Time-Course of Alterations in the Endocannabinoid System after Viral-Mediated Overexpression of α-Synuclein in the Rat Brain

Since the discovery of α-synuclein as the major component in Lewy bodies, research into this protein in the context of Parkinson’s disease pathology has been exponential. Cannabinoids are being investigated as potential therapies for Parkinson’s disease from numerous aspects, but still little is known about the links between the cannabinoid system and the pathogenic α-synuclein protein; understanding these links will be necessary if cannabinoid therapies are to reach the clinic in the future. Therefore, the aim of this study was to investigate the time-course of alterations in components of the endocannabinoid system after viral-mediated α-synuclein overexpression in the rat brain. Rats were given unilateral intranigral injections of AAV-GFP or AAV-α-synuclein and sacrificed 4, 8 and 12 weeks later for qRT-PCR and liquid chromatography–mass spectrometry analyses of the endocannabinoid system, in addition to histological visualization of α-synuclein expression along the nigrostriatal pathway. As anticipated, intranigral delivery of AAV-α-synuclein induced widespread overexpression of human α-synuclein in the nigrostriatal pathway, both at the mRNA level and the protein level. However, despite this profound α-synuclein overexpression, we detected no differences in CB1 or CB2 receptor expression in the nigrostriatal pathway; however, interestingly, there was a reduction in the expression of neuroinflammatory markers. Furthermore, there was a reduction in the levels of the endocannabinoid 2-AG and the related lipid immune mediator OEA at week 12 post-surgery, indicating that α-synuclein overexpression triggers dysregulation of the endocannabinoid system. Although this research does show that the endocannabinoid system is impacted by α-synuclein, further research is necessary to more comprehensively understand the link between the cannabinoid system and the α-synuclein aspect of Parkinson’s disease pathology in order for cannabinoid-based therapies to be feasible for the treatment of this disease in the coming years.

Components of the Endogenous Cannabinoid System as Potential Biomarkers for Interstitial Cystitis/Bladder Pain Syndrome

Interstitial cystitis/bladder pain syndrome (IC/BPS) is a chronic condition causing bladder pressure and pain. The condition is of unknown etiology and is often accompanied by other symptoms, including chronic pelvic pain, increased urinary urgency, and frequency. There is no definitive diagnosis for IC/BPS, and treatment options are currently limited to physical therapy and medications to help alleviate symptoms. The endogenous cannabinoid system (ECS) is an important regulator of numerous physiological systems, including the urinary system. Modulations of the ECS have been shown to be beneficial for IC/BPS-associated pain and inflammation in rodents. As an attempt to identify potential biomarkers for IC/BPS, we reviewed experimental studies where the components of the ECS have been quantified in experimental models of IC/BPS. Further investigations using well-defined animal models and patients’ data are required to obtain stronger evidence regarding the potential for ECS components to be definitive biomarkers for IC/BPS.

Cannabinoid receptor 1 expression is higher in muscle of old vs. young males, and increases upon resistance exercise in older adults

Aged skeletal muscle undergoes metabolic and structural alterations eventually resulting in a loss of muscle strength and mass, i.e. age-related sarcopenia. Therefore, novel targets for muscle growth purposes in elderly are needed. Here, we explored the role of the cannabinoid system in muscle plasticity through the expression of muscle cannabinoid receptors (CBs) in young and old humans. The CB1 expression was higher (+ 25%; p = 0.04) in muscle of old (≥ 65 years) vs. young adults (20–27 years), whereas CB2 was not differently expressed. Furthermore, resistance exercise tended to increase the CB1 (+ 11%; p = 0.055) and CB2 (+ 37%; p = 0.066) expression in muscle of older adults. Interestingly, increases in the expression of CB2 following resistance exercise positively correlated with changes in key mechanisms of muscle homeostasis, such as catabolism (FOXO3a) and regenerative capacity (Pax7, MyoD). This study for the first time shows that CB1 is differentially expressed with aging and that changes in CB2 expression upon resistance exercise training correlate with changes in mediators that play a central role in muscle plasticity. These data confirm earlier work in cells and mice showing that the cannabinoid system might orchestrate muscle growth, which is an incentive to further explore CB-based strategies that might counteract sarcopenia.

