Functions of cannabinoid receptors in the hippocampus

The Sobering Sting: Oleoyl Serotonin Is a Novel Stephanoconus Snail Venom-Derived Antagonist of Cannabinoid Receptors That Counteracts Learning and Memory Deficits

Cannabinoid receptors (CB1 and CB2) are promising targets for a better understanding of neurological diseases. Nevertheless, only a few ligands of CB have reached clinical application so far. Venoms are considered as interesting sources of novel biologically active compounds. Here, we describe an endocannabinoid-like molecule, oleoyl serotonin (OS), present in the venom of Stephanoconus snails. Using electrophysiological assays, it was shown that OS inhibits CB1 and CB2. Structure-activity relationship studies using a chimeric CB1/2 revealed that the domain encompassing the transmembrane helix V (TMHV)- intracellular loop 3 (ICL3)-TMHVI of the CB2 is critical for the binding and function of OS. We concluded that OS binds to sites of the CB2 that are different from the binding sites of the non-selective CB agonist WIN55,212-2. Behavioral assays in mice showed that OS counteracted learning and memory deficits caused by WIN55,212-2. Furthermore, a selectivity screening of OS showed high selectivity for CB over various ion channels and receptors. Overall, OS may represent a new approach to the prevention and treatment of learning and memory cognition impairment in neurological diseases.

HIV chronicity as a predictor of hippocampal memory deficits in daily cannabis users living with HIV

Background

Antiretroviral medications have increased the lifespan of persons living with HIV (PLWH) thereby unmasking memory decline that may be attributed to chronological age, HIV symptomatology, HIV disease chronicity, and/or substance use (especially cannabis use which is common among PLWH). To date, few studies have attempted to disentangle these effects. In a sample of daily cannabis-using PLWH, we investigated whether hippocampal memory function, assessed via an object-location associative learning task, was associated with age, HIV chronicity and symptom severity, or substance use.

Methods

48 PLWH (12.9 ± 9.6 years since HIV diagnosis), who were 44 years old on average (range: 24-64 years; 58 % male) and reported daily cannabis use (recent use confirmed by urinalysis) completed the study. We assessed each participant's demographics, substance use, medical history, current HIV symptoms, and hippocampal memory function via a well-validated object-location associative learning task.

Results

Multiple regression analyses found that living more years since HIV+ diagnosis predicted significantly worse associative learning total score (r=-0.40) and learning rate (r=-0.34) whereas chronological age, cannabis-use characteristics, and recent HIV symptom severity were not significantly related to hippocampal memory function.

Conclusions

In daily cannabis-using PLWH, HIV chronicity was related to worse hippocampal memory function independent from cannabis use, age, and HIV symptomatology. Object-location associative learning performance could serve as an 'early-warning' metric of cognitive decline among PLWH. Future research should examine longitudinal changes in associative learning proficiency and evaluate interventions to prevent hippocampal memory decline among PLWH. ClinicalTrials.gov: NCT01536899.

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.

Rational drug design of CB2 receptor ligands: from 2012 to 2021

Cannabinoid receptors belong to the large family of G-protein-coupled receptors, which can be divided into two receptor types, cannabinoid receptor type-1 (CB1) and cannabinoid receptor type-2 (CB2). Marinol, Cesamet and Sativex are marketed CB1 drugs which are still in use and work well, but the central nervous system side effects caused by activation CB1, which limited the development of CB1 ligands. So far, no selective CB2 ligand has been approved for marketing, but lots of its ligands in the clinical stage and pre-clinical stage have positive effects on the treatment of some disease models and have great potential for development. Most selective CB2 agonists are designed and synthesized based on non-selective CB2 agonists through the classical med-chem strategies, e.g. molecular hybridization, scaffold hopping, bioisosterism, etc. During these processes, the balance between selectivity, activity, and pharmacokinetic properties needs to be achieved. Hence, we summarized some reported ligands on the basis of the optimization strategies in recent 10 years, and the limitations and future directions.

Cannabinoid receptor type 1 antagonists alter aspects of risk/reward decision making independent of toluene-mediated effects

Drugs of abuse including cannabis and inhalants impair risk/reward decision making. Cannabis use is often concurrent with inhalant intoxication; yet, preclinical studies investigating the role of endocannabinoids in inhalant misuse are limited. To address this gap in the literature, we used the well-validated probabilistic discounting task to assess risk/reward decision making in rodents following combinations of toluene vapor (a common inhalant) and manipulations of cannabinoid receptor type 1 (CB1R) signaling. As reported previously, acute exposure to toluene vapor disrupted behavioral flexibility during probabilistic discounting. Systemic administration of the CB1R inverse agonist AM281 did not prevent toluene-induced alterations in risky choices, but did independently reduce win-stay behavior, increase choice latency, and increase omissions. Toluene-induced deficits in probabilistic discounting are thought to involve impaired medial prefrontal cortex (mPFC) activity. As we previously reported that some of toluene's inhibitory effects on glutamatergic signaling in the mPFC are endocannabinoid-dependent, we tested the hypothesis that mPFC CB1R activity mediates toluene-induced deficits in discounting. However, bilateral injection of the CB1R inverse agonist AM251 prior to toluene vapor exposure had no effect on toluene-induced changes in risk behavior. In a final set of experiments, we injected the CB1R inverse agonist AM251 (5 and 50 ng), the CB1R agonist WIN55,212-2 (50 ng and 500 ng), or vehicle into the mPFC prior to testing. While mPFC CB1R stimulation did not affect any of the measures tested, the CB1R inverse agonist caused a dose-dependent reduction in win-stay behavior without altering any other measures. Together, these studies indicate that toluene-induced deficits in probabilistic discounting are largely distinct from CB1R-dependent effects that include decreased effectiveness of positive reinforcement (mPFC CB1Rs), decision making speed, and task engagement (non-mPFC CB1Rs).

Hippocampal Cannabinoid 1 Receptors Are Modulated Following Cocaine Self-administration in Male Rats

Cocaine addiction is a complex pathology inducing long-term neuroplastic changes that, in turn, contribute to maladaptive behaviors. This behavioral dysregulation is associated with transcriptional reprogramming in brain reward circuitry, although the mechanisms underlying this modulation remain poorly understood. The endogenous cannabinoid system may play a role in this process in that cannabinoid mechanisms modulate drug reward and contribute to cocaine-induced neural adaptations. In this study, we investigated whether cocaine self-administration induces long-term adaptations, including transcriptional modifications and associated epigenetic processes. We first examined endocannabinoid gene expression in reward-related brain regions of the rat following self-administered (0.33 mg/kg intravenous, FR1, 10 days) cocaine injections. Interestingly, we found increased Cnr1 expression in several structures, including prefrontal cortex, nucleus accumbens, dorsal striatum, hippocampus, habenula, amygdala, lateral hypothalamus, ventral tegmental area, and rostromedial tegmental nucleus, with most pronounced effects in the hippocampus. Endocannabinoid levels, measured by mass spectrometry, were also altered in this structure. Chromatin immunoprecipitation followed by qPCR in the hippocampus revealed that two activating histone marks, H3K4Me3 and H3K27Ac, were enriched at specific endocannabinoid genes following cocaine intake. Targeting CB1 receptors using chromosome conformation capture, we highlighted spatial chromatin re-organization in the hippocampus, as well as in the nucleus accumbens, suggesting that destabilization of the chromatin may contribute to neuronal responses to cocaine. Overall, our results highlight a key role for the hippocampus in cocaine-induced plasticity and broaden the understanding of neuronal alterations associated with endocannabinoid signaling. The latter suggests that epigenetic modifications contribute to maladaptive behaviors associated with chronic drug use.

