Localization of the cannabinoid type-1 receptor in subcellular astrocyte compartments of mutant mouse hippocampus

Cannabidiol improves maternal obesity-induced behavioral, neuroinflammatory and neurochemical dysfunctions in the juvenile offspring

Maternal obesity is associated with an increased risk of psychiatric disorders such as anxiety, depression, schizophrenia and autism spectrum disorder in the offspring. While numerous studies focus on preventive measures targeting the mothers, only a limited number provide practical approaches for addressing the damages once they are already established. We have recently demonstrated the interplay between maternal obesity and treatment with cannabidiol (CBD) on hypothalamic inflammation and metabolic disturbances, however, little is known about this relationship on behavioral manifestations and neurochemical imbalances in other brain regions. Therefore, here we tested whether CBD treatment could mitigate anxiety-like and social behavioral alterations, as well as neurochemical disruptions in both male and female offspring of obese dams. Female Wistar rats were fed a cafeteria diet for 12 weeks prior to mating, and during gestation and lactation. Offspring received CBD (50 mg/kg) from weaning for 3 weeks. Behavioral tests assessed anxiety-like manifestations and social behavior, while neuroinflammatory and neurochemical markers were evaluated in the prefrontal cortex (PFC) and hippocampus. CBD treatment attenuated maternal obesity-induced anxiety-like and social behavioral alterations, followed by rescuing effects on imbalanced neurotransmitter and endocannabinoid concentrations and altered expression of glial markers, CB1, oxytocin and dopamine receptors, with important differences between sexes. Overall, the findings of this study provide insight into the signaling pathways for the therapeutic benefits of CBD on neuroinflammation and neurochemical imbalances caused by perinatal maternal obesity in the PFC and the hippocampus, which translates into the behavioral manifestations, highlighting the sexual dimorphism encompassing both the transgenerational effect of obesity and the endocannabinoid system.

Unveiling the Potential of Cannabinoids in Multiple Sclerosis and the Dawn of Nano-Cannabinoid Medicine

Multiple sclerosis is the predominant autoimmune disorder affecting the central nervous system in adolescents and adults. Specific treatments are categorized as disease-modifying, whereas others are symptomatic treatments to alleviate painful symptoms. Currently, no singular conventional therapy is universally effective for all patients across all stages of the illness. Nevertheless, cannabinoids exhibit significant promise in their capacity for neuroprotection, anti-inflammation, and immunosuppression. This review will examine the traditional treatment for multiple sclerosis, the increasing interest in using cannabis as a treatment method, its role in protecting the nervous system and regulating the immune system, commercially available therapeutic cannabinoids, and the emerging use of cannabis in nanomedicine. In conclusion, cannabinoids exhibit potential as a disease-modifying treatment rather than merely symptomatic relief. However, further research is necessary to unveil their role and establish the safety and advancements in nano-cannabinoid medicine, offering the potential for reduced toxicity and fewer adverse effects, thereby maximizing the benefits of cannabinoids.

Astrocytic Regulation of Endocannabinoid-Dependent Synaptic Plasticity in the Dorsolateral Striatum

Astrocytes are pivotal for synaptic transmission and may also play a role in the induction and expression of synaptic plasticity, including endocannabinoid-mediated long-term depression (eCB-LTD). In the dorsolateral striatum (DLS), eCB signaling plays a major role in balancing excitation and inhibition and promoting habitual learning. The aim of this study was to outline the role of astrocytes in regulating eCB signaling in the DLS. To this end, we employed electrophysiological slice recordings combined with metabolic, chemogenetic and pharmacological approaches in an attempt to selectively suppress astrocyte function. High-frequency stimulation induced eCB-mediated LTD (HFS-LTD) in brain slices from both male and female rats. The metabolic uncoupler fluorocitrate (FC) reduced the probability of transmitter release and depressed synaptic output in a manner that was independent on cannabinoid 1 receptor (CB1R) activation. Fluorocitrate did not affect the LTD induced by the CB1R agonist WIN55,212-2, but enhanced CB1R-dependent HFS-LTD. Reduced neurotransmission and facilitated HFS-LTD were also observed during chemogenetic manipulation using Gi-coupled DREADDs targeting glial fibrillary acidic protein (GFAP)-expressing cells, during the pharmacological inhibition of connexins using carbenoxolone disodium, or during astrocytic glutamate uptake using TFB-TBOA. While pretreatment with the N-methyl-D-aspartate (NMDA) receptor antagonist 2-amino-5-phosphonopentanoic acid (APV) failed to prevent synaptic depression induced by FC, it blocked the facilitation of HFS-LTD. While the lack of tools to disentangle astrocytes from neurons is a major limitation of this study, our data collectively support a role for astrocytes in modulating basal neurotransmission and eCB-mediated synaptic plasticity.

Omega-3 Recovers Cannabinoid 1 Receptor Expression in the Adult Mouse Brain after Adolescent Binge Drinking

Adolescent binge drinking is a social problem with a long-lasting impact on cognitive functions. The cannabinoid type-1 (CB1) receptor of the endocannabinoid system (ECS) is involved in brain synaptic plasticity, cognition and behavior via receptor localization at specific subcellular compartments of the cortical, limbic and motor regions. Alcohol (EtOH) intake affects the ECS, CB1 and their functions. Evidence indicates that binge drinking during adolescence impairs memory via the abrogation of CB1-dependent synaptic plasticity in the hippocampus. However, the impact of EtOH consumption on global CB1 receptor expression in the adult brain is unknown. We studied this using optical density analysis throughout brain regions processed for light microscopy (LM) immunohistotochemistry. CB1 staining decreased significantly in the secondary motor cortex, cerebellum, cingulate cortex, amygdala and nucleus accumbens. Next, as omega-3 (n-3) polyunsaturated fatty acids (PUFAs) rescue synaptic plasticity and improve EtOH-impaired cognition, we investigated whether docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) had any effect on CB1 receptors. N-3 intake during EtOH abstinence restored CB1 immunostaining in the secondary motor cortex, cerebellum and amygdala, and ameliorated receptor density in the cingulate cortex. These results show that n-3 supplementation recovers CB1 receptor expression disrupted by EtOH in distinct brain regions involved in motor functions and cognition.

Interplay Between Astroglial Endocannabinoid System and the Cognitive Dysfunction in Alzheimer's Disease

Cannabinoid CB1 receptors have been shown to regulate wide array of functions ranging from homeostasis to the cognitive functioning but recent data support the hypothesis that astrocytes also operate as a mediator of synaptic plasticity and contribute to cognition and learning. The receptor heterogeneity plays a key role in understanding the molecular mechanisms underlying these processes. Despite the fact that the majority of CB1 receptors act on neurons, studies have revealed that cannabinoids have direct control over astrocytes, including energy generation and neuroprotection. The tripartite synapse connects astrocytes to neurons and allows them to interact with one another and the astrocytes are key players in synaptic plasticity, which is associated with cognitive functions. This review focuses on our growing understanding of the intricate functions of astroglial CB1 that underpin physiological brain function, and in Alzheimer's disease.

