this effect is blocked by co-administration of the orexin-A neuropeptide, which is co-released with DYN in PVN from neurons located in the lateral hypothalamus. While PVN administration of DYN increases palatable food intake, whether it increases food-seeking behaviors has yet to be examined. We tested the effects of DYN and norBNI (a KOR antagonist) on the seeking and consumption of sucrose using a progressive ratio (PR) and demand curve (DC) tasks. In PVN, DYN did not alter the sucrose breaking point (BP) in the PR task nor the elasticity or intensity of demand for sucrose in the DC task. Still, DYN reduced the delay in obtaining sucrose and increased licks during sucrose intake in the PR task, irrespective of the co-administration of orexin-A. In PVN, norBNI increased the delay in obtaining sucrose and reduced licks during sucrose intake in the PR task while increasing elasticity without altering intensity of demand in the DC task. However, subcutaneous norBNI reduced the BP for sucrose and increased the delay in obtaining sucrose in the PR task while reducing the elasticity of demand. Together, these data show different effects of systemic and PVN blockade of KOR on food-seeking, consummatory behaviors, and incentive motivation for sucrose and suggest that KOR activity in PVN is necessary but not sufficient to drive seeking behaviors for palatable food.
Assuntos
Dinorfinas , Motivação , Núcleo Hipotalâmico Paraventricular , Receptores Opioides kappa , Receptores Opioides kappa/metabolismo , Dinorfinas/farmacologia , Dinorfinas/metabolismo , Núcleo Hipotalâmico Paraventricular/metabolismo , Núcleo Hipotalâmico Paraventricular/efeitos dos fármacos , Animais , Masculino , Motivação/efeitos dos fármacos , Orexinas , Ratos , Ratos Sprague-Dawley , Naltrexona/farmacologia , Naltrexona/análogos & derivados , Ingestão de Alimentos/efeitos dos fármacos , Ingestão de Alimentos/fisiologia , Ingestão de Alimentos/psicologia , Sacarose , Comportamento Alimentar/efeitos dos fármacos , Comportamento Alimentar/psicologia , Antagonistas de Entorpecentes/farmacologiaRESUMO
The opioid receptors (OR) regulate food intake. Still, despite extensive pre-clinical research, the overall effects and individual contribution of the mu (MOR), kappa (KOR), and delta (DOR) OR subtypes to feeding behaviors and food intake remain unclear. To address this, we conducted a pre-registered systematic search and meta-analysis of rodent dose-response studies to evaluate the impact of central and peripheral administration of non-selective and selective OR ligands on intake, motivation, and choice of food. All studies had a high bias risk. Still, the meta-analysis confirmed the overall orexigenic and anorexigenic effects of OR agonists and antagonists, respectively. Our results support a larger orexigenic role for central MOR agonists among OR subtypes and that peripheral OR antagonists reduce motivation for and intake of preferred foods. In binary food choice studies, peripheral OR agonists selectively increase the intake of fat-preferred foods; in contrast, they did not increase the intake of sweet carbohydrate-preferred foods. Overall, these data support that OR regulation of intake, motivation, and choice is influenced by food macronutrient composition.
Assuntos
Motivação , Receptores Opioides , Analgésicos Opioides/farmacologia , Ingestão de Alimentos , Comportamento Alimentar , Ligantes , Receptores Opioides muRESUMO
The dopamine mesolimbic system is a major circuit involved in controlling goal-directed behaviors. Dopamine D2 receptors (D2R) and kappa opioid receptors (KOR) are abundant Gi protein-coupled receptors in the mesolimbic system. D2R and KOR share several functions in dopamine mesencephalic neurons, such as regulation of dopamine release and uptake, and firing of dopamine neurons. In addition, KOR and D2R modulate each other functioning. This evidence indicates that both receptors functionally interact, however, their colocalization in the mesostriatal system has not been addressed. Immunofluorescent assays were performed in cultured dopamine neurons and adult mice's brain tissue to answer this question. We observed that KOR and D2R are present in similar density in dendrites and soma of cultured dopamine neurons, but in a segregated manner. Interestingly, KOR immunolabelling was observed in the first part of the axon, colocalizing with Ankyrin in 20% of cultured dopamine neurons, indicative that KOR is present in the axon initial segment (AIS) of a group of dopaminergic neurons. In the adult brain, KOR and D2R are also segregated in striatal tissue. While the KOR label is in fiber tracts such as the striatal streaks, corpus callosum, and anterior commissure, D2R is located mainly within the striatum and nucleus accumbens, surrounding fiber tracts. D2R is also localized in some fibers that are mostly different from those positives for KOR. In conclusion, KOR and D2R are present in the soma and dendrites of mesencephalic dopaminergic neurons, but KOR is also found in the AIS of a subpopulation of these neurons.