Rapamycin prevents the long-term impairing effects of adolescence Δ-9-tetrahydrocannabinol on memory and plasticity in male rats

Long-lasting cognitive impairment is one of the most central negative consequences related to the exposure to cannabis during adolescence and particularly of Δ-9-tetrahydrocannabinol (THC). The aim of this study was to compare the protracted effects of adolescent versus late-adolescent chronic exposure to THC on short-term memory and plasticity and to examine whether rapamycin, a blocker of the mammalian target of rapamycin (mTOR) pathway, can restore THC-induced deficits in memory and plasticity. Male rats were injected with ascending doses of THC [2.5, 5, 10 mg/kg; intraperitoneally (i.p.)] during adolescence and late-adolescence (post-natal days 30-41 and 45-56, respectively), followed by daily injections of rapamycin (1 mg/kg, i.p.) during the first 10 days of cessation from THC. Thirty days after the last injection, rats were tested for short-term and working memory, anxiety-like behaviour, and plasticity in the pathways projecting from the ventral subiculum (vSub) of the hippocampus to the prefrontal cortex (PFC) and nucleus accumbens (NAc). THC exposure in adolescence, but not late-adolescence, was found to induce long-term deficits in object recognition short-term memory and synaptic plasticity in the hippocampal-accumbens pathway. Importantly, rapamycin rescued these persistent effects of THC administered during adolescence. Our findings show that some forms of memory and plasticity are sensitive to chronic THC administration during adolescence and that rapamycin administered during THC cessation may restore cognitive function and plasticity, thus potentially protecting against the possible long-term harmful effects of THC.

The role of Tetrahydrocannabinol in inducing disrupted signaling cascades, hippocampal atrophy and memory defects

Tetrahydrocannabinol (THC), a major psychoactive constituent of marijuana, can substantially change the function of several brain areas, leading to behavioral impairment including memory and learning dysfunction. Given the importance of hippocampus as one of the chief parts of the brain involved in memory processing, the present study seeks to investigate structural and histological alterations in hippocampus as well as behavioral defects provoked by THC treatment. Besides, using genome-wide sequencing, we adopted a pathway-based approach to discover dysregulated molecular pathways. Our results demonstrated remarkable hippocampal atrophy, and also interrupted memory function and long term potentiation (LTP) under THC exposure. We also detected several dysregulated signaling pathways involved in synaptic plasticity as well as cell-cell interaction in the hippocampus of THC-treated rats. Overall, the results indicate a potential correlation between disrupted signaling cascades, hippocampal atrophy and memory defects caused by THC treatment.

Imaging Cannabinoid Receptors: A Brief Collection of Covalent and Fluorescent Probes for CB1 and CB2 Receptors

There has been an expanding public interest towards the notion that modulation of the sophisticated endocannabinoid system can lead to various therapeutic benefits that are yet to be fully explored. In recent years, the drug discovery paradigm in this field has been largely based on the development of selective CB2 receptor agonists, avoiding the unwanted CB1 receptor-mediated psychoactive side effects. Mechanistically, target engagement studies are crucial for confirming the ligand–receptor interaction and the subsequent biological cascades that lead to the observed therapeutic effects. Concurrently, imaging techniques for visualisation of cannabinoid receptors are increasingly reported in the literature. Small molecule imaging tools ranging from phytocannabinoids such as tetrahydrocannabinol (THC) and cannabidiol (CBD) to the endocannabinoids as well as the purely synthetic cannabimimetics, have been explored to date with varying degrees of success. This Review will cover currently known photoactivatable, electrophilic, and fluorescent ligands for both the CB1 and CB2 receptors. Structural insights from techniques such as ligand-assisted protein structure (LAPS) and the discovery of novel allosteric modulators are significant additions for better understanding of the endocannabinoid system. There has also been a plethora of fluorescent conjugates that have been assessed for their binding to cannabinoid receptors as well as their potential for cellular imaging. More recently, bifunctional probes containing either fluorophores or electrophilic tags are becoming more prevalent in the literature. Collectively, these molecular tools are invaluable in demonstrating target engagement within the human endocannabinoid system.

In utero Δ9-tetrahydrocannabinol exposure confers vulnerability towards cognitive impairments and alcohol drinking in the adolescent offspring: Is there a role for neuropeptide Y?

BACKGROUND

Cannabinoid consumption during pregnancy has been increasing on the wave of the broad-based legalisation of cannabis in Western countries, raising concern about the putative detrimental outcomes on foetal neurodevelopment. Indeed, since the endocannabinoid system regulates synaptic plasticity, emotional and cognitive processes from early stages of life interfering with it and other excitability endogenous modulators, such as neuropeptide Y (NPY), might contribute to the occurrence of a vulnerable phenotype later in life.

AIMS

This research investigated whether in utero exposure to Δ9-tetrahydrocannabinol (THC) may induce deficits in emotional/cognitive processes and alcohol vulnerability in adolescent offspring. NPY and excitatory postsynaptic density (PSD) machinery were measured as markers of neurobiological vulnerability.

METHODS

Following in utero THC exposure (2 mg/kg delivered subcutaneously), preadolescent male rat offspring were assessed for: behavioural reactivity in the open field test, neutral declarative memory and aversive limbic memory in the Novel Object and Emotional Object Recognition tests, immunofluorescence for NPY neurons and the PSD proteins Homer-1, 1b/c and 2 in the prefrontal cortex, amygdala and nucleus accumbens at adolescence (cohort 1); and instrumental learning, alcohol taking, relapse and conflict behaviour in the operant chamber throughout adolescence until early adulthood (cohort 2).

RESULTS

In utero THC-exposed adolescent rats showed: (a) increased locomotor activity; (b) no alteration in neutral declarative memory; (c) impaired aversive limbic memory; (d) decreased NPY-positive neurons in limbic regions; (e) region-specific variations in Homer-1, 1b/c and 2 immunoreactivity; (f) decreased instrumental learning and increased alcohol drinking, relapse and conflict behaviour in the operant chamber.

CONCLUSION

Gestational THC impaired the formation of memory traces when integration between environmental encoding and emotional/motivational processing was required and promoted the development of alcohol-addictive behaviours. The abnormalities in NPY signalling and PSD make-up may represent the common neurobiological background, suggesting new targets for future research.

Interaction of Cannabis Use and Aging: From Molecule to Mind

Given the aging Baby Boomer generation, changes in cannabis legislation, and the growing acknowledgment of cannabis for its therapeutic potential, it is predicted that cannabis use in the older population will escalate. It is, therefore, important to determine the interaction between the effects of cannabis and aging. The aim of this report is to describe the link between cannabis use and the aging brain. Our review of the literature found few and inconsistent empirical studies that directly address the impact of cannabis use on the aging brain. However, research focused on long-term cannabis use points toward cumulative effects on multimodal systems in the brain that are similarly affected during aging. Specifically, the effects of cannabis and aging converge on overlapping networks in the endocannabinoid, opioid, and dopamine systems that may affect functional decline particularly in the hippocampus and prefrontal cortex, which are critical areas for memory and executive functioning. To conclude, despite the limited current knowledge on the potential interactive effects between cannabis and aging, evidence from the literature suggests that cannabis and aging effects are concurrently present across several neurotransmitter systems. There is a great need for future research to directly test the interactions between cannabis and aging.

