Cell-specific STORM super-resolution imaging reveals nanoscale organization of cannabinoid signaling

SGIP1 binding to the α-helical H9 domain of cannabinoid receptor 1 promotes axonal surface expression

Endocannabinoid signalling mediated by cannabinoid receptor 1 (CB1R, also known as CNR1) is critical for homeostatic neuromodulation of both excitatory and inhibitory synapses. This requires highly polarised axonal surface expression of CB1R, but how this is achieved remains unclear. We previously reported that the α-helical H9 domain in the intracellular C terminus of CB1R contributes to axonal surface expression by an unknown mechanism. Here, we show in rat primary neuronal cultures that the H9 domain binds to the endocytic adaptor protein SGIP1 to promote CB1R expression in the axonal membrane. Overexpression of SGIP1 increases CB1R axonal surface localisation but has no effect on CB1R lacking the H9 domain (CB1RΔH9). Conversely, SGIP1 knockdown reduces axonal surface expression of CB1R but does not affect CB1RΔH9. Furthermore, SGIP1 knockdown diminishes CB1R-mediated inhibition of presynaptic Ca2+ influx in response to neuronal activity. Taken together, these data advance mechanistic understanding of endocannabinoid signalling by demonstrating that SGIP1 interaction with the H9 domain underpins axonal CB1R surface expression to regulate presynaptic responsiveness.

Presynaptic nanoscale components of retrograde synaptic signaling

While our understanding of the nanoscale architecture of anterograde synaptic transmission is rapidly expanding, the qualitative and quantitative molecular principles underlying distinct mechanisms of retrograde synaptic communication remain elusive. We show that a particular form of tonic cannabinoid signaling is essential for setting target cell-dependent synaptic variability. It does not require the activity of the two major endocannabinoid-producing enzymes. Instead, by developing a workflow for physiological, anatomical, and molecular measurements at the same unitary synapse, we demonstrate that the nanoscale stoichiometric ratio of type 1 cannabinoid receptors (CB1Rs) to the release machinery is sufficient to predict synapse-specific release probability. Accordingly, selective decrease of extrasynaptic CB1Rs does not affect synaptic transmission, whereas in vivo exposure to the phytocannabinoid Δ9-tetrahydrocannabinol disrupts the intrasynaptic nanoscale stoichiometry and reduces synaptic variability. These findings imply that synapses leverage the nanoscale stoichiometry of presynaptic receptor coupling to the release machinery to establish synaptic strength in a target cell-dependent manner.

Cholecystokinin neurotransmission in the central nervous system: Insights into its role in health and disease

Cholecystokinin (CCK) plays a key role in various brain functions, including both health and disease states. Despite the extensive research conducted on CCK, there remain several important questions regarding its specific role in the brain. As a result, the existing body of literature on the subject is complex and sometimes conflicting. The primary objective of this review article is to provide a comprehensive overview of recent advancements in understanding the central nervous system role of CCK, with a specific emphasis on elucidating CCK's mechanisms for neuroplasticity, exploring its interactions with other neurotransmitters, and discussing its significant involvement in neurological disorders. Studies demonstrate that CCK mediates both inhibitory long-term potentiation (iLTP) and excitatory long-term potentiation (eLTP) in the brain. Activation of the GPR173 receptor could facilitate iLTP, while the Cholecystokinin B receptor (CCKBR) facilitates eLTP. CCK receptors' expression on different neurons regulates activity, neurotransmitter release, and plasticity, emphasizing CCK's role in modulating brain function. Furthermore, CCK plays a pivotal role in modulating emotional states, Alzheimer's disease, addiction, schizophrenia, and epileptic conditions. Targeting CCK cell types and circuits holds promise as a therapeutic strategy for alleviating these brain disorders.

Shedding light on cholecystokinin's role in hippocampal neuroplasticity and memory formation

The hippocampus is a crucial brain region involved in the process of forming and consolidating memories. Memories are consolidated in the brain through synaptic plasticity, and a key mechanism underlying this process is called long-term potentiation (LTP). Recent research has shown that cholecystokinin (CCK) plays a role in facilitating the formation of LTP, as well as learning and memory consolidation. However, the specific mechanisms by which CCK is involved in hippocampal neuroplasticity and memory formation are complicated or poorly understood. This literature review aims to explore the role of LTP in memory formation, particularly in relation to hippocampal memory, and to discuss the implications of CCK and its receptors in the formation of hippocampal memories. Additionally, we will examine the circuitry of CCK in the hippocampus and propose potential CCK-dependent mechanisms of synaptic plasticity that contribute to memory formation.

Cannabinoid Receptor Signaling is Dependent on Sub-Cellular Location

G protein-coupled receptors (GPCRs) are membrane bound signaling molecules that regulate many aspects of human physiology. Recent advances have demonstrated that GPCR signaling can occur both at the cell surface and internal cellular membranes. Our findings suggest that cannabinoid receptor 1 (CB1) signaling is highly dependent on its subcellular location. We find that intracellular CB1 receptors predominantly couple to Gαi while plasma membrane receptors couple to Gαs. Here we show subcellular location of CB1, and its signaling, is contingent on the choice of promoters and receptor tags. Heterologous expression with a strong promoter or N-terminal tag resulted in CB1 predominantly localizing to the plasma membrane and signaling through Gαs. Conversely, CB1 driven by low expressing promoters and lacking N-terminal genetic tags largely localized to internal membranes and signals via Gαi. Lastly, we demonstrate that genetically encodable non-canonical amino acids (ncAA) offer a solution to the problem of non-native N-terminal tags disrupting CB1 signaling. We identified sites in CB1R and CB2R which can be tagged with fluorophores without disrupting CB signaling or trafficking using (trans-cyclooctene attached to lysine (TCO*A)) and copper-free click chemistry to attach fluorophores in live cells. Together, our data demonstrate the origin of location bias in cannabinoid signaling which can be experimentally controlled and tracked in living cells through promoters and novel CBR tagging strategies.

Cannabis Dependence is Associated with Reduced Hippocampal Subregion Volumes Independently of Sex: Findings from an ENIGMA Addiction Working Group Multi-Country Study

Background: Males and females who consume cannabis can experience different mental health and cognitive problems. Neuroscientific theories of addiction postulate that dependence is underscored by neuroadaptations, but do not account for the contribution of distinct sexes. Further, there is little evidence for sex differences in the neurobiology of cannabis dependence as most neuroimaging studies have been conducted in largely male samples in which cannabis dependence, as opposed to use, is often not ascertained. Methods: We examined subregional hippocampus and amygdala volumetry in a sample of 206 people recruited from the ENIGMA Addiction Working Group. They included 59 people with cannabis dependence (17 females), 49 cannabis users without cannabis dependence (20 females), and 98 controls (33 females). Results: We found no group-by-sex effect on subregional volumetry. The left hippocampal cornu ammonis subfield 1 (CA1) volumes were lower in dependent cannabis users compared with non-dependent cannabis users (p<0.001, d=0.32) and with controls (p=0.022, d=0.18). Further, the left cornu ammonis subfield 3 (CA3) and left dentate gyrus volumes were lower in dependent versus non-dependent cannabis users but not versus controls (p=0.002, d=0.37, and p=0.002, d=0.31, respectively). All models controlled for age, intelligence quotient (IQ), alcohol and tobacco use, and intracranial volume. Amygdala volumetry was not affected by group or group-by-sex, but was smaller in females than males. Conclusions: Our findings suggest that the relationship between cannabis dependence and subregional volumetry was not moderated by sex. Specifically, dependent (rather than non-dependent) cannabis use may be associated with alterations in selected hippocampus subfields high in cannabinoid type 1 (CB1) receptors and implicated in addictive behavior. As these data are cross-sectional, it is plausible that differences predate cannabis dependence onset and contribute to the initiation of cannabis dependence. Longitudinal neuroimaging work is required to examine the time-course of the onset of subregional hippocampal alterations in cannabis dependence, and their progression as cannabis dependence exacerbates or recovers over time.

