RESUMO
BACKGROUND AND PURPOSE: The endocannabinoids anandamide and 2-arachidonoylglycerol (2-AG) bind to CB1 and CB2 cannabinoid receptors in the brain and modulate the mesolimbic dopaminergic pathway. This neurocircuitry is engaged by psychostimulant drugs, including cocaine. Although CB1 receptor antagonism and CB2 receptor activation are known to inhibit certain effects of cocaine, they have been investigated separately. Here, we tested the hypothesis that there is a reciprocal interaction between CB1 receptor blockade and CB2 receptor activation in modulating behavioural responses to cocaine. EXPERIMENTAL APPROACH: Male Swiss mice received i.p. injections of cannabinoid-related drugs followed by cocaine, and were then tested for cocaine-induced hyperlocomotion, c-Fos expression in the nucleus accumbens and conditioned place preference. Levels of endocannabinoids after cocaine injections were also analysed. KEY RESULTS: The CB1 receptor antagonist, rimonabant, and the CB2 receptor agonist, JWH133, prevented cocaine-induced hyperlocomotion. The same results were obtained by combining sub-effective doses of both compounds. The CB2 receptor antagonist, AM630, reversed the inhibitory effects of rimonabant in cocaine-induced hyperlocomotion and c-Fos expression in the nucleus accumbens. Selective inhibitors of anandamide and 2-AG hydrolysis (URB597 and JZL184, respectively) failed to modify this response. However, JZL184 prevented cocaine-induced hyperlocomotion when given after a sub-effective dose of rimonabant. Cocaine did not change brain endocannabinoid levels. Finally, CB2 receptor blockade reversed the inhibitory effect of rimonabant in the acquisition of cocaine-induced conditioned place preference. CONCLUSION AND IMPLICATIONS: The present data support the hypothesis that CB1 and CB2 receptors work in concert with opposing functions to modulate certain addiction-related effects of cocaine. LINKED ARTICLES: This article is part of a themed section on 8th European Workshop on Cannabinoid Research. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.10/issuetoc.
Assuntos
Ácidos Araquidônicos/metabolismo , Cocaína/farmacologia , Endocanabinoides/metabolismo , Glicerídeos/metabolismo , Alcamidas Poli-Insaturadas/metabolismo , Receptor CB1 de Canabinoide/antagonistas & inibidores , Receptor CB2 de Canabinoide/agonistas , Recompensa , Animais , Comportamento Animal/efeitos dos fármacos , Agonistas de Receptores de Canabinoides/farmacologia , Antagonistas de Receptores de Canabinoides/farmacologia , Condicionamento Clássico , Masculino , Camundongos , Atividade Motora/efeitos dos fármacos , Ligação Proteica , Proteínas Proto-Oncogênicas c-fos/metabolismoRESUMO
The neural substrates and mechanisms mediating the antinociceptive effects of the endogenous bioactive lipid, N-palmitoylethanolamide (PEA), require further investigation. We investigated the effects of exogenous PEA administration into the anterior cingulate cortex (ACC), an important brain region linked with cognitive and affective modulation of pain, on formalin-evoked nociceptive behaviour in rats. Potential involvement of peroxisome proliferator-activated receptor isoforms (PPAR) α and γ or endocannabinoid-mediated entourage effects at cannabinoid1 (CB1) receptors or transient receptor potential subfamily V member 1 (TRPV1) in mediating the effects of PEA was also investigated. Intra-ACC administration of PEA significantly attenuated the first and early second phases of formalin-evoked nociceptive behaviour. This effect was attenuated by the CB1 receptor antagonist AM251, but not by the PPARα antagonist GW6471, the PPARγ antagonist GW9662, or the TRPV1 antagonist 5'-iodo resiniferatoxin. All antagonists, administered alone, significantly reduced formalin-evoked nociceptive behaviour, suggesting facilitatory/permissive roles for these receptors in the ACC in inflammatory pain. Post-mortem tissue analysis revealed a strong trend for increased levels of the endocannabinoid anandamide in the ACC of rats that received intra-ACC PEA. Expression of c-Fos, a marker of neuronal activity, was significantly reduced in the basolateral nucleus of the amygdala, but not in the central nucleus of the amygdala, the rostral ventromedial medulla or the dorsal horn of the spinal cord. In conclusion, these data indicate that PEA in the ACC can reduce inflammatory pain-related behaviour, possibly via AEA-induced activation of CB1 receptors and associated modulation of neuronal activity in the basolateral amygdala.