Adolescent Δ9-Tetrahydrocannabinol Exposure and Astrocyte-Specific Genetic Vulnerability Converge on Nuclear Factor-κB-Cyclooxygenase-2 Signaling to Impair Memory in Adulthood

BACKGROUND

Although several studies have linked adolescent cannabis use to long-term cognitive dysfunction, there are negative reports as well. The fact that not all users develop cognitive impairment suggests a genetic vulnerability to adverse effects of cannabis, which are attributed to action of Δ9-tetrahydrocannabinol (Δ⁹-THC), a cannabis constituent and partial agonist of brain cannabinoid receptor 1. As both neurons and glial cells express cannabinoid receptor 1, genetic vulnerability could influence Δ⁹-THC-induced signaling in a cell type-specific manner.

METHODS

Here we use an animal model of inducible expression of dominant-negative disrupted in schizophrenia 1 (DN-DISC1) selectively in astrocytes to evaluate the molecular mechanisms, whereby an astrocyte genetic vulnerability could interact with adolescent Δ⁹-THC exposure to impair recognition memory in adulthood.

RESULTS

Selective expression of DN-DISC1 in astrocytes and adolescent treatment with Δ⁹-THC synergistically affected recognition memory in adult mice. Similar deficits in recognition memory were observed following knockdown of endogenous Disc1 in hippocampal astrocytes in mice treated with Δ⁹-THC during adolescence. At the molecular level, DN-DISC1 and Δ⁹-THC synergistically activated the nuclear factor-κB-cyclooxygenase-2 pathway in astrocytes and decreased immunoreactivity of parvalbumin-positive presynaptic inhibitory boutons around pyramidal neurons of the hippocampal CA3 area. The cognitive abnormalities were prevented in DN-DISC1 mice exposed to Δ⁹-THC by simultaneous adolescent treatment with the cyclooxygenase-2 inhibitor, NS398.

CONCLUSIONS

Our data demonstrate that individual vulnerability to cannabis can be exclusively mediated by astrocytes. Results of this work suggest that genetic predisposition within astrocytes can exaggerate Δ⁹-THC-produced cognitive impairments via convergent inflammatory signaling, suggesting possible targets for preventing adverse effects of cannabis within susceptible individuals.

Feasibility and effects of galantamine on cognition in humans with cannabis use disorder

BACKGROUND

As long-term use of medicinal and recreational cannabis becomes more common and concentrations of delta-9-tetrahydrocannabinol (THC) in cannabis increase, it is timely to identify strategies to counteract the cognitive effects of cannabinoids.

OBJECTIVE

Galantamine is an acetylcholinesterase inhibitor approved for the treatment of Alzheimer's disease and other dementias. This study aimed to investigate the feasibility of galantamine administration to individuals with cannabis use disorder (CUD), and the effects of galantamine on cognition. We hypothesized galantamine would be well tolerated and would not have procognitive effects in the absence of acute cannabis intoxication.

METHODS

Thirty individuals with CUD (73.5% male, 26.5% female) participated in a randomized, double-blind, parallel-group trial. Participants completed a baseline session followed by a 10-day outpatient treatment period, during which they received either 8 mg/day of galantamine orally or placebo. Cognitive assessments were conducted at three time points and self-reported measures that may impact cognitive performance (cannabis withdrawal, craving, and mood) were completed at six time points.

RESULTS

There were no significant differences in demographic and baseline variables between groups (galantamine vs. placebo). There were no significant adverse effects from galantamine. Cannabis withdrawal and craving continuously decreased over the study. We saw evidence of a modest improvement in cognitive outcomes during the 10-day period, exemplified by a statistically significant increase in measures of response inhibition (increased median reaction time on the Stop Signal Task), and a trend for improvement in measures of attention (increased RVP A'), for both groups. Analyses did not show, however, a significant main effect for treatment or treatment-by-time interactions.

CONCLUSIONS

The findings of this pilot study support the feasibility of the administration of galantamine for individuals with CUD. Adequately powered, randomized, placebo-controlled trials are required to investigate the potential of galantamine to improve cognitive deficits associated with CUD.

Hippocampal Stratum Oriens Somatostatin-Positive Cells Undergo CB1-Dependent Long-Term Potentiation and Express Endocannabinoid Biosynthetic Enzymes

The hippocampus is thought to encode information by altering synaptic strength via synaptic plasticity. Some forms of synaptic plasticity are induced by lipid-based endocannabinoid signaling molecules that act on cannabinoid receptors (CB1). Endocannabinoids modulate synaptic plasticity of hippocampal pyramidal cells and stratum radiatum interneurons; however, the role of endocannabinoids in mediating synaptic plasticity of stratum oriens interneurons is unclear. These feedback inhibitory interneurons exhibit presynaptic long-term potentiation (LTP), but the exact mechanism is not entirely understood. We examined whether oriens interneurons produce endocannabinoids, and whether endocannabinoids are involved in presynaptic LTP. Using patch-clamp electrodes to extract single cells, we analyzed the expression of endocannabinoid biosynthetic enzyme mRNA by reverse transcription and then real-time PCR (RT-PCR). The cellular expression of calcium-binding proteins and neuropeptides were used to identify interneuron subtype. RT-PCR results demonstrate that stratum oriens interneurons express mRNA for both endocannabinoid biosynthetic enzymes and the type I metabotropic glutamate receptors (mGluRs), necessary for endocannabinoid production. Immunohistochemical staining further confirmed the presence of diacylglycerol lipase alpha, an endocannabinoid-synthesizing enzyme, in oriens interneurons. To test the role of endocannabinoids in synaptic plasticity, we performed whole-cell experiments using high-frequency stimulation to induce long-term potentiation in somatostatin-positive cells. This plasticity was blocked by AM-251, demonstrating CB1-dependence. In addition, in the presence of a fatty acid amide hydrolase inhibitor (URB597; 1 µM) and MAG lipase inhibitor (JZL184; 1 µM) that increase endogenous anandamide and 2-arachidonyl glycerol, respectively, excitatory current responses were potentiated. URB597-induced potentiation was blocked by CB1 antagonist AM-251 (2 µM). Collectively, this suggests somatostatin-positive oriens interneuron LTP is CB1-dependent.

A translational perspective on neural circuits of fear extinction: Current promises and challenges

Fear extinction is the well-known process of fear reduction through repeated re-exposure to a feared stimulus without the aversive outcome. The last two decades have witnessed a surge of interest in extinction learning. First, extinction learning is observed across species, and especially research on rodents has made great strides in characterising the physical substrate underlying extinction learning. Second, extinction learning is considered of great clinical significance since it constitutes a crucial component of exposure treatment. While effective in reducing fear responding in the short term, extinction learning can lose its grip, resulting in a return of fear (i.e., laboratory model for relapse of anxiety symptoms in patients). Optimization of extinction learning is, therefore, the subject of intense investigation. It is thought that the success of extinction learning is, at least partly, determined by the mismatch between what is expected and what actually happens (prediction error). However, while much of our knowledge about the neural circuitry of extinction learning and factors that contribute to successful extinction learning comes from animal models, translating these findings to humans has been challenging for a number of reasons. Here, we present an overview of what is known about the animal circuitry underlying extinction of fear, and the role of prediction error. In addition, we conducted a systematic literature search to evaluate the degree to which state-of-the-art neuroimaging methods have contributed to translating these findings to humans. Results show substantial overlap between networks in animals and humans at a macroscale, but current imaging techniques preclude comparisons at a smaller scale, especially in sub-cortical areas that are functionally heterogeneous. Moreover, human neuroimaging shows the involvement of numerous areas that are not typically studied in animals. Results obtained in research aimed to map the extinction circuit are largely dependent on the methods employed, not only across species, but also across human neuroimaging studies. Directions for future research are discussed.

