Endocannabinoid signaling in synaptic function

Role of endocannabinoid neurotransmission in the insular cortex on cardiovascular, autonomic and behavioral responses evoked by acute restraint stress in rats

This study aimed to investigate the role of endocannabinoid mechanisms present within the insular cortex (IC) on cardiovascular, autonomic and anxiogenic-like responses evoked by an acute session of restraint in rats. For this, bilateral guide cannulas directed to the IC were implanted in male Wistar rats for intrabrain microinjection of the selective CB1 receptor antagonist AM251, the selective TRPV1 receptor antagonist capsazepine, the fatty acid amide hydrolase (FAAH) inhibitor URB597 or the monoacylglycerol lipase (MAGL) inhibitor JZL184. The effects of pharmacological treatments were evaluated on restraint-evoked increases in blood pressure and heart rate, sympathetically-mediated cutaneous vasoconstriction and in delayed anxiogenic-like effect assessed 24h after stress exposure in the elevated plus maze (EPM) and open field (OF). We observed that acute restraint stress decreased the exploration of both EPM open arms and OF center region in animals treated with vehicle into the IC, thus indicating an anxiogenic-like effect. Inhibition of MAGL within the IC evoked by local treatment with JZL184 avoided the restraint-evoked anxiogenic effect. IC treatment with JZL184 also attenuated the tachycardia during restraint. The other pharmacological treatments did not modify the cardiovascular, autonomic and behavioral responses evoked by restraint. Taken together, these findings suggest that endocannabinoid neurotransmission in the IC, potentially acting through the endocannabinoid 2-arachidonoylglycerol, plays an inhibitory role in both tachycardia and anxiogenic-like effect evoked by stressful events.

The CB1R of mPFC is involved in anxiety-like behavior induced by 0.8/2.65 GHz dual-frequency electromagnetic radiation

As mobile phones and communication base stations become more widespread, concerns have arisen regarding the potential risks of environmental exposure to multi-frequency electromagnetic radiation (EMR) and its effects on mental health. To address these concerns, our study established a dual-frequency EMR mouse model at 0.8/2.65 GHz to explore potential molecular mechanisms and intervention targets. Our results revealed that exposure to this dual-frequency EMR significantly induced anxiety-like behavior in mice. Molecular experiments further showed a significant decrease in cannabinoid receptor type 1 (CB1R) levels in the medial prefrontal cortex (mPFC) of the mice, along with a notable reduction in the endogenous cannabinoids 2-arachidonoylglycerol and anandamide. This led to a downregulation of the entire endocannabinoid system (ECS). Additional confirmation was obtained by overexpressing and knocking down CB1R in the mPFC. We found that increasing mPFC CB1R levels could effectively reduce anxiety-like behavior, while decreasing mPFC CB1R levels exacerbated it. Furthermore, we found dual-frequency EMR induced the change of ECS in the basolateral amygdala (BLA). Notably, female mice exhibited similar behavioral phenotypes and molecular mechanisms in response to dual-frequency EMR. In summary, our study demonstrates that anxiety induced by dual-frequency EMR is closely linked to the function of the ECS in the mPFC and BLA, and that CB1R expression in the mPFC plays a significant role in modulating emotional behavior in mice.

Adenosine and Cortical Plasticity

Brain plasticity is the ability of the nervous system to change its structure and functioning in response to experiences. These changes occur mainly at synaptic connections, and this plasticity is named synaptic plasticity. During postnatal development, environmental influences trigger changes in synaptic plasticity that will play a crucial role in the formation and refinement of brain circuits and their functions in adulthood. One of the greatest challenges of present neuroscience is to try to explain how synaptic connections change and cortical maps are formed and modified to generate the most suitable adaptive behavior after different external stimuli. Adenosine is emerging as a key player in these plastic changes at different brain areas. Here, we review the current knowledge of the mechanisms responsible for the induction and duration of synaptic plasticity at different postnatal brain development stages in which adenosine, probably released by astrocytes, directly participates in the induction of long-term synaptic plasticity and in the control of the duration of plasticity windows at different cortical synapses. In addition, we comment on the role of the different adenosine receptors in brain diseases and on the potential therapeutic effects of acting via adenosine receptors.