Retrograde endocannabinoid signaling at inhibitory synapses in vivo

Endocannabinoid (eCB)-mediated suppression of inhibitory synapses has been hypothesized, but this has not yet been demonstrated to occur in vivo because of the difficulty in tracking eCB dynamics and synaptic plasticity during behavior. In mice navigating a linear track, we observed location-specific eCB signaling in hippocampal CA1 place cells, and this was detected both in the postsynaptic membrane and the presynaptic inhibitory axons. All-optical in vivo investigation of synaptic responses revealed that postsynaptic depolarization was followed by a suppression of inhibitory synaptic potentials. Furthermore, interneuron-specific cannabinoid receptor deletion altered place cell tuning. Therefore, rapid, postsynaptic, activity-dependent eCB signaling modulates inhibitory synapses on a timescale of seconds during behavior.

Ventral hippocampal cholecystokinin interneurons gate contextual reward memory

Associating contexts with rewards depends on hippocampal circuits, with local inhibitory interneurons positioned to play an important role in shaping activity. Here, we demonstrate that the encoding of context-reward memory requires a ventral hippocampus (vHPC) to nucleus accumbens (NAc) circuit that is gated by cholecystokinin (CCK) interneurons. In a sucrose conditioned place preference (CPP) task, optogenetically inhibiting vHPC-NAc terminals impaired the acquisition of place preference. Transsynaptic rabies tracing revealed vHPC-NAc neurons were monosynaptically innervated by CCK interneurons. Using intersectional genetic targeting of CCK interneurons, ex vivo optogenetic activation of CCK interneurons increased GABAergic transmission onto vHPC-NAc neurons, while in vivo optogenetic inhibition of CCK interneurons increased cFos in these projection neurons. Notably, CCK interneuron inhibition during sucrose CPP learning increased time spent in the sucrose-associated location, suggesting enhanced place-reward memory. Our findings reveal a previously unknown hippocampal microcircuit crucial for modulating the strength of contextual reward learning.

Blood oxygen regulation via P2Y12R expressed in the carotid body

BACKGROUND

Peripheral blood oxygen monitoring via chemoreceptors in the carotid body (CB) is an integral function of the autonomic cardiorespiratory regulation. The presence of the purinergic P2Y12 receptor (P2Y12R) has been implicated in CB; however, the exact role of the receptor in O2 sensing and signal transduction is unknown.

METHODS

The presence of P2Y12R was established by immunoblotting, RT qPCR and immunohistochemistry. Primary glomus cells were used to assess P2Y12R function during hypoxia and hypercapnia, where monoamines were measured by HPLC; calcium signal was recorded utilizing OGB-1 and N-STORM Super-Resolution System. Ingravescent hypoxia model was tested in anaesthetized mice of mixed gender and cardiorespiratory parameters were recorded in control and receptor-deficient or drug-treated experimental animals.

RESULTS

Initially, the expression of P2Y12R in adult murine CB was confirmed. Hypoxia induced a P2Y12R-dependent release of monoamine transmitters from isolated CB cells. Receptor activation with the endogenous ligand ADP promoted release of neurotransmitters under normoxic conditions, while blockade disrupted the amplitude and duration of the intracellular calcium concentration. In anaesthetised mice, blockade of P2Y12R expressed in the CB abrogated the initiation of compensatory cardiorespiratory changes in hypoxic environment, while centrally inhibited receptors (i.e. microglial receptors) or receptor-deficiency induced by platelet depletion had limited influence on the physiological adjustment to hypoxia.

CONCLUSIONS

Peripheral P2Y12R inhibition interfere with the complex mechanisms of acute oxygen sensing by influencing the calcium signalling and the release of neurotransmitter molecules to evoke compensatory response to hypoxia. Prospectively, the irreversible blockade of glomic receptors by anti-platelet drugs targeting P2Y12Rs, propose a potential, formerly unrecognized side-effect to anti-platelet medications in patients with pulmonary morbidities.

Microscopy and spectroscopy approaches to study GPCR structure and function

The GPCR signalling cascade is a key pathway responsible for the signal transduction of a multitude of physical and chemical stimuli, including light, odorants, neurotransmitters and hormones. Understanding the structural and functional properties of the GPCR cascade requires direct observation of signalling processes in high spatial and temporal resolution, with minimal perturbation to endogenous systems. Optical microscopy and spectroscopy techniques are uniquely suited to this purpose because they excel at multiple spatial and temporal scales and can be used in living objects. Here, we review recent developments in microscopy and spectroscopy technologies which enable new insights into GPCR signalling. We focus on advanced techniques with high spatial and temporal resolution, single-molecule methods, labelling strategies and approaches suitable for endogenous systems and large living objects. This review aims to assist researchers in choosing appropriate microscopy and spectroscopy approaches for a variety of applications in the study of cellular signalling.

Cannabinoid CB1 Receptor Expression and Localization in the Dorsal Horn of Male and Female Rat and Human Spinal Cord

Background

Preclinical and clinical evidence suggests that cannabis has potential analgesic properties. However, cannabinoid receptor expression and localization within spinal cord pain processing circuits remain to be characterized across sex and species.

Aims

We aimed to investigate the differential expression of the cannabinoid type 1 (CB1) receptor across dorsal horn laminae and cell populations in male and female adult rats and humans.

Methods

To investigate and quantify CB1 receptor expression in the spinal dorsal horn across species, we refined immunohistochemical procedures for successful rat and human fixed tissue staining and confocal imaging. Immunohistochemical results were complemented with analysis of CB1 gene (CNR1) expression within rodent and human dorsal horn using single-cell/nuclei RNA sequencing data sets.

Results

We found that CB1 was preferentially localized to the neuropil within the superficial dorsal horn of both rats and humans, with CB1 somatic staining across dorsal horn laminae. CB1 receptor immunoreactivity was significantly higher in the superficial dorsal horn compared to the deeper dorsal horn laminae for both rats and humans, which was conserved across sex. Interestingly, we found that CB1 immunoreactivity was not primarily localized to peptidergic afferents in rats and humans and that CNR1 (CB1) but not CNR2 (CB2) was robustly expressed in dorsal horn neuron subpopulations of both rodents and humans.

Conclusions

The conserved preferential expression of CB1 receptors in the superficial dorsal horn in male and female rodents and humans has significant implications for understanding the roles of this cannabinoid receptor in spinal mechanisms of nociception and analgesia.

Imaging and Genetic Tools for the Investigation of the Endocannabinoid System in the CNS

As central nervous system (CNS)-related disorders present an increasing cause of global morbidity, mortality, and high pressure on our healthcare system, there is an urgent need for new insights and treatment options. The endocannabinoid system (ECS) is a critical network of endogenous compounds, receptors, and enzymes that contribute to CNS development and regulation. Given its multifaceted involvement in neurobiology and its significance in various CNS disorders, the ECS as a whole is considered a promising therapeutic target. Despite significant advances in our understanding of the ECS's role in the CNS, its complex architecture and extensive crosstalk with other biological systems present challenges for research and clinical advancements. To bridge these knowledge gaps and unlock the full therapeutic potential of ECS interventions in CNS-related disorders, a plethora of molecular-genetic tools have been developed in recent years. Here, we review some of the most impactful tools for investigating the neurological aspects of the ECS. We first provide a brief introduction to the ECS components, including cannabinoid receptors, endocannabinoids, and metabolic enzymes, emphasizing their complexity. This is followed by an exploration of cutting-edge imaging tools and genetic models aimed at elucidating the roles of these principal ECS components. Special emphasis is placed on their relevance in the context of CNS and its associated disorders.