An enquiry to the role of CB1 receptors in neurodegeneration

Neurodegenerative disorders are debilitating conditions that impair patient quality of life and that represent heavy social-economic burdens to society. Whereas the root of some of these brain illnesses lies in autosomal inheritance, the origin of most of these neuropathologies is scantly understood. Similarly, the cellular and molecular substrates explaining the progressive loss of brain functions remains to be fully described too. Indeed, the study of brain neurodegeneration has resulted in a complex picture, composed of a myriad of altered processes that include broken brain bioenergetics, widespread neuroinflammation and aberrant activity of signaling pathways. In this context, several lines of research have shown that the endocannabinoid system (ECS) and its main signaling hub, the type-1 cannabinoid (CB1) receptor are altered in diverse neurodegenerative disorders. However, some of these data are conflictive or poorly described. In this review, we summarize the findings about the alterations in ECS and CB1 receptors signaling in three representative brain illnesses, the Alzheimer's, Parkinson's and Huntington's diseases, and we discuss the relevance of these studies in understanding neurodegeneration development and progression, with a special focus on astrocyte function. Noteworthy, the analysis of ECS defects in neurodegeneration warrant much more studies, as our conceptual understanding of ECS function has evolved quickly in the last years, which now include glia cells and the subcellular-specific CB1 receptors signaling as critical players of brain functions.

Endocannabinoid signaling in adult hippocampal neurogenesis: A mechanistic and integrated perspective

Dentate gyrus of the hippocampus continuously gives rise to new neurons, namely, adult-born granule cells, which contribute to conferring plasticity to the mature brain throughout life. Within this neurogenic region, the fate and behavior of neural stem cells (NSCs) and their progeny result from a complex balance and integration of a variety of cell-autonomous and cell-to-cell-interaction signals and underlying pathways. Among these structurally and functionally diverse signals, there are endocannabinoids (eCBs), the main brain retrograde messengers. These pleiotropic bioactive lipids can directly and/or indirectly influence adult hippocampal neurogenesis (AHN) by modulating, both positively and negatively, multiple molecular and cellular processes in the hippocampal niche, depending on the cell type or stage of differentiation. Firstly, eCBs act directly as cell-intrinsic factors, cell-autonomously produced by NSCs following their stimulation. Secondly, in many, if not all, niche-associated cells, including some local neuronal and nonneuronal elements, the eCB system indirectly modulates the neurogenesis, linking neuronal and glial activity to regulating distinct stages of AHN. Herein, we discuss the crosstalk of the eCB system with other neurogenesis-relevant signal pathways and speculate how the hippocampus-dependent neurobehavioral effects elicited by (endo)cannabinergic medications are interpretable in light of the key regulatory role that eCBs play on AHN.

Mitochondrial cannabinoid receptors gate corticosterone impact on novel object recognition

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.

Brightness and shadows of mitochondrial ROS in the brain

Mitochondrial reactive oxygen species (mROS) have been generally considered harmful byproducts wanted to clear when elevated to avoid brain damage. However, the abundance of mROS in astrocytes is very high -about one order of magnitude above that in neurons-, despite they are essential to preserve cell metabolism and animal behavior. Here, we have focused on this apparent ambiguity by discussing (i) the intrinsic mechanisms accounting for the higher production of mROS by the mitochondrial respiratory chain in astrocytes than in neurons, (ii) the specific molecular targets of astrocytic beneficial mROS, and (iii) how decreased astrocytic mROS causes excess neuronal mROS leading to cellular and organismal damage. We hope that this mini-review serves to clarifying the apparent controversy on the beneficial versus deleterious faces of ROS in the brain from molecular to higher-order organismal levels.

Role of Calcium Modulation in the Pathophysiology and Treatment of Alzheimer's Disease

Alzheimer's disease (AD) is a chronic neurodegenerative disease and the most frequent cause of progressive dementia in senior adults. It is characterized by memory loss and cognitive impairment secondary to cholinergic dysfunction and N-methyl-D-aspartate (NMDA)-mediated neurotoxicity. Intracellular neurofibrillary tangles, extracellular plaques composed of amyloid-β (Aβ), and selective neurodegeneration are the anatomopathological hallmarks of this disease. The dysregulation of calcium may be present in all the stages of AD, and it is associated with other pathophysiological mechanisms, such as mitochondrial failure, oxidative stress, and chronic neuroinflammation. Although the cytosolic calcium alterations in AD are not completely elucidated, some calcium-permeable channels, transporters, pumps, and receptors have been shown to be involved at the neuronal and glial levels. In particular, the relationship between glutamatergic NMDA receptor (NMDAR) activity and amyloidosis has been widely documented. Other pathophysiological mechanisms involved in calcium dyshomeostasis include the activation of L-type voltage-dependent calcium channels, transient receptor potential channels, and ryanodine receptors, among many others. This review aims to update the calcium-dysregulation mechanisms in AD and discuss targets and molecules with therapeutic potential based on their modulation.

Cannabinoids and Multiple Sclerosis: A Critical Analysis of Therapeutic Potentials and Safety Concerns

Multiple sclerosis (MS) is a complicated condition in which the immune system attacks myelinated axons in the central nervous system (CNS), destroying both myelin and axons to varying degrees. Several environmental, genetic, and epigenetic factors influence the risk of developing the disease and how well it responds to treatment. Cannabinoids have recently sparked renewed interest in their therapeutic applications, with growing evidence for their role in symptom control in MS. Cannabinoids exert their roles through the endogenous cannabinoid (ECB) system, with some reports shedding light on the molecular biology of this system and lending credence to some anecdotal medical claims. The double nature of cannabinoids, which cause both positive and negative effects, comes from their actions on the same receptor. Several mechanisms have been adopted to evade this effect. However, there are still numerous limitations to using cannabinoids to treat MS patients. In this review, we will explore and discuss the molecular effect of cannabinoids on the ECB system, the various factors that affect the response to cannabinoids in the body, including the role of gene polymorphism and its relation to dosage, assessing the positive over the adverse effects of cannabinoids in MS, and finally, exploring the possible functional mechanism of cannabinoids in MS and the current and future progress of cannabinoid therapeutics.