RESUMO
The orexin peptides promote hedonic intake and other reward behaviors through different brain sites. The opioid dynorphin peptides are co-released with orexin peptides but block their effects on reward in the ventral tegmental area (VTA). We previously showed that in the paraventricular hypothalamic nucleus (PVN), dynorphin and not orexin peptides enhance hedonic intake, suggesting they have brain-site-specific effects. Obesity alters the expression of orexin and dynorphin receptors, but whether their expression across different brain sites is important to hedonic intake is unclear. We hypothesized that hedonic intake is regulated by orexin and dynorphin peptides in PVN and that hedonic intake in obesity correlates with expression of their receptors. Here we show that in mice, injection of DYN-A1-13 (an opioid dynorphin peptide) in the PVN enhanced hedonic intake, whereas in the VTA, injection of OXA (orexin-A, an orexin peptide) enhanced hedonic intake. In PVN, OXA blunted the increase in hedonic intake caused by DYN-A1-13. In PVN, injection of norBNI (opioid receptor antagonist) reduced hedonic intake but a subsequent OXA injection failed to increase hedonic intake, suggesting that OXA activity in PVN is not influenced by endogenous opioid activity. In the PVN, DYN-A1-13 increased the intake of the less-preferred food in a two-food choice task. In obese mice fed a cafeteria diet, orexin 1 receptor mRNA across brain sites involved in hedonic intake correlated with fat preference but not caloric intake. Together, these data support that orexin and dynorphin peptides regulate hedonic intake in an opposing manner with brain-site-specific effects.
Assuntos
Dinorfinas , Núcleo Hipotalâmico Paraventricular , Analgésicos Opioides/metabolismo , Analgésicos Opioides/farmacologia , Animais , Encéfalo/metabolismo , Dinorfinas/metabolismo , Dinorfinas/farmacologia , Camundongos , Obesidade/metabolismo , Orexinas/metabolismoRESUMO
OBJECTIVES: Bone resorption associated to chronic diseases, such as arthritis and periodontitis, results from exacerbated immuno-inflammatory host response that leads to tissue breakdown. The significance of opioid pathways as endogenous modulators of inflammatory events has already been described. Thus, the aim of this work is to determine whether some of the main three opioid receptors are endogenously activated to prevent bone loss during experimentally-induced alveolar bone resorption. DESIGN: This study used an experimental model of alveolar bone resorption induced by ligature in rats. A silk thread was placed around the 2nd maxillary molar of male Wistar rats. In the 3rd, 4th and 5th day after ligation the rats received a local injection of different concentrations of opioid antagonists Cyprodime, Naltrindole, or Nor-binaltorphimine, which specifically block mü, delta and kappa opioid receptors, respectively. In the 7th experimental day, rats were euthanized and their maxillae collected for evaluation of alveolar bone and fiber attachment loss, morphometric counting of osteoclasts and osteoblasts, as well as the levels of cytokines IL-1ß, IFN-γ, and IL-6 by ELISA. RESULTS: Selective antagonism of kappa opioid receptors, but not mü and delta, exacerbated alveolar bone resorption induced by ligature in rats. The increased bone loss associated with higher number of osteoclasts surrounding alveolar bone, although osteoblasts' counting remained unchanged. The concentrations of IL-1ß and IL-6 in periodontal tissues were also significantly higher in the rats treated with the kappa antagonist. CONCLUSION: Inhibiting kappa opioid receptors exacerbates alveolar bone resorption.
