Presynaptically located CB1 cannabinoid receptors regulate GABA release from axon terminals of specific hippocampal interneurons

Hippocampal cholecystokinin-expressing interneurons regulate temporal coding and contextual learning

Cholecystokinin-expressing interneurons (CCKIs) are hypothesized to shape pyramidal cell-firing patterns and regulate network oscillations and related network state transitions. To directly probe their role in the CA1 region, we silenced their activity using optogenetic and chemogenetic tools in mice. Opto-tagged CCKIs revealed a heterogeneous population, and their optogenetic silencing triggered wide disinhibitory network changes affecting both pyramidal cells and other interneurons. CCKI silencing enhanced pyramidal cell burst firing and altered the temporal coding of place cells: theta phase precession was disrupted, whereas sequence reactivation was enhanced. Chemogenetic CCKI silencing did not alter the acquisition of spatial reference memories on the Morris water maze but enhanced the recall of contextual fear memories and enabled selective recall when similar environments were tested. This work suggests the key involvement of CCKIs in the control of place-cell temporal coding and the formation of contextual memories.

CCK+ Interneurons Contribute to Thalamus-Evoked Feed-Forward Inhibition in the Prelimbic Prefrontal Cortex

Interneurons in the medial prefrontal cortex (PFC) regulate local neural activity to influence cognitive, motivated, and emotional behaviors. Parvalbumin-expressing (PV+) interneurons are the primary mediators of thalamus-evoked feed-forward inhibition across the mouse cortex, including the anterior cingulate cortex, where they are engaged by inputs from the mediodorsal (MD) thalamus. In contrast, in the adjacent prelimbic (PL) cortex, we find that PV+ interneurons are scarce in the principal thalamorecipient layer 3 (L3), suggesting distinct mechanisms of inhibition. To identify the interneurons that mediate MD-evoked inhibition in PL, we combine slice physiology, optogenetics, and intersectional genetic tools in mice of both sexes. We find interneurons expressing cholecystokinin (CCK+) are abundant in L3 of PL, with cells exhibiting fast-spiking (fs) or non-fast-spiking (nfs) properties. MD inputs make stronger connections onto fs-CCK+ interneurons, driving them to fire more readily than nearby L3 pyramidal cells and other interneurons. CCK+ interneurons in turn make inhibitory, perisomatic connections onto L3 pyramidal cells, where they exhibit cannabinoid 1 receptor (CB1R) mediated modulation. Moreover, MD-evoked feed-forward inhibition, but not direct excitation, is also sensitive to CB1R modulation. Our findings indicate that CCK+ interneurons contribute to MD-evoked inhibition in PL, revealing a mechanism by which cannabinoids can modulate MD-PFC communication.

Positive allosteric modulation of the cannabinoid CB1 receptor potentiates endocannabinoid signalling and changes ERK1/2 phosphorylation kinetics

BACKGROUND AND PURPOSE

Activation of CB1 by exogenous agonists causes adverse effects in vivo. Positive allosteric modulation may offer improved therapeutic potential and a reduced on-target adverse effect profile compared with orthosteric agonists, due to reduced desensitisation/tolerance, but this has not been directly tested. This study investigated the ability of PAMs/ago-PAMs to induce receptor regulation pathways, including desensitisation and receptor internalisation.

EXPERIMENTAL APPROACH

Bioluminescence resonance energy transfer (BRET) assays in HEK293 cells were performed to investigate G protein dissociation, ERK1/2 phosphorylation and β-arrestin 2 translocation, while immunocytochemistry was performed to measure internalisation of CB1 in response to the PAMs ZCZ011, GAT229 and ABD1236 alone and in combination with the orthosteric agonists AEA, 2-AG, and AMB-FUBINACA.

KEY RESULTS

ZCZ011, GAT229 and ABD1236 were allosteric agonists in all pathways tested. The ago-PAM ZCZ011 induced a biphasic ERK1/2 phosphorylation time course compared to transient activation by orthosteric agonists. In combination with 2-AG but not AEA or AMB-FUBINACA, ZCZ011 and ABD1236 caused the transient peak of ERK1/2 phosphorylation to become sustained. All PAMs increased the potency and efficacy of AEA-induced signalling in all pathways tested; however, no notable potentiation of 2-AG or AMB-FUBINACA was observed.

CONCLUSION AND IMPLICATIONS

Ago-PAMs can potentiate endocannabinoid CB1 agonism by AEA to a larger extent compared with 2-AG. However, all compounds were found to be allosteric agonists and induce activation of CB1 in the absence of endocannabinoid, including β-arrestin 2 recruitment and internalisation. Thus, the spatiotemporal signalling of endogenous cannabinoids will not be retained in vivo.

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.

Acetylcholine Engages Distinct Amygdala Microcircuits to Gate Internal Theta Rhythm

Acetylcholine (ACh) is released from basal forebrain cholinergic neurons in response to salient stimuli and engages brain states supporting attention and memory. These high ACh states are associated with theta oscillations, which synchronize neuronal ensembles. Theta oscillations in the basolateral amygdala (BLA) in both humans and rodents have been shown to underlie emotional memory, yet their mechanism remains unclear. Here, using brain slice electrophysiology in male and female mice, we show large ACh stimuli evoke prolonged theta oscillations in BLA local field potentials that depend upon M3 muscarinic receptor activation of cholecystokinin (CCK) interneurons (INs) without the need for external glutamate signaling. Somatostatin (SOM) INs inhibit CCK INs and are themselves inhibited by ACh, providing a functional SOM→CCK IN circuit connection gating BLA theta. Parvalbumin (PV) INs, which can drive BLA oscillations in baseline states, are not involved in the generation of ACh-induced theta, highlighting that ACh induces a cellular switch in the control of BLA oscillatory activity and establishes an internally BLA-driven theta oscillation through CCK INs. Theta activity is more readily evoked in BLA over the cortex or hippocampus, suggesting preferential activation of the BLA during high ACh states. These data reveal a SOM→CCK IN circuit in the BLA that gates internal theta oscillations and suggest a mechanism by which salient stimuli acting through ACh switch the BLA into a network state enabling emotional memory.

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 treatments in epilepsy and seizure disorders

Cannabis has been used to treat convulsions and other disorders since ancient times. In the last few decades, preclinical animal studies and clinical investigations have established the role of cannabidiol (CBD) in treating epilepsy and seizures and support potential therapeutic benefits for cannabinoids in other neurological and psychiatric disorders. Here, we comprehensively review the role of cannabinoids in epilepsy. We briefly review the diverse physiological processes mediating the central nervous system response to cannabinoids, including Δ9-tetrahydrocannabinol (Δ9-THC), cannabidiol, and terpenes. Next, we characterize the anti- and proconvulsive effects of cannabinoids from animal studies of acute seizures and chronic epileptogenesis. We then review the clinical literature on using cannabinoids to treat epilepsy, including anecdotal evidence and case studies as well as the more recent randomized controlled clinical trials that led to US Food and Drug Administration approval of CBD for some types of epilepsy. Overall, we seek to evaluate our current understanding of cannabinoids in epilepsy and focus future research on unanswered questions.

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.

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.

T-DOpE probes reveal sensitivity of hippocampal oscillations to cannabinoids in behaving mice

Understanding the neural basis of behavior requires monitoring and manipulating combinations of physiological elements and their interactions in behaving animals. We developed a thermal tapering process enabling fabrication of low-cost, flexible probes combining ultrafine features: dense electrodes, optical waveguides, and microfluidic channels. Furthermore, we developed a semi-automated backend connection allowing scalable assembly. We demonstrate T-DOpE (Tapered Drug delivery, Optical stimulation, and Electrophysiology) probes achieve in single neuron-scale devices (1) high-fidelity electrophysiological recording (2) focal drug delivery and (3) optical stimulation. The device tip can be miniaturized (as small as 50 µm) to minimize tissue damage while the ~20 times larger backend allows for industrial-scale connectorization. T-DOpE probes implanted in mouse hippocampus revealed canonical neuronal activity at the level of local field potentials (LFP) and neural spiking. Taking advantage of the triple-functionality of these probes, we monitored LFP while manipulating cannabinoid receptors (CB1R; microfluidic agonist delivery) and CA1 neuronal activity (optogenetics). Focal infusion of CB1R agonist downregulated theta and sharp wave-ripple oscillations (SPW-Rs). Furthermore, we found that CB1R activation reduces sharp wave-ripples by impairing the innate SPW-R-generating ability of the CA1 circuit.