Altered glial expression of the cannabinoid 1 receptor in the subiculum of a mouse model of Alzheimer's disease

The alteration of the endocannabinoid tone usually associates with changes in the expression and/or function of the cannabinoid CB₁ receptor. In Alzheimer's disease (AD), amyloid beta (Aβ)-containing aggregates induce a chronic inflammatory response leading to reactivity of both microglia and astrocytes. However, how this glial response impacts on the glial CB₁ receptor expression in the subiculum of a mouse model of AD, a brain region particularly affected by large accumulation of plaques and concomitant subcellular changes in microglia and astrocytes, is unknown. The CB₁ receptor localization in both glial cells was investigated in the subiculum of male 5xFAD/CB₂ ^EGFP/f/f (AD model) and CB₂ ^EGFP/f/f mice by immuno-electron microscopy. The findings revealed that glial CB₁ receptors suffer remarkable changes in the AD mouse. Thus, CB₁ receptor expression increases in reactive microglia in 5xFAD/CB₂ ^EGFP/f/f , but remains constant in astrocytes with CB₁ receptor labeling rising proportionally to the perimeter of the reactive astrocytes. Not least, the CB₁ receptor localization in microglial processes in the subiculum of controls and closely surrounding amyloid plaques and dystrophic neurites of the AD model, supports previous suggestions of the presence of the CB₁ receptor in microglia. These findings on the correlation between glial reactivity and the CB₁ receptor expression in microglial cells and astrocytes, contribute to the understanding of the role of the endocannabinoid system in the pathophysiology of Alzheimer's disease.

Comparative assessment of the effects of DREADDs and endogenously expressed GPCRs in hippocampal astrocytes on synaptic activity and memory

Designer Receptors Exclusively Activated by Designer Drugs (DREADDs) have proven themselves as one of the key in vivo techniques of modern neuroscience, allowing for unprecedented access to cellular manipulations in living animals. With respect to astrocyte research, DREADDs have become a popular method to examine the functional aspects of astrocyte activity, particularly G-protein coupled receptor (GPCR)-mediated intracellular calcium (Ca2+) and cyclic adenosine monophosphate (cAMP) dynamics. With this method it has become possible to directly link the physiological aspects of astrocytic function to cognitive processes such as memory. As a result, a multitude of studies have explored the impact of DREADD activation in astrocytes on synaptic activity and memory. However, the emergence of varying results prompts us to reconsider the degree to which DREADDs expressed in astrocytes accurately mimic endogenous GPCR activity. Here we compare the major downstream signaling mechanisms, synaptic, and behavioral effects of stimulating Gq-, Gs-, and Gi-DREADDs in hippocampal astrocytes of adult mice to those of endogenously expressed GPCRs.

Astroglial CB1 receptors, energy metabolism, and gliotransmission: an integrated signaling system?

Astrocytes are key players in brain homeostasis and function. During the last years, several studies have cemented this notion by showing that these cells respond to neuronal signals and, via the release of molecules that modulate and support synaptic activity (gliotransmission) participates in the functions of the so-called tripartite synapse. Thus, besides their established control of brain metabolism, astrocytes can also actively control synaptic activity and behavior. Among the signaling pathways that shape the functions of astrocyte, the cannabinoid type-1 (CB1) receptor is emerging as a critical player in the control of both gliotransmission and the metabolic cooperation between astrocytes and neurons. In the present short review, we describe known and newly discovered properties of the astroglial CB1 receptors and their role in modulating brain function and behavior. Based on this evidence, we finally discuss how the functions and mode of actions of astrocyte CB1 receptors might represent a clear example of the inextricable relationship between energy metabolism and gliotransmission. These tight interactions will need to be taken into account for future research in astrocyte functions and call for a reinforcement of the theoretical and experimental bridges between studies on metabolic and synaptic functions of astrocytes.

The unbroken Krebs cycle. Hormonal-like regulation and mitochondrial signaling to control mitophagy and prevent cell death

The tricarboxylic acid (TCA) or Krebs cycle, which takes place in prokaryotic cells and in the mitochondria of eukaryotic cells, is central to life on Earth and participates in key events such as energy production and anabolic processes. Despite its relevance, it is not perceived as tightly regulated compared to other key metabolisms such as glycolysis/gluconeogenesis. A better understanding of the functioning of the TCA cycle is crucial due to mitochondrial function impairment in several diseases, especially those that occur with neurodegeneration. This article revisits what is known about the regulation of the Krebs cycle and hypothesizes the need for large-scale, rapid regulation of TCA cycle enzyme activity. Evidence of mitochondrial enzyme activity regulation by activation/deactivation of protein kinases and phosphatases exists in the literature. Apart from indirect regulation via G protein-coupled receptors (GPCRs) at the cell surface, signaling upon activation of GPCRs in mitochondrial membranes may lead to a direct regulation of the enzymes of the Krebs cycle. Hormonal-like regulation by posttranscriptional events mediated by activable kinases and phosphatases deserve proper assessment using isolated mitochondria. Also see the video abstract here: https://youtu.be/aBpDSWiMQyI.

Human Astrocyte Spheroids as Suitable In Vitro Screening Model to Evaluate Synthetic Cannabinoid MAM2201-Induced Effects on CNS

There is growing concern about the consumption of synthetic cannabinoids (SCs), one of the largest groups of new psychoactive substances, its consequence on human health (general population and workers), and the continuous placing of new SCs on the market. Although drug-induced alterations in neuronal function remain an essential component for theories of drug addiction, accumulating evidence indicates the important role of activated astrocytes, whose essential and pleiotropic role in brain physiology and pathology is well recognized. The study aims to clarify the mechanisms of neurotoxicity induced by one of the most potent SCs, named MAM-2201 (a naphthoyl-indole derivative), by applying a novel three-dimensional (3D) cell culture model, mimicking the physiological and biochemical properties of brain tissues better than traditional two-dimensional in vitro systems. Specifically, human astrocyte spheroids, generated from the D384 astrocyte cell line, were treated with different MAM-2201 concentrations (1-30 µM) and exposure times (24-48 h). MAM-2201 affected, in a concentration- and time-dependent manner, the cell growth and viability, size and morphological structure, E-cadherin and extracellular matrix, CB1-receptors, glial fibrillary acidic protein, and caspase-3/7 activity. The findings demonstrate MAM-2201-induced cytotoxicity to astrocyte spheroids, and support the use of this human 3D cell-based model as species-specific in vitro tool suitable for the evaluation of neurotoxicity induced by other SCs.

Endocannabinoid signaling in brain diseases: Emerging relevance of glial cells

The discovery of cannabinoid receptors as the primary molecular targets of psychotropic cannabinoid Δ⁹ -tetrahydrocannabinol (Δ⁹ -THC) in late 1980s paved the way for investigations on the effects of cannabis-based therapeutics in brain pathology. Ever since, a wealth of results obtained from studies on human tissue samples and animal models have highlighted a promising therapeutic potential of cannabinoids and endocannabinoids in a variety of neurological disorders. However, clinical success has been limited and major questions concerning endocannabinoid signaling need to be satisfactorily addressed, particularly with regard to their role as modulators of glial cells in neurodegenerative diseases. Indeed, recent studies have brought into the limelight diverse, often unexpected functions of astrocytes, oligodendrocytes, and microglia in brain injury and disease, thus providing scientific basis for targeting glial cells to treat brain disorders. This Review summarizes the current knowledge on the molecular and cellular hallmarks of endocannabinoid signaling in glial cells and its clinical relevance in neurodegenerative and chronic inflammatory disorders.