Assuntos
Perda do Osso Alveolar , Reabsorção Óssea , Antagonistas de Entorpecentes/efeitos adversos , Periodontite , Receptores Opioides , Animais , Citocinas , Modelos Animais de Doenças , Masculino , Morfinanos , Naltrexona/análogos & derivados , Osteoblastos , Osteoclastos , Ratos , Ratos WistarRESUMO
The strength of goal-oriented behaviors is regulated by midbrain dopamine neurons. Dysfunctions of dopaminergic circuits are observed in drug addiction and obsessive-compulsive disorder. Compulsive behavior is a feature that both disorders share, which is associated to a heightened dopamine neurotransmission. The activity of midbrain dopamine neurons is principally regulated by the homeostatic action of dopamine through D2 receptors (D2R) that decrease the firing of neurons as well as dopamine synthesis and release. Dopamine transmission is also regulated by heterologous neurotransmitter systems such as the kappa opioid system, among others. Much of our current knowledge of the kappa opioid system and its influence on dopamine transmission comes from preclinical animal models of brain diseases. In 1988, using cerebral microdialysis, it was shown that the acute activation of the Kappa Opioid Receptors (KOR) decreases synaptic levels of dopamine in the striatum. This inhibitory effect of KOR opposes to the facilitating influence of drugs of abuse on dopamine release, leading to the proposition of the use of KOR agonists as pharmacological therapy for compulsive drug intake. Surprisingly, 30 years later, KOR antagonists are instead proposed to treat drug addiction. What may have happened during these years that generated this drastic change of paradigm? The collected evidence suggested that the effect of KOR on synaptic dopamine levels is complex, depending on the frequency of KOR activation and timing with other incoming stimuli to dopamine neurons, as well as sex and species differences. Conversely to its acute effect, chronic KOR activation seems to facilitate dopamine neurotransmission and dopamine-mediated behaviors. The opposing actions exerted by acute versus chronic KOR activation have been associated with an initial aversive and a delayed rewarding effect, during the exposure to drugs of abuse. Compulsive behaviors induced by repeated activation of D2R are also potentiated by the sustained co-activation of KOR, which correlates with decreased synaptic levels of dopamine and sensitized D2R. Thus, the time-dependent activation of KOR impacts directly on dopamine levels affecting the tuning of motivated behaviors. This review analyzes the contribution of the kappa opioid system to the dopaminergic correlates of compulsive behaviors.
RESUMO
Kappa-opioid receptors (KOR) control dopamine (DA) levels in the striatum and contribute significantly to the progression of drug addiction. Repeated exposure to psychostimulants has been associated with up-regulated KOR activity and increased DA levels in dorsal striatum. However, it has not been tested if both processes are linked. In this work, we studied if a mechanism mediated by KOR is contributing to the increase in DA levels in the dorsolateral striatum (DLS) after amphetamine (AMPH) sensitization. The AMPH sensitization was assessed after single or repeated once-a-day AMPH injections (1 mg/kg). Only repeated AMPH exposure produced a significant locomotor sensitization. No-net flux microdialysis was used to assess basal DA dialysate, DA extracellular concentration (Cext ), and DA uptake in DLS of anesthetized rats. The role of KOR on DA dynamics in DLS was evaluated by local perfusion (250 µM) and systemic administration (10 mg/kg) of the KOR antagonist nor-binaltorphimine. A significant decrease in DA Cext is observed in the DLS after an AMPH challenge in rats exposed to a single dose of AMPH. The decrease in DA Cext was associated with both a decreased basal DA dialysate and an increased DA uptake. Conversely, the expression of AMPH sensitization was accompanied by a significant increase in DA Cext associated with an increased basal DA dialysate and an attenuation in DA uptake. Both local and systemic administration of nor-binaltorphimine reversed changes in DLS after AMPH pre-treatment. These findings indicate that endogenous KOR system tunes DLS DA dynamics during the progression to AMPH sensitization.
