RESUMO
The study of the astrocytic contribution to brain functions has been growing in popularity in the neuroscience field. In the last years, and especially since the demonstration of the involvement of astrocytes in synaptic functions, the astrocyte field has revealed multiple functions of these cells that seemed inconceivable not long ago. In parallel, cannabinoid investigation has also identified different ways by which cannabinoids are able to interact with these cells, modify their functions, alter their communication with neurons and impact behavior. In this review, we will describe the expression of different endocannabinoid system members in astrocytes. Moreover, we will relate the latest findings regarding cannabinoid modulation of some of the most relevant astroglial functions, namely calcium (Ca2+ ) dynamics, gliotransmission, metabolism, and inflammation.
Assuntos
Astrócitos , Canabinoides , Astrócitos/metabolismo , Endocanabinoides/metabolismo , Neurônios/metabolismo , Cálcio/metabolismo , Sinalização do Cálcio/fisiologiaRESUMO
The development of tolerance and drug dependence limit the clinical application of opioids for the treatment of severe pain. Glucocorticoid receptors (GRs) are among molecular substrates involved in these processes. Most studies focus on the role of neuronal GR, while the involvement of GR on glial cells is not fully understood. To address this issue, we used a transgenic model of conditional GR knockout mice, targeted to connexin 30-expressing astrocytes, treated with repeated doses of morphine. We observed no difference between control mice and astrocytic GR knockouts in the development of antinociceptive tolerance. Nevertheless, when animals were subjected to precipitated withdrawal, knockouts presented some attenuated symptoms, including jumping. Taken together, our data suggest that hippocampal and spinal astrocytic GRs appear to be involved in opioid withdrawal, and drugs targeting the GR may relieve some symptoms of morphine withdrawal without influencing its antinociceptive properties.
Assuntos
Dependência de Morfina , Síndrome de Abstinência a Substâncias , Analgésicos Opioides , Animais , Astrócitos , Camundongos , Camundongos Knockout , Morfina , Receptores de GlucocorticoidesRESUMO
The expression of the Calcium/Calmodulin-Dependent Protein Kinase I gamma (encoded by the Camk1g gene) depends on the activation of glucocorticoid receptors (GR) and is strongly regulated by stress. Since Camk1g is primarily expressed in neuronal cells of the limbic system in the brain, we hypothesized that it could be involved in signaling mechanisms that underlie the adaptive or maladaptive responses to stress. Here, we find that restraint-induced stress and the GR agonist dexamethasone robustly increase the expression of Camk1g in neurons of the amygdalar nuclei in the mouse brain. To assess the functional role of Camk1g expression, we performed a virally induced knock-down of the transcript. Mice with bilateral amygdala-specific Camk1g knock-down showed increased anxiety-like behaviors in the light-dark box, and an increase in freezing behavior after fear-conditioning, but normal spatial working memory during exploration of a Y-maze. Thus, we confirm that Camk1g is a neuron-specific GR-regulated transcript, and show that it is specifically involved in behaviors related to anxiety, as well as responses conditioned by aversive stimuli.
Assuntos
Núcleo Central da Amígdala , Glucocorticoides , Camundongos , Animais , Glucocorticoides/farmacologia , Núcleo Central da Amígdala/metabolismo , Receptores de Glucocorticoides/genética , Receptores de Glucocorticoides/metabolismo , Cálcio , Proteína Quinase Tipo 1 Dependente de Cálcio-Calmodulina/metabolismo , Ansiedade/metabolismo , Dexametasona/farmacologia , Comportamento AnimalRESUMO
Chronic exposure to opioids induces adaptations in brain function that lead to the formation of the behavioral and physiological symptoms of drug dependence and addiction. Animal models commonly used to test these symptoms typically last less than two weeks, which is presumably too short to observe the alterations in the brain that accompany drug addiction. Here, we analyzed the phenotypic and molecular effects of nearly lifelong morphine or saccharin intake in C57BL/6J mice. We used multiple paradigms to evaluate the symptoms of compulsive drug intake: a progressive ratio schedule, intermittent access and a schedule involving a risk of punishment were programmed into an automated IntelliCage system. Gene expression profiles were evaluated in the striatum using whole-genome microarrays and further validated using quantitative polymerase chain reaction in the striatum and the prefrontal cortex. Mice voluntary self-administering morphine showed addiction-related behavioral pattern that included: higher motivation to work for a drug reward, increased reward seeking and increased craving. The analysis of molecular changes revealed a tolerance effect in the transcriptional response to morphine injection (20 mg/kg, ip), as well as some long-lasting alterations in gene expression profiles between the analyzed groups of animals. Interestingly, among the morphine-drinking animals, certain transcriptional profiles were found to be associated with alterations in behavior. In conclusion, our model represents a novel approach for investigating the behavioral and molecular mechanisms underlying opioid addiction. Prolonged morphine intake caused adaptive processes in the brain that manifested as altered behavior and transcriptional sensitivity to opioids.