Endocannabinoid hydrolase and cannabinoid receptor 1 are involved in the regulation of hypothalamus-pituitary-adrenal axis in type 2 diabetes

Hypothalamus-pituitary-adrenal (HPA) axis, as the key moderator in energy metabolism, plays an important role in diabetes. The endogenous cannabinoid system (eCBs) involves in neuronal functions, and simultaneously cannabinoid receptors are almost expressed in all regions of the hypothalamus according to a spate of reports. However, few data investigate the changes of eCBs and HPA axis in type 2 diabetes. In this study, five diabetes mellitus rhesus monkeys, five prediabetes rhesus monkeys and five healthy rhesus monkeys were observed. In the present study, we detected cell swelling and necrosis extensively in the paraventricular nucleus (PVN) and neurohypophysis in prediabetes and overt diabetes monkeys. The adrenocorticotropic hormone in the pituitary gland, adrenocorticotropic hormone receptor, and 11β-hydroxysteroid dehydrogenase in the adrenal gland were all hyper-secreted and expressed from healthy to overt diabetes. Meanwhile, the cortisol concentration in the adrenal gland was increased along with the progress of diabetes. It could be concluded that hyperfunction of the HPA axis exists in the type 2 Diabetes pathogenesis. However, we also found a weakened expression and secretion of corticotrophin releasing hormone and glucocorticoids receptor in PVN. The expression of corticotropin releasing hormone receptor 1 in pituitary gland decreased in prediabetes monkeys, but increased in overt diabetes monkeys. The downregulation of cannabinoid receptor 1 and upregulation of monoglycerol lipase and fatty acid amide hydrolase in PVN was involved in the pathogenesis of type 2 diabetes. Collectively, we can conclude that changes in endocannabinoid hydrolase and cannabinoid receptor might indicate the effect of downregulation of eCBs. It can be assumed that hyper-function of the HPA axis from healthy to overt diabetes is due to the undermining inhibition of eCBs. However, the regulatory mechanism of eCBs targets on the HPA axis need to be further explored.

Functional Relevance of Endocannabinoid-Dependent Synaptic Plasticity in the Central Nervous System

The endocannabinoid (eCB) signaling system plays a key role in short-term and long-term synaptic plasticity in brain regions involved in various neural functions ranging from action selection to appetite control. This review will explore the role of eCBs in shaping neural circuit function to regulate behaviors. In particular, we will discuss the behavioral consequences of eCB mediated long-term synaptic plasticity in different brain regions. This review brings together evidence from in vitro and ex vivo studies and points out the need for more in vivo studies.

Role for fatty acid amide hydrolase (FAAH) in the leptin-mediated effects on feeding and energy balance

Endocannabinoid signaling regulates feeding and metabolic processes and has been linked to obesity development. Several hormonal signals, such as glucocorticoids and ghrelin, regulate feeding and metabolism by engaging the endocannabinoid system. Similarly, studies have suggested that leptin interacts with the endocannabinoid system, yet the mechanism and functional relevance of this interaction remain elusive. Therefore, we explored the interaction between leptin and endocannabinoid signaling with a focus on fatty acid amide hydrolase (FAAH), the primary degradative enzyme for the endocannabinoid N-arachidonoylethanolamine (anandamide; AEA). Mice deficient in leptin exhibited elevated hypothalamic AEA levels and reductions in FAAH activity while leptin administration to WT mice reduced AEA content and increased FAAH activity. Following high fat diet exposure, mice developed resistance to the effects of leptin administration on hypothalamic AEA content and FAAH activity. At a functional level, pharmacological inhibition of FAAH was sufficient to prevent leptin-mediated effects on body weight and food intake. Using a novel knock-in mouse model recapitulating a common human polymorphism (FAAH C385A; rs324420), which reduces FAAH activity, we investigated whether human genetic variance in FAAH affects leptin sensitivity. While WT (CC) mice were sensitive to leptin-induced reductions in food intake and body weight gain, low-expressing FAAH (AA) mice were unresponsive. These data demonstrate that FAAH activity is required for leptin's hypophagic effects and, at a translational level, suggest that a genetic variant in the FAAH gene contributes to differences in leptin sensitivity in human populations.

Oprm1 A112G, a single nucleotide polymorphism, alters expression of stress-responsive genes in multiple brain regions in male and female mice

BACKGROUND

OPRM1 A118G, a functional human mu-opioid receptor (MOR) polymorphism, is associated with drug dependence and altered stress responsivity in humans as well as altered MOR signaling. MOR signaling can regulate many cellular processes, including gene expression, and many of the long-term, stable effects of drugs and stress may stem from changes in gene expression in diverse brain regions. A mouse model bearing an equivalent polymorphism (Oprm1 A112G) was previously generated and studied. Mice homozygous for the G112 allele show differences in opioid- and stress-related phenotypes.

APPROACH

The current study examines the expression of 24 genes related to drug and stress responsivity in the caudoputamen, nucleus accumbens, hypothalamus, hippocampus, and amygdala of drug-naïve, stress-minimized, male and female mice homozygous for either the G112 variant allele or the wild-type A112 allele.

RESULTS

We detected nominal genotype-dependent changes in gene expression of multiple genes. We also detected nominal sex-dependent as well as sex-by-genotype interaction effects on gene expression. Of these, four genotype-dependent differences survived correction for multiple testing: Avp and Gal in the hypothalamus and Oprl1 and Cnr1 in the hippocampus.

CONCLUSIONS

Changes in the regulation of these genes by mu-opioid receptors encoded by the G112 allele may be involved in some of the behavioral and molecular consequences of this polymorphism observed in mice.

Cross state-dependency of learning between arachidonylcyclopropylamide (ACPA) and muscimol in the mouse dorsal hippocampus

The aim of the present study was to examine cross state-dependent learning between ACPA (a selective cannabinoid CB1 receptor agonist) and muscimol (a selective GABAA receptor agonist) in the step-down inhibitory avoidance learning task. The dorsal hippocampal CA1 regions of adult male NMRI mice were bilaterally cannulated, and all drugs were microinjected into the intended sites of injection. Post-training and/or pre-test administration of ACPA (1 and 2ng/mouse) dose-dependently induced amnesia. Pre-test microinjection of the same doses of ACPA reversed the post-training ACPA-induced amnesia. This event has been named ACPA state-dependent learning (SDL). Post-training and/or pre-test microinjection of muscimol (0.05 and 0.1μg/mouse) dose-dependently induced amnesia. Pre-test administration of the same doses of muscimol reversed the post-training muscimol-induced amnesia, suggesting muscimol SDL. The amnesia induced by post-training administration of ACPA was reversed by pre-test administration of muscimol (0.05 and 0.1μg/mouse). Furthermore, the pre-test microinjection of muscimol (0.025 and 0.05μg/mouse) with an ineffective dose of ACPA (0.5ng/mouse) significantly restored memory retrieval and induced ACPA SDL. In another series of experiments, the amnesia induced by post-training administration of muscimol was reversed by pre-test administration of ACPA (1 and 2ng/mouse). Moreover, pre-test microinjection of ACPA (0.5 and 1ng/mouse) with an ineffective dose of muscimol (0.025μg/mouse) significantly restored memory retrieval and induced muscimol SDL. It is important to note that pre-test intra-CA1 injection of a selective GABAA receptor antagonist, bicuculline (0.125 and 0.25μg/mouse), 5min before the administration of muscimol (0.1μg/mouse) or ACPA (2ng/mouse) dose-dependently inhibited muscimol- and ACPA-induced SDL, respectively. Pre-test intra-CA1 administration of bicuculline (0.0625, 0.125 and 0.25μg/mouse) by itself did not affect memory retention. In conclusion, the data strongly revealed a cross SDL among ACPA and muscimol in the dorsal hippocampal CA1 regions.