Assuntos
Transtornos Relacionados ao Uso de Anfetaminas/metabolismo , Corpo Estriado/metabolismo , Dopamina/metabolismo , Receptores Opioides kappa/metabolismo , Anfetamina/farmacologia , Animais , Estimulantes do Sistema Nervoso Central/farmacologia , Corpo Estriado/efeitos dos fármacos , Masculino , Ratos , Ratos Sprague-DawleyRESUMO
Alguns estudos sugerem que as vias opioidérgicas centrais parecem desempenhar um papel regulatório no controle da ingestão de água e sal em mamíferos. As ações dos opioides centrais sobre a regulação do controle hidroeletrolítico são mediadas por vários dos subtipos de receptores opioides. O papel dos receptores delta e kappa-opioides centrais neste processo não está adequadamente elucidado sendo necessário mais estudos que o esclareçam. Objetivo: Este estudo investigou o envolvimento dos receptores delta e kappa-opioides centrais no apetite por sódio em ratos depletados deste íon e em rato ativados centralmente com angiotensina. Material e Métodos: Foram utilizados ratos Wistar (270 ± 20 g), submetidos à cirurgia estereotáxica para implante de cânula guia no ventrículo lateral esquerdo (VL), no órgão subfornical (OSF), no núcleo preóptico mediano (MnPO) e no núcleo basolateral da amígdala (BLA). No protocolo de depleção de sódio os animais foram submetidos à injeção subcutânea de furosemida combinada com dieta hipossódica quatro dias após a cirurgia. Neste modelo de estudo os animais receberam injeção intracerebroventricular (i.c.v.) do antagonista delta-opioide naltrindole no quinto dia pós-cirúrgico, nas doses de 5, 10 e 20 nmol/2 μL e do antagonista kappa-opioide, norbinaltorfimina, injetado no OSF, MnPO e BLA, nas doses de 0,5, 1,0 e 2,0 nmol/0,2 μL...
Central opioid pathways seem to have an important role on the control of water and salt intake in mammals, and brain opioid peptides may influence hydroelectrolyte balance through a myriad of actions mediated by distinct opioid receptors. The specific role of central delta and kappa-opioid receptors (DOR and KOR) in this process is far from being fully understood. In the present work, we investigated the role of those receptors in the control of water and salt intake, in sodium-depleted rats and rats with activation central angiotensinergic. Method: Wistar male rats (250 ± 20 g) were used in the experiment after stereotaxic cannulation of the VL left, SFO, MnPO and BLA. To study the effect of the blockade of central DOR and KOR on water and salt intake in rats were sodium depleted by the concomitant use of s.c. injections of furosemide and were kept in hypossodic diet, five days after surgery. In the sixth day, they received i.c.v. injections of a selective delta-opioid receptor antagonist (naltrindole) at the doses of 5, 10 and 20 nmol/2 μL and injections in the SFO, MnPO and BLA of a selective kappa-opioid receptor antagonist (norbinaltorphimine) at the doses of 0.5, 1.0 and 2.0 nmol/0.2 μL...
Assuntos
Animais , Apetite , Apetite/fisiologia , Apetite/imunologia , Receptores Opioides delta/análise , Receptores Opioides delta/classificação , Receptores Opioides delta/isolamento & purificação , Receptores Opioides delta/metabolismo , Receptores Opioides kappa/análise , Receptores Opioides kappa/imunologiaRESUMO
En el presente trabajo se considera la investigación multidisciplinaria sobre Salvia divinorum y sus principios químicos activos con el objeto de valorar si la etnobotánica, la fitoquímica, la psicofarmacología y la neurofarmacología de esta planta psicoactiva y su principal producto químico, la salvinorina A, clarifican sus efectos mentales y sus usos adivinatorios. Esta labor científica ha trascurrido desde el registro inicial de ceremonias y creencias, ha continuado con la identificación botánica, el aislamiento de los principios químicos, la caracterización de los efectos mentales y cerebrales, las posibles aplicaciones terapéuticas y ha llegado a incurrir en el problema mente-cuerpo. Dado que el punto de partida de esta investigación es la transdisciplina de la etnofarmacología, se retoman aquí las creencias tradicionales, los usos rituales y los efectos mentales de esta menta sagrada de los indios mazatecos tal y como fueron registrados durante un proyecto de campo y laboratorio llevado a cabo entre 1973 y 1983. Un brebaje acuoso de hojas maceradas produjo un breve periodo de ligereza cefálica, disforia, sensaciones táctiles y propioceptivas exacerbadas, un sentido de despersonalización, percepción amplificada de sonidos y un aumento de la imaginación visual y auditiva, pero no verdaderas alucinaciones. Posteriormente otros autores describieron efectos similares