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.

Early endocannabinoid-mediated depolarization-induced suppression of excitation delays the appearance of the epileptic phenotype in synapsin II knockout mice

The mechanism underlying the transition from the pre-symptomatic to the symptomatic state is a crucial aspect of epileptogenesis. SYN2 is a member of a multigene family of synaptic vesicle phosphoproteins playing a fundamental role in controlling neurotransmitter release. Human SYN2 gene mutations are associated with epilepsy and autism spectrum disorder. Mice knocked out for synapsin II (SynII KO) are prone to epileptic seizures that appear after 2 months of age. However, the involvement of the endocannabinoid system, known to regulate seizure development and propagation, in the modulation of the excitatory/inhibitory balance in the epileptic hippocampal network of SynII KO mice has not been explored. In this study, we investigated the impact of endocannabinoids on glutamatergic and GABAergic synapses at hippocampal dentate gyrus granule cells in young pre-symptomatic (1-2 months old) and adult symptomatic (5-8 months old) SynII KO mice. We observed an increase in endocannabinoid-mediated depolarization-induced suppression of excitation in young SynII KO mice, compared to age-matched wild-type controls. In contrast, the endocannabinoid-mediated depolarization-induced suppression of inhibition remained unchanged in SynII KO mice at both ages. This selective alteration of excitatory synaptic transmission was accompanied by changes in hippocampal endocannabinoid levels and cannabinoid receptor type 1 distribution among glutamatergic and GABAergic synaptic terminals contacting the granule cells of the dentate gyrus. Finally, inhibition of type-1 cannabinoid receptors in young pre-symptomatic SynII KO mice induced seizures during a tail suspension test. Our results suggest that endocannabinoids contribute to maintaining network stability in a genetic mouse model of human epilepsy.

Effects of combined exposure to ethanol and delta-9-tetrahydrocannabinol during adolescence on synaptic plasticity in the prefrontal cortex of Long Evans rats

Significant exposure to alcohol or cannabis during adolescence can induce lasting disruptions of neuronal signaling in brain regions that are later to mature, such as the medial prefrontal cortex (mPFC). Considerably less is known about the effects of alcohol and cannabis co-use, despite its common occurrence. Here, we used male and female Long-Evans rats to investigate the effects of early-life exposure to ethanol, delta-9-tetrahydrocannabinol (THC), or their combination on high frequency stimulation (HFS)-induced plasticity in the prelimbic region of the mPFC. Animals were injected daily from postnatal days 30-45 with vehicle or THC (escalating doses, 3-20 mg/kg) and allowed to drink vehicle (0.1% saccharin) or 10% ethanol immediately after each injection. In vitro brain slice electrophysiology was then used to record population responses of layer V neurons following HFS in layer II/III after 3-4 weeks of abstinence. We found that THC exposure reduced body weight gains observed in ad libitum fed rats, and reduced intake of saccharin and ethanol. Compared to controls, there was a significant reduction in HFS-induced long-term depression (LTD) in rats exposed to either drug alone, and an absence of LTD in rats exposed to the drug combination. Bath application of indiplon or AR-A014418, which enhance GABAA receptor function or inhibit glycogen synthase kinase 3β (GSK3β), respectively, suggested the effects of ethanol, THC or their combination were due in part to lasting adaptations in GABA and GSK3β signaling. These results suggest the potential for long-lasting adaptations in mPFC output following co-exposure to alcohol and THC.

Interplay between endocannabinoid and endovanilloid mechanisms in fear conditioning

OBJECTIVE

The transient receptor potential cation channel, subfamily V (vanilloid), member 1 (TRPV1) mediates pain perception to thermal and chemical stimuli in peripheral neurons. The cannabinoid receptor type 1 (CB1), on the other hand, promotes analgesia in both the periphery and the brain. TRPV1 and CB1 have also been implicated in learned fear, which involves the association of a previously neutral stimulus with an aversive event. In this review, we elaborate on the interplay between CB1 receptors and TRPV1 channels in learned fear processing.

METHODS

We conducted a PubMed search for a narrative review on endocannabinoid and endovanilloid mechanisms on fear conditioning.

RESULTS

TRPV1 and CB1 receptors are activated by a common endogenous agonist, arachidonoyl ethanolamide (anandamide), Moreover, they are expressed in common neuroanatomical structures and recruit converging cellular pathways, acting in concert to modulate fear learning. However, evidence suggests that TRPV1 exerts a facilitatory role, whereas CB1 restrains fear responses.

CONCLUSION

TRPV1 and CB1 seem to mediate protective and aversive roles of anandamide, respectively. However, more research is needed to achieve a better understanding of how these receptors interact to modulate fear learning.

CBD lengthens sleep but shortens ripples and leads to intact simple but worse cumulative memory

Cannabidiol (CBD) is on the rise as over-the-counter medication to treat sleep disturbances, anxiety, pain, and epilepsy due to its action on the excitatory/inhibitory balance in the brain. However, it remains unclear if CBD also leads to adverse effects on memory via changes of sleep macro- and microarchitecture. To investigate the effect of CBD on sleep and memory consolidation, we performed two experiments using the object space task testing for both simple and cumulative memory in rats. We show that oral CBD administration extended the sleep period but changed the properties of rest and non-REM sleep oscillations (delta, spindle, ripples). Specifically, CBD also led to less long (>100 ms) ripples and, consequently, worse cumulative memory consolidation. In contrast, simple memories were not affected. In sum, we can confirm the beneficial effect of CBD on sleep; however, this comes with changes in oscillations that negatively impact memory consolidation.

Anxiety Modulation by Cannabinoids-The Role of Stress Responses and Coping

Endocannabinoids were implicated in a variety of pathological conditions including anxiety and are considered promising new targets for anxiolytic drug development. The optimism concerning the potentials of this system for anxiolysis is probably justified. However, the complexity of the mechanisms affected by endocannabinoids, and discrepant findings obtained with various experimental approaches makes the interpretation of research results difficult. Here, we review the anxiety-related effects of the three main interventions used to study the endocannabinoid system: pharmacological agents active at endocannabinoid-binding sites present on both the cell membrane and in the cytoplasm, genetic manipulations targeting cannabinoid receptors, and function-enhancers represented by inhibitors of endocannabinoid degradation and transport. Binding-site ligands provide inconsistent findings probably because they activate a multitude of mechanisms concomitantly. More robust findings were obtained with genetic manipulations and particularly with function enhancers, which heighten ongoing endocannabinoid activation rather than affecting all mechanisms indiscriminately. The enhancement of ongoing activity appears to ameliorate stress-induced anxiety without consistent effects on anxiety in general. Limited evidence suggests that this effect is achieved by promoting active coping styles in critical situations. These findings suggest that the functional enhancement of endocannabinoid signaling is a promising drug development target for stress-related anxiety disorders.