A cortico-amygdala neural substrate for endocannabinoid modulation of fear extinction

Preclinical and clinical studies implicate endocannabinoids (eCBs) in fear extinction, but the underlying neural circuit basis of these actions is unclear. Here, we employed in vivo optogenetics, eCB biosensor imaging, ex vivo electrophysiology, and CRISPR-Cas9 gene editing in mice to examine whether basolateral amygdala (BLA)-projecting medial prefrontal cortex (mPFC) neurons represent a neural substrate for the effects of eCBs on extinction. We found that photoexcitation of mPFC axons in BLA during extinction mobilizes BLA eCBs. eCB biosensor imaging showed that eCBs exhibit a dynamic stimulus-specific pattern of activity at mPFC→BLA neurons that tracks extinction learning. Furthermore, using CRISPR-Cas9-mediated gene editing, we demonstrated that extinction memory formation involves eCB activity at cannabinoid CB1 receptors expressed at vmPFC→BLA synapses. Our findings reveal the temporal characteristics and a neural circuit basis of eCBs' effects on fear extinction and inform efforts to target the eCB system as a therapeutic approach in extinction-deficient neuropsychiatric disorders.

Perturbation of 3D nuclear architecture, epigenomic aging and dysregulation, and cannabinoid synaptopathy reconfigures conceptualization of cannabinoid pathophysiology: part 2-Metabolome, immunome, synaptome

The second part of this paper builds upon and expands the epigenomic-aging perspective presented in Part 1 to describe the metabolomic and immunomic bases of the epigenomic-aging changes and then considers in some detail the application of these insights to neurotoxicity, neuronal epigenotoxicity, and synaptopathy. Cannabinoids are well-known to have bidirectional immunomodulatory activities on numerous parts of the immune system. Immune perturbations are well-known to impact the aging process, the epigenome, and intermediate metabolism. Cannabinoids also impact metabolism via many pathways. Metabolism directly impacts immune, genetic, and epigenetic processes. Synaptic activity, synaptic pruning, and, thus, the sculpting of neural circuits are based upon metabolic, immune, and epigenomic networks at the synapse, around the synapse, and in the cell body. Many neuropsychiatric disorders including depression, anxiety, schizophrenia, bipolar affective disorder, and autistic spectrum disorder have been linked with cannabis. Therefore, it is important to consider these features and their complex interrelationships in reaching a comprehensive understanding of cannabinoid dependence. Together these findings indicate that cannabinoid perturbations of the immunome and metabolome are important to consider alongside the well-recognized genomic and epigenomic perturbations and it is important to understand their interdependence and interconnectedness in reaching a comprehensive appreciation of the true nature of cannabinoid pathophysiology. For these reasons, a comprehensive appreciation of cannabinoid pathophysiology necessitates a coordinated multiomics investigation of cannabinoid genome-epigenome-transcriptome-metabolome-immunome, chromatin conformation, and 3D nuclear architecture which therefore form the proper mechanistic underpinning for major new and concerning epidemiological findings relating to cannabis exposure.

Mechanisms of cannabinoid tolerance

Cannabis has been used recreationally and medically for centuries, yet research into understanding the mechanisms of its therapeutic effects has only recently garnered more attention. There is evidence to support the use of cannabinoids for the treatment of chronic pain, muscle spasticity, nausea and vomiting due to chemotherapy, improving weight gain in HIV-related cachexia, emesis, sleep disorders, managing symptoms in Tourette syndrome, and patient-reported muscle spasticity from multiple sclerosis. However, tolerance and the risk for cannabis use disorder are two significant disadvantages for cannabinoid-based therapies in humans. Recent work has revealed prominent sex differences in the acute response and tolerance to cannabinoids in both humans and animal models. This review will discuss evidence demonstrating cannabinoid tolerance in rodents, non-human primates, and humans and our current understanding of the neuroadaptations occurring at the cannabinoid type 1 receptor (CB1R) that are responsible tolerance. CB1R expression is downregulated in tolerant animals and humans while there is strong evidence of CB1R desensitization in cannabinoid tolerant rodent models. Throughout the review, critical knowledge gaps are indicated and discussed, such as the lack of a neuroimaging probe to assess CB1R desensitization in humans. The review discusses the intracellular signaling pathways that are responsible for mediating CB1R desensitization and downregulation including the action of G protein-coupled receptor kinases, β-arrestin2 recruitment, c-Jun N-terminal kinases, protein kinase A, and the intracellular trafficking of CB1R. Finally, the review discusses approaches to reduce cannabinoid tolerance in humans based on our current understanding of the neuroadaptations and mechanisms responsible for this process.

Advanced imaging techniques for tracking drug dynamics at the subcellular level

Optical microscopes are an important imaging tool that have effectively advanced the development of modern biomedicine. In recent years, super-resolution microscopy (SRM) has become one of the most popular techniques in the life sciences, especially in the field of living cell imaging. SRM has been used to solve many problems in basic biological research and has great potential in clinical application. In particular, the use of SRM to study drug delivery and kinetics at the subcellular level enables researchers to better study drugs' mechanisms of action and to assess the efficacy of their targets in vivo. The purpose of this paper is to review the recent advances in SRM and to highlight some of its applications in assessing subcellular drug dynamics.

SGIP1 in axons prevents internalization of desensitized CB1R and modifies its function

In the central nervous system (CNS), cannabinoid receptor 1 (CB1R) is preferentially expressed in axons where it has a unique property, namely resistance to agonist-driven endocytosis. This review aims to summarize what we know about molecular mechanisms of CB1R cell surface stability in axonal compartments, how these impact CB1R signaling, and to consider their physiological consequences. This review then focuses on a potential candidate for maintaining axonal CB1R at the cell surface, Src homology 3-domain growth factor receptor-bound 2-like endophilin interacting protein 1 (SGIP1). SGIP1 may contribute to the polarized distribution of CB1R and modify its signaling in axons. In addition, deletion of SGIP1 results in discrete behavioral changes in modalities controlled by the endocannabinoid system in vivo. Several drugs acting directly via CB1R have important therapeutic potential, however their adverse effects limit their clinical use. Future studies might reveal chemical approaches to target the SGIP1-CB1R interaction, with the aim to exploit the endocannabinoid system pharmaceutically in a discrete way, with minimized undesired consequences.

When Super-Resolution Microscopy Meets Microfluidics: Enhanced Biological Imaging and Analysis with Unprecedented Resolution

Super-resolution microscopy is rapidly developed in recent years, allowing biologists to extract more quantitative information on subcellular processes in live cells that is usually not accessible with conventional techniques. However, super-resolution imaging is not fully exploited because of the lack of an appropriate and multifunctional experimental platform. As an important tool in life sciences, microfluidics is capable of cell manipulation and the regulation of the cellular environment because of its superior flexibility and biocompatibility. The combination of microfluidics and super-resolution microscopy revolutionizes the study of complex cellular properties and dynamics, providing valuable insights into cellular structure and biological functions at the single-molecule level. In this perspective, an overview of the main advantages of microfluidic technology that are essential to the performance of super-resolution microscopy are offered. The main benefits of performing super-resolution imaging with microfluidic devices are highlighted and perspectives on the diverse applications that are facilitated by combining these two powerful techniques are provided.

Cannabidiol modulates excitatory-inhibitory ratio to counter hippocampal hyperactivity

Cannabidiol (CBD), a non-euphoric component of cannabis, reduces seizures in multiple forms of pediatric epilepsies, but the mechanism(s) of anti-seizure action remain unclear. In one leading model, CBD acts at glutamatergic axon terminals, blocking the pro-excitatory actions of an endogenous membrane phospholipid, lysophosphatidylinositol (LPI), at the G-protein-coupled receptor GPR55. However, the impact of LPI-GPR55 signaling at inhibitory synapses and in epileptogenesis remains underexplored. We found that LPI transiently increased hippocampal CA3-CA1 excitatory presynaptic release probability and evoked synaptic strength in WT mice, while attenuating inhibitory postsynaptic strength by decreasing GABAARγ2 and gephyrin puncta. LPI effects at excitatory and inhibitory synapses were eliminated by CBD pre-treatment and absent after GPR55 deletion. Acute pentylenetrazole-induced seizures elevated GPR55 and LPI levels, and chronic lithium-pilocarpine-induced epileptogenesis potentiated LPI's pro-excitatory effects. We propose that CBD exerts potential anti-seizure effects by blocking LPI's synaptic effects and dampening hyperexcitability.