Genetic Tools in Rodents to Study Cannabinoid Functions

During the past 30 years, the endocannabinoid system (ECS) has emerged as a major signalling system in the mammalian brain regulating neurotransmission in numerous brain regions and in various cell populations. Endocannabinoids are able to regulate specific physiological functions and thus modify their behavioural manifestations and allostatic alterations of the ECS linked to different pathological conditions. As discussed in detail in other chapters of this book, endocannabinoids are involved in learning and memory, stress, and anxiety, feeding, energy balance, development, and ageing. Likewise, many CNS disorders (e.g. schizophrenia, epilepsy, substance use disorders, and multiple sclerosis) are associated with dysregulation of the ECS. Discerning the physiological functions of the synthetic and degrading enzymes of endocannabinoids and their receptors is a challenging task because of their distinct and complex expression patterns. Techniques of genetic engineering have been able to shed light on a number of complex ECS-related tasks during the past years. In this chapter, first, we take a critical look at the toolbox available to researchers who would like to investigate cannabinoid effects using genetic engineering techniques, then we comprehensively discuss genetically modified rodent models in various neuronal and non-neuronal cell populations, both within and outside the nervous system.

Developmental Spike Timing-Dependent Long-Term Depression Requires Astrocyte d-Serine at L2/3-L2/3 Synapses of the Mouse Somatosensory Cortex

Spike timing-dependent plasticity (STDP) is a learning rule important for synaptic refinement and for learning and memory during development. While different forms of presynaptic t-LTD have been deeply investigated, little is known about the mechanisms of somatosensory cortex postsynaptic t-LTD. In the present work, we investigated the requirements and mechanisms for induction of developmental spike timing-dependent long-term depression (t-LTD) at L2/3-L2/3 synapses in the juvenile mouse somatosensory cortex. We found that postnatal day (P) 13-21 mice of either sex show t-LTD at L2/3-L2/3 synapses induced by pairing single presynaptic activity with single postsynaptic action potentials at low stimulation frequency (0.2 Hz) that is expressed postsynaptically and requires the activation of ionotropic postsynaptic NMDA-type glutamate receptors containing GluN2B subunits. In addition, it requires postsynaptic Ca2+, Ca2+ release from internal stores, calcineurin, postsynaptic endocannabinoid synthesis, activation of CB1 receptors, and astrocytic signaling to release the gliotransmitter d-serine to activate postsynaptic NMDARs to induce t-LTD. These results show direct evidence of the mechanism involved in developmental postsynaptic t-LTD at L2/3-L2/3 synapses, revealing a central role of astrocytes and their release of d-serine in its induction.

Cannabis and Cannabinoid Signaling: Research Gaps and Opportunities

Cannabis and its products have been used for centuries for both medicinal and recreational purposes. The recent widespread legalization of cannabis has vastly expanded its use in the United States across all demographics except for adolescents. Meanwhile, decades of research have advanced our knowledge of cannabis pharmacology and particularly of the endocannabinoid system with which the components of cannabis interact. This research has revealed multiple targets and approaches for manipulating the system for therapeutic use and to ameliorate cannabis toxicity or cannabis use disorder. Research has also led to new questions that underscore the potential risks of its widespread use, particularly the enduring consequences of exposure during critical windows of brain development or for consumption of large daily doses of cannabis with high content Δ 9-tetrahydrocannabinol. This article highlights current neuroscience research on cannabis that has shed light on therapeutic opportunities and potential adverse consequences of misuse and points to gaps in knowledge that can guide future research. SIGNIFICANCE STATEMENT: Cannabis use has escalated with its increased availability. Here, the authors highlight the challenges of cannabis research and the gaps in our knowledge of cannabis pharmacology and of the endocannabinoid system that it targets. Future research that addresses these gaps is needed so that the endocannabinoid system can be leveraged for safe and effective use.