Amidoalkylindoles as Potent and Selective Cannabinoid Type 2 Receptor Agonists with in Vivo Efficacy in a Mouse Model of Multiple Sclerosis

Selective CB₂ agonists represent an attractive therapeutic strategy for the treatment of a variety of diseases without psychiatric side effects mediated by the CB₁ receptor. We carried out a rational optimization of a black market designer drug SDB-001 that led to the identification of potent and selective CB₂ agonists. A 7-methoxy or 7-methylthio substitution at the 3-amidoalkylindoles resulted in potent CB₂ antagonists (27 or 28, IC₅₀ = 16-28 nM). Replacement of the amidoalkyls from 3-position to the 2-position of the indole ring dramatically increased the agonist selectivity on the CB₂ over CB₁ receptor. Particularly, compound 57 displayed a potent agonist activity on the CB₂ receptor (EC₅₀ = 114-142 nM) without observable agonist or antagonist activity on the CB₁ receptor. Furthermore, 57 significantly alleviated the clinical symptoms and protected the murine central nervous system from immune damage in an experimental autoimmune encephalomyelitis (EAE) mouse model of multiple sclerosis.

Cannabinoid Type 1 Receptor (CB1) Ligands with Therapeutic Potential for Withdrawal Syndrome in Chemical Dependents of Cannabis sativa

Cannabis sativa withdrawal syndrome is characterized mainly by psychological symptoms. By using computational tools, the aim of this study was to propose drug candidates for treating withdrawal syndrome based on the natural ligands of the cannabinoid type 1 receptor (CB1). One compound in particular, 2-n-butyl-5-n-pentylbenzene-1,3-diol (ZINC1730183, also known as stemphol), showed positive predictions as a human CB1 ligand and for facile synthetic accessibility. Therefore, ZINC1730183 is a favorable candidate scaffold for further research into pharmacotherapeutic alternatives to treat C. sativa withdrawal syndrome.

Effects of cannabinoid and vanilloid receptor agonists and their interaction on learning and memory in rats

Despite previous findings on the effects of cannabinoid and vanilloid systems on learning and memory, the effects of the combined stimulation of these 2 systems on learning and memory have not been studied. Therefore, in this study, we tested the interactive effects of cannabinoid and vanilloid systems on learning and memory in rats by using passive avoidance learning (PAL) tests. Forty male Wistar rats were divided into the following 4 groups: (1) control (DMSO+saline), (2) WIN55,212–2, (3) capsaicin, and (4) WIN55,212–2 + capsaicin. On test day, capsaicin, a vanilloid receptor type 1 (TRPV1) agonist, or WIN55,212–2, a cannabinoid receptor (CB1/CB2) agonist, or both substances were injected intraperitoneally. Compared to the control group, the group treated with capsaicin (TRPV1 agonist) had better scores in the PAL acquisition and retention test, whereas treatment with WIN55,212–2 (CB1/CB2 agonist) decreased the test scores. Capsaicin partly reduced the effects of WIN55,212–2 on PAL and memory. We conclude that the acute administration of a TRPV1 agonist improves the rats’ cognitive performance in PAL tasks and that a vanilloid-related mechanism may underlie the agonistic effect of WIN55,212–2 on learning and memory.

Cannabinoid Transmission in the Hippocampus Activates Nucleus Accumbens Neurons and Modulates Reward and Aversion-Related Emotional Salience

BACKGROUND

Cannabinoid receptor transmission strongly influences emotional processing, and disturbances in cannabinoid signaling are associated with various neuropsychiatric disorders. The mammalian ventral hippocampus (vHipp) is a critical neural region controlling mesolimbic activity via glutamatergic projections to the nucleus accumbens. Furthermore, vHipp abnormalities are linked to schizophrenia-related psychopathology. Nevertheless, the mechanisms by which intra-vHipp cannabinoid signaling may modulate mesolimbic activity states and emotional processing are not currently understood.

METHODS

Using an integrative combination of in vivo electrophysiological recordings and behavioral pharmacologic assays in rats, we tested whether activation of cannabinoid type 1 receptors (CB1R) in the vHipp may modulate neuronal activity in the shell subregion of the nucleus accumbens (NASh). We next examined how vHipp CB1R signaling may control the salience of rewarding or aversive emotional memory formation and social interaction/recognition behaviors via intra-NASh glutamatergic transmission.

RESULTS

We demonstrate for the first time that vHipp CB1R transmission can potently modulate NASh neuronal activity and can differentially control the formation of context-dependent and context-independent forms of rewarding or aversion-related emotional associative memories. In addition, we found that activation of vHipp CB1R transmission strongly disrupts normal social behavior and cognition. Finally, we report that these behavioral effects are dependent upon intra-NASh alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid/N-methyl-D-aspartate receptor transmission.

CONCLUSIONS

Together, these findings demonstrate a critical role for hippocampal cannabinoid signaling in the modulation of mesolimbic neuronal activity states and suggest that dysregulation of CB1R transmission in the vHipp→NASh circuit may underlie hippocampal-mediated affective and social behavioral disturbances present in neuropsychiatric disorders.

Early Cannabis Use, Polygenic Risk Score for Schizophrenia and Brain Maturation in Adolescence

IMPORTANCE

Cannabis use during adolescence is known to increase the risk for schizophrenia in men. Sex differences in the dynamics of brain maturation during adolescence may be of particular importance with regard to vulnerability of the male brain to cannabis exposure.

OBJECTIVE

To evaluate whether the association between cannabis use and cortical maturation in adolescents is moderated by a polygenic risk score for schizophrenia.

DESIGN, SETTING, AND PARTICIPANTS

Observation of 3 population-based samples included initial analysis in 1024 adolescents of both sexes from the Canadian Saguenay Youth Study (SYS) and follow-up in 426 adolescents of both sexes from the IMAGEN Study from 8 European cities and 504 male youth from the Avon Longitudinal Study of Parents and Children (ALSPAC) based in England. A total of 1577 participants (aged 12-21 years; 899 [57.0%] male) had (1) information about cannabis use; (2) imaging studies of the brain; and (3) a polygenic risk score for schizophrenia across 108 genetic loci identified by the Psychiatric Genomics Consortium. Data analysis was performed from March 1 through December 31, 2014.

MAIN OUTCOMES AND MEASURES

Cortical thickness derived from T1-weighted magnetic resonance images. Linear regression tests were used to assess the relationships between cannabis use, cortical thickness, and risk score.

RESULTS

Across the 3 samples of 1574 participants, a negative association was observed between cannabis use in early adolescence and cortical thickness in male participants with a high polygenic risk score. This observation was not the case for low-risk male participants or for the low- or high-risk female participants. Thus, in SYS male participants, cannabis use interacted with risk score vis-à-vis cortical thickness (P = .009); higher scores were associated with lower thickness only in males who used cannabis. Similarly, in the IMAGEN male participants, cannabis use interacted with increased risk score vis-à-vis a change in decreasing cortical thickness from 14.5 to 18.5 years of age (t137 = -2.36; P = .02). Finally, in the ALSPAC high-risk group of male participants, those who used cannabis most frequently (≥61 occasions) had lower cortical thickness than those who never used cannabis (difference in cortical thickness, 0.07 [95% CI, 0.01-0.12]; P = .02) and those with light use (<5 occasions) (difference in cortical thickness, 0.11 [95% CI, 0.03-0.18]; P = .004).

CONCLUSIONS AND RELEVANCE

Cannabis use in early adolescence moderates the association between the genetic risk for schizophrenia and cortical maturation among male individuals. This finding implicates processes underlying cortical maturation in mediating the link between cannabis use and liability to schizophrenia.