Differential effects of group III metabotropic glutamate receptors on spontaneous inhibitory synaptic currents in spine-innervating double bouquet and parvalbumin-expressing dendrite-targeting GABAergic interneurons in human neocortex

Diverse neocortical GABAergic neurons specialize in synaptic targeting and their effects are modulated by presynaptic metabotropic glutamate receptors (mGluRs) suppressing neurotransmitter release in rodents, but their effects in human neocortex are unknown. We tested whether activation of group III mGluRs by L-AP4 changes GABAA receptor-mediated spontaneous inhibitory postsynaptic currents (sIPSCs) in 2 distinct dendritic spine-innervating GABAergic interneurons recorded in vitro in human neocortex. Calbindin-positive double bouquet cells (DBCs) had columnar "horsetail" axons descending through layers II-V innervating dendritic spines (48%) and shafts, but not somata of pyramidal and nonpyramidal neurons. Parvalbumin-expressing dendrite-targeting cell (PV-DTC) axons extended in all directions innervating dendritic spines (22%), shafts (65%), and somata (13%). As measured, 20% of GABAergic neuropil synapses innervate spines, hence DBCs, but not PV-DTCs, preferentially select spine targets. Group III mGluR activation paradoxically increased the frequency of sIPSCs in DBCs (to median 137% of baseline) but suppressed it in PV-DTCs (median 92%), leaving the amplitude unchanged. The facilitation of sIPSCs in DBCs may result from their unique GABAergic input being disinhibited via network effect. We conclude that dendritic spines receive specialized, diverse GABAergic inputs, and group III mGluRs differentially regulate GABAergic synaptic transmission to distinct GABAergic cell types in human cortex.

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.

STORM Super-Resolution Imaging of CB1 Receptors in Tissue Preparations

Single-molecule localization microscopy (SMLM) opened new possibilities to study the spatial arrangement of molecular distribution and disease-associated redistribution at a previously unprecedented resolution that was not achievable with optical microscopy approaches. Recent discoveries based on SMLM techniques uncovered specific nanoscale organizational principles of signaling proteins in several biological systems including the chemical synapses in the brain. Emerging data suggest that the spatial arrangement of the molecular players of the endocannabinoid system is also precisely regulated at the nanoscale level in synapses and in other neuronal and glial subcellular compartments. The precise nanoscale distribution pattern is likely to be important to subserve several specific signaling functions of this important messenger system in a cell-type- and subcellular domain-specific manner.STochastic Optical Reconstruction Microscopy (STORM) is an especially suitable SMLM modality for cell-type-specific nanoscale molecular imaging due to its compatibility with traditional diffraction-limited microscopy approaches and classical staining methods. Here, we describe a detailed protocol for STORM imaging in mouse brain tissue samples with a focus on the CB₁ cannabinoid receptor, one of the most abundant synaptic receptors in the brain. We also summarize important conceptual and methodical details that are essential for the valid interpretation of single-molecule localization microscopy data.

Diverse organization of voltage-gated calcium channels at presynaptic active zones

Synapses are highly organized but are also highly diverse in their organization and properties to allow for optimizing the computing power of brain circuits. Along these lines, voltage-gated calcium (CaV) channels at the presynaptic active zone are heterogeneously organized, which creates a variety of calcium dynamics profiles that can shape neurotransmitter release properties of individual synapses. Extensive studies have revealed striking diversity in the subtype, number, and distribution of CaV channels, as well as the nanoscale topographic relationships to docked synaptic vesicles. Further, multi-protein complexes including RIMs, RIM-binding proteins, CAST/ELKS, and neurexins are required for coordinating the diverse organization of CaV channels at the presynaptic active zone. In this review, we highlight major advances in the studies of the functional organization of presynaptic CaV channels and discuss their physiological implications for synaptic transmission and short-term plasticity.

Adherens junctions organize size-selective proteolytic hotspots critical for Notch signalling

Adherens junctions (AJs) create spatially, chemically and mechanically discrete microdomains at cellular interfaces. Here, using a mechanogenetic platform that generates artificial AJs with controlled protein localization, clustering and mechanical loading, we find that AJs also organize proteolytic hotspots for γ-secretase with a spatially regulated substrate selectivity that is critical in the processing of Notch and other transmembrane proteins. Membrane microdomains outside of AJs exclusively organize Notch ligand-receptor engagement (LRE microdomains) to initiate receptor activation. Conversely, membrane microdomains within AJs exclusively serve to coordinate regulated intramembrane proteolysis (RIP microdomains). They do so by concentrating γ-secretase and primed receptors while excluding full-length Notch. AJs induce these functionally distinct microdomains by means of lipid-dependent γ-secretase recruitment and size-dependent protein segregation. By excluding full-length Notch from RIP microdomains, AJs prevent inappropriate enzyme-substrate interactions and suppress spurious Notch activation. Ligand-induced ectodomain shedding eliminates size-dependent segregation, releasing Notch to translocate into AJs for processing by γ-secretase. This mechanism directs radial differentiation of ventricular zone-neural progenitor cells in vivo and more broadly regulates the proteolysis of other large cell-surface receptors such as amyloid precursor protein. These findings suggest an unprecedented role of AJs in creating size-selective spatial switches that choreograph γ-secretase processing of multiple transmembrane proteins regulating development, homeostasis and disease.

Mapping the Nicotinic Acetylcholine Receptor Nanocluster Topography at the Cell Membrane with STED and STORM Nanoscopies

The cell-surface topography and density of nicotinic acetylcholine receptors (nAChRs) play a key functional role in the synapse. Here we employ in parallel two labeling and two super-resolution microscopy strategies to characterize the distribution of this receptor at the plasma membrane of the mammalian clonal cell line CHO-K1/A5. Cells were interrogated with two targeted techniques (confocal microscopy and stimulated emission depletion (STED) nanoscopy) and single-molecule nanoscopy (stochastic optical reconstruction microscopy, STORM) using the same fluorophore, Alexa Fluor 647, tagged onto either α-bungarotoxin (BTX) or the monoclonal antibody mAb35. Analysis of the topography of nanometer-sized aggregates (“nanoclusters”) was carried out using STORMGraph, a quantitative clustering analysis for single-molecule localization microscopy based on graph theory and community detection, and ASTRICS, an inter-cluster similarity algorithm based on computational geometry. Antibody-induced crosslinking of receptors resulted in nanoclusters with a larger number of receptor molecules and higher densities than those observed in BTX-labeled samples. STORM and STED provided complementary information, STED rendering a direct map of the mesoscale nAChR distribution at distances ~10-times larger than the nanocluster centroid distances measured in STORM samples. By applying photon threshold filtering analysis, we show that it is also possible to detect the mesoscale organization in STORM images.

Combining multiple fluorescence imaging techniques in biology: when one microscope is not enough

While fluorescence microscopy has proven to be an exceedingly useful tool in bioscience, it is difficult to offer simultaneous high resolution, fast speed, large volume, and good biocompatibility in a single imaging technique. Thus, when determining the image data required to quantitatively test a complex biological hypothesis, it often becomes evident that multiple imaging techniques are necessary. Recent years have seen an explosion in development of novel fluorescence microscopy techniques, each of which features a unique suite of capabilities. In this Technical Perspective, we highlight recent studies to illustrate the benefits, and often the necessity, of combining multiple fluorescence microscopy modalities. We provide guidance in choosing optimal technique combinations to effectively address a biological question. Ultimately, we aim to promote a more well-rounded approach in designing fluorescence microscopy experiments, leading to more robust quantitative insight.