Reduced Cholecystokinin-Expressing Interneuron Input Contributes to Disinhibition of the Hippocampal CA2 Region in a Mouse Model of Temporal Lobe Epilepsy

A significant proportion of temporal lobe epilepsy (TLE) patients experience drug-resistant seizures associated with mesial temporal sclerosis, in which there is extensive cell loss in the hippocampal CA1 and CA3 subfields, with a relative sparing of dentate gyrus granule cells and CA2 pyramidal neurons (PNs). A role for CA2 in seizure generation was suggested based on findings of a reduction in CA2 synaptic inhibition (Williamson and Spencer, 1994) and the presence of interictal-like spike activity in CA2 in resected hippocampal tissue from TLE patients (Wittner et al., 2009). We recently found that in the pilocarpine-induced status epilepticus (PILO-SE) mouse model of TLE there was an increase in CA2 intrinsic excitability associated with a loss of CA2 synaptic inhibition. Furthermore, chemogenetic silencing of CA2 significantly reduced seizure frequency, consistent with a role of CA2 in promoting seizure generation and/or propagation (Whitebirch et al., 2022). In the present study, we explored the cellular basis of this inhibitory deficit using immunohistochemical and electrophysiological approaches in PILO-SE male and female mice. We report a widespread decrease in the density of pro-cholecystokinin-immunopositive (CCK+) interneurons and a functional impairment of CCK+ interneuron-mediated inhibition of CA2 PNs. We also found a disruption in the perisomatic perineuronal net in the CA2 stratum pyramidale. Such pathologic alterations may contribute to an enhanced excitation of CA2 PNs and CA2-dependent seizure activity in the PILO-SE mouse model.SIGNIFICANCE STATEMENT Impaired synaptic inhibition in hippocampal circuits has been identified as a key feature that contributes to the emergence and propagation of seizure activity in human patients and animal models of temporal lobe epilepsy (TLE). Among the hippocampal subfields, the CA2 region is particularly resilient to seizure-associated neurodegeneration and has been suggested to play a key role in seizure activity in TLE. Here we report that perisomatic inhibition of CA2 pyramidal neurons mediated by cholecystokinin-expressing interneurons is selectively reduced in acute hippocampal slices from epileptic mice. Parvalbumin-expressing interneurons, in contrast, appear relatively conserved in epileptic mice. These findings advance our understanding of the cellular mechanisms underlying inhibitory disruption in hippocampal circuits in a mouse model of spontaneous recurring seizures.

Effects of combined exposure to ethanol and delta-9-tetrahydrocannabinol during adolescence on synaptic plasticity in the prefrontal cortex of Long Evans rats

Significant exposure to alcohol or cannabis during adolescence can induce lasting disruptions of neuronal signaling in brain regions that are later to mature, such as the medial prefrontal cortex (mPFC). Considerably less is known about the effects of alcohol and cannabis co-use, despite its common occurrence. Here, we used male and female Long-Evans rats to investigate the effects of early-life exposure to ethanol, delta-9-tetrahydrocannabinol (THC), or their combination on high frequency stimulation (HFS)-induced plasticity in the prelimbic region of the mPFC. Animals were injected daily from postnatal days 30 to 45 with vehicle or THC (escalating doses, 3-20 mg/kg) and allowed to drink vehicle (0.1% saccharin) or 10% ethanol immediately after each injection. In vitro brain slice electrophysiology was then used to record population responses of layer V neurons following HFS in layer II/III after 3-4 weeks of abstinence. We found that THC exposure reduced body weight gains observed in ad libitum fed rats, and reduced intake of saccharin and ethanol. Compared to controls, there was a significant reduction in HFS-induced long-term depression (LTD) in rats exposed to either drug alone, and an absence of LTD in rats exposed to the drug combination. Bath application of indiplon or AR-A014418, which enhance GABAA receptor function or inhibit glycogen synthase kinase 3β (GSK3β), respectively, suggested the effects of ethanol, THC or their combination were due in part to lasting adaptations in GABA and GSK3β signaling. These results suggest the potential for long-lasting adaptations in mPFC output following co-exposure to alcohol and THC.

Cannabinoid receptor gene CNR1 is downregulated in subcortical brain samples and upregulated in blood samples of individuals with schizophrenia: A participant data systematic meta-analysis

Cannabis use leads to symptom exacerbation in schizophrenia patients, and endocannabinoid ligands have been studied as tentative schizophrenia therapeutics. Here, we aimed to characterise the connection between schizophrenia and the cannabinoid receptor 1 gene (CNR1) and explore possible mechanisms affecting its expression in schizophrenia. We performed a participant data systematic meta-analysis of CNR1 gene expression and additional endocannabinoid system genes in both brain (subcortical areas) and blood samples. We integrated eight brain sample datasets (overall 316 samples; 149 schizophrenia and 167 controls) and two blood sample datasets (overall 90 samples; 53 schizophrenia and 37 controls) while following the PRISMA meta-analysis guidelines. CNR1 was downregulated in subcortical regions and upregulated in blood samples of patients with schizophrenia. CNR2 and genes encoding endocannabinoids synthesis and degradation did not show differential expression in the brain or blood, except fatty acid amide hydrolase (FAAH), which showed a downregulation trend in blood. In addition, the brain expression levels of CNR1 and three GABA receptor genes, GABRA1, GABRA6 and GABRG2, were positively correlated (R = .57, .36, .54; p = 2.7 × 10-14 , 6.9 × 10-6 and 1.1 × 10-12 , respectively). Brain CNR1 downregulation and the positive correlation with three GABA receptor genes suggest an association with GABA neurotransmission and possible effects on negative schizophrenia symptoms. Further studies are required for clarifying the opposite CNR1 dysregulation in the brain and blood of schizophrenia patients and the potential of endocannabinoid ligands as schizophrenia therapeutics.

Cannabis during pregnancy: A way to transfer an impairment to later life

Epidemiological studies examining the influence of cannabis across the lifespan show that exposure to cannabis during gestation or during the perinatal period is associated with later-life mental health issues that manifest during childhood, adolescence, and adulthood. The risk of later-life negative outcomes following early exposure is particularly high in persons who have specific genetic variants, implying that cannabis usage interacts with genetics to heighten mental health risks. Prenatal and perinatal exposure to psychoactive components has been shown in animal research to be associated with long-term effects on neural systems relevant to psychiatric and substance use disorders. The long-term molecular, epigenetic, electrophysiological, and behavioral consequences of prenatal and perinatal exposure to cannabis are discussed in this article. Animal and human studies, as well as in vivo neuroimaging methods, are used to provide insights into the changes induced in the brain by cannabis. Here, based on the literature from both animal models and humans, it can be concluded that prenatal cannabis exposure alters the developmental route of several neuronal regions with correlated functional consequences evidenced as changes in social behavior and executive functions throughout life.

Terminal type-specific cannabinoid CB1 receptor alterations in patients with schizophrenia: A pilot study

BACKGROUND

Individuals with schizophrenia are at elevated genetic risks for comorbid cannabis use, and often experience exacerbations of cognitive and psychotic symptoms when exposed to cannabis. These findings have led a number of investigators to examine cannabinoid CB1 receptor (CB1R) alterations in schizophrenia, though with conflicting results. We recently demonstrated the presence of CB1R in both excitatory and inhibitory boutons in the human prefrontal cortex, with differential levels of the receptor between bouton types. We hypothesized that the differential enrichment of CB1R between bouton types - a factor previously unaccounted for when examining CB1R changes in schizophrenia - may resolve prior discrepant reports and increase our insight into the effects of CB1R alterations on the pathophysiology of schizophrenia.

METHODS

Using co-labeling immunohistochemistry and fluorescent microscopy, we examined total CB1R levels and CB1R levels within excitatory (vGlut1-positive) and inhibitory (vGAT-positive) boutons of prefrontal cortex samples from ten pairs of individuals (nine male pairs and one female pair) diagnosed with schizophrenia and non-psychiatric comparisons.

RESULTS

Significantly higher total CB1R levels were found within samples from individuals with schizophrenia. Terminal type-specific analyses identified significantly higher CB1R levels within excitatory boutons in samples from individuals with schizophrenia relative to comparisons. In contrast, CB1R levels within the subset of inhibitory boutons that normally express high CB1R levels (presumptive cholecystokinin neuron boutons) were lower in samples from individuals with schizophrenia relative to comparison samples.