Genetic deletion of monoacylglycerol lipase leads to impaired cannabinoid receptor CB₁R signaling and anxiety-like behavior

Endocannabinoids (eCB) are key regulators of excitatory/inhibitory neurotransmission at cannabinoid-1-receptor (CB1 R)-expressing axon terminals. The most abundant eCB in the brain, that is 2-arachidonoylglycerol (2-AG), is hydrolyzed by the enzyme monoacylglycerol lipase (MAGL), whose chronic inhibition in the brain was reported to cause CB1 R desensitization. We employed the MAGL knock-out mouse (MAGL-/-), a genetic model of congenital and sustained elevation of 2-AG levels in the brain, to provide morphological and biochemical evidence for β-arrestin2-mediated CB1 R desensitization in brain regions involved in the control of emotional states, that is, the prefrontal cortex (PFC), amygdala, hippocampus and cerebellar cortex. We found a widespread CB1 R/β-arrestin2 co-expression in the mPFC, amygdala and hippocampus accompanied by impairment of extracellular signal-regulated kinase signaling and elevation of vesicular glutamate transporter (VGluT1) at CB1 R-positive excitatory terminals in the mPFC, or vesicular GABA transporter (VGAT) at CB1 R-positive inhibitory terminals in the amygdala and hippocampus. The impairment of CB1 R signaling in MAGL-/- mice was also accompanied by enhanced excitatory drive in the basolateral amygdala (BLA)-mPFC circuit, with subsequent elevation of glutamate release to the mPFC and anxiety-like and obsessive-compulsive behaviors, as assessed by the light/dark box and marble burying tests, respectively. Collectively, these data provide evidence for a β-arrestin2-mediated desensitization of CB1 R in MAGL-/- mice, with impact on the synaptic plasticity of brain circuits involved in emotional functions. In this study, the authors provide evidence that congenitally enhanced endocannabinoid levels in the neuronal circuits underlying anxiety-like behavioral states (mainly medial prefrontal cortex, amygdala and hippocampus) lead to CB1R desenistization and anxiety and depression. MAGL-/- mice, a model of congenital overactivity of the eCB system, exhibited a compensatory impairment of CB1R signaling in anxiety-associated brain areas and a subsequent change in excitatory/inhibitory tone associated with altered score in the marble burying and light/dark box test, in concomitance with anxiety and depression behavior states. These findings may have potential relevance to the understanding of the neurochemical effects of chronic CB1R overstimulation in cannabis abusers.

The influence of cannabinoids on learning and memory processes of the dorsal striatum

Extensive evidence indicates that the mammalian endocannabinoid system plays an integral role in learning and memory. Our understanding of how cannabinoids influence memory comes predominantly from studies examining cognitive and emotional memory systems mediated by the hippocampus and amygdala, respectively. However, recent evidence suggests that cannabinoids also affect habit or stimulus-response (S-R) memory mediated by the dorsal striatum. Studies implementing a variety of maze tasks in rats indicate that systemic or intra-dorsolateral striatum infusions of cannabinoid receptor agonists or antagonists impair habit memory. In mice, cannabinoid 1 (CB1) receptor knockdown can enhance or impair habit formation, whereas Δ(9)THC tolerance enhances habit formation. Studies in human cannabis users also suggest an enhancement of S-R/habit memory. A tentative conclusion based on the available data is that acute disruption of the endocannabinoid system with either agonists or antagonists impairs, whereas chronic cannabinoid exposure enhances, dorsal striatum-dependent S-R/habit memory. CB1 receptors are required for multiple forms of striatal synaptic plasticity implicated in memory, including short-term and long-term depression. Interactions with the hippocampus-dependent memory system may also have a role in some of the observed effects of cannabinoids on habit memory. The impairing effect often observed with acute cannabinoid administration argues for cannabinoid-based treatments for human psychopathologies associated with a dysfunctional habit memory system (e.g. post-traumatic stress disorder and drug addiction/relapse). In addition, the enhancing effect of repeated cannabinoid exposure on habit memory suggests a novel neurobehavioral mechanism for marijuana addiction involving the dorsal striatum-dependent memory system.

The dual effect of CA1 NMDA receptor modulation on ACPA-induced amnesia in step-down passive avoidance learning task

It is well documented that cannabinoids play an important role in certain hippocampal memory processes in rodents. On the other hand, N-Methyl-d-aspartate receptors (NMDARs) mediate the synaptic plasticity related to learning and memory processes which take place in the hippocampus. Such insights prompted us to investigate the influence of dorsal hippocampal (CA1) NMDA receptor agents on amnesia induced by cannabinoid CB1 receptor agonist, arachidonylcyclopropylamide (ACPA) in male mice. One-trial step-down passive avoidance and hole-board apparatuses were used to examine the memory retrieval and exploratory behaviors, respectively. Based on our findings, pre-training intraperitoneal (i.p.) administration of ACPA (0.01mg/kg) decreased memory acquisition. Moreover, pre-training intra-CA1 infusion of NMDA (0.001, 0.0125, 0.025 and 0.2µg/mouse), d-AP7 (0.5 and 1µg/mouse) or AM251 (50ng/mouse) impaired the memory acquisition. Meanwhile, NMDA-treated animals at the doses of 0.0005, 0.05 and 0.1µg/mouse acquired memory formation. In addition, intra-CA1 microinjection of NMDA (0.0005) plus different doses of ACPA potentiated the ACPA response, while NMDA (0.1) plus the lower or the higher dose of ACPA potentiated or restored the ACPA response, respectively. Further investigation revealed that a subthreshold dose of d-AP7 could potentiate the memory acquisition impairment induced by ACPA. Moreover, the subthreshold dose of AM251 did not alter the ACPA response, while the effective dose of the drug restored the memory acquisition impairment induced by ACPA. According to these results, we concluded that activation of the NMDA receptors in the CA1 mediates a dual effect on ACPA-induced amnesia in step-down passive avoidance learning task.

Attenuation of kainic acid-induced status epilepticus by inhibition of endocannabinoid transport and degradation in guinea pigs

Status epilepticus (SE) is a medical emergency associated with a high rate of mortality if not treated promptly. Exogenous and endogenous cannabinoids have been shown to possess anticonvulsant properties both in vivo and in vitro. Here we study the influence of endocannabinoid metabolism on the development of kainic acid-induced SE in guinea pigs. For this purpose, the inhibitors of endocannabinoid transport, AM404, and enzymatic (fatty acid amide hydrolase) degradation, URB597, were applied. Cannabinoid CB1 receptor antagonist, AM251, was also tested. Animal behavior as well as local electric field potentials in four structures: medial septum, hippocampus, entorhinal cortex and amygdala were analyzed when AM404 (120nmol), URB597 (4.8nmol) or AM251 (20nmol) were administrated alone or together with 0.4μg of kainic acid. All substances were injected i.c.v. AM404, URB597 or AM251 administered alone did not alter markedly local field potentials of all four studied structures in the long-term compared with their basal activity. AM404 and URB597 significantly alleviated kainic acid-induced SE, decreasing behavioral manifestations, duration of seizure events and SE in general without changing the amplitude of local field potentials. AM251 did not produce distinct effects on SE in terms of our experimental paradigm. There was no apparent change of the seizure initiation pattern when kainic acid was coadministrated with AM404, URB597 or AM251. The present study provides electrophysiologic and behavioral evidences that inhibition of endocannabinoid metabolism plays a protective role against kainic acid-induced SE and may be employed for therapeutic purposes. Further investigations of the influences of cannabinoid-related compounds on SE genesis and especially epileptogenesis are required.

Rivastigmine but not vardenafil reverses cannabis-induced impairment of verbal memory in healthy humans

RATIONALE

One of the most often reported cognitive deficits of acute cannabis administration is an impaired recall of previously learned information.