Teneurins assemble into presynaptic nanoclusters that promote synapse formation via postsynaptic non-teneurin ligands

Extensive studies concluded that homophilic interactions between pre- and postsynaptic teneurins, evolutionarily conserved cell-adhesion molecules, encode the specificity of synaptic connections. However, no direct evidence is available to demonstrate that teneurins are actually required on both pre- and postsynaptic neurons for establishing synaptic connections, nor is it known whether teneurins are localized to synapses. Using super-resolution microscopy, we demonstrate that Teneurin-3 assembles into presynaptic nanoclusters of approximately 80 nm in most excitatory synapses of the hippocampus. Presynaptic deletions of Teneurin-3 and Teneurin-4 in the medial entorhinal cortex revealed that they are required for assembly of entorhinal cortex-CA1, entorhinal cortex-subiculum, and entorhinal cortex-dentate gyrus synapses. Postsynaptic deletions of teneurins in the CA1 region, however, had no effect on synaptic connections from any presynaptic input. Our data suggest that different from the current prevailing view, teneurins promote the establishment of synaptic connections exclusively as presynaptic cell-adhesion molecules, most likely via their nanomolar-affinity binding to postsynaptic latrophilins.

Cannabis sativa as a Treatment for Obesity: From Anti-Inflammatory Indirect Support to a Promising Metabolic Re-Establishment Target

Introduction: Obesity is defined as an excess of accumulation of fat that can be harmful to health. Storage of excess fat in the adipose tissue triggers an inflammatory process, which makes obesity a low-grade chronic inflammatory disease. Obesity is considered a complex and multifactorial disease; hence, no intervention strategy appears to be an ideal treatment for all individuals. Therefore, new therapeutic alternatives are often studied for the treatment of this disease. Currently, herbal medicines are gaining ground in the treatment of obesity and its comorbidities. In this context, much attention is being paid to Cannabis sativa derivatives, and their therapeutic functions are being widely studied, including in treating obesity. Objective: Highlight the pharmacological properties of Δ9-tetrahydrocannabivarin (THCV), Δ9-tetrahydrocannabidinol (THC), and cannabidiol (CBD), the predominant isolated components of Cannabis sativa, as well as its therapeutic potential in the treatment of obesity. Methods: This is a narrative review that shows the existing scientific evidence on the clinical application of Cannabis sativa as a possible treatment for obesity. Data collection was performed in the PubMed electronic database. The following word combinations were used: Cannabis and obesity, Cannabis sativa and obesity, THCV and obesity, THC and obesity, CBD and obesity, and Cannabis sativa and inflammation. Results: Evidence shows that Cannabis sativa derivatives have therapeutic potential due to their anti-inflammatory properties. In addition, people who use cannabis have a lower body mass index than those who do not, making the plant an option to reduce and reverse inflammation and comorbidities in obesity. Conclusion: It is concluded that phytocannabinoids derived from Cannabis sativa have therapeutic potential due to its anti-inflammatory, antioxidant, and neuroprotective properties, making the plant a study option to reduce and reverse inflammation and comorbidities associated with obesity.

Endocannabinoid system contributions to sex-specific adolescent neurodevelopment

With an increasing number of countries and states adopting legislation permitting the use of cannabis for medical purposes, there is a growing interest among health and research professionals into the system through which cannabinoids principally act, the endocannabinoid system (ECS). Much of the seminal research into the ECS dates back only 30 years and, although there has been tremendous development within the field during this time, many questions remain. More recently, investigations have emerged examining the contributions of the ECS to normative development and the effect of altering this system during important critical periods. One such period is adolescence, a unique period during which brain and behaviours are maturing and reorganizing in preparation for adulthood, including shifts in endocannabinoid biology. The purpose of this review is to discuss findings to date regarding the maturation of the ECS during adolescence and the consequences of manipulations of the ECS during this period to normative neurodevelopmental processes, as well as highlight sex differences in ECS function, important technical considerations, and future directions. Because most of what we know is derived from preclinical studies on rodents, we provide relevant background of this model and some commentary on the translational relevance of the research in this area.

Total variation and spatial iteration-based 3D structured illumination microscopy

Three-dimensional structured illumination microscopy (3D-SIM) plays an essential role in biological volumetric imaging with the capabilities of improving lateral and axial resolution. However, the traditional linear 3D algorithm is sensitive to noise and generates artifacts, while the low temporal resolution hinders live-cell imaging. In this paper, we propose a novel 3D-SIM algorithm based on total variation (TV) and fast iterative shrinkage threshold algorithm (FISTA), termed TV-FISTA-SIM. Compared to conventional algorithms, TV-FISTA-SIM achieves higher reconstruction fidelity with the least artifacts, even when the signal-to-noise ratio (SNR) is as low as 5 dB, and a faster reconstruction rate. Through simulation, we have verified that TV-FISTA-SIM can effectively reduce the amount of required data with less deterioration. Moreover, we demonstrate TV-FISTA-SIM for high-quality multi-color 3D super-resolution imaging, which can be potentially applied to live-cell imaging applications.

Imaging the endocannabinoid signaling system

The endocannabinoid (eCB) system is one of the most widespread neuromodulatory systems in the mammalian brain, with a multifaceted role in functions ranging from development to synaptic plasticity. Endocannabinoids are synthesized on demand from membrane lipid precursors, and act primarily on a single G-protein coupled receptor type, CB1, to carry out diverse functions. Despite the importance of the eCB system both in healthy brain function and in disease, critically important details of eCB signaling remained unknown. How eCBs are released from the membrane, how these lipid molecules are transported between cells, and how the distribution of their receptors is controlled, remained elusive. Recent advances in optical microscopy methods and biosensor engineering may open up new avenues for studying eCB signaling. We summarize applications of superresolution microscopy using single molecule localization to reveal distinct patterns of nanoscale CB1 distribution in neuronal axons and axon terminals. We review single particle tracking studies using quantum dots that allowed visualizing CB1 trajectories. We highlight the recent development of fluorescent eCB biosensors, that revealed spatiotemporally specific eCB release in live cells and live animals. Finally, we discuss future directions where method development may help to advance a precise understanding of eCB signaling.

5-HT3Rs Maintain Hippocampal LTP in a CB1R-GABAA -Dependent Manner for Spatial Memory

BACKGROUND AND PURPOSE

As the only ionotropic receptor in 5-HT receptor family, 5-HT3 receptor (5-HT3R) involves in psychiatric disorders and its modulators have potential therapeutic effects for cognitive impairment in these disorders. However, it remains unclear how 5-HT3Rs shape synaptic plasticity for memory function.

EXPERIMENTAL APPROACH

Extracellular as well as whole-cell recordings were used to monitor hippocampal long-term potentiation (LTP) and synaptic transmission in hippocampal slices from 5-HT3AR knock-out or 5-HT3AR-GFP mice. Immunocytochemistry, qRT-PCR and Western blot were used to measure receptor expression. We also assessed hippocampal dependent cognition and memory using the Morris water maze (MWM) and novel object recognition.

KEY RESULTS

We found that 5-HT3R dysfunction impaired hippocampal LTP in Schaffer collateral (SC)-CA1 pathway in hippocampal slices by facilitating GABAergic inputs in pyramidal cells. This effect was dependent on 5-HT3Rs on axon-terminals. It resulted from reduced expression and function of cannabinoid receptor 1 (CB1R) co-localized with 5-HT3Rs on axon terminals, which led to diminishment of tonic inhibition of GABA release by CB1Rs. Inhibition of CB1Rs mimicked the facilitation of GABAergic transmission by 5-HT3R disruption. Consequently, mice with hippocampal 5-HT3R disruption exhibited impaired spatial memory in Morris water maze tasks.