The Effects of Repeated Morphine Treatment on the Endogenous Cannabinoid System in the Ventral Tegmental Area

The therapeutic utility of opioids is diminished by their ability to induce rewarding behaviors that may lead to opioid use disorder. Recently, the endogenous cannabinoid system has emerged as a hot topic in the study of opioid reward but relatively little is known about how repeated opioid exposure may affect the endogenous cannabinoid system in the mesolimbic reward circuitry. In the present study, we investigated how sustained morphine may modulate the endogenous cannabinoid system in the ventral tegmental area (VTA) of Sprague Dawley rats, a critical region in the mesolimbic reward circuitry. Studies here using proteomic analysis and quantitative real-time PCR (qRT-PCR) found that the VTA expresses 32 different proteins or genes related to the endogenous cannabinoid system; three of these proteins or genes (PLCγ2, ABHD6, and CB2R) were significantly affected after repeated morphine exposure (CB2R was only detected by qRT-PCR but not proteomics). We also identified that repeated morphine treatment does not alter either anandamide (AEA) or 2-arachidonoylglycerol (2-AG) levels in the VTA compared to saline treatment; however, there may be diminished levels of anandamide (AEA) production in the VTA 4 h after a single morphine injection in both chronic saline and morphine pretreated cohorts. Treating the animals with an inhibitor of 2-AG degradation significantly decreased repeated opioid rewarding behavior. Taken together, our studies reveal a potential influence of sustained opioids on the endocannabinoid system in the VTA, suggesting that the endogenous cannabinoid system may participate in the opioid-induced reward.

Traumatic Stress, Chronic Ethanol Exposure, or the Combination, Alter Cannabinoid System Components in Reward and Limbic Regions of the Mouse Brain

The cannabinoid system is independently affected by stress and chronic ethanol exposure. However, the extent to which co-occurrence of traumatic stress and chronic ethanol exposure modulates the cannabinoid system remains unclear. We examined levels of cannabinoid system components, anandamide, 2-arachidonoylglycerol, fatty acid amide hydrolase, and monoacylglycerol lipase after mouse single-prolonged stress (mSPS) or non-mSPS (Control) exposure, with chronic intermittent ethanol (CIE) vapor or without CIE vapor (Air) across several brain regions using ultra-high-performance liquid chromatography tandem mass spectrometry or immunoblotting. Compared to mSPS-Air mice, anandamide and 2-arachidonoylglycerol levels in the anterior striatum were increased in mSPS-CIE mice. In the dorsal hippocampus, anandamide content was increased in Control-CIE mice compared to Control-Air, mSPS-Air, or mSPS-CIE mice. Finally, amygdalar anandamide content was increased in Control-CIE mice compared to Control-Air, or mSPS-CIE mice, but the anandamide content was decreased in mSPS-CIE compared to mSPS-Air mice. Based on these data we conclude that the effects of combined traumatic stress and chronic ethanol exposure on the cannabinoid system in reward pathway regions are driven by CIE exposure and that traumatic stress affects the cannabinoid components in limbic regions, warranting future investigation of neurotherapeutic treatment to attenuate these effects.

Chronic Effects of Indirect and Direct Cannabinoid Receptor Agonists on Addiction-Related Behaviors and Dopamine Release

A major problem with current anxiolytic medications is abuse liability; thus, new pharmaceutical targets are being explored. The cannabinoid system is one potential target. The current paper examined behavioral and neurochemical changes related to abuse liability following chronic administration of the indirect cannabinoid agonist arachidonoyl serotonin (AA-5-HT) and the direct cannabinoid type 1 receptor (CB1R) agonist arachidonyl-2-chloro-ethylamide (ACEA). AA-5-HT indirectly agonizes the cannabinoid system via inhibition of the dual fatty acid amide hydrolase (FAAH) while also inhibiting transient vanilloid type 1 (TRPV1) channels. Neither AA-5-HT nor ACEA induced conditioned place preference (CPP) or altered behaviors during open field (OF) or saccharin preference testing. AA-5-HT did not alter phasic dopamine release in the nucleus accumbens, as measured with in vivo fixed potential amperometry; however, ACEA decreased dopamine release and enhanced the dopaminergic effect of cocaine. Overall, neither AA-5-HT nor ACEA induced behavioral or neurochemical changes associated with abuse liability; however, indirect mechanisms of agonizing the cannabinoid system may be a better alternative than direct mechanisms if concerned with disrupting dopamine function.HighlightsThe indirect cannabinoid agonist AA-5-HT did not alter dopamine release or measured behaviors.The direct cannabinoid receptor agonist ACEA did not alter measured behaviors.ACEA decreased dopamine release and the dopaminergic response to cocaine.Neither drug indicated abuse liability, although ACEA did alter dopamine functioning.