OBJECTIVE

The aim of the present study was to determine whether cannabis-induced memory impairment in humans is mediated via glutamatergic or cholinergic pathways.

METHODS

Fifteen occasional cannabis users participated in a double-blind, placebo-controlled, six-way cross-over study. On separate test days, subjects received combinations of pretreatment (placebo, vardenafil 20 mg or rivastigmine 3 mg) and treatment (placebo or 1,376 mg cannabis/kg body weight). Cognitive tests were administered immediately after inhalation of treatment was finished and included measures of memory (visual verbal learning task, prospective memory test, Sternberg memory test), perceptual-motor control (critical tracking task), attention (divided attention task) and motor impulsivity (stop signal task).

RESULTS

The results of this study demonstrate that subjects under the influence of cannabis were impaired in all memory tasks, in critical tracking, divided attention and the stop signal task. Pretreatment with rivastigmine attenuated the effect of cannabis on delayed recall and showed a trend towards significance on immediate recall. When cannabis was given in combination with vardenafil, there were no significant interaction effects in any of the tasks.

CONCLUSIONS

The present data therefore suggest that acetylcholine plays an important role in cannabis-induced memory impairment, whereas similar results for glutamate have not been demonstrated in this study.

Endocannabinoid signalling in Alzheimer's disease

The ECs (endocannabinoids) AEA (anandamide) and 2-AG (2-arachidonoylglycerol) and their lipid congeners OEA (N-oleoylethanolamide) and PEA (N-palmitoylethanolamide) are multifunctional lipophilic signalling molecules. The ECs, OEA and PEA have multiple physiological roles including involvement in learning and memory, neuroinflammation, oxidative stress, neuroprotection and neurogenesis. They have also been implicated in the pathology of, or perhaps protective responses to, neurodegenerative diseases. This is particularly the case with Alzheimer's disease, the most common age-related dementia associated with impairments in learning and memory accompanied by neuroinflammation, oxidative stress and neurodegeneration. The present mini-review examines the evidence supporting the roles that ECs appear to play in Alzheimer's disease and the potential for beneficial therapeutic manipulation of the EC signalling system.

β-Amyloid inhibits E-S potentiation through suppression of cannabinoid receptor 1-dependent synaptic disinhibition

It has been widely reported that β-amyloid peptide (Aβ) blocks long-term potentiation (LTP) of hippocampal synapses. Here, we show evidence that Aβ more potently blocks the potentiation of excitatory postsynaptic potential (EPSP)-spike coupling (E-S potentiation). This occurs, not by direct effect on excitatory synapses or postsynaptic neurons, but rather through an indirect mechanism: reduction of endocannabinoid-mediated peritetanic disinhibition. During high-frequency (tetanic) stimulation, somatic synaptic inhibition is suppressed by endocannabinoids. We find that Aβ prevents this endocannabinoid-mediated disinhibition, thus leaving synaptic inhibition more intact during tetanic stimulation. This intact inhibition opposes the normal depolarization of hippocampal pyramidal neurons that occurs during tetanus, thus opposing the induction of synaptic plasticity. Thus, a pathway through which Aβ can act to modulate neural activity is identified, relevant to learning and memory and how it may mediate aspects of the cognitive decline seen in Alzheimer's disease.

Propagation of cortical spreading depression into the hippocampus: The role of the entorhinal cortex

Propagation of cortical spreading depression (CSD) to the subcortical structures could be the underlying mechanism of some neurological deficits in migraine with aura. The entorhinal cortex (EC) as a gray matter bridge between the neocortex and subcortical regions plays an important role in this propagation. In vitro combined neocortex-hippocampus brain slices were used to study the propagation pattern of CSD between the neocortex and the hippocampus. The effects of different compounds as well as tetanic electrical stimulations in the EC on propagation of CSD to the hippocampus were investigated. Repetitive induction of CSD by KCl injection in the somatosensory cortex enhanced the probability of CSD entrance to the hippocampus via EC. Local application of AMPA receptor blocker CNQX and cannabinoid receptor agonist WIN 55212-2 in EC facilitated the propagation of CSD to the hippocampus, whereas application of NMDA receptor blocker APV and GABA_A receptor blocker bicuculline in this region reduced the probability of CSD penetration to the hippocampus. Application of tetanic stimulation in EC also facilitated the propagation of CSD entrance to the hippocampus. Our data suggest the importance of synaptic plasticity of EC in filtering the propagation of CSD into subcortical structures and possibly the occurrence of concomitant neurological deficits. Synapse 68:574-584, 2014. © 2014 Wiley Periodicals, Inc.

In vivo type 1 cannabinoid receptor availability in Alzheimer's disease

The endocannabinoid system (ECS) is an important modulatory and potentially neuroprotective homeostatic system in the brain. In Alzheimer's disease (AD), the role of type 1 cannabinoid receptor (CB₁R) is unclear, with contradictory findings in post-mortem studies showing upregulation, downregulation or unchanged CB₁R status. We have investigated CB₁R availability in vivo in patients with AD, in relation to amyloid deposition, cognitive functioning and apolipoprotein E (ApoE) genotype. Eleven AD patients and 7 healthy volunteers (HV) underwent combined [¹⁸F]MK-9470 PET and [¹¹C]PIB PET scans to assess CB₁R availability and amyloid deposition, respectively, and T1 volumetric MRI for partial volume correction. We found no difference in CB₁R availability between AD and HV, VOI-based fractional uptake values (FUR) were 0.043±0.01 for AD and 0.045±0.01 for controls (p=0.9). CB₁R availability did not correlate with neuropsychological test scores and was not modulated by ApoE genotype. As expected, global [¹¹C]PIB SUVR (standardized uptake value ratio) was increased in AD (SUVR 1.9±0.3) compared to HV (1.2±0.1) with p<0.001, but no correlation was found between amyloid β (Aβ) deposition and CB₁R availability. In conclusion, we found no in vivo evidence for a difference in CB₁R availability in AD compared to age-matched controls. Taken together with recently reported in vivo CB₁R changes in Parkinson's and Huntington's disease, these data suggest that the CB₁R is differentially involved in neurodegenerative disorders.

A role for the endocannabinoid system in exercise-induced spatial memory enhancement in mice

It is well known that physical exercise has positive effects on cognitive functions and hippocampal plasticity. However, the underlying mechanisms have remained to be further investigated. Here we investigated the hypothesis that the memory-enhancement promoted by physical exercise relies on facilitation of the endocannabinoid system. We observed that the spatial memory tested in the object location paradigm did not persist in sedentary mice, but could be improved by 1 week of treadmill running. In addition, exercise up-regulated CB1 receptor and BDNF expression in the hippocampus. To verify if these changes required CB1 activation, we treated the mice with the selective antagonist, AM251, before each period of physical activity. In line with our hypothesis, this drug prevented the exercise-induced memory enhancement and BDNF expression. Furthermore, AM251 reduced CB1 expression. To test if facilitating the endocannabinoid system signaling would mimic the alterations observed after exercise, we treated sedentary animals during 1 week with the anandamide-hydrolysis inhibitor, URB597. Mice treated with this drug recognized the object in a new location and have increased levels of CB1 and BDNF expression in the hippocampus, showing that potentiating the endocanabinoid system equally benefits memory. In conclusion, the favorable effects of exercise upon spatial memory and BDNF expression depend on facilitation of CB1 receptor signaling, which can be mimic by inhibition of anandamide hydrolysis in sedentary animals. Our results suggest that, at least in part, the promnesic effect of the exercise is dependent of CB1 receptor activation and is mediated by BDNF.