Endocannabinoid signaling in the central nervous system

It is hard to overestimate the influence of the endocannabinoid signaling (ECS) system on central nervous system (CNS) function. In the 40 years since cannabinoids were found to trigger specific cell signaling cascades, studies of the ECS system continue to cause amazement, surprise, and confusion! CB1 cannabinoid receptors are expressed widely in the CNS and regulate cell-cell communication via effects on the release of both neurotransmitters and gliotransmitters. CB2 cannabinoid receptors are difficult to detect in the CNS but seem to "punch above their weight" as compounds targeting these receptors have significant effects on inflammatory state and behavior. Positive and negative allosteric modulators for both receptors have been identified and examined in preclinical studies. Concentrations of the endocannabinoid ligands, N-arachidonoylethanolamine and 2-arachidonoylglycerol (2-AG), are regulated by a combination of enzymatic synthesis and degradation and inhibitors of these processes are available and making their way into clinical trials. Importantly, ECS regulates many essential brain functions, including regulation of reward, anxiety, inflammation, motor control, and cellular development. While the field is on the cusp of preclinical discoveries providing impactful clinical and therapeutic insights into many CNS disorders, there is still much to be learned about this remarkable and versatile modulatory system.

Endocannabinoid signaling in glioma

High-grade gliomas constitute the most frequent and aggressive form of primary brain cancer in adults. These tumors express cannabinoid CB₁ and CB₂ receptors, as well as other elements of the endocannabinoid system. Accruing preclinical evidence supports that pharmacological activation of cannabinoid receptors located on glioma cells exerts overt anti-tumoral effects by modulating key intracellular signaling pathways. The mechanism of this cannabinoid receptor-evoked anti-tumoral activity in experimental models of glioma is intricate and may involve an inhibition not only of cancer cell survival/proliferation, but also of invasiveness, angiogenesis, and the stem cell-like properties of cancer cells, thereby affecting the complex tumor microenvironment. However, the precise biological role of the endocannabinoid system in the generation and progression of glioma seems very context-dependent and remains largely unknown. Increasing our basic knowledge on how (endo)cannabinoids act on glioma cells could help to optimize experimental cannabinoid-based anti-tumoral therapies, as well as the preliminary clinical testing that is currently underway.

Endocannabinoids at the synapse and beyond: implications for neuropsychiatric disease pathophysiology and treatment

Endocannabinoids (eCBs) are lipid neuromodulators that suppress neurotransmitter release, reduce postsynaptic excitability, activate astrocyte signaling, and control cellular respiration. Here, we describe canonical and emerging eCB signaling modes and aim to link adaptations in these signaling systems to pathological states. Adaptations in eCB signaling systems have been identified in a variety of biobehavioral and physiological process relevant to neuropsychiatric disease states including stress-related disorders, epilepsy, developmental disorders, obesity, and substance use disorders. These insights have enhanced our understanding of the pathophysiology of neurological and psychiatric disorders and are contributing to the ongoing development of eCB-targeting therapeutics. We suggest future studies aimed at illuminating how adaptations in canonical as well as emerging cellular and synaptic modes of eCB signaling contribute to disease pathophysiology or resilience could further advance these novel treatment approaches.

Endocannabinoid signaling in astrocytes

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.

GLAST versus GFAP as astroglial marker for the subcellular study of cannabinoid CB1 receptors in astrocytes

The cannabinoid CB₁ receptor-mediated functions in astrocytes are highly dependent on the CB₁ receptor distribution in these glial cells relative to neuronal sites, particularly at the nearby synapses under normal or pathological conditions. However, the portrait of the CB₁ receptor distribution in astroglial compartments remains uncompleted because of the scarce CB₁ receptor expression in these cells and the limited identification of astrocytes. The glial fibrillary acidic protein (GFAP) is commonly used as astroglial marker. However, because GFAP is a cytoskeleton protein mostly restricted to the astroglial cell bodies and their main branches, it seems not ideal for the localization of CB₁ receptor distribution in astrocytes. Therefore, alternative markers to decipher the actual astroglial CB₁ receptors are required. In this work, we have compared the glutamate aspartate transporter (GLAST) versus GFAP for the CB₁ receptor localization in astrocytes. We found by immunoelectron microscopy that GLAST reveals almost three-fold astroglial area and four-fold astroglial membranes compared to GFAP. In addition, this better visualization of astrocytes was associated with the detection of 12% of the total CB₁ receptor labeling in GLAST-positive astrocytes.

Astrocytes as a Therapeutic Target in Alzheimer's Disease-Comprehensive Review and Recent Developments

Alzheimer's disease (AD) is a frequent and disabling neurodegenerative disorder, in which astrocytes participate in several pathophysiological processes including neuroinflammation, excitotoxicity, oxidative stress and lipid metabolism (along with a critical role in apolipoprotein E function). Current evidence shows that astrocytes have both neuroprotective and neurotoxic effects depending on the disease stage and microenvironmental factors. Furthermore, astrocytes appear to be affected by the presence of amyloid-beta (Aβ), with alterations in calcium levels, gliotransmission and proinflammatory activity via RAGE-NF-κB pathway. In addition, astrocytes play an important role in the metabolism of tau and clearance of Aβ through the glymphatic system. In this review, we will discuss novel pharmacological and non-pharmacological treatments focused on astrocytes as therapeutic targets for AD. These interventions include effects on anti-inflammatory/antioxidant systems, glutamate activity, lipid metabolism, neurovascular coupling and glymphatic system, calcium dysregulation, and in the release of peptides which affects glial and neuronal function. According to the AD stage, these therapies may be of benefit in either preventing or delaying the progression of the disease.

The synaptic lipidome in health and disease

Adequate homeostasis of lipid, protein and carbohydrate metabolism is essential for cells to perform highly specific tasks in our organism, and the brain, with its uniquely high energetic requirements, posesses singular characteristics. Some of these are related to its extraordinary dotation of synapses, the specialized subcelluar structures where signal transmission between neurons occurs in the central nervous system. The post-synaptic compartment of excitatory synapses, the dendritic spine, harbors key molecules involved in neurotransmission tightly packed within a minute volume of a few femtoliters. The spine is further compartmentalized into nanodomains that facilitate the execution of temporo-spatially separate functions in the synapse. Lipids play important roles in this structural and functional compartmentalization and in mechanisms that impact on synaptic transmission. This review analyzes the structural and dynamic processes involving lipids at the synapse, highlighting the importance of their homeostatic balance for the physiology of this complex and highly specialized structure, and underscoring the pathologies associated with disbalances of lipid metabolism, particularly in the perinatal and late adulthood periods of life. Although small variations of the lipid profile in the brain take place throughout the adult lifespan, the pathophysiological consequences are clinically manifested mostly during late adulthood. Disturbances in lipid homeostasis in the perinatal period leads to alterations during nervous system development, while in late adulthood they favor the occurrence of neurodegenerative diseases.