CONCLUSION

Given CB1R's role in suppressing neurotransmission upon activation, these results suggest an overall shift in excitatory and inhibitory balance regulation toward a net reduction of excitatory activity in schizophrenia.

Daily Cannabidiol Administration for 10 Weeks Modulates Hippocampal and Amygdalar Resting-State Functional Connectivity in Cannabis Users: A Functional Magnetic Resonance Imaging Open-Label Clinical Trial

Introduction: Cannabis use is associated with brain functional changes in regions implicated in prominent neuroscientific theories of addiction. Emerging evidence suggests that cannabidiol (CBD) is neuroprotective and may reverse structural brain changes associated with prolonged heavy cannabis use. In this study, we examine how an ∼10-week exposure of CBD in cannabis users affected resting-state functional connectivity in brain regions functionally altered by cannabis use. Materials and Methods: Eighteen people who use cannabis took part in a ∼10 weeks open-label pragmatic trial of self-administered daily 200 mg CBD in capsules. They were not required to change their cannabis exposure patterns. Participants were assessed at baseline and post-CBD exposure with structural magnetic resonance imaging (MRI) and a functional MRI resting-state task (eyes closed). Seed-based connectivity analyses were run to examine changes in the functional connectivity of a priori regions-the hippocampus and the amygdala. We explored if connectivity changes were associated with cannabinoid exposure (i.e., cumulative cannabis dosage over trial, and plasma CBD concentrations and Δ9-tetrahydrocannabinol (THC) plasma metabolites postexposure), and mental health (i.e., severity of anxiety, depression, and positive psychotic symptom scores), accounting for cigarette exposure in the past month, alcohol standard drinks in the past month and cumulative CBD dose during the trial. Results: Functional connectivity significantly decreased pre-to-post the CBD trial between the anterior hippocampus and precentral gyrus, with a strong effect size (d=1.73). Functional connectivity increased between the amygdala and the lingual gyrus pre-to-post the CBD trial, with a strong effect size (d=1.19). There were no correlations with cannabinoids or mental health symptom scores. Discussion: Prolonged CBD exposure may restore/reduce functional connectivity differences reported in cannabis users. These new findings warrant replication in a larger sample, using robust methodologies-double-blind and placebo-controlled-and in the most vulnerable people who use cannabis, including those with more severe forms of Cannabis Use Disorder and experiencing worse mental health outcomes (e.g., psychosis, depression).

Monoacylglycerol Lipase Protects the Presynaptic Cannabinoid 1 Receptor from Desensitization by Endocannabinoids after Persistent Inflammation

Cannabinoid-targeted pain therapies are increasing with the expansion of cannabis legalization, however, their efficacy may be limited by pain-induced adaptations in the cannabinoid system. Cannabinoid receptor subtype 1 (CB1R) inhibition of spontaneous, GABAergic miniature IPSCs (mIPSCs) and evoked IPSCs (eIPSCs) in the ventrolateral periaqueductal gray (vlPAG) were compared in slices from naive and inflamed male and female Sprague Dawley rats. Complete Freund's Adjuvant (CFA) injections into the hindpaw induced persistent inflammation. In naive rats, exogenous cannabinoid agonists robustly reduce both eIPSCs and mIPSCs. After 5-7 d of inflammation, the effects of exogenous cannabinoids are significantly reduced because of CB1R desensitization via GRK2/3, as function is recovered in the presence of the GRK2/3 inhibitor, Compound 101 (Cmp101). Inhibition of GABA release by presynaptic μ-opioid receptors in the vlPAG does not desensitize with persistent inflammation. Unexpectedly, while CB1R desensitization significantly reduces the inhibition produced by exogenous agonists, depolarization-induced suppression of inhibition protocols that promote 2-arachidonoylglycerol (2-AG) synthesis exhibit prolonged CB1R activation after inflammation. 2-AG tone is detected in slices from CFA-treated rats when GRK2/3 is blocked, suggesting an increase in 2-AG synthesis after persistent inflammation. Inhibiting 2-AG degradation with the monoacylglycerol lipase (MAGL) inhibitor JZL184 during inflammation results in the desensitization of CB1Rs by endocannabinoids that is reversed with Cmp101. Collectively, these data indicate that persistent inflammation primes CB1Rs for desensitization, and MAGL degradation of 2-AG protects CB1Rs from desensitization in inflamed rats. These adaptations with inflammation have important implications for the development of cannabinoid-based pain therapeutics targeting MAGL and CB1Rs.SIGNIFICANCE STATEMENT Presynaptic G-protein-coupled receptors are resistant to desensitization. Here we find that persistent inflammation increases endocannabinoid levels, priming presynaptic cannabinoid 1 receptors for desensitization on subsequent addition of exogenous agonists. Despite the reduced efficacy of exogenous agonists, endocannabinoids have prolonged efficacy after persistent inflammation. Endocannabinoids readily induce cannabinoid 1 receptor desensitization if their degradation is blocked, indicating that endocannabinoid concentrations are maintained at subdesensitizing levels and that degradation is critical for maintaining endocannabinoid regulation of presynaptic GABA release in the ventrolateral periaqueductal gray during inflammatory states. These adaptations with inflammation have important implications for the development of cannabinoid-based pain therapies.

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.

Tapered Drug delivery, Optical stimulation, and Electrophysiology (T-DOpE) probes reveal the importance of cannabinoid signaling in hippocampal CA1 oscillations in behaving mice

Understanding the neural basis of behavior requires monitoring and manipulating combinations of physiological elements and their interactions in behaving animals. Here we developed a thermal tapering process (TTP) which enables the fabrication of novel, low-cost, flexible probes that combine ultrafine features of dense electrodes, optical waveguides, and microfluidic channels. Furthermore, we developed a semi-automated backend connection allowing scalable assembly of the probes. We demonstrate that our T-DOpE ( T apered D rug delivery, Op tical stimulation, and E lectrophysiology) probe achieves in a single neuron-scale device (1) high-fidelity electrophysiological recording (2) focal drug delivery and (3) optical stimulation. With a tapered geometry, the device tip can be minimized (as small as 50 μm) to ensure minimal tissue damage while the backend is ~20 times larger allowing for direct integration with industrial-scale connectorization. Acute and chronic implantation of the probes in mouse hippocampus CA1 revealed canonical neuronal activity at the level of local field potentials and spiking. Taking advantage of the triple-functionality of the T-DOpE probe, we monitored local field potentials with simultaneous manipulation of endogenous type 1 cannabinoid receptors (CB1R; via microfluidic agonist delivery) and CA1 pyramidal cell membrane potential (optogenetic activation). Electro-pharmacological experiments revealed that focal infusion of CB1R agonist CP-55,940 in dorsal CA1 downregulated theta and sharp wave-ripple oscillations. Furthermore, using the full electro-pharmacological-optical feature set of the T-DOpE probe we found that CB1R activation reduces sharp wave-ripples (SPW-Rs) by impairing the innate SPW-R-generating ability of the CA1 circuit.

Pannexin-1 Modulates Inhibitory Transmission and Hippocampal Synaptic Plasticity

Pannexin-1 (Panx1) hemichannel is a non-selective transmembrane channel that may play important roles in intercellular signaling by allowing the permeation of ions and metabolites, such as ATP. Although recent evidence shows that the Panx1 hemichannel is involved in controlling excitatory synaptic transmission, the role of Panx1 in inhibitory transmission remains unknown. Here, we studied the contribution of Panx1 to the GABAergic synaptic efficacy onto CA1 pyramidal neurons (PyNs) by using patch-clamp recordings and pharmacological approaches in wild-type and Panx1 knock-out (Panx1-KO) mice. We reported that blockage of the Panx1 hemichannel with the mimetic peptide ¹⁰Panx1 increases the synaptic level of endocannabinoids (eCB) and the activation of cannabinoid receptors type 1 (CB1Rs), which results in a decrease in hippocampal GABAergic efficacy, shifting excitation/inhibition (E/I) balance toward excitation and facilitating the induction of long-term potentiation. Our finding provides important insight unveiling that Panx1 can strongly influence the overall neuronal excitability and play a key role in shaping synaptic changes affecting the amplitude and direction of plasticity, as well as learning and memory processes.