Cellular and intracellular mechanisms involved in the cognitive impairment of cannabinoids

Exogenous cannabinoids, such as delta9-tetrahydrocannabinol (THC), as well as the modulation of endogenous cannabinoids, affect cognitive function through the activation of cannabinoid receptors. Indeed, these compounds modulate a number of signalling pathways critically implicated in the deleterious effect of cannabinoids on learning and memory. Thus, the involvement of the mammalian target of rapamycin pathway and extracellular signal-regulated kinases, together with their consequent regulation of cellular processes such as protein translation, play a critical role in the amnesic-like effects of cannabinoids. In this study, we summarize the cellular and molecular mechanisms reported in the modulation of cognitive function by the endocannabinoid system.

Endocannabinoids in nervous system health and disease: the big picture in a nutshell

The psychoactive component of the cannabis resin and flowers, delta9-tetrahydrocannabinol (THC), was first isolated in 1964, and at least 70 other structurally related 'phytocannabinoid' compounds have since been identified. The serendipitous identification of a G-protein-coupled cannabinoid receptor at which THC is active in the brain heralded an explosion in cannabinoid research. Elements of the endocannabinoid system (ECS) comprise the cannabinoid receptors, a family of nascent lipid ligands, the 'endocannabinoids' and the machinery for their biosynthesis and metabolism. The function of the ECS is thus defined by modulation of these receptors, in particular, by two of the best-described ligands, 2-arachidonoyl glycerol and anandamide (arachidonylethanolamide). Research on the ECS has recently aroused enormous interest not only for the physiological functions, but also for the promising therapeutic potentials of drugs interfering with the activity of cannabinoid receptors. Many of the former relate to stress-recovery systems and to the maintenance of homeostatic balance. Among other functions, the ECS is involved in neuroprotection, modulation of nociception, regulation of motor activity, neurogenesis, synaptic plasticity and the control of certain phases of memory processing. In addition, the ECS acts to modulate the immune and inflammatory responses and to maintain a positive energy balance. This theme issue aims to provide the reader with an overview of ECS pharmacology, followed by discussions on the pivotal role of this system in the modulation of neurogenesis in the developing and adult organism, memory processes and synaptic plasticity, as well as in pathological pain and brain ageing. The volume will conclude with discussions that address the proposed therapeutic applications of targeting the ECS for the treatment of neurodegeneration, pain and mental illness.

The effect of cannabis use on memory function: an update

Investigating the effects of cannabis use on memory function appears challenging. While early observational investigations aimed to elucidate the longer-term effects of cannabis use on memory function in humans, findings remained equivocal and pointed to a pattern of interacting factors impacting on the relationship between cannabis use and memory function, rather than a simple direct effect of cannabis. Only recently, a clearer picture of the chronic and acute effects of cannabis use on memory function has emerged once studies have controlled for potential confounding factors and started to investigate the acute effects of delta-9-tetrahydrocannabinol (Δ9-THC) and cannabidiol (CBD), the main ingredients in the extract of the cannabis plant in pharmacological challenge experiments. Relatively consistent findings have been reported regarding the acute impairments induced by a single dose of Δ9-THC on verbal and working memory. It is unclear whether they may persist beyond the intoxication state. In the long-term, these impairments seem particularly likely to manifest and may also persist following abstinence if regular and heavy use of cannabis strains high in Δ9-THC is started at an early age. Although still at an early stage, studies that employed advanced neuroimaging techniques have started to model the neural underpinnings of the effects of cannabis use and implicate a network of functional and morphological alterations that may moderate the effects of cannabis on memory function. Future experimental and epidemiological studies that take into consideration individual differences, particularly previous cannabis history and demographic characteristics, but also the precise mixture of the ingredients of the consumed cannabis are necessary to clarify the magnitude and the mechanisms by which cannabis-induced memory impairments occur and to elucidate underlying neurobiological mechanisms.

Developmentally-induced hypothyroidism alters the expression of Egr-1 and Arc genes and the sensitivity to cannabinoid agonists in the hippocampus. Possible implications for memory and learning

We analyzed the role of the cannabinoid system in the cognitive deficits caused by developmentally-induced hypothyroidism. We studied in control and hypothyroid rats the effect of a cannabinoid agonist on spatial memory, hippocampal phosphorylation of CREB and expression of early genes. Our results show that, 1-basal hippocampal expression of early genes and spatial learning are decreased in hypothyroid rats; 2-hypothyroid rats are very sensitive to cannabinoid agonists. Low dose of cannabinoid agonist ineffective in controls altered spatial memory, CREB's phosphorylation and early gene expression in hypothyroids. These effects are not due a change in CB1 receptor (CB1R) content. 3-Treatment of hypothyroid rats with thyroid hormones normalized the biochemical and behavioral responses to cannabinoid agonists but did not correct the low basal levels of early gene transcripts and the deficits in spatial learning. All these data suggest that the hippocampal deregulation of early genes expression could play an important role in the basal cognitive deficits of hypothyroid rats.

Modulation of ATP-induced LTP by cannabinoid receptors in rat hippocampus

Cannabinoids exert powerful action on various forms of synaptic plasticity. These retrograde messengers modulate GABA and glutamate release from presynaptic terminals by acting on presynaptic CB1 receptors. In particular, they inhibit long-term potentiation (LTP) elicited by electrical stimulation of excitatory pathways in rat hippocampus. Recently, LTP of the field excitatory postsynaptic potential (fEPSP) induced by exogenous ATP has been thoroughly explored. The present study demonstrates that cannabinoids inhibit ATP-induced LTP in hippocampal slices of rat. Administration of 10 μM of ATP led to strong inhibition of fEPSPs in CA1/CA3 hippocampal synapses. Within 40 min after ATP removal from bath solution, robust LTP was observed (fEPSP amplitude comprised 130.1 ± 3.8% of control, n = 10). This LTP never appeared when ATP was applied in addition to cannabinoid receptor agonist WIN55,212-2 (100 nM). Selective CB1 receptor antagonist, AM251 (500 nM), completely abolished this effect of WIN55,212-2. Our data indicate that like canonical LTP elicited by electrical stimulation, ATP-induced LTP is under control of CB1 receptors.

Failure to extinguish fear and genetic variability in the human cannabinoid receptor 1

Failure to extinguish fear can lead to persevering anxiety and has been postulated as an important mechanism in the pathogenesis of human anxiety disorders. In animals, it is well documented that the endogenous cannabinoid system has a pivotal role in the successful extinction of fear, most importantly through the cannabinoid receptor 1. However, no human studies have reported a translation of this preclinical evidence yet. Healthy medication-free human subjects (N=150) underwent a fear conditioning and extinction procedure in a virtual reality environment. Fear potentiation of the eyeblink startle reflex was measured to assess fear-conditioned responding, and subjective fear ratings were collected. Participants were genotyped for two polymorphisms located within the promoter region (rs2180619) and the coding region (rs1049353) of cannabinoid receptor 1. As predicted from the preclinical literature, acquisition and expression of conditioned fear did not differ between genotypes. Crucially, whereas both homozygote (G/G, N=23) and heterozygote (A/G, N=68) G-allele carriers of rs2180619 displayed robust extinction of fear, extinction of fear-potentiated startle was absent in A/A homozygotes (N=51). Additionally, this resistance to extinguish fear left A/A carriers of rs2180619 with significantly higher levels of fear-potentiated startle at the end of the extinction training. No effects of rs1049353 genotype were observed regarding fear acquisition and extinction. These results suggest for the first time involvement of the human endocannabinoid system in fear extinction. Implications are that genetic variability in this system may underlie individual differences in anxiety, rendering cannabinoid receptor 1 a potential target for novel pharmacological treatments of anxiety disorders.