Mitochondrial signal transduction

The analogy of mitochondria as powerhouses has expired. Mitochondria are living, dynamic, maternally inherited, energy-transforming, biosynthetic, and signaling organelles that actively transduce biological information. We argue that mitochondria are the processor of the cell, and together with the nucleus and other organelles they constitute the mitochondrial information processing system (MIPS). In a three-step process, mitochondria (1) sense and respond to both endogenous and environmental inputs through morphological and functional remodeling; (2) integrate information through dynamic, network-based physical interactions and diffusion mechanisms; and (3) produce output signals that tune the functions of other organelles and systemically regulate physiology. This input-to-output transformation allows mitochondria to transduce metabolic, biochemical, neuroendocrine, and other local or systemic signals that enhance organismal adaptation. An explicit focus on mitochondrial signal transduction emphasizes the role of communication in mitochondrial biology. This framework also opens new avenues to understand how mitochondria mediate inter-organ processes underlying human health.

Cannabinoid CB1 receptor expression in oligodendrocyte progenitors of the hippocampus revealed by the NG2-EYFP-knockin mouse

Adult oligodendrocyte progenitor cells (OPCs) give rise to myelinating oligodendrocytes through life and play crucial roles in brain homeostasis and plasticity during health and disease. Cannabinoid compounds acting through CB1 receptors promote the proliferation and differentiation of OPCs in vitro and facilitate developmental myelination and myelin repair in vivo. However, CB1 receptor expression in adult OPCs in situ has not been corroborated by anatomical studies and the contribution of this receptor population to the (re)myelination effects of cannabinoids remains a matter of debate. Using electron microscopy methods applied to NG2-EYFP reporter mice we assessed the localization of CB1 receptors in OPCs of the adult mouse hippocampus. To control for the specificity of CB1 receptor immunostaining we generated transgenic mice bearing EYFP expression in NG2 glia and wild-type (NG2-EYFP-CB1+/+) and knockout (NG2-EYFP-CB1–/–) for CB1 receptors. Double immunogold and immunoperoxidase labeling for CB1 and EYFP, respectively, revealed that CB1 receptors are present in a low proportion of NG2 positive profiles within hippocampal stratum radiatum of NG2-EYFP-CB1+/+ mice. Quantitative analysis of immunogold particles in synaptic structures and NG2 profiles showed that CB1 receptors are expressed at lower density in adult OPCs than in glutamatergic cells of the rodent hippocampus. These results highlight the presence of CB1 receptors in adult OPCs thus providing an anatomical substrate for the remyelination promoting effects of cannabinoids and open a novel perspective on the roles of the endocannabinoid system in brain physiology through the modulation of NG2 glia.

Cytotoxic Effects of Cannabidiol on Neonatal Rat Cortical Neurons and Astrocytes: Potential Danger to Brain Development

The influence of cannabidiol (CBD) on brain development is inadequately understood. Since CBD is considered a non-intoxicating drug, it has attracted great interest concerning its potential medical applicability, including in pregnant women and children. Here, we elucidated the response of perinatal rat cortical neurons and astrocytes to CBD at submicromolar (0.1, 0.5, 1, 5 µM) concentrations attainable in humans. The effect of CBD was concentration- and time-dependent and cell-specific. In neurons, 0.1 µM CBD induced an early and transient change in mitochondrial membrane potential (ΔΨm), ATP depletion, and caspase-8 activation, followed by rapid ATP recovery and progressive activation of caspase-9 and caspase-3/7, resulting in early apoptotic cell death with reduction and shortening of dendrites, cell shrinkage, and chromatin condensation. The decrease in neuronal viability, ATP depletion, and caspase activation due to CBD exposure was prevented by transient receptor potential vanilloid 1 (TRPV1) antagonist. In astrocytes, 0.5 µM CBD caused an immediate short-term dysregulation of ΔΨm, followed by ATP depletion with transient activation of caspase-8 and progressive activation of caspase-9 and caspase-3/7, leading to early apoptosis and subsequent necroptosis. In astrocytes, both TRPV1 and cannabinoid receptor 1 (CB₁) antagonists protected viability and prevented apoptosis. Given that CBD is a non-intoxicating drug, our results clearly show that this is not the case during critical periods of brain development when it can significantly interfere with the endogenous cannabinoid system.

Design and validation of recombinant protein standards for quantitative Western blot analysis of cannabinoid CB1 receptor density in cell membranes: an alternative to radioligand binding methods

Background

Replacement of radioligand binding assays with antibody-antigen interaction-based approaches for quantitative analysis of G protein-coupled receptor (GPCR) levels requires the use of purified protein standards containing the antigen. GPCRs in general and cannabinoid CB₁ receptor in particular show a progressive tendency to aggregate and precipitate in aqueous solution outside of their biological context due to the low solubility that the hydrophobic nature imprinted by their seven transmembrane domains. This renders full-length recombinant GPCRs useless for analytical purposes, a problem that can be overcome by engineering soluble recombinant fragments of the receptor containing the antigen.

Results

Here we generated highly soluble and stable recombinant protein constructs GST-CB1_414–472 and GST-CB1_414-442 containing much of the human CB₁ receptor C-terminal tail for use as standard and negative control, respectively, in quantitative Western blot analysis of CB₁ receptor expression on crude synaptosomes of the adult rat brain cortex. To this end we used three different antibodies, all raised against a peptide comprising the C-terminal residues 443–473 of the mouse CB₁ receptor that corresponds to residues 442–472 in the human homolog. Estimated values of CB₁ receptor density obtained by quantitative Western blot were of the same order of magnitude but slightly higher than values obtained by the radioligand saturation binding assay.

Conclusions

Collectively, here we provide a suitable Western blot-based design as a simple, cost-effective and radioactivity-free alternative for the quantitative analysis of CB₁ receptor expression, and potentially of any GPCR, in a variety of biological samples. The discrepancies between the results obtained by quantitative Western blot and radioligand saturation binding techniques are discussed in the context of their particular theoretical bases and methodological constraints.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12934-022-01914-1.

Expression of Functional Cannabinoid Type-1 (CB1) Receptor in Mitochondria of White Adipocytes

Via activation of the cannabinoid type-1 (CB₁) receptor, endogenous and exogenous cannabinoids modulate important biochemical and cellular processes in adipocytes. Several pieces of evidence suggest that alterations of mitochondrial physiology might be a possible mechanism underlying cannabinoids' effects on adipocyte biology. Many reports suggest the presence of CB₁ receptor mRNA in both white and brown adipose tissue, but the detailed subcellular localization of CB₁ protein in adipose cells has so far been scarcely addressed. In this study, we show the presence of the functional CB₁ receptor at different subcellular locations of adipocytes from epididymal white adipose tissue (eWAT) depots. We observed that CB₁ is located at different subcellular levels, including the plasma membrane and in close association with mitochondria (mtCB₁). Functional analysis in tissue homogenates and isolated mitochondria allowed us to reveal that cannabinoids negatively regulate complex-I-dependent oxygen consumption in eWAT. This effect requires mtCB₁ activation and consequent regulation of the intramitochondrial cAMP-PKA pathway. Thus, CB₁ receptors are functionally present at the mitochondrial level in eWAT adipocytes, adding another possible mechanism for peripheral regulation of energy metabolism.