Assuntos
Analgésicos Opioides/farmacologia , Comportamento Animal/efeitos dos fármacos , Encéfalo/efeitos dos fármacos , Redes Reguladoras de Genes/efeitos dos fármacos , Transtornos Relacionados ao Uso de Opioides/fisiopatologia , Analgésicos Opioides/administração & dosagem , Animais , Modelos Animais de Doenças , Feminino , Camundongos , Camundongos Endogâmicos C57BL , AutoadministraçãoRESUMO
Emotions and behavior can be affected by social chemosignals from conspecifics. For instance, olfactory signals from stressed individuals induce stress-like physiological and synaptic changes in naïve partners. Direct stress also alters cognition, but the impact of socially transmitted stress on memory processes is currently unknown. Here we show that exposure to chemosignals produced by stressed individuals is sufficient to impair memory retrieval in unstressed male mice. This requires astrocyte control of information in the olfactory bulb mediated by mitochondria-associated CB1 receptors (mtCB1). Targeted genetic manipulations, in vivo Ca2+ imaging and behavioral analyses reveal that mtCB1-dependent control of mitochondrial Ca2+ dynamics is necessary to process olfactory information from stressed partners and to define their cognitive consequences. Thus, olfactory bulb astrocytes provide a link between social odors and their behavioral meaning.
Assuntos
Astrócitos , Cognição , Odorantes , Bulbo Olfatório , Estresse Psicológico , Animais , Masculino , Astrócitos/metabolismo , Bulbo Olfatório/metabolismo , Camundongos , Cognição/fisiologia , Mitocôndrias/metabolismo , Receptor CB1 de Canabinoide/metabolismo , Camundongos Endogâmicos C57BL , Cálcio/metabolismo , Comportamento Social , Memória/fisiologia , Olfato/fisiologia , Comportamento Animal/fisiologiaRESUMO
Corticosteroid-mediated stress responses require the activation of complex brain circuits involving mitochondrial activity, but the underlying cellular and molecular mechanisms are scantly known. The endocannabinoid system is implicated in stress coping, and it can directly regulate brain mitochondrial functions via type 1 cannabinoid (CB1) receptors associated with mitochondrial membranes (mtCB1). In this study, we show that the impairing effect of corticosterone in the novel object recognition (NOR) task in mice requires mtCB1 receptors and the regulation of mitochondrial calcium levels in neurons. Different brain circuits are modulated by this mechanism to mediate the impact of corticosterone during specific phases of the task. Thus, whereas corticosterone recruits mtCB1 receptors in noradrenergic neurons to impair NOR consolidation, mtCB1 receptors in local hippocampal GABAergic interneurons are required to inhibit NOR retrieval. These data reveal unforeseen mechanisms mediating the effects of corticosteroids during different phases of NOR, involving mitochondrial calcium alterations in different brain circuits.
Assuntos
Neurônios Adrenérgicos , Corticosterona , Camundongos , Animais , Corticosterona/farmacologia , Receptores de Canabinoides , Cálcio , Mitocôndrias , Endocanabinoides , Receptor CB1 de Canabinoide , Hipocampo/fisiologiaRESUMO
Cannabinoids reduce tremor associated with motor disorders induced by injuries and neurodegenerative disease. Here we show that this effect is mediated by cannabinoid receptors on astrocytes in the ventral horn of the spinal cord, where alternating limb movements are initiated. We first demonstrate that tremor is reduced in a mouse model of essential tremor after intrathecal injection of the cannabinoid analog WIN55,212-2. We investigate the underlying mechanism using electrophysiological recordings in spinal cord slices and show that endocannabinoids released from depolarized interneurons activate astrocytic cannabinoid receptors, causing an increase in intracellular Ca2+, subsequent release of purines and inhibition of excitatory neurotransmission. Finally, we show that the anti-tremor action of WIN55,212-2 in the spinal cords of mice is suppressed after knocking out CB1 receptors in astrocytes. Our data suggest that cannabinoids reduce tremor via their action on spinal astrocytes.