Assuntos
Etanolaminas/farmacologia , Etanolaminas/uso terapêutico , Giro do Cíngulo/efeitos dos fármacos , Dor/tratamento farmacológico , Ácidos Palmíticos/farmacologia , Ácidos Palmíticos/uso terapêutico , Receptor CB1 de Canabinoide/metabolismo , Amidas , Animais , Anti-Inflamatórios não Esteroides/farmacologia , Anti-Inflamatórios não Esteroides/uso terapêutico , Antagonistas de Receptores de Canabinoides/farmacologia , Antagonistas de Receptores de Canabinoides/uso terapêutico , Estudos de Coortes , Modelos Animais de Doenças , Diterpenos/uso terapêutico , Fixadores/toxicidade , Formaldeído/toxicidade , Giro do Cíngulo/fisiologia , Locomoção/efeitos dos fármacos , Masculino , Microdissecção , Microinjeções , PPAR gama/administração & dosagem , Dor/induzido quimicamente , Medição da Dor , Proteínas Proto-Oncogênicas c-fos/genética , Proteínas Proto-Oncogênicas c-fos/metabolismo , Ratos , Ratos Sprague-Dawley , Receptor CB1 de Canabinoide/genéticaRESUMO
In recent years, it has become evident that Parkinson's disease is associated with a self-sustaining cycle of neuroinflammation and neurodegeneration, with dying neurons activating microglia, which, once activated, can release several factors that kill further neurons. One emerging pharmacological target that has the potential to break this cycle is the microglial CB2 receptor which, when activated, can suppress microglial activity and reduce their neurotoxicity. However, very little is known about CB2 receptor expression in animal models of Parkinson's disease which is essential for valid preclinical assessment of the anti-Parkinsonian efficacy of drugs targeting the CB2 receptor. Therefore, the aim of this study was to investigate and compare the changes that occur in CB2 receptor expression in environmental and inflammation-driven models of Parkinson's disease. To do so, male Sprague Dawley rats were given unilateral, intra-striatal injections of the Parkinson's disease-associated agricultural pesticide, rotenone, or the viral-like inflammagen, polyinosinic:polycytidylic acid (Poly (I:C)). Animals underwent behavioural testing for motor dysfunction on days 7, 14 and 28 post-surgery, and were sacrificed on days 1, 4, 14 and 28. Changes in the endocannabinoid system and neuroinflamamtion were investigated by qRT-PCR, liquid chromatography-mass spectrometry and immunohistochemistry. After injection of rotenone or Poly (I:C) into the rat striatum, we found that expression of the CB2 receptor was significantly elevated in both models, and that this increase correlated significantly with an increase in microglial activation in the rotenone model. Interestingly, the increase in CB2 receptor expression in the inflammation-driven Poly (I:C) model was significantly more pronounced than that in the neurotoxic rotenone model. Thus, this study has shown that CB2 receptor expression is dysregulated in animal models of Parkinson's disease, and has also revealed significant differences in the level of dysregulation between the models themselves. This study indicates that these models may be useful for further investigation of the CB2 receptor as a target for anti-inflammatory disease modification in Parkinson's disease.
Assuntos
Meio Ambiente , Doença de Parkinson/etiologia , Doença de Parkinson/metabolismo , Receptor CB2 de Canabinoide/metabolismo , Regulação para Cima/fisiologia , Análise de Variância , Animais , Antígeno CD11b/metabolismo , Cromatografia Líquida de Alta Pressão , Modelos Animais de Doenças , Lateralidade Funcional/efeitos dos fármacos , Lateralidade Funcional/fisiologia , Inseticidas/toxicidade , Masculino , Atividade Motora/efeitos dos fármacos , Poli I-C/toxicidade , RNA Mensageiro/metabolismo , Ratos , Ratos Sprague-Dawley , Receptor CB2 de Canabinoide/genética , Rotenona/toxicidade , Espectrometria de Massas em Tandem , Fatores de Tempo , Regulação para Cima/efeitos dos fármacosRESUMO
The cannabinoid CB2 receptor has recently emerged as a potential anti-inflammatory target to break the self-sustaining cycle of neuroinflammation and neurodegeneration that is associated with neurodegenerative diseases. However, in order to facilitate the development of cannabinoid drugs for neurodegenerative disease, the changes that occur in the endocannabinoid system in response to different neurodegenerative triggers needs to be elucidated. Therefore, the aim of this study was to investigate and compare the changes that occur in the endocannabinoid system in neurotoxic and inflammation-driven models of Parkinson's disease. To do so, male Sprague Dawley rats were given unilateral, intra-striatal injections of the dopaminergic neurotoxin, 6-hydroxydopamine, or the bacterial inflammagen, lipopolysaccharide (LPS). Animals underwent behavioural testing for motor dysfunction on Days 7, 14 and 28 post-surgery, and were sacrificed on Days 1, 4, 14 and 28. Changes in the endocannabinoid system were investigated by qRT-PCR, liquid chromatography-mass spectrometry and immunohistochemistry. After injection of 6-hydroxydopamine or LPS into the rat striatum, we found that expression of the CB2 receptor was significantly elevated in both models, and that this increase correlated significantly with an increase in microglial activation. Interestingly, the increase in CB2 receptor expression in the inflammation-driven model was significantly more pronounced than that in the neurotoxic model. Moreover, endocannabinoid levels were also elevated in the LPS model but not the 6-hydroxydopamine model. Thus, this study has shown that the endocannabinoid system is dysregulated in animal models of Parkinson's disease, and has also revealed significant differences in the level of dysregulation between the models themselves. This study indicates that targeting the CB2 receptor may represent a viable target for anti-inflammatory disease modification in Parkinson's disease.