usando cuestionarios y eventualmente fueron imputados al diterpeno salvinorina-A, pero no es posible explicar los efectos mentales sólo por la potente actividad agonista del receptor kappa a los opioides encontrada para la salvinorina; de allí el enigma psicofarmacológico. Se proponen algunos requerimientos para una clasificación de drogas que alteran cualitativamente el estado de conciencia e incluyen la activación de redes neuronales que necesariamente comprenden diversos sistemas neuroquímicos y módulos nerviosos. Para caracterizar estas redes será necesario emprender un tipo de investigación top-down, es decir el análisis de imágenes cerebrales obtenidas durante la experiencia psicoactiva analizada mediante un método narrativo, lo cual eventualmente podría permitir la exploración de efectos étnicos diferenciales. Como sucede con otras preparaciones que alteran la conciencia, una investigación rigurosa de la psicofarmacología de esta planta y su principio psicoactivo será relevante a empresas académicas tan diversas como el problema mente-cuerpo, la mejor comprensión del éxtasis chamánico y la posible generación de fármacos analgésicos, antidepresivos y moderadores de la drogadicción.
In the present paper, the multidisciplinary research on Salvia divinorum and its chemical principles is analyzed regarding whether the ethnobotany, phytochemistry, psychopharmacology, and neuropharmacology of this sacred psychoactive plant and main principle clarify its experienced effects and divinatory uses. The scientific endeavor traverses from the recorded traditional ceremonies and beliefs, continues with the botanical identification, the isolation of active molecules, the characterization of mental and neural effects, the possible therapeutic applications, and impinges upon the mind-body problem. The departure point of this search is ethnopharmacology, and therefore the traditional beliefs, ritual uses, and mental effects of this Mazatec sacred mint recorded during a 1973-1983 field research project are described. A water potion of crushed leaves produced short-lasting light-headedness, dysphoria, tactile and proprioceptive sensations, a sense of depersonalization, amplified sound perception, and increased visual and auditory imagery, but no actual hallucinations. Similar effects were described using questionnaires and are attributable to the diteprene salvinorin A, but cannot be explained solely by its specific and potent brain kappa-opioid receptor agonist activity. Some requirements for a feasible classification and mechanism of action of consciousness-altering products are proposed and include the activation of neural networks comprising several neurochemical systems. Top-down analyses should be undertaken in order to characterize such neural networks and eventually allowing to explore the differential ethnic effects. As is the case for other consciousness-altering preparations, a careful and encompassing research on this plant and principle can be consequential to academic undertakings ranging from the mind-body problem and a better understanding of shamanic ecstasy, to the potential generation of analgesic, antidepressant, and drug-abuse attenuating products.
RESUMO
Salvia divinorum is a sage endemic to a small region of Mexico and has been traditionally used by the Mazatec Indians for divination and spiritual healing. Recently, it has gained increased popularity as a recreational drug, used by adolescents and young adults as an alternative to marijuana and LSD. Salvinorin A, the major active ingredient of the plant, is considered to be the most potent known hallucinogen of natural origin. This review surveys the current state of knowledge on the neurochemical, pharmacokinetic, and pharmacological properties of salvinorin A, the trends and motivation behind S. divinorum use, and the health problems among users of the plant's products. S. divinorum induces intense, but short-lived, psychedelic-like changes in mood and perception, with concomitant hallucinations and disorientation. Many websites have misinterpreted the limited existing research-based information on the side effects of salvia as evidence for its safety. However, data accumulated over the last few years indicate that potential health risks are associated with the use of S. divinorum, especially by teenagers, users of other substances of abuse, and individuals with underlying psychotic disturbances. Taken together, the data presented in this review point to the need for further basic and clinical studies to create a basis for the development of well-addressed prevention and treatment strategies.