Women are Taking the Hit: Examining the Unique Consequences of Cannabis Use Across the Female Lifespan

Cannabis use has risen dramatically in recent years due to global decriminalization and a resurgence in the interest of potential therapeutic benefits. While emerging research is shaping our understanding of the benefits and harms of cannabis, there remains a paucity of data specifically focused on how cannabis affects the female population. The female experience of cannabis use is unique, both in the societal context and because of the biological ramifications. This is increasingly important given the rise in cannabis potency, as well as the implications this has for the prevalence of Cannabis Use Disorder (CUD). Therefore, this scoping review aims to discuss the prevalence of cannabis use and CUD in women throughout their lifespan and provide a balanced prospective on the positive and negative consequences of cannabis use. In doing so, this review will highlight the necessity for continued research that goes beyond sex differences.

Activation of ventral hippocampal CB1 receptors inhibits ketamine-induced anxiogenic-like behavior: Alteration of BDNF/c-Fos levels in the mouse hippocampus

Considering the increasing usage of ketamine as a recreational drug with hallucinogenic properties and also scarce studies about receptor systems responsible for its effects, in the present study we aimed to investigate whether the activation of the ventral hippocampal (VH) CB1 cannabinoid receptors affects the anxiety-like behaviors induced by ketamine. Also, the levels of BDNF and c-Fos proteins in the mouse hippocampus were measured following the treatments. For this purpose, male NMRI mice were cannulated bilaterally in the VH with a stereotaxic apparatus. Anxiety properties and protein changes were measured using elevated plus-maze (EPM) and western blotting respectively. The results revealed that intraperitoneal (i.p.) administration of ketamine (5-20 mg/kg) significantly decreased the percentage of open arm time (%OAT) and open arm entry (%OAE) in the EPM with no alteration in the locomotor activity suggesting an anxiogenic-like behavior to ketamine. Furthermore, ketamine administration (10 mg/kg, i.p.) increased BDNF and c-Fos levels in the hippocampus. Interestingly, activation of the VH CB1 receptors by ACPA (0.5-4 ng/mouse) inhibited the anxiogenic-like behaviors produced by ketamine, whereas the microinjection of the same doses of ACPA into VH by itself had no effect on the EPM parameters. Hippocampal levels of BDNF and c-Fos decreased after treatment with combined ketamine with ACPA. These results suggest the therapeutic potency of cannabinoid receptor agonists for ketamine-induced anxiogenic-related responses. This effect might be at least partially mediated by the alteration of BDNF and c-Fos signaling in the hippocampus.

The complement inhibitor CD59 is required for GABAergic synaptic transmission in the dentate gyrus

Complement-dependent microglia pruning of excitatory synapses has been widely reported in physiological and pathological conditions, with few reports concerning pruning of inhibitory synapses or direct regulation of synaptic transmission by complement components. Here, we report that loss of CD59, an important endogenous inhibitor of the complement system, leads to compromised spatial memory performance. Furthermore, CD59 deficiency impairs GABAergic synaptic transmission in the hippocampal dentate gyrus (DG). This depends on regulation of GABA release triggered by Ca2+ influx through voltage-gated calcium channels (VGCCs) rather than inhibitory synaptic pruning by microglia. Notably, CD59 colocalizes with inhibitory pre-synaptic terminals and regulates SNARE complex assembly. Together, these results demonstrate that the complement regulator CD59 plays an important role in normal hippocampal function.

Terminal type-specific cannabinoid CB1 receptor alterations in patients with schizophrenia: a pilot study

Background

Individuals with schizophrenia are at elevated genetic risks for comorbid cannabis use, and often experience exacerbations of cognitive and psychotic symptoms when exposed to cannabis. These findings have led a number of investigators to examine cannabinoid CB1 receptor (CB1R) alterations in schizophrenia, though with conflicting results. We recently demonstrated the presence of CB1R in both excitatory and inhibitory boutons in the human prefrontal cortex, with differential levels of the receptor between bouton types. We hypothesized that the differential enrichment of CB1R between bouton types - a factor previously unaccounted for when examining CB1R changes in schizophrenia - may resolve prior discrepant reports and increase our insight into the effects of CB1R alterations on the pathophysiology of schizophrenia.

Methods

Using co-labeling immunohistochemistry and fluorescent microscopy, we examined total CB1R levels and CB1R levels within excitatory (vGlut1-positive) and inhibitory (vGAT-positive) boutons of prefrontal cortex samples from ten pairs of individuals diagnosed with schizophrenia and non-psychiatric comparisons.

Results

Significantly higher total CB1R levels were found within samples from individuals with schizophrenia. Terminal type-specific analyses identified significantly higher CB1R levels within excitatory boutons in samples from individuals with schizophrenia relative to comparisons. In contrast, CB1R levels within the subset of inhibitory boutons that normally express high CB1R levels (presumptive cholecystokinin neuron boutons) were lower in samples from individuals with schizophrenia relative to comparison samples.

Conclusion

Given CB1R's role in suppressing neurotransmission upon activation, these results suggest an overall shift in excitatory and inhibitory balance regulation toward a net reduction of excitatory activity in schizophrenia.

Expression of Cytokines and Neurodegeneration in the Rat Hippocampus and Cortex in the Lithium-Pilocarpine Model of Status Epilepticus and the Role of Modulation of Endocannabinoid System

A significant body of evidence shows that neuroinflammation is one of the key processes in the development of brain pathology in trauma, neurodegenerative disorders, and epilepsy. Various brain insults, including severe and prolonged seizure activity during status epilepticus (SE), trigger proinflammatory cytokine release. We investigated the expression of the proinflammatory cytokines interleukin-1β (Il1b) and interleukin-6 (Il6), and anti-inflammatory fractalkine (Cx3cl1) in the hippocampus, entorhinal cortex, and neocortex of rats 24 h, 7 days, and 5 months after lithium-pilocarpine SE. We studied the relationship between cytokine expression and neuronal death in the hippocampus and evaluated the effect of modulation of endocannabinoid receptors on neuroinflammation and neurodegeneration after SE. The results of the present study showed that inhibition of endocannabinoid CB1 receptors with AM251 early after SE had a transient neuroprotective effect that was absent in the chronic period and did not affect the development of spontaneous seizures after SE. At the same time, AM251 reduced the expression of Il6 in the chronic period after SE. Higher Cx3cl1 levels were found in rats with more prominent hippocampal neurodegeneration.

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.

Regular recreational Cannabis users exhibit altered neural oscillatory dynamics during attention reorientation

BACKGROUND

Cannabis is the most widely used illicit drug in the United States and is often associated with changes in attention function, which may ultimately impact numerous other cognitive faculties (e.g. memory, executive function). Importantly, despite the increasing rates of cannabis use and widespread legalization in the United States, the neural mechanisms underlying attentional dysfunction in chronic users are poorly understood.

METHODS

We used magnetoencephalography (MEG) and a modified Posner cueing task in 21 regular cannabis users and 32 demographically matched non-user controls. MEG data were imaged in the time-frequency domain using a beamformer and peak voxel time series were extracted to quantify the oscillatory dynamics underlying use-related aberrations in attentional reorienting, as well as the impact on spontaneous neural activity immediately preceding stimulus onset.

RESULTS

Behavioral performance on the task (e.g. reaction time) was similar between regular cannabis users and non-user controls. However, the neural data indicated robust theta-band synchronizations across a distributed network during attentional reorienting, with activity in the bilateral inferior frontal gyri being markedly stronger in users relative to controls (p's < 0.036). Additionally, we observed significantly reduced spontaneous theta activity across this distributed network during the pre-stimulus baseline in cannabis users relative to controls (p's < 0.020).