Cannabinoids and PPAR Ligands: The Future in Treatment of Polycystic Ovary Syndrome Women with Obesity and Reduced Fertility

Cannabinoids (CBs) are used to treat chronic pain, chemotherapy-induced nausea and vomiting, and multiple sclerosis spasticity. Recently, the medicinal use of CBs has attracted increasing interest as a new therapeutic in many diseases. Data indicate a correlation between CBs and PPARs via diverse mechanisms. Both the endocannabinoid system (ECS) and peroxisome proliferator-activated receptors (PPARs) may play a significant role in PCOS and PCOS related disorders, especially in disturbances of glucose-lipid metabolism as well as in obesity and fertility. Taking into consideration the ubiquity of PCOS in the human population, it seems indispensable to search for new potential therapeutic targets for this condition. The aim of this review is to examine the relationship between metabolic disturbances and obesity in PCOS pathology. We discuss current and future therapeutic interventions for PCOS and related disorders, with emphasis on the metabolic pathways related to PCOS pathophysiology. The link between the ECS and PPARs is a promising new target for PCOS, and we examine this relationship in depth.

Sex-specific characteristics of cells expressing the cannabinoid 1 receptor in the dorsal horn of the lumbar spinal cord

It is becoming increasingly clear that robust sex differences exist in the processing of acute and chronic pain in both rodents and humans. However, the underlying mechanism has not been well characterized. The dorsal horn of the lumbar spinal cord is the fundamental building block of ascending and descending pain pathways. It has been shown that numerous neurotransmitter and neuromodulator systems in the spinal cord, including the endocannabinoid system and its main receptor, the cannabinoid 1 receptor (CB₁ R), play vital roles in processing nociceptive information. Our previous findings have shown that CB₁ R mRNA is widely expressed in the brain in sex-dependent patterns. However, the sex-, lamina-, and cell-type-specific characteristics of CB₁ R expression in the spinal cord have not been fully described. In this study, the CB₁ R-iCre-EGFP mouse strain was generated to label and identify CB₁ R-positive (CB₁ R^GFP ) cells. We reported no sex difference in CB₁ R expression in the lumbar dorsal horn of the spinal cord, but a dynamic distribution within superficial laminae II and III in female mice between estrus and nonestrus phases. Furthermore, the cell-type-specific CB₁ R expression pattern in the dorsal horn was similar in both sexes. Over 50% of CB₁ R^GFP cells were GABAergic neurons, and approximately 25% were glycinergic and 20-30% were glutamatergic neurons. The CB₁ R-expressing cells also represented a subset of spinal projection neurons. Overall, our work indicates a highly consistent distribution pattern of CB₁ R^GFP cells in the dorsal horn of lumbar spinal cord in males and females.

Endocannabinoid signaling in oligodendroglia

In the central nervous system, oligodendrocytes synthesize the myelin, a specialized membrane to wrap axons in a discontinuous way allowing a rapid saltatory nerve impulse conduction. Oligodendrocytes express a number of growth factors and neurotransmitters receptors that allow them to sense the environment and interact with neurons and other glial cells. Depending on the cell cycle stage, oligodendrocytes may respond to these signals by regulating their survival, proliferation, migration, and differentiation. Among these signals are the endocannabinoids, lipidic molecules synthesized from phospholipids in the plasma membrane in response to cell activation. Here, we discuss the evidence showing that oligodendrocytes express a full endocannabinoid signaling machinery involved in physiological oligodendrocyte functions that can be therapeutically exploited to promote remyelination in central nervous system pathologies.

Mitochondrial Localization of CB1 in Progesterone-producing Cells of Ovarian Interstitial Glands of Adult Mice

Localization of cannabinoid receptor type 1 (CB1) immunoreactivity on mitochondrial membranes, at least their outer membranes distinctly, was detected in progesterone-producing cells characterized by mitochondria having tubular cristae and aggregations of lipid droplets in ovarian interstitial glands in situ of adult mice. Both immunoreactive and immunonegative mitochondria were contained in one and the same cell. Considering that the synthesis of progesterone is processed in mitochondria, the mitochondrial localization of CB1 in the interstitial gland cells suggests the possibility that endocannabinoids modulate the synthetic process of progesterone in the cells through CB1.

Astroglial ER-mitochondria calcium transfer mediates endocannabinoid-dependent synaptic integration

Intracellular calcium signaling underlies the astroglial control of synaptic transmission and plasticity. Mitochondria-endoplasmic reticulum contacts (MERCs) are key determinants of calcium dynamics, but their functional impact on astroglial regulation of brain information processing is unexplored. We found that the activation of astrocyte mitochondrial-associated type-1 cannabinoid (mtCB₁) receptors determines MERC-dependent intracellular calcium signaling and synaptic integration. The stimulation of mtCB₁ receptors promotes calcium transfer from the endoplasmic reticulum to mitochondria through a specific molecular cascade, involving the mitochondrial calcium uniporter (MCU). Physiologically, mtCB₁-dependent mitochondrial calcium uptake determines the dynamics of cytosolic calcium events in astrocytes upon endocannabinoid mobilization. Accordingly, electrophysiological recordings in hippocampal slices showed that conditional genetic exclusion of mtCB₁ receptors or dominant-negative MCU expression in astrocytes blocks lateral synaptic potentiation, through which astrocytes integrate the activity of distant synapses. Altogether, these data reveal an endocannabinoid link between astroglial MERCs and the regulation of brain network functions.

The Endocannabinoid System in Glial Cells and Their Profitable Interactions to Treat Epilepsy: Evidence from Animal Models

Epilepsy is one of the most common neurological conditions. Yearly, five million people are diagnosed with epileptic-related disorders. The neuroprotective and therapeutic effect of (endo)cannabinoid compounds has been extensively investigated in several models of epilepsy. Therefore, the study of specific cell-type-dependent mechanisms underlying cannabinoid effects is crucial to understanding epileptic disorders. It is estimated that about 100 billion neurons and a roughly equal number of glial cells co-exist in the human brain. The glial population is in charge of neuronal viability, and therefore, their participation in brain pathophysiology is crucial. Furthermore, glial malfunctioning occurs in a wide range of neurological disorders. However, little is known about the impact of the endocannabinoid system (ECS) regulation over glial cells, even less in pathological conditions such as epilepsy. In this review, we aim to compile the existing knowledge on the role of the ECS in different cell types, with a particular emphasis on glial cells and their impact on epilepsy. Thus, we propose that glial cells could be a novel target for cannabinoid agents for treating the etiology of epilepsy and managing seizure-like disorders.