Pleasant Odor Decreases Mouse Anxiety-like Behaviors by Regulating Hippocampal Endocannabinoid Signaling

Anxiety disorder is one of the most common neuropsychiatric disorders, and affects many people's daily activities. Although the pathogenesis and treatments of anxiety disorder have been studied for several decades, the underlying mechanisms remain elusive. Here, we provide evidence that olfactory stimuli with inhaled linalool or 2-phenylethanol decreased mouse anxiety-like behaviors and increased the activities of hippocampal dentate granule cells (DGCs). RNA-sequencing analysis identified retrograde endocannabinoid signaling, which is a critical pathway for mood regulation and neuron activation, is altered in the hippocampus of both linalool- and 2-phenylethanol-exposed mice. Further studies found that selective inhibition of endocannabinoid signaling by injecting rimonabant abolished the activation of DGCs and the anxiolytic effect induced by linalool or 2-phenylethanol. Together, these results uncovered a novel mechanism by which linalool or 2-phenylethanol decreases mouse anxiety-like behaviors and increases DG activity likely through activating hippocampal retrograde endocannabinoid signaling.

Effects of in utero delta-9-tetrahydrocannabinol (THC) exposure on fetal and infant musculoskeletal development in a preclinical nonhuman primate model

The endocannabinoid system (ECS) plays a major role in the maintenance of bodily homeostasis and adaptive response to external insults. It has been shown to regulate crucial physiological processes and behaviors, spanning nervous functions, anxiety, cognition, and pain sensation. Due to this broad activity, the ECS has been explored as a potential therapeutic target in the treatment of select diseases. However, until there is a more comprehensive understanding of how ECS activation by exogenous and endogenous ligands manifests across disparate tissues and cells, discretion should be exercised. Previous work has investigated how endogenous cannabinoid signaling impacts skeletal muscle development and differentiation. However, the effects of activation of the ECS by delta-9-tetrahydrocannabinol (THC, the most psychoactive component of cannabis) on skeletal muscle development, particularly in utero, remain unclear. To address this research gap, we used a highly translational non-human primate model to examine the potential impact of chronic prenatal THC exposure on fetal and infant musculoskeletal development. RNA was isolated from the skeletal muscle and analyzed for differential gene expression using a Nanostring nCounter neuroinflammatory panel comprised of 770 genes. Histomorphological evaluation of muscle morphology and composition was also performed. Our findings suggest that while prenatal THC exposure had narrow overall effects on fetal and infant muscle development, the greatest impacts were observed within pathways related to inflammation and cytokine signaling, which suggest the potential for tissue damage and atrophy. This pilot study establishes feasibility to evaluate neuroinflammation due to prenatal THC exposure and provides rationale for follow-on studies that explore the longer-term implications and functional consequences encountered by offspring as they continue to mature.

Astrocytic transcriptional and epigenetic mechanisms of drug addiction

Addiction is a leading cause of disease burden worldwide and remains a challenge in current neuroscience research. Drug-induced lasting changes in gene expression are mediated by transcriptional and epigenetic regulation in the brain and are thought to underlie behavioral adaptations. Emerging evidence implicates astrocytes in regulating drug-seeking behaviors and demonstrates robust transcriptional response to several substances of abuse. This review focuses on the astrocytic transcriptional and epigenetic mechanisms of drug action.

rTMS ameliorates depressive-like behaviors and regulates the gut microbiome and medium- and long-chain fatty acids in mice exposed to chronic unpredictable mild stress

INTRODUCTION

Repetitive transcranial magnetic stimulation (rTMS) is a clinically useful therapy for depression. However, the effects of rTMS on the metabolism of fatty acids (FAs) and the composition of gut microbiota in depression are not well established.

METHODS

Mice received rTMS (15 Hz, 1.26 T) for seven consecutive days after exposure to chronic unpredictable mild stress (CUMS). The subsequent depressive-like behaviors, the composition of gut microbiota of stool samples, as well as medium- and long-chain fatty acids (MLCFAs) in the plasma, prefrontal cortex (PFC), and hippocampus (HPC) were evaluated.