CONCLUSION AND IMPLICATIONS

These results suggest that 5-HT3Rs are crucial in enabling hippocampal synaptic plasticity via a novel CB1R-GABA_A -dependent pathway to regulate spatial memory.

Cannabinoid Cancer Biology and Prevention

Plant-based, synthetic, and endogenous cannabinoids have been shown to control a diverse array of biological processes, including regulation of cell fate across cancers. Their promise as broad-based antitumor agents in preclinical models has led to the initiation of pilot clinical trials. Session 5 of the National Cancer Institute's Cannabis, Cannabinoids and Cancer Research Symposium provides an overview of this research topic. Overall, the presentations highlight cannabinoid signal transduction and specific molecular mechanisms underlying cannabinoid antitumor activity. They also demonstrate the broad-based antitumor activity of the plant-based, synthetic, and endogenous cannabinoid compounds. Importantly, evidence is presented demonstrating when cannabinoids may be contraindicated as a treatment for cancer, as in the case of human papilloma virus-meditated oropharynx cancer or potentially other p38 MAPK pathway-driven cancers. Finally, it is discussed that a key to advancing cannabinoids into the clinic is to conduct well-designed, large-scale clinical trials to determine whether cannabinoids are effective antitumor agents in cancer patients.

Nanoscale Sub-Compartmentalization of the Dendritic Spine Compartment

Compartmentalization of the membrane is essential for cells to perform highly specific tasks and spatially constrained biochemical functions in topographically defined areas. These membrane lateral heterogeneities range from nanoscopic dimensions, often involving only a few molecular constituents, to micron-sized mesoscopic domains resulting from the coalescence of nanodomains. Short-lived domains lasting for a few milliseconds coexist with more stable platforms lasting from minutes to days. This panoply of lateral domains subserves the great variety of demands of cell physiology, particularly high for those implicated in signaling. The dendritic spine, a subcellular structure of neurons at the receiving (postsynaptic) end of central nervous system excitatory synapses, exploits this compartmentalization principle. In its most frequent adult morphology, the mushroom-shaped spine harbors neurotransmitter receptors, enzymes, and scaffolding proteins tightly packed in a volume of a few femtoliters. In addition to constituting a mesoscopic lateral heterogeneity of the dendritic arborization, the dendritic spine postsynaptic membrane is further compartmentalized into spatially delimited nanodomains that execute separate functions in the synapse. This review discusses the functional relevance of compartmentalization and nanodomain organization in synaptic transmission and plasticity and exemplifies the importance of this parcelization in various neurotransmitter signaling systems operating at dendritic spines, using two fast ligand-gated ionotropic receptors, the nicotinic acetylcholine receptor and the glutamatergic receptor, and a second-messenger G-protein coupled receptor, the cannabinoid receptor, as paradigmatic examples.

PharmacoSTORM nanoscale pharmacology reveals cariprazine binding on Islands of Calleja granule cells

Immunolabeling and autoradiography have traditionally been applied as the methods-of-choice to visualize and collect molecular information about physiological and pathological processes. Here, we introduce PharmacoSTORM super-resolution imaging that combines the complementary advantages of these approaches and enables cell-type- and compartment-specific nanoscale molecular measurements. We exploited rational chemical design for fluorophore-tagged high-affinity receptor ligands and an enzyme inhibitor; and demonstrated broad PharmacoSTORM applicability for three protein classes and for cariprazine, a clinically approved antipsychotic and antidepressant drug. Because the neurobiological substrate of cariprazine has remained elusive, we took advantage of PharmacoSTORM to provide in vivo evidence that cariprazine predominantly binds to D3 dopamine receptors on Islands of Calleja granule cell axons but avoids dopaminergic terminals. These findings show that PharmacoSTORM helps to quantify drug-target interaction sites at the nanoscale level in a cell-type- and subcellular context-dependent manner and within complex tissue preparations. Moreover, the results highlight the underappreciated neuropsychiatric significance of the Islands of Calleja in the ventral forebrain.

Super-resolving Microscopy in Neuroscience

Fluorescence imaging techniques play a pivotal role in our understanding of the nervous system. The emergence of various super-resolution microscopy methods and specialized fluorescent probes enables direct insight into neuronal structure and protein arrangements in cellular subcompartments with so far unmatched resolution. Super-resolving visualization techniques in neurons unveil a novel understanding of cytoskeletal composition, distribution, motility, and signaling of membrane proteins, subsynaptic structure and function, and neuron-glia interaction. Well-defined molecular targets in autoimmune and neurodegenerative disease models provide excellent starting points for in-depth investigation of disease pathophysiology using novel and innovative imaging methodology. Application of super-resolution microscopy in human brain samples and for testing clinical biomarkers is still in its infancy but opens new opportunities for translational research in neurology and neuroscience. In this review, we describe how super-resolving microscopy has improved our understanding of neuronal and brain function and dysfunction in the last two decades.

Single-Molecule Imaging Reveals Rapid Estradiol Action on the Surface Movement of AMPA Receptors in Live Neurons

Gonadal steroid 17β-estradiol (E2) exerts rapid, non-genomic effects on neurons and strictly regulates learning and memory through altering glutamatergic neurotransmission and synaptic plasticity. However, its non-genomic effects on AMPARs are not well understood. Here, we analyzed the rapid effect of E2 on AMPARs using single-molecule tracking and super-resolution imaging techniques. We found that E2 rapidly decreased the surface movement of AMPAR via membrane G protein-coupled estrogen receptor 1 (GPER1) in neurites in a dose-dependent manner. The cortical actin network played a pivotal role in the GPER1 mediated effects of E2 on the surface mobility of AMPAR. E2 also decreased the surface movement of AMPAR both in synaptic and extrasynaptic regions on neurites and increased the synaptic dwell time of AMPARs. Our results provide evidence for understanding E2 action on neuronal plasticity and glutamatergic neurotransmission at the molecular level.

Axonal CB1 Receptors Mediate Inhibitory Bouton Formation via cAMP Increase and PKA

Experience-dependent formation and removal of inhibitory synapses are essential throughout life. For instance, GABAergic synapses are removed to facilitate learning, and strong excitatory activity is accompanied by the formation of inhibitory synapses to maintain coordination between excitation and inhibition. We recently discovered that active dendrites trigger the growth of inhibitory synapses via CB1 receptor-mediated endocannabinoid signaling, but the underlying mechanism remained unclear. Using two-photon microscopy to monitor the formation of individual inhibitory boutons in hippocampal organotypic slices from mice (both sexes), we found that CB1 receptor activation mediated the formation of inhibitory boutons and promoted their subsequent stabilization. Inhibitory bouton formation did not require neuronal activity and was independent of G_i/o-protein signaling, but was directly induced by elevating cAMP levels using forskolin and by activating G_s-proteins using DREADDs. Blocking PKA activity prevented CB1 receptor-mediated inhibitory bouton formation. Our findings reveal that axonal CB1 receptors signal via unconventional downstream pathways and that inhibitory bouton formation is triggered by an increase in axonal cAMP levels. Our results demonstrate an unexpected role for axonal CB1 receptors in axon-specific, and context-dependent, inhibitory synapse formation.SIGNIFICANCE STATEMENT Coordination between excitation and inhibition is required for proper brain function throughout life. It was previously shown that new inhibitory synapses can be formed in response to strong excitation to maintain this coordination, and this was mediated by endocannabinoid signaling via CB1 receptors. As activation of CB1 receptors generally results in the suppression of synaptic transmission, it remained unclear how CB1 receptors can mediate the formation of inhibitory synapses. Here we show that CB1 receptors on inhibitory axons signal via unconventional intracellular pathways and that inhibitory bouton formation is triggered by an increase in axonal cAMP levels and requires PKA activity. Our findings point to a central role for axonal cAMP signaling in activity-dependent inhibitory synapse formation.