Assuntos
Doença de Parkinson/metabolismo , Receptor CB2 de Canabinoide/metabolismo , Animais , Corpo Estriado/metabolismo , Modelos Animais de Doenças , Endocanabinoides/metabolismo , Inflamação/metabolismo , Masculino , Degeneração Neural/metabolismo , Ratos Sprague-Dawley , Receptor CB1 de Canabinoide/metabolismo , Substância Negra/metabolismo , Regulação para CimaRESUMO
Background and aims The clinical management of chronic neuropathic pain remains a global health challenge. Current treatments are either ineffective, or associated with unwanted side-effects. The development of effective, safe therapies requires the identification of novel therapeutic targets using clinically relevant animal models of neuropathic pain. Peroxisome proliferator activated receptor alpha (PPARα), is a member of the nuclear hormone family of transcription factors, which is widely distributed in the peripheral and central nervous systems. Pharmacological studies report antinociceptive effects of PPARα agonists following systemic administration in rodent models of neuropathic pain, however the neuronal mechanisms and sites of action mediating these effects are unclear. The aim of this study was to investigate the effects of systemic administration of the synthetic PPARα agonist, WY-14643 on mechanically-evoked responses of spinal cord dorsal horn wide dynamic range (WDR) neurones in the spinal nerve ligated (SNL) model of neuropathic pain in rats. In addition, comparative molecular analysis of mRNA coding for PPARα and PPARα protein expression in the spinal cord of sham-operated and neuropathic rats was performed. Methods Lumbar L5-L6 spinal nerve ligation was performed in male Sprague-Dawley rats (110-130 g) under isoflurane anaesthesia. Sham controls underwent similar surgical conditions, but without ligation of the L5-L6 spinal nerves. Hindpaw withdrawal thresholds were measured on the day of surgery -day 0, and on days- 2, 4, 7, 10 and 14 post-surgery. At day 14 extracellular single-unit recordings of spinal (WDR) dorsal horn neurons were performed in both sham and SNL neuropathic rats under anaesthesia. The effects of intraperitoneal (i.p.) administration of WY-14643 (15 and 30 mg/kg) or vehicle on evoked responses of WDR neurons to punctate mechanical stimulation of the peripheral receptive field of varying bending force (8-60 g) were recorded. In a separate cohort of SNL and sham neuropathic rats, the expression of mRNA coding for PPARα and protein expression in the ipsilateral and contralateral spinal cord was determined using quantitative real time polymerase chain reaction (qRT-PCR) and western blotting techniques respectively. Results WY-14643 (15 and 30mg/kg i.p.) rapidly attenuated mechanically evoked (8, 10 and 15g) responses of spinal WDR neurones in SNL, but not sham-operated rats. Molecular analysis revealed significantly increased PPARα protein, but not mRNA, expression in the ipsilateral spinal cord of SNL, compared to the contralateral side in SNL rats. There were no changes in PPARα mRNA or protein expression in the sham controls. Conclusion The observation that levels of PPARα protein were increased in ipsilateral spinal cord of neuropathic rats supports a contribution of spinal sites of action mediating the effects of systemic WY-14643. Our data suggests that the inhibitory effects of a PPARα agonist on spinal neuronal responses may account, at least in part, for their analgesic effects of in neuropathic pain. Implication Selective activation of PPARα in the spinal cord may be therapeutically relevant for the treatment of neuropathic pain.