CONCLUSIONS

Despite similar performance on the task, we observed specific alterations in the neural dynamics serving attentional reorienting in regular cannabis users compared to controls. These data suggest that regular cannabis users may employ compensatory processing in the prefrontal cortices to efficiently reorient their attention relative to non-user controls.

Hippocampal expression of the cannabinoid receptor type 1 in canine epilepsy

Canine drug-resistant epilepsy is a prevailing issue in veterinary neurology. Alternative or additional treatment with cannabinoids is showing promising results in seizure management. A crucial component of the endocannabinoid system, cannabinoid receptor type 1 (CB1R), is heavily involved in the control of neurotransmitter release. Knowledge of its distribution in the epileptic brain would serve a better understanding of disease pathology and application of cannabinoids in dogs with epilepsy. CB1R distribution was assessed in sub-regions of hippocampus of dogs with idiopathic epilepsy, structural epilepsy and without cerebral pathology. In dogs with idiopathic epilepsy, significantly decreased CB1R expression compared to control animals was observed in CA1. In dogs with structural epilepsy, a significant increase in CB1R signal intensity in comparison to controls was observed. CB1R expression was higher in the structural group as compared to the idiopathic. Double immunofluorescence showed co-localization between CB1R and an astrocytic marker in about 50% of cells, regardless of the diagnosis. In summary, CB1R expression in canine hippocampus undergoes modification by the epileptic process and the direction of this change depends on the etiology of the disease. The distinct disease-associated CB1R expression needs to be considered in new treatment development for dogs with epilepsy.

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.

Adolescent Δ-9-tetrahydrocannabinol exposure induces differential acute and long-term neuronal and molecular disturbances in dorsal vs. ventral hippocampal subregions

Chronic exposure to Δ-9-tetrahydrocannabinol (THC) during adolescence is associated with long-lasting cognitive impairments and enhanced susceptibility to anxiety and mood disorders. Previous evidence has revealed functional and anatomical dissociations between the posterior vs. anterior portions of the hippocampal formation, which are classified as the dorsal and ventral regions in rodents, respectively. Notably, the dorsal hippocampus is critical for cognitive and contextual processing, whereas the ventral region is critical for affective and emotional processing. While adolescent THC exposure can induce significant morphological disturbances and glutamatergic signaling abnormalities in the hippocampus, it is not currently understood how the dorsal vs. ventral hippocampal regions are affected by THC during neurodevelopment. In the present study, we used an integrative combination of behavioral, molecular, and neural assays in a neurodevelopmental rodent model of adolescent THC exposure. We report that adolescent THC exposure induces long-lasting memory deficits and anxiety like-behaviors concomitant with a wide range of differential molecular and neuronal abnormalities in dorsal vs. ventral hippocampal regions. In addition, using matrix-assisted laser desorption/ionization imaging mass spectrometry (MALDI-IMS), we show for the first time that adolescent THC exposure induces significant and enduring dysregulation of GABA and glutamate levels in dorsal vs. ventral hippocampus. Finally, adolescent THC exposure induced dissociable dysregulations of hippocampal glutamatergic signaling, characterized by differential glutamatergic receptor expression markers, profound alterations in pyramidal neuronal activity and associated oscillatory patterns in dorsal vs. ventral hippocampal subregions.

Underlying mechanisms of long-term potentiation during the inhibition of the cannabinoid CB1 and GABAB receptors in the dentate gyrus of hippocampus

BACKGROUND

The release of various neurotransmitters and thereby the excitability of neuronal circuits are regulated by the endocannabinoid system in an activity-dependent manner. Hippocampal long-term potentiation (LTP) is augmented in cannabinoid type 1 (CB1) receptor-deficient mice. CB1 receptors exist on GABAergic axon terminals in the hippocampus. In our previous work, we showed that CB1 antagonists increased the population spike (PS) amplitude, field excitatory post-synaptic potential (fEPSP), and the LTP induction in the dentate gyrus (DG) of the rat hippocampus while the GABA_B antagonist decreased these parameters. Determining the underlying mechanisms of the pre- and/or postsynaptic locus of LTP expression is of great importance. In this study, we investigated whether LTP alteration acutely caused by CB1 and GABA_B receptor antagonists (AM251 and CGP55845, respectively) happens at the postsynaptic or presynaptic regions, or at both. Therefore, the paired-pulse ratio (PPR) was assessed prior to and following the LTP induction in the studied groups.

METHODS

Male Wistar rats were randomly assigned to the groups of control, AM251, CGP55845, CGP55845 + AM251. A high-frequency stimulation (HFS) of the perforant path (PP) was used to induce LTP in the DG region.

RESULTS

Statistical analysis revealed that AM251 produced significant increase in excitatory postsynaptic potential (EPSP) slope and amplitude of PS. Conversely, administration of CGP55845 produced decrease in slope of EPSP. The current results indicated that the PPR was not influenced by LTP induction in the presence of AM251 or CGP55845 either alone or their combination.

CONCLUSIONS

It can be concluded that the site causing LTP expression is, at least in part, the postsynaptic site because PPR was not influenced by LTP induction in the presence of AM251 or CGP55845 either alone or their combination.

Effects of Prenatal Cannabinoids Exposure upon Placenta and Development of Respiratory Neural Circuits

Cannabis use has risen dangerously during pregnancy in the face of incipient therapeutic use and a growing perception of safety. The main psychoactive compound of the Cannabis sativa plant is the phytocannabinoid delta-9-tetrahydrocannabinol (A-9 THC), and its status as a teratogen is controversial. THC and its endogenous analogues, anandamide (AEA) and 2-AG, exert their actions through specific receptors (eCBr) that activate intracellular signaling pathways. CB1r and CB2r, also called classic cannabinoid receptors, together with their endogenous ligands and the enzymes that synthesize and degrade them, constitute the endocannabinoid system. This system is distributed ubiquitously in various central and peripheral tissues. Although the endocannabinoid system's most studied role is controlling the release of neurotransmitters in the central nervous system, the study of long-term exposure to cannabinoids on fetal development is not well known and is vital for understanding environmental or pathological embryo-fetal or postnatal conditions. Prenatal exposure to cannabinoids in animal models has induced changes in placental and embryo-fetal organs. Particularly, cannabinoids could influence both neural and nonneural tissues and induce embryo-fetal pathological conditions in critical processes such as neural respiratory control. This review aims at the acute and chronic effects of prenatal exposure to cannabinoids on placental function and the embryo-fetal neurodevelopment of the respiratory pattern. The information provided here will serve as a theoretical framework to critically evaluate the teratogen effects of the consumption of cannabis during pregnancy.

The potential role of the cholecystokinin system in declarative memory

As one of the most abundant neuropeptides in the central nervous system, cholecystokinin (CCK) has been suggested to be associated with higher brain functions, including learning and memory. In this review, we examined the potential role of the CCK system in declarative memory. First, we summarized behavioral studies that provide evidence for an important role of CCK in two forms of declarative memory-fear memory and spatial memory. Subsequently, we examined the electrophysiological studies that support the diverse roles of CCK-2 receptor activation in neocortical and hippocampal synaptic plasticity, and discussed the potential mechanisms that may be involved. Last but not least, we discussed whether the reported CCK-mediated synaptic plasticity can explain the strong influence of the CCK signaling system in neocortex and hippocampus dependent declarative memory. The available research supports the role of CCK-mediated synaptic plasticity in neocortex dependent declarative memory acquisition, but further study on the association between CCK-mediated synaptic plasticity and neocortex dependent declarative memory consolidation and retrieval is necessary. Although a direct link between CCK-mediated synaptic plasticity and hippocampus dependent declarative memory is missing, noticeable evidence from morphological, behavioral, and electrophysiological studies encourages further investigation regarding the potential role of CCK-dependent synaptic plasticity in hippocampus dependent declarative memory.

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.