RESULTS

CUMS induced remarkable changes in gut microbiotas and fatty acids, specifically in community diversity of gut microbiotas and PUFAs in the brain. 15 Hz rTMS treatment alleviates depressive-like behaviors and partially normalized CUMS induced alterations of microbiotas and MLCFAs, especially the abundance of Cyanobacteria, Actinobacteriota, and levels of polyunsaturated fatty acids (PUFAs) in the hippocampus and PFC.

CONCLUSION

These findings revealed that the modulation of gut microbiotas and PUFAs metabolism might partly contribute to the antidepressant effect of rTMS.

Effect of Docosahexaenoic Acid Encapsulation with Whey Proteins on Rat Growth and Tissue Endocannabinoid Profile

Modifying the food structure allows a nutrient to be delivered differently, which can modify not only its digestion process but also its subsequent metabolism. In this study, rats received 3 g of omelette daily containing docosahexaenoic acid (DHA) as crude oil or previously encapsulated with whey proteins, whereas a control group received a DHA-free omelette. The results showed that DHA encapsulation markedly induced a different feeding behaviour so animals ate more and grew faster. Then, after four weeks, endocannabinoids and other N-acyl ethanolamides were quantified in plasma, brain, and heart. DHA supplementation strongly reduced endocannabinoid derivatives from omega-6 fatty acids. However, DHA encapsulation had no particular effect, other than a great increase in the content of DHA-derived docosahexaenoyl ethanolamide in the heart. While DHA supplementation has indeed shown an effect on cannabinoid profiles, its physiological effect appears to be mediated more through more efficient digestion of DHA oil droplets in the case of DHA encapsulation. Thus, the greater release of DHA and other dietary cannabinoids present may have activated the cannabinoid system differently, possibly more locally along the gastrointestinal tract. However, further studies are needed to evaluate the synergy between DHA encapsulation, fasting, hormones regulating food intake, and animal growth.

The endogenous cannabinoid system modulates male sexual behavior expression

The endocannabinoid system (ECS) plays a key neuromodulatory role in the brain. Main features of endocannabinoids (eCBs) are that they are produced on demand, in response to enhanced neuronal activity, act as retrograde messengers, and participate in the induction of brain plasticity processes. Sexual activity is a motivated behavior and therefore, the mesolimbic dopaminergic system (MSL) plays a central role in the control of its appetitive component (drive to engage in copulation). In turn, copulation activates mesolimbic dopamine neurons and repeated copulation produces the continuous activation of the MSL system. Sustained sexual activity leads to the achievement of sexual satiety, which main outcome is the transient transformation of sexually active male rats into sexually inhibited animals. Thus, 24 h after copulation to satiety, the sexually satiated males exhibit a decreased sexual motivation and do not respond to the presence of a sexually receptive female with sexual activity. Interestingly, blockade of cannabinoid receptor 1 (CB1R) during the copulation to satiety process, interferes with both the appearance of the long-lasting sexual inhibition and the decrease in sexual motivation in the sexually satiated males. This effect is reproduced when blocking CB1R at the ventral tegmental area evidencing the involvement of MSL eCBs in the induction of this sexual inhibitory state. Here we review the available evidence regarding the effects of cannabinoids, including exogenously administered eCBs, on male rodent sexual behavior of both sexually competent animals and rat sub populations spontaneously showing copulatory deficits, considered useful to model some human male sexual dysfunctions. We also include the effects of cannabis preparations on human male sexual activity. Finally, we review the role played by the ECS in the control of male sexual behavior expression with the aid of the sexual satiety phenomenon. Sexual satiety appears as a suitable model for the study of the relationship between eCB signaling, MSL synaptic plasticity and the modulation of male sexual motivation under physiological conditions that might be useful for the understanding of MSL functioning, eCB-mediated plasticity and their relationship with motivational processes.