Assuntos
Astrócitos/metabolismo , Tremor Essencial/metabolismo , Interneurônios/metabolismo , Receptores de Canabinoides/metabolismo , Medula Espinal/metabolismo , Animais , Astrócitos/efeitos dos fármacos , Benzoxazinas/farmacologia , Agonistas de Receptores de Canabinoides/farmacologia , Modelos Animais de Doenças , Interneurônios/efeitos dos fármacos , Camundongos , Morfolinas/farmacologia , Naftalenos/farmacologia , Medula Espinal/efeitos dos fármacos , Transmissão Sináptica/efeitos dos fármacos , Transmissão Sináptica/fisiologiaRESUMO
To date, neurons have been the primary focus of research on the role of glucocorticoids in the regulation of brain function and pathological behaviors, such as addiction. Astrocytes, which are also glucocorticoid-responsive, have been recently implicated in the development of drug abuse, albeit through as yet undefined mechanisms. Here, using a spectrum of tools (whole-transcriptome profiling, viral-mediated RNA interference in vitro and in vivo, behavioral pharmacology and electrophysiology), we demonstrate that astrocytes in the nucleus accumbens (NAc) are an important locus of glucocorticoid receptor (GR)-dependent transcriptional changes that regulate rewarding effects of morphine. Specifically, we show that targeted knockdown of the GR in the NAc astrocytes enhanced conditioned responses to morphine, with a concomitant inhibition of morphine-induced neuronal excitability and plasticity. Interestingly, GR knockdown did not influence sensitivity to cocaine. Further analyses revealed GR-dependent regulation of astroglial metabolism. Notably, GR knockdown inhibited induced by glucocorticoids lactate release in astrocytes. Finally, lactate administration outbalanced conditioned responses to morphine in astroglial GR knockdown mice. These findings demonstrate a role of GR-dependent regulation of astrocytic metabolism in the NAc and a key role of GR-expressing astrocytes in opioid reward processing.
Assuntos
Analgésicos Opioides/farmacologia , Astrócitos/metabolismo , Condicionamento Psicológico/fisiologia , Ácido Láctico/metabolismo , Morfina/farmacologia , Receptores de Glucocorticoides/metabolismo , Animais , Astrócitos/efeitos dos fármacos , Células Cultivadas , Condicionamento Psicológico/efeitos dos fármacos , Camundongos , Camundongos Endogâmicos C57BL , Camundongos TransgênicosRESUMO
Novelty- and sensation-seeking behaviors induce activity of the brain reward system and are associated with increased susceptibility to drug abuse. Endogenous opioids have been implicated in reward-related behavior; however, the involvement of specific opioid receptors in the mechanism of sensation seeking is unknown. Here, we show that selective inhibition of opioid receptors reduce operant sensation seeking in mice. Administration of naltrexone (a nonselective opioid antagonist) reduced instrumental responding for sensory stimuli at one of the tested doses (2 mg/kg). More robust effects were observed in the case of cyprodime, a selective µ opioid receptor antagonist, which reduced instrumental responses by â¼50% at doses of 0.5 mg/kg and larger. Conversely, selective δ and κ receptor antagonists (naltrindole and nor-binaltorphimine, respectively) had no effect on sensation-seeking behavior. Importantly, while naltrexone produces aversion in the conditioned place preference test, cyprodime had no such effect. Therefore, reduced instrumental responding was not correlated with aversive effects of the opioid antagonists. In conclusion, our results revealed a novel mechanism of action of selective opioid receptors antagonists, which may have relevance for their efficacy in the treatment of drug abuse.