Ventral hippocampal diacylglycerol lipase-alpha deletion decreases avoidance behaviors and alters excitation-inhibition balance

The endogenous cannabinoid, 2-arachidonoylglycerol (2-AG), plays a key role in the regulation of anxiety- and stress-related behavioral phenotypes and may represent a novel target for the treatment of anxiety disorders. However, recent studies have suggested a more complex role for 2-AG signaling in the regulation of stress responsivity, including increases in acute fear responses after 2-AG augmentation under some conditions. Thus, 2-AG signaling within distinct brain regions and circuits could regulate anxiety-like behavior and stress responsivity in opposing manners. The ventral hippocampus (vHPC) is a critical region for emotional processing, anxiety-like behaviors, and stress responding. Here, we use a conditional knock-out of the 2-AG synthesis enzyme, diacylglycerol lipase α (DAGLα), to study the role of vHPC 2-AG signaling in the regulation of affective behavior. We show that vHPC DAGLα deletion decreases avoidance behaviors both basally and following an acute stress exposure. Genetic deletion of vHPC DAGLα also promotes stress resiliency, with no effect on fear acquisition, expression, or contextual fear generalization. Using slice electrophysiology, we demonstrate that vHPC DAGLα deletion shifts vHPC activity towards enhanced inhibition. Together, these data indicate endogenous 2-AG signaling in the vHPC promotes avoidance and increases stress reactivity, confirming the notion that 2-AG signaling within distinct brain regions may exert divergent effects on anxiety states and stress adaptability.

Regular cannabis use modulates the impact of HIV on the neural dynamics serving cognitive control

BACKGROUND

Cannabis use and HIV are independently associated with decrements in cognitive control. However, the combined effects of HIV and regular cannabis use on the brain circuitry serving higher-order cognition are unclear.

AIMS

Investigate the interaction between cannabis and HIV on neural interference effects during the flanker task and spontaneous activity in regions underlying higher-order cognition.

METHODS

The sample consisted of 100 participants, including people with HIV (PWH) who use cannabis, PWH who do not use cannabis, uninfected cannabis users, and uninfected nonusers. Participants underwent an interview regarding their substance use history and completed the Eriksen flanker task during magnetoencephalography (MEG). MEG data were imaged in the time-frequency domain and oscillatory maps depicting the neural flanker interference effect were probed for group differences. Voxel time series were then assessed for group-level differences in spontaneous activity.

RESULTS

Group differences in behavioral performance were identified along with group differences in theta and alpha neural interference responses in higher-order regions across the cortex, with nonusers with HIV generally exhibiting the most aberrant responses. Likewise, time series analyses indicated that nonusers with HIV also had significantly elevated spontaneous alpha activity in the left inferior frontal and dorsolateral prefrontal cortices (dlPFC). Finally, we found that spontaneous and oscillatory alpha activity were significantly coupled in the inferior frontal cortex and dlPFC among cannabis users, but not nonusers.

CONCLUSIONS

Regular cannabis use appears to suppress the impact of HIV on spontaneous and oscillatory alpha deficits in the left inferior frontal cortex and dlPFC.

Social Play Behavior Is Critical for the Development of Prefrontal Inhibitory Synapses and Cognitive Flexibility in Rats

Sensory driven activity during early life is critical for setting up the proper connectivity of the sensory cortices. We ask here whether social play behavior, a particular form of social interaction that is highly abundant during postweaning development, is equally important for setting up connections in the developing prefrontal cortex (PFC). Young male rats were deprived from social play with peers during the period in life when social play behavior normally peaks [postnatal day 21-42] (SPD rats), followed by resocialization until adulthood. We recorded synaptic currents in layer 5 cells in slices from medial PFC of adult SPD and control rats and observed that inhibitory synaptic currents were reduced in SPD slices, while excitatory synaptic currents were unaffected. This was associated with a decrease in perisomatic inhibitory synapses from parvalbumin-positive GABAergic cells. In parallel experiments, adult SPD rats achieved more reversals in a probabilistic reversal learning (PRL) task, which depends on the integrity of the PFC, by using a more simplified cognitive strategy than controls. Interestingly, we observed that one daily hour of play during SPD partially rescued the behavioral performance in the PRL, but did not prevent the decrease in PFC inhibitory synaptic inputs. Our data demonstrate the importance of unrestricted social play for the development of inhibitory synapses in the PFC and cognitive skills in adulthood and show that specific synaptic alterations in the PFC can result in a complex behavioral outcome.SIGNIFICANCE STATEMENT This study addressed the question whether social play behavior in juvenile rats contributes to functional development of the prefrontal cortex (PFC). We found that rats that had been deprived from juvenile social play (social play deprivation - SPD) showed a reduction in inhibitory synapses in the PFC and a simplified strategy to solve a complex behavioral task in adulthood. Providing one daily hour of play during SPD partially rescued the cognitive skills in these rats, but did not prevent the reduction in PFC inhibitory synapses. Our results demonstrate a key role for unrestricted juvenile social play in PFC development and emphasize the complex relation between PFC circuit connectivity and cognitive function.

Seizure-induced overexpression of NPY induces epileptic tolerance in a mouse model of spontaneous recurrent seizures

Epileptic seizures result in pronounced over-expression of neuropeptide Y (NPY). In vivo and in vitro studies revealed that NPY exerts potent anticonvulsive actions through presynaptic Y2 receptors by suppressing glutamate release from principal neurons. We now investigated whether seizure-induced over-expression of NPY contributes to epileptic tolerance induced by preceding seizures. We used a previously established animal model based on selective inhibition of GABA release from parvalbumin (PV)-containing interneurons in the subiculum in mice. The animals present spontaneous recurrent seizures (SRS) and clusters of interictal spikes (IS). The frequency of SRS declined after five to six weeks, indicating development of seizure tolerance. In interneurons of the subiculum and sector CA1, SRS induced over-expression of NPY that persisted there for a prolonged time despite of a later decrease in SRS frequency. In contrast to NPY, somatostatin was not overexpressed in the respective axon terminals. Contrary to interneurons, NPY was only transiently expressed in mossy fibers. To demonstrate a protective function of endogenous, over-expressed NPY, we injected the selective NPY-Y2 receptor antagonist JNJ 5207787 simultaneously challenging the mice by a low dose of pentylenetetrazol (PTZ, 30 or 40 mg/kg, i.p.). In control mice, neither PTZ nor PTZ plus JNJ 5207787 induced convulsions. In mice with silenced GABA/PV neurons, PTZ alone only modestly enhanced EEG activity. When we injected JNJ 5207787 together with PTZ (either dose) the number of seizures, however, became significantly increased. In addition, in the epileptic mice CB1 receptor immunoreactivity was reduced in terminal areas of basket cells pointing to reduced presynaptic inhibition of GABA release from these neurons. Our experiments demonstrate that SRS result in overexpression of NPY in hippocampal interneurons. NPY overexpression persists for several weeks and may be related to later decreasing SRS frequency. Injection of the Y2 receptor antagonist JNJ 5207787 prevents this protective action of NPY only when release of the peptide is triggered by injection of PTZ and induces pronounced convulsions. Thus, over-expressed NPY released “on demand” by seizures may help terminating acute seizures and may prevent from recurrent epileptic activity.

Endocannabinoid System of the Blood-Brain Barrier: Current Understandings and Therapeutic Potentials

The endocannabinoid system (ECS) has been found at the blood-brain barrier (BBB), as Cannabinoid receptors were characterized in human brain microvascular endothelial cells and astrocytes. In several in vitro and in vivo studies, cannabinoids decreased BBB permeability and enhanced membrane integrity, which may be achieved through endothelial tight junctions and other mechanisms. These permeability regulation effects of cannabinoids suggested that the ECS may protect the brain by enhancing barrier integrity. Related questions about cannabinoid-drug interaction and drug distribution across the BBB are also raised. Specifically, can cannabinoids significantly reduce drug bioavailability to the brain? More in-depth and systematic investigations are needed to characterize and quantify these effects of cannabinoids on brain microvasculature physiopathology. Therefore, this review summarizes literatures from different disciplines to promote more research on assessing the therapeutic benefits and risks of using cannabinoids to protect BBB from dysfunctions or breakdown, and to avoid consequent brain damages due to inflammation, neurodegenerations, hemorrhage, ischemia, or other causes.