Microglial Cannabinoid Type 1 Receptor Regulates Brain Inflammation in a Sex-Specific Manner

Background: Neuroinflammation is a key feature shared by most, if not all, neuropathologies. It involves complex biological processes that act as a protective mechanism to fight against the injurious stimuli, but it can lead to tissue damage if self-perpetuating. In this context, microglia, the main cellular actor of neuroinflammation in the brain, are seen as a double-edged sword. By phagocyting neuronal debris, these cells can not only provide tissue repair but can also contribute to neuronal damage by releasing harmful substances, including inflammatory cytokines. The mechanisms guiding these apparent opposing actions are poorly known. The endocannabinoid system modulates the release of inflammatory factors such as cytokines and could represent a functional link between microglia and neuroinflammatory processes. According to transcriptomic databases and in vitro studies, microglia, the main source of cytokines in pathological conditions, express the cannabinoid type 1 receptor (CB1R). Methods: We thus developed a conditional mouse model of CB1R deletion specifically in microglia, which was subjected to an immune challenge (peripheral lipopolysaccharide injection). Results: Our results reveal that microglial CB1R differentially controls sickness behavior in males and females. Conclusion: These findings add to the comprehension of neuroinflammatory processes and might be of great interest for future studies aimed at developing therapeutic strategies for brain disorders with higher prevalence in men.

Alterations in Brain Cannabinoid Receptor Levels Are Associated with HIV-Associated Neurocognitive Disorders in the ART Era: Implications for Therapeutic Strategies Targeting the Endocannabinoid System

HIV-associated neurocognitive disorders (HAND) persist despite the advent of antiretroviral therapy (ART), suggesting underlying systemic and central nervous system (CNS) inflammatory mechanisms. The endogenous cannabinoid receptors 1 and 2 (CB₁ and CB₂) modulate inflammatory gene expression and play an important role in maintaining neuronal homeostasis. Cannabis use is disproportionately high among people with HIV (PWH) and may provide a neuroprotective effect for those on ART due to its anti-inflammatory properties. However, expression profiles of CB₁ and CB₂ in the brains of PWH on ART with HAND have not been reported. In this study, biochemical and immunohistochemical analyses were performed to determine CB₁ and CB₂ expression in the brain specimens of HAND donors. Immunoblot revealed that CB₁ and CB₂ were differentially expressed in the frontal cortices of HAND brains compared to neurocognitively unimpaired (NUI) brains of PWH. CB₁ expression levels negatively correlated with memory and information processing speed. CB₁ was primarily localized to neuronal soma in HAND brains versus a more punctate distribution of neuronal processes in NUI brains. CB₁ expression was increased in cells with glial morphology and showed increased colocalization with an astroglial marker. These results suggest that targeting the endocannabinoid system may be a potential therapeutic strategy for HAND.

Fit-for-purpose based testing and validation of antibodies to amino- and carboxy-terminal domains of cannabinoid receptor 1

Specific and selective anti-CB₁ antibodies are among the most powerful research tools to unravel the complex biological processes mediated by the CB₁ receptor in both physiological and pathological conditions. However, low performance of antibodies remains a major source of inconsistency between results from different laboratories. Using a variety of techniques, including some of the most commonly accepted ones for antibody specificity testing, we identified three of five commercial antibodies against different regions of CB₁ receptor as the best choice for specific end-use purposes. Specifically, an antibody against a long fragment of the extracellular amino tail of CB₁ receptor (but not one against a short sequence of the extreme amino-terminus) detected strong surface staining when applied to live cells, whereas two different antibodies against an identical fragment of the extreme carboxy-terminus of CB₁ receptor (but not one against an upstream peptide) showed acceptable performance on all platforms, although they behaved differently in immunohistochemical assays depending on the tissue fixation procedure used and showed different specificity in Western blot assays, which made each of them particularly suitable for one of those techniques. Our results provide a framework to interpret past and future results derived from the use of different anti-CB₁ antibodies in the context of current knowledge about the CB₁ receptor at the molecular level, and highlight the need for an adequate validation for specific purposes, not only before antibodies are placed on the market, but also before the decision to discontinue them is made.

Noncanonical Activity of Endocannabinoids and Their Receptors in Central and Peripheral Synapses

This review focuses on new aspects of endocannabinoid functions and mechanisms of activity in central and peripheral synapses, different from the general viewpoint that endocannabinoids are retrograde signaling molecules, which inhibit neurotransmitter release by activating specific presynaptic endocannabinoid receptors CB1 and CB2. Biased agonism of the endogenous and synthetic cannabinoids as well as ability of the CB-receptors to couple not only with classical G_i-proteins, but also with G_s- and G_q-proteins and, moreover, with β-arrestins (thereby triggering additional signaling pathways in synapses) are described here in detail. Examples of noncanonical tonic activity of endocannabinoids and their receptors and their role in synaptic function are also presented. The role of endocannabinoids in short-term and long-term potentiation of neurotransmitter release in central synapses and their facilitating effect on quantal size and other parameters of acetylcholine release in mammalian neuromuscular junctions are highlighted in this review. In conclusion, it is stated that the endocannabinoid system has a wider range of various multidirectional modulating effects (both potentiating and inhibiting) on neurotransmitter release than initially recognized. Re-evaluation of the functions of endocannabinoid system with consideration of its noncanonical features will lead to better understanding of its role in the normal and pathological functioning of the nervous system and other systems of the body, which has an enormous practical value.

CB1R-dependent regulation of astrocyte physiology and astrocyte-neuron interactions

The endocannabinoid system (ECS) is involved in a variety of brain functions, mainly through the activation of the type-1 cannabinoid receptors (CB1R). CB1R are highly expressed throughout the brain at different structural, cellular and subcellular locations and its activity and expression levels have a direct impact in synaptic activity and behavior. In the last few decades, astrocytes have arisen as active players of brain physiology through their participation in the tripartite synapse and through their metabolic interaction with neurons. Here, we discuss some of the mechanisms by which astroglial CB1R at different subcellular locations, regulate astrocyte calcium signals and have an impact on gliotransmission and metabolic regulation. In addition, we discuss evidence pointing at astrocytes as potential important sources of endocannabinoid synthesis and release. Thus, we summarize recent findings that add further complexity and establish that the ECS is a fundamental effector of astrocyte functions in the brain. This article is part of the special issue on 'Cannabinoids'.

The endocannabinoid system as a therapeutic target for schizophrenia: Failures and potentials

Owing to its psychotropic effects, Cannabis has been stigmatized by its recreational use leading to a dramatic decline in the experimentations about its medical use in the twentieth century. The medical properties of the plant - known since ancient times - have received increased attention over recent years; yet, the research on its potential application in the field of psychiatry is still nascent. In this connection, the non-psychotropic cannabidiol (CBD) has emerged as a phytocannabinoid compound with promising antipsychotic effects. In addition, advances in our understanding of the endocannabinoid system, along with accumulating evidence implicating this system in the pathophysiology of schizophrenia, have stimulated research by the pharmaceutical industry to explore whether alteration of this system can be of medical benefit. This review examines the current state of evidence regarding the clinical potential of cannabinoid-based drugs as a treatment for schizophrenia, while discussing various limitations with the therapeutic approaches considered so far. In the second part, the author highlights the most promising strategies, as well as the most interesting directions one could follow, in the emerging field of cannabinoid therapies for schizophrenia.