Assuntos
Encéfalo/efeitos dos fármacos , Condicionamento Operante/efeitos dos fármacos , Comportamento Exploratório/efeitos dos fármacos , Antagonistas de Entorpecentes/farmacologia , Animais , Comportamento Apetitivo/efeitos dos fármacos , Comportamento Apetitivo/fisiologia , Encéfalo/metabolismo , Condicionamento Operante/fisiologia , Relação Dose-Resposta a Droga , Comportamento Exploratório/fisiologia , Masculino , Camundongos Endogâmicos C57BL , Morfinanos/farmacologia , Motivação/efeitos dos fármacos , Motivação/fisiologia , Atividade Motora/efeitos dos fármacos , Atividade Motora/fisiologia , Naltrexona/análogos & derivados , Naltrexona/farmacologia , Distribuição Aleatória , Receptores Opioides/metabolismo , Receptores Opioides mu/metabolismo , RecompensaRESUMO
BACKGROUND AND PURPOSE: The concept of opioid ligands biased towards the G protein pathway with minimal recruitment of ß-arrestin-2 is a promising approach for the development of novel, efficient, and potentially nonaddictive opioid therapeutics. A recently discovered biased µ-opioid receptor agonist, PZM21, showed analgesic effects with reduced side effects. Here, we aimed to further investigate the behavioural and biochemical properties of PZM21. EXPERIMENT APPROACH: We evaluated antinociceptive effects of systemic and intrathecal PZM21 administration. Its addiction-like properties were determined using several behavioural approaches: conditioned place preference, locomotor sensitization, precipitated withdrawal, and self-administration. Also, effects of PZM21 on morphine-induced antinociception, tolerance, and reward were assessed. Effects of PZM21 on striatal release of monoamines were evaluated using brain microdialysis. KEY RESULTS: PZM21 caused long-lasting dose-dependent antinociception. It did not induce reward- and reinforcement-related behaviour; however, its repeated administration led to antinociceptive tolerance and naloxone-precipitated withdrawal symptoms. Pretreatment with PZM21 enhanced morphine-induced antinociception and attenuated the expression of morphine reward. In comparison to morphine, PZM21 administration induced a moderate release of dopamine and a robust release of 5-HT in the striatum. CONCLUSIONS AND IMPLICATIONS: PZM21 exhibited antinociceptive efficacy, without rewarding or reinforcing properties. However, its clinical application may be restricted, as it induces tolerance and withdrawal symptoms. Notably, its ability to diminish morphine reward implies that PZM21 may be useful in treatment of opioid use disorders.
Assuntos
Analgésicos Opioides/farmacologia , Comportamento Animal/efeitos dos fármacos , Locomoção/efeitos dos fármacos , Morfina/antagonistas & inibidores , Tiofenos/farmacologia , Ureia/análogos & derivados , Analgésicos Opioides/administração & dosagem , Analgésicos Opioides/síntese química , Animais , Relação Dose-Resposta a Droga , Sistemas de Liberação de Medicamentos , Injeções Intravenosas , Injeções Espinhais , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Morfina/farmacologia , Ratos , Ratos Sprague-Dawley , Ratos Wistar , Relação Estrutura-Atividade , Tiofenos/administração & dosagem , Tiofenos/síntese química , Ureia/administração & dosagem , Ureia/síntese química , Ureia/farmacologiaRESUMO
Stress elicits the release of glucocorticoids (GCs) that regulate energy metabolism and play a role in emotional memory. Astrocytes express glucocorticoid receptors (GR), but their contribution to cognitive effects of GC's action in the brain is unknown. To address this question, we studied how astrocyte-specific elimination of GR affects animal behavior known to be regulated by stress. Mice with astrocyte-specific ablation of GR presented impaired aversive memory expression in two different paradigms of Pavlovian learning: contextual fear conditioning and conditioned place aversion. These mice also displayed compromised regulation of genes encoding key elements of the glucose metabolism pathway upon GR stimulation. In particular, we identified that the glial, but not the neuronal isoform of a crucial stress-response molecule, Sgk1, undergoes GR-dependent regulation in vivo and demonstrated the involvement of SGK1 in regulation of glucose uptake in astrocytes. Together, our results reveal astrocytes as a central element in GC-dependent formation of aversive memory and suggest their relevance for stress-induced alteration of brain glucose metabolism. Consequently, astrocytes should be considered as a cellular target of therapies of stress-induced brain diseases.