Assuntos
Diterpenos Clerodânicos/química , Alucinógenos/química , Drogas Ilícitas/química , Medicina Tradicional , Salvia , Animais , Diterpenos Clerodânicos/administração & dosagem , Alucinógenos/administração & dosagem , Humanos , Drogas Ilícitas/farmacologia , MéxicoRESUMO
During the past five years, the three-dimensional structures of 14 different G-protein coupled receptors (GPCRs) have been resolved by X-ray crystallography. The most recently published structures, those of the opioid receptors (ORs), are remarkably important in pain modulation, drug addiction, and mood disorders. These structures, confirmed previously proposed key interactions conferring potency and antagonistic properties, including the well-known interaction with Asp138, conserved in all aminergic GPCRs. In addition, crystallization of the opioid receptors highlighted the potential function of the ECL2 and ICL2 loops. We have previously reported a set of potent and selective kappa opioid receptor peptide agonists, of which ff(D-nle)r-NH2 is among the most potent and selective ones. These peptides were identified from the deconvolution of a 6,250,000 tetrapeptide combinatorial library. A derivative of this set is currently the subject of a phase 2 clinical trial in the United States. In this work, we describe comparative molecular modeling studies of kappa-OR peptide agonists with the co-crystallized antagonist, JDTic, and also report structure-activity relationships of 23 tetrapeptides. The overall binding and contact interactions are sound and interactions known to favor selectivity and potency were observed. Additional modeling studies will reveal conformational changes that the kappa-OR undergoes upon binding to these peptide agonists.
Assuntos
Receptores Opioides kappa/metabolismo , Sítios de Ligação , Cristalografia por Raios X , Ligantes , Modelos Moleculares , Peptídeos Cíclicos/química , Peptídeos Cíclicos/metabolismo , Peptídeos Cíclicos/farmacologia , Piperidinas/química , Piperidinas/metabolismo , Piperidinas/farmacologia , Ligação Proteica , Conformação Proteica , Receptores Opioides kappa/agonistas , Receptores Opioides kappa/antagonistas & inibidores , Receptores Opioides kappa/química , Relação Estrutura-Atividade , Tetra-Hidroisoquinolinas/química , Tetra-Hidroisoquinolinas/metabolismo , Tetra-Hidroisoquinolinas/farmacologiaRESUMO
The periaqueductal gray (PAG) has been reported to be a location for opioid regulation of pain and a potential site for behavioral selection in females. Opioid-mediated behavioral and physiological responses differ according to the activity of opioid receptor subtypes. The present study investigated the effects of the peripheral injection of the kappa-opioid receptor agonist U69593 into the dorsal subcutaneous region of animals on maternal behavior and on Oprk1 gene activity in the PAG of female rats. Female Wistar rats weighing 200-250 g at the beginning of the study were randomly divided into 2 groups for maternal behavior and gene expression experiments. On day 5, pups were removed at 7:00 am and placed in another home cage that was distant from their mother. Thirty minutes after removing the pups, the dams were treated with U69593 (0.15 mg/kg, sc) or 0.9% saline (up to 1 mL/kg) and after 30 min were evaluated in the maternal behavior test. Latencies in seconds for pup retrieval, grouping, crouching, and full maternal behavior were scored. The results showed that U69593 administration inhibited maternal behavior (P < 0.05) because a lower percentage of kappa group dams showed retrieval of first pup, retrieving all pups, grouping, crouching and displaying full maternal behavior compared to the saline group. Opioid gene expression was evaluated using real-time reverse-transcription polymerase chain reaction (RT-PCR). A single injection of U69593 increased Oprk1 PAG expression in both virgin (P < 0.05) and lactating female rats (P < 0.01), with no significant effect on Oprm1 or Oprd1 gene activity. Thus, the expression of kappa-opioid receptors in the PAG may be modulated by single opioid receptor stimulation and behavioral meaningful opioidergic transmission in the adult female might occur simultaneously to specific changes in gene expression of kappa-opioid receptor subtype. This is yet another alert for the complex role of the opioid ...