Cannabinoids modulate proliferation, differentiation, and migration signaling pathways in oligodendrocytes

Cannabinoid signaling, mainly via CB1 and CB2 receptors, plays an essential role in oligodendrocyte health and functions. However, the specific molecular signals associated with the activation or blockade of CB1 and CB2 receptors in this glial cell have yet to be elucidated. Mass spectrometry-based shotgun proteomics and in silico biology tools were used to determine which signaling pathways and molecular mechanisms are triggered in a human oligodendrocytic cell line (MO3.13) by several pharmacological stimuli: the phytocannabinoid cannabidiol (CBD); CB1 and CB2 agonists ACEA, HU308, and WIN55, 212-2; CB1 and CB2 antagonists AM251 and AM630; and endocannabinoids anandamide (AEA) and 2-arachidonoylglycerol (2-AG). The modulation of cannabinoid signaling in MO3.13 was found to affect pathways linked to cell proliferation, migration, and differentiation of oligodendrocyte progenitor cells. Additionally, we found that carbohydrate and lipid metabolism, as well as mitochondrial function, were modulated by these compounds. Comparing the proteome changes and upstream regulators among treatments, the highest overlap was between the CB1 and CB2 antagonists, followed by overlaps between AEA and 2-AG. Our study opens new windows of opportunities, suggesting that cannabinoid signaling in oligodendrocytes might be relevant in the context of demyelinating and neurodegenerative diseases. Proteomics data are available at ProteomeXchange (PXD031923).

The Neuroprotective Effects of mGlu1 Receptor Antagonists Are Mediated by an Enhancement of GABAergic Synaptic Transmission via a Presynaptic CB1 Receptor Mechanism

In this study, we investigated the cross-talk between mGlu1 and CB1 receptors in modulating GABA hippocampal output in whole-cell voltage clamp recordings in rat hippocampal acute slices, in organotypic hippocampal slices exposed to oxygen and glucose deprivation (OGD) and in gerbils subjected to global ischemia. CB1 receptor expression was studied using immunohistochemistry and the CA1 contents of anandamide (AEA) and 2-arachidonoylglycerol (2-AG) were measured by LC-MS/MS. Our results show that mGlu1 receptor antagonists enhance sIPSCs in CA1 pyramidal cells and the basal and ischemic hippocampal release of GABA in vivo in a manner that is mediated by CB1 receptor activation. In hippocampal slices exposed to OGD and in ischemic gerbils, mGlu1 receptor antagonists protected CA1 pyramidal cells against post-ischemic injury and this effect was reduced by CB1 receptor activation. OGD induced a transient increase in the hippocampal content of AEA and this effect is prevented by mGlu1 receptor antagonist. Finally, OGD induced a late disruption of CB1 receptors in the CA1 region and the effect was prevented when CA1 pyramidal cells were protected by mGlu1 antagonists. Altogether, these results suggest a cooperative interaction between mGlu1 receptors and the endocannabinoid system in the mechanisms that lead to post-ischemic neuronal death.

Endocannabinoids regulate cocaine-associated memory through brain AEA-CB1R signalling activation

Objective

Contextual drug-associated memory precipitates craving and relapse in substance users, and the risk of relapse is a major challenge in the treatment of substance use disorders. Thus, understanding the neurobiological underpinnings of how this association memory is formed and maintained will inform future advances in the treatment of drug addiction. Brain endocannabinoids (eCBs) signalling has been associated with drug-induced neuroadaptations, but the role of lipases that mediate small lipid ligand biosynthesis and metabolism in regulating drug-associated memory has not been examined. Here, we explored how manipulation of the lipase fatty acid amide hydrolase (FAAH), which is involved in mediating the level of the lipid ligand anandamide (AEA), affects cocaine-associated memory formation.

Methods

We applied behavioural, pharmacological and biochemical methods to detect cocaine-associated memory formation, eCBs in the dorsal dentate gyrus (dDG), and the activity of related enzymes. We further examined the roles of abnormal FAAH activity and AEA–CB1R signalling in the regulation of cocaine-associated memory formation and granule neuron dendritic structure alterations in the dDG through Western blotting, electron microscopy and immunofluorescence.

Results

In the present study, we found that cocaine induced a decrease in the level of FAAH in the dDG and increased the level of AEA. A high level of AEA activated cannabinoid type 1 receptors (CB1Rs) and further triggered CB1R signalling activation and granule neuron dendritic remodelling, and these effects were reversed by blockade of CB1Rs in the brain. Furthermore, inhibition of FAAH in the dDG markedly increased AEA levels and promoted cocaine-associated memory formation through CB1R signalling activation.

Conclusions

Together, our findings demonstrate that the lipase FAAH influences CB1R signalling activation and granule neuron dendritic structure alteration in the dDG by regulating AEA levels and that AEA and AEA metabolism play a key role in cocaine-associated memory formation. Manipulation of AEA production may serve as a potential therapeutic strategy for drug addiction and relapse prevention.

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AEA plays an important role in the cocaine-associated memory formation through triggering CB1Rs.

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Cocaine decreases FAAH level and leads to AEA increasing, which activate CB1R signaling and remodel dendritic spines structure of granule neurons.

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Regulating AEA degradation through manipulation of FAAH, governs the cocaine-associated memory formation.

Task-independent acute effects of delta-9-tetrahydrocannabinol on human brain function and its relationship with cannabinoid receptor gene expression: A neuroimaging meta-regression analysis

The neurobiological mechanisms underlying the effects of delta-9-tetrahydrocannabinol (THC) remain unclear. Here, we examined the spatial acute effect of THC on human regional brain activation or blood flow (hereafter called 'activation signal') in a 'core' network of brain regions from 372 participants, tested using a within-subject repeated measures design under experimental conditions. We also investigated whether the neuromodulatory effects of THC are related to the local expression of the cannabinoid-type-1 (CB1R) and type-2 (CB2R) receptors. Finally, we investigated the dose-response relationship between THC and key brain substrates. These meta-analytic findings shed new light on the localisation of the effects of THC in the human brain, suggesting that THC has neuromodulatory effects in regions central to many cognitive tasks and processes, related to dose, with greater effects in regions with higher levels of CB1R expression.

Visual-area-specific tonic modulation of GABA release by endocannabinoids sets the activity and coordination of neocortical principal neurons

Perisomatic inhibition of pyramidal neurons (PNs) coordinates cortical network activity during sensory processing, and this role is mainly attributed to parvalbumin-expressing basket cells (BCs). However, cannabinoid receptor type 1 (CB1)-expressing interneurons are also BCs, but the connectivity and function of these elusive but prominent neocortical inhibitory neurons are unclear. We find that their connectivity pattern is visual area specific. Persistently active CB1 signaling suppresses GABA release from CB1 BCs in the medial secondary visual cortex (V2M), but not in the primary visual cortex (V1). Accordingly, in vivo, tonic CB1 signaling is responsible for higher but less coordinated PN activity in the V2M than in the V1. These differential firing dynamics in the V1 and V2M can be captured by a computational network model that incorporates visual-area-specific properties. Our results indicate a differential CB1-mediated mechanism controlling PN activity, suggesting an alternative connectivity scheme of a specific GABAergic circuit in different cortical areas.

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CB1⁺ basket cells exhibit visual-area-specific morphology and connectivity patterns

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Tonic CB1 signaling underlies high pyramidal neurons (PN) activity in V2M but not V1

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Tonic CB1 signaling differentially modulates PN-correlated activity in V1 and V2M

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Numerical simulations capture specific CB1-dependent firing dynamics of V1 and V2M