A correlative super-resolution protocol to visualise structural underpinnings of fast second-messenger signalling in primary cell types

Nanometre-scale cellular information obtained through super-resolution microscopies are often unaccompanied by functional information, particularly transient and diffusible signals through which life is orchestrated in the nano-micrometre spatial scale. We describe a correlative imaging protocol which allows the ubiquitous intracellular second messenger, calcium (Ca2+), to be directly visualised against nanoscale patterns of the ryanodine receptor (RyR) Ca2+ channels which give rise to these Ca2+ signals in wildtype primary cells. This was achieved by combining total internal reflection fluorescence (TIRF) imaging of the elementary Ca2+ signals, with the subsequent DNA-PAINT imaging of the RyRs. We report a straightforward image analysis protocol of feature extraction and image alignment between correlative datasets and demonstrate how such data can be used to visually identify the ensembles of Ca2+ channels that are locally activated during the genesis of cytoplasmic Ca2+ signals.

Mechanisms of endocannabinoid control of synaptic plasticity

The endogenous cannabinoid transmitter system regulates synaptic transmission throughout the nervous system. Unlike conventional transmitters, specific stimuli induce synthesis of endocannabinoids (eCBs) in the postsynaptic neuron, and these travel backwards to modulate presynaptic inputs. In doing so, eCBs can induce short-term changes in synaptic strength and longer-term plasticity. While this eCB regulation is near ubiquitous, it displays major regional and synapse specific variations with different synapse specific forms of short-versus long-term plasticity throughout the brain. These differences are due to the plethora of pre- and postsynaptic mechanisms which have been implicated in eCB signalling, the intricacies of which are only just being realised. In this review, we shall describe the current understanding and highlight new advances in this area, with a focus on the retrograde action of eCBs at CB1 receptors (CB₁Rs).

Vangl2 limits chaperone-mediated autophagy to balance osteogenic differentiation in mesenchymal stem cells

Lysosomes are the recycling center and nutrient signaling hub of the cell. Here, we show that lysosomes also control mesenchymal stem cell (MSC) differentiation by proteomic reprogramming. The chaperone-mediated autophagy (CMA) lysosome subgroup promotes osteogenesis, while suppressing adipogenesis, by selectively removing osteogenesis-deterring factors, especially master transcriptional factors, such as adipogenic TLE3, ZNF423, and chondrogenic SOX9. The activity of the CMA-committed lysosomes in MSCs are controlled by Van-Gogh-like 2 (Vangl2) at lysosomes. Vangl2 directly binds to lysosome-associated membrane protein 2A (LAMP-2A) and targets it for degradation. MSC-specific Vangl2 ablation in mice increases LAMP-2A expression and CMA-lysosome numbers, promoting bone formation while reducing marrow fat. The Vangl2:LAMP-2A ratio in MSCs correlates inversely with the capacity of the cells for osteoblastic differentiation in humans and mice. These findings demonstrate a critical role for lysosomes in MSC lineage acquisition and establish Vangl2-LAMP-2A signaling as a critical control mechanism.

Repeated exposure to JWH-018 induces adaptive changes in the mesolimbic and mesocortical dopaminergic pathways, glial cells alterations, and behavioural correlates

Background and Purpose

Spice/K2 herbal mixtures, containing synthetic cannabinoids such as JWH‐018, have been marketed as marijuana surrogates since 2004. JWH‐018 has cannabinoid CB₁ receptor‐dependent reinforcing properties and acutely increases dopaminergic transmission selectively in the NAc shell. Here, we tested the hypothesis that repeated administration of JWH‐018 (i) modulates behaviour, (ii) affects dopaminergic transmission and its responsiveness to motivational stimuli, and (iii) is associated with a neuroinflammatory phenotype.

Experimental Approach

Rats were administered with JWH‐018 once a day for 14 consecutive days. We then performed behavioural, electrophysiological, and neurochemical evaluation at multiple time points after drug discontinuation.

Key Results

Repeated JWH‐018 exposure (i) induced anxious and aversive behaviours, transitory attentional deficits, and withdrawal signs; (ii) decreased spontaneous activity and number of dopamine neurons in the VTA; and (iii) reduced stimulation of dopaminergic transmission in the NAc shell while potentiating that in the NAc core, in response to acute JWH‐018 challenge. Moreover, (iv) we observed a decreased dopamine sensitivity in the NAc shell and core, but not in the mPFC, to a first chocolate exposure; conversely, after a second exposure, dialysate dopamine fully increased in the NAc shell and core but not in the mPFC. Finally, selected dopamine brain areas showed (v) astrogliosis (mPFC, NAc shell and core, VTA), microgliosis (NAc shell and core), and downregulation of CB₁ receptors (mPFC, NAc shell and core).

Conclusion and Implications

Repeated exposure to JWH‐018 may provide a useful model to clarify the detrimental effects of recurring use of Spice/K2 drugs.

Cannabis use, abuse, and withdrawal: Cannabinergic mechanisms, clinical, and preclinical findings

Cannabis sativa is the most widely used illicit drug in the world. Its main psychoactive component is delta‐9‐tetrahydrocannabinol (THC), one of over 100 phytocannabinoid compounds produced by the cannabis plant. THC is the primary compound that drives cannabis abuse potential and is also used and prescribed medically for therapeutic qualities. Despite its therapeutic potential, a significant subpopulation of frequent cannabis or THC users will develop a drug use syndrome termed cannabis use disorder. Individuals suffering from cannabis use disorder exhibit many of the hallmarks of classical addictions including cravings, tolerance, and withdrawal symptoms. Currently, there are no efficacious treatments for cannabis use disorder or withdrawal symptoms. This makes both clinical and preclinical research on the neurobiological mechanisms of these syndromes ever more pertinent. Indeed, basic research using animal models has provided valuable evidence of the neural molecular and cellular actions of cannabis that mediate its behavioral effects. One of the main components being central action on the cannabinoid type‐one receptor and downstream intracellular signaling related to the endogenous cannabinoid system. Back‐translational studies have provided insight linking preclinical basic and behavioral biology research to better understand symptoms observed at the clinical level. This narrative review aims to summarize major research elucidating the molecular, cellular, and behavioral manifestations of cannabis/THC use that play a role in cannabis use disorder and withdrawal.

Impairment of Synaptic Plasticity by Cannabis, Δ9-THC, and Synthetic Cannabinoids

The ability of neurons to dynamically and flexibly encode synaptic inputs via short- and long-term plasticity is critical to an organism's ability to learn and adapt to the environment. Whereas synaptic plasticity may be encoded by pre- or postsynaptic mechanisms, current evidence suggests that optimization of learning requires both forms of plasticity. Endogenous cannabinoids (eCBs) play critical roles in modulating synaptic transmission via activation of cannabinoid CB1 receptors (CB1Rs) in many central nervous system (CNS) regions, and the eCB system has been implicated, either directly or indirectly, in several forms of synaptic plasticity. Because of this, perturbations within the eCB signaling system can lead to impairments in a variety of learned behaviors. One agent of altered eCB signaling is exposure to "exogenous cannabinoids" such as the primary psychoactive constituent of cannabis, Δ⁹-THC, or illicit synthetic cannabinoids that in many cases have higher potency and efficacy than Δ⁹-THC. Thus, by targeting the eCB system, these agonists can produce widespread impairment of synaptic plasticity by disrupting ongoing eCB function. Here, we review studies in which Δ⁹-THC and synthetic cannabinoids impair synaptic plasticity in a variety of neuronal circuits and examine evidence that this contributes to their well-documented ability to disrupt cognition and behavior.

