The role of cannabinoids in modulating emotional and non-emotional memory processes in the hippocampus

Fear conditioning depends on the nature of the unconditional stimulus and may be related to hair levels of endocannabinoids

The replicability of fear conditioning research has come under recent scrutiny, with increasing acknowledgment that the use of differing materials and methods may lead to incongruent results. Direct comparisons between the main two unconditional stimuli used in fear conditioning - an electric shock or a loud scream-are scarce, and yet these stimuli are usually used interchangeably. In the present study, we tested whether a scream, a shock, or an unpredictable combination of the two affected fear acquisition, extinction, and return of fear amongst healthy participants (N = 109, 81 female). We also collected hair samples and tested the relationship between fear conditioning and hair endocannabinoid levels. Our findings suggest that, although subjective ratings of pleasantness, arousal, and anxiety were similar regardless of the unconditional stimuli used, skin conductance responses were significantly lower for stimuli paired with the scream compared to a shock alone. Further, reducing the predictability of the unconditional stimulus reduced habituation of skin conductance responses during acquisition and reacquisition, but did not produce stronger conditioning compared to shock alone. Exploratory analyses suggested that hair endocannabinoids were associated with overall physiological arousal during fear conditioning, as well as higher return of fear to the threat cue, but not to the safety cue. These findings have multiple implications for the design and replicability of fear conditioning research and provide the first evidence for an association between hair levels of endocannabinoids and human fear conditioning.

Challenges and considerations for treating PTSD with medicinal cannabis: the Australian clinician's perspective

INTRODUCTION

Preclinical and experimental research have provided promising evidence that medicinal cannabis may be efficacious in the treatment of posttraumatic stress disorder (PTSD). However, implementation of medicinal cannabis into routine clinical therapies may not be straightforward.

AREAS COVERED

In this review, we describe some of the clinical, practical, and safety challenges that must be addressed for cannabis-based treatment of PTSD to be feasible in a real-world setting. These issues are especially prevalent if medicinal cannabis is to be combined with trauma-focused psychotherapy.

EXPERT OPINION

Future consideration of the clinical and practical considerations of cannabis use in PTSD therapy will be essential to both the efficacy and safety of the treatment protocols that are being developed. These issues include dose timing and titration, potential for addiction, product formulation, windows of intervention, and route of administration. In particular, exposure therapy for PTSD involves recall of intense emotions, and the interaction between cannabis use and reliving of trauma memories must be explored in terms of patient safety and impact on therapeutic outcomes.

Behavioral, biochemical and histopathological toxic profiles induced by sub-chronic cannabimimetic WIN55, 212-2 administration in mice

WIN55, 212-2 mesylate is a synthetic cannabinoid (SC) agonist of CB1 and CB2 receptors with much higher affinity to CB1 receptor than tetrahydrocannabinol and many potential therapeutic effects. Few studies have evaluated SCs effects on more complex animal behavior and sex differences in cannabinoids toxicology. The current study was undertaken for determination of behavioral (Open Field test), biochemical (liver and kidney function test plus GABA & Glutamate levels), histopathological and CB1 immunohistochemistry risks of sub-chronic administration of SC WIN55, 212-2 mesylate in male and female mice. A total of 40 healthy adult mice were randomly divided into four groups (5 mice each): a negative control group, a vehicle group, a low dose (0.05 mg/kg) group and a high dose group (0.1 mg/kg) for each gender.Open Field Test revealed dose and gender-dependent anxiogenic effect with reduced locomotor activity in both sexes especially the higher doses with female mice being less compromised. GABA and glutamate levels increased significantly in both dose groups compared to controls alongside female mice versus males. No significant biochemical alterations were found in all groups with minimal histopathological changes. The CB1 receptors immunohistochemistry revealed a significant increase in the number of CB1 positive neurons in both low and high dose groups against controls with higher expression in female brains.ConclusionsThere were sexual dimorphism effects induced by sub-chronic exposure to WIN55, 212-2 with lesser female mice affection and dose-dependent influences.

Frustrative nonreward and cannabinoid receptors: Chronic (but not acute) WIN 55,212-2 treatment increased resistance to change in two reward downshift tasks

Assessing the role of cannabinoid (CB) receptors in behavior is relevant given the trend toward the legalization of medicinal and recreational marijuana. The present research aims at bridging a gap in our understanding of CB-receptor function in animal models of frustrative nonreward. These experiments were designed to (1) determine the effects of chronic administration of the nonselective CB1-receptor agonist WIN 55,212-2 (WIN) on reward downshift in rats and (