Cannabinoid control of hippocampal functions: the where matters

In the brain, hippocampal circuits are crucial for cognitive performance (e.g., memory) and deeply affected in pathological conditions (e.g., epilepsy, Alzheimer). Specialized molecular mechanisms regulate different cell types underlying hippocampal circuitries functions. Among them, cannabinoid receptors exhibit various roles depending on the cell type (e.g., neuron, glial cell) or subcellular organelle (e.g., mitochondria). Determining the site of action and precise mechanisms triggered by cannabinoid receptor activation at a local cellular and subcellular level helps us understand hippocampal pathophysiological states. In doing so, past and current research have advanced our knowledge of cannabinoid functions and proposed novel routes for potential therapeutics. By outlining these data in this work, we aim to showcase current findings and highlight the pathophysiological impact of the cannabinoid receptor type 1 (CB1) localization/activation in hippocampal circuits.

The Absence of the Transient Receptor Potential Vanilloid 1 Directly Impacts on the Expression and Localization of the Endocannabinoid System in the Mouse Hippocampus

The transient receptor potential vanilloid 1 (TRPV1) is a non-selective ligand-gated cation channel involved in synaptic transmission, plasticity, and brain pathology. In the hippocampal dentate gyrus, TRPV1 localizes to dendritic spines and dendrites postsynaptic to excitatory synapses in the molecular layer (ML). At these same synapses, the cannabinoid CB₁ receptor (CB₁R) activated by exogenous and endogenous cannabinoids localizes to the presynaptic terminals. Hence, as both receptors are activated by endogenous anandamide, co-localize, and mediate long-term depression of the excitatory synaptic transmission at the medial perforant path (MPP) excitatory synapses though by different mechanisms, it is plausible that they might be exerting a reciprocal influence from their opposite synaptic sites. In this anatomical scenario, we tested whether the absence of TRPV1 affects the endocannabinoid system. The results obtained using biochemical techniques and immunoelectron microscopy in a mouse with the genetic deletion of TRPV1 show that the expression and localization of components of the endocannabinoid system, included CB₁R, change upon the constitutive absence of TRPV1. Thus, the expression of fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL) drastically increased in TRPV1^-/- whole homogenates. Furthermore, CB₁R and MAGL decreased and the cannabinoid receptor interacting protein 1a (CRIP1a) increased in TRPV1^-/- synaptosomes. Also, CB₁R positive excitatory terminals increased, the number of excitatory terminals decreased, and CB₁R particles dropped significantly in inhibitory terminals in the dentate ML of TRPV1^-/- mice. In the outer 2/3 ML of the TRPV1^-/- mutants, the proportion of CB₁R particles decreased in dendrites, and increased in excitatory terminals and astrocytes. In the inner 1/3 ML, the proportion of labeling increased in excitatory terminals, neuronal mitochondria, and dendrites. Altogether, these observations indicate the existence of compensatory changes in the endocannabinoid system upon TRPV1 removal, and endorse the importance of the potential functional adaptations derived from the lack of TRPV1 in the mouse brain.

Acute Δ9-tetrahydrocannabinol prompts rapid changes in cannabinoid CB1 receptor immunolabeling and subcellular structure in CA1 hippocampus of young adult male mice

The use and abuse of cannabis can be associated with significant pathophysiology, however, it remains unclear whether (1) acute administration of Δ-9-tetrahydrocannabinol (THC) during early adulthood alters the cannabinoid type 1 (CB₁ ) receptor localization and expression in cells of the brain, and (2) THC produces structural brain changes. Here we use electron microscopy and a highly sensitive pre-embedding immunogold method to examine CB₁ receptors in the hippocampus cornu ammonis subfield 1 (CA1) 30 min after male mice were exposed to a single THC injection (5 mg/kg). The findings show that acute exposure to THC can significantly decrease the percentage of CB₁ receptor immunopositive terminals making symmetric synapses, mitochondria, and astrocytes. The percentage of CB₁ receptor-labeled terminals forming asymmetric synapses was unaffected. Lastly, CB₁ receptor expression was significantly lower at terminals of symmetric and asymmetric synapses as well as in mitochondria. Structurally, CA1 dendrites were significantly larger, and contained more spines and mitochondria following acute THC administration. The area of the dendritic spines, synaptic terminals, mitochondria, and astrocytes decreased significantly following acute THC exposure. Altogether, these results indicate that even a single THC exposure can have a significant impact on CB₁ receptor expression, and can alter CA1 ultrastructure, within 30 min of drug exposure. These changes may contribute to the behavioral alterations experienced by young individuals shortly after cannabis intoxication.

Low Basal CB2R in Dopamine Neurons and Microglia Influences Cannabinoid Tetrad Effects

There are two well-characterized cannabinoid receptors (CB1R and CB2R and other candidates): the central nervous system (CNS) enriched CB1R and peripheral tissue enriched CB2R with a wide dynamic range of expression levels in different cell types of human tissues. Hepatocytes and neurons express low baseline CB1R and CB2R, respectively, and their cell-type-specific functions are not well defined. Here we report inducible expression of CB1R in the liver by high-fat and high sugar diet and CB2R in cortical neurons by methamphetamine. While there is less controversy about hepatocyte CB1R, the presence of functional neuronal CB2R is still debated to date. We found that neuron CB2R basal expression was higher than that of hepatocyte CB1R by measuring mRNA levels of specific isoform CB2A in neurons isolated by fluorescence-activated cell sorting (FACS) and CB1A in hepatocytes isolated by collagenase perfusion of liver. For in vivo studies, we generated hepatocyte, dopaminergic neuron, and microglia-specific conditional knockout mice (Abl-Cnr1Δ, Dat-Cnr2Δ, and Cx3cr1-Cnr2Δ) of CB1R and CB2R by crossing Cnr1f/f and Cnr2f/f strains to Abl-Cre, Dat-Cre, and Cx3cr1-Cre deleter mouse strains, respectively. Our data reveals that neuron and microglia CB2Rs are involved in the "tetrad" effects of the mixed agonist WIN 55212-2, CB1R selective agonist arachidonyl-2'-chloroethylamide (ACEA), and CB2R selective agonist JWH133. Dat-Cnr2Δ and Cx3cr1-Cnr2Δ mice showed genotypic differences in hypomobility, hypothermia, analgesia, and catalepsy induced by the synthetic cannabinoids. Alcohol conditioned place preference was abolished in DAT-Cnr2Δ mice and remained intact in Cx3cr1-Cnr2Δ mice in comparison to WT mice. These Cre-loxP recombinant mouse lines provide unique approaches in cannabinoid research for dissecting the complex endocannabinoid system that is implicated in many chronic disorders.