Advanced imaging and labelling methods to decipher brain cell organization and function

The brain is arguably the most complex organ. The branched and extended morphology of nerve cells, their subcellular complexity, the multiplicity of brain cell types as well as their intricate connectivity and the scattering properties of brain tissue present formidable challenges to the understanding of brain function. Neuroscientists have often been at the forefront of technological and methodological developments to overcome these hurdles to visualize, quantify and modify cell and network properties. Over the last few decades, the development of advanced imaging methods has revolutionized our approach to explore the brain. Super-resolution microscopy and tissue imaging approaches have recently exploded. These instrumentation-based innovations have occurred in parallel with the development of new molecular approaches to label protein targets, to evolve new biosensors and to target them to appropriate cell types or subcellular compartments. We review the latest developments for labelling and functionalizing proteins with small localization and functionalized reporters. We present how these molecular tools are combined with the development of a wide variety of imaging methods that break either the diffraction barrier or the tissue penetration depth limits. We put these developments in perspective to emphasize how they will enable step changes in our understanding of the brain.

The endocannabinoid system in the amygdala and modulation of fear

Posttraumatic stress disorder (PTSD) is a persistent, trauma induced psychiatric condition characterized by lifelong complex cognitive, emotional and behavioral phenotype. Although many individuals that experience trauma are able to gradually diminish their emotional responding to trauma-related stimuli over time, known as extinction learning, individuals suffering from PTSD are impaired in this capacity. An inability to decline this initially normal and adaptive fear response, can be confronted with exposure-based therapies, often in combination with pharmacological treatments. Due to the complexity of PTSD, currently available pharmacotherapeutics are inadequate in treating the deficient extinction observed in many PTSD patients. To develop novel therapeutics, researchers have exploited the conserved nature of fear and stress-associated behavioral responses and neurocircuits across species in an attempt to translate knowledge gained from preclinical studies into the clinic. There is growing evidence on the endocannabinoid modulation of fear and stress due to their 'on demand' synthesis and degradation. Involvement of the endocannabinoids in fear extinction makes the endocannabinoid system very attractive for finding effective therapeutics for trauma and stress related disorders. In this review, a brief introduction on neuroanatomy and circuitry of fear extinction will be provided as a model to study PTSD. Then, the endocannabinoid system will be discussed as an important component of extinction modulation. In this regard, anandamide degrading enzyme, fatty acid amide hydrolase (FAAH) will be exemplified as a target identified and validated strongly from preclinical to clinical translational studies of enhancing extinction.

SGIP1 is involved in regulation of emotionality, mood, and nociception and modulates in vivo signalling of cannabinoid CB1 receptors

Background and Purpose

Src homology 3‐domain growth factor receptor‐bound 2‐like endophilin interacting protein 1 (SGIP1) interacts with cannabinoid CB₁ receptors. SGIP1 is abundantly and principally expressed within the nervous system. SGIP1 and CB₁ receptors co‐localize in axons and presynaptic boutons. SGIP1 interferes with the internalization of activated CB₁ receptors in transfected heterologous cells. Consequently, the transient association of CB₁ receptors with β‐arrestin2 is enhanced and prolonged, and CB₁ receptor‐mediated ERK1/2 signalling is decreased. Because of these actions, SGIP1 may modulate affect, anxiety, pain processing, and other physiological processes controlled by the endocannabinoid system (ECS).

Experimental Approach

Using a battery of behavioural tests, we investigated the consequences of SGIP1 deletion in tasks regulated by the ECS in SGIP1 constitutive knockout (SGIP1^−/−) mice.

Key Results

In SGIP1^−/− mice, sensorimotor gating, exploratory levels, and working memory are unaltered. SGIP1^−/− mice have decreased anxiety‐like behaviours. Fear extinction to tone is facilitated in SGIP1^−/− females. Several cannabinoid tetrad behaviours are altered in the absence of SGIP1. SGIP1^−/− males exhibit abnormal behaviours on Δ⁹‐tetrahydrocannabinol withdrawal. SGIP1 deletion also reduces acute nociception, and SGIP1^−/− mice are more sensitive to analgesics.

Conclusion and Implications

SGIP1 was detected as a novel protein associated with CB₁ receptors, and profoundly modified CB₁ receptor signalling. Genetic deletion of SGIP1 particularly affected behavioural tests of mood‐related assessment and the cannabinoid tetrad. SGIP1^−/− mice exhibit decreased nociception and augmented responses to CB₁ receptor agonists and morphine. These in vivo findings suggest that SGIP1 is a novel modulator of CB₁ receptor‐mediated behaviour.

NECAB1 and NECAB2 are Prevalent Calcium-Binding Proteins of CB1/CCK-Positive GABAergic Interneurons

The molecular repertoire of the "Ca2+-signaling toolkit" supports the specific kinetic requirements of Ca2+-dependent processes in different neuronal types. A well-known example is the unique expression pattern of calcium-binding proteins, such as parvalbumin, calbindin, and calretinin. These cytosolic Ca2+-buffers control presynaptic and somatodendritic processes in a cell-type-specific manner and have been used as neurochemical markers of GABAergic interneuron types for decades. Surprisingly, to date no typifying calcium-binding proteins have been found in CB1 cannabinoid receptor/cholecystokinin (CB1/CCK)-positive interneurons that represent a large population of GABAergic cells in cortical circuits. Because CB1/CCK-positive interneurons display disparate presynaptic and somatodendritic Ca2+-transients compared with other interneurons, we tested the hypothesis that they express alternative calcium-binding proteins. By in silico data mining in mouse single-cell RNA-seq databases, we identified high expression of Necab1 and Necab2 genes encoding N-terminal EF-hand calcium-binding proteins 1 and 2, respectively, in CB1/CCK-positive interneurons. Fluorescent in situ hybridization and immunostaining revealed cell-type-specific distribution of NECAB1 and NECAB2 throughout the isocortex, hippocampal formation, and basolateral amygdala complex. Combination of patch-clamp electrophysiology, confocal, and STORM super-resolution microscopy uncovered subcellular nanoscale differences indicating functional division of labor between the two calcium-binding proteins. These findings highlight NECAB1 and NECAB2 as predominant calcium-binding proteins in CB1/CCK-positive interneurons.

STochastic Optical Reconstruction Microscopy (STORM) reveals the nanoscale organization of pathological aggregates in human brain

AIMS

Histological analysis of brain tissue samples provides valuable information about the pathological processes leading to common neurodegenerative disorders. In this context, the development of novel high-resolution imaging approaches is a current challenge in neuroscience.

METHODS

To this end, we used a recent super-resolution imaging technique called STochastic Optical Reconstruction Microscopy (STORM) to analyse human brain sections. We combined STORM cell imaging protocols with neuropathological techniques to image cryopreserved brain samples from control subjects and patients with neurodegenerative diseases.

RESULTS

This approach allowed us to perform 2D-, 3D- and two-colour-STORM in neocortex, white matter and brainstem samples. STORM proved to be particularly effective at visualizing the organization of dense protein inclusions and we imaged with a <50 nm resolution pathological aggregates within the central nervous system of patients with Alzheimer's disease, Parkinson's disease, Lewy body dementia and fronto-temporal lobar degeneration. Aggregated Aβ branches appeared reticulated and cross-linked in the extracellular matrix, with widths from 60 to 240 nm. Intraneuronal Tau and TDP-43 inclusions were denser, with a honeycomb pattern in the soma and a filamentous organization in the axons. Finally, STORM imaging of α-synuclein pathology revealed the internal organization of Lewy bodies that could not be observed by conventional fluorescence microscopy.

CONCLUSIONS

STORM imaging of human brain samples opens further gates to a more comprehensive understanding of common neurological disorders. The convenience of this technique should open a straightforward extension of its application for super-resolution imaging of the human brain, with promising avenues to current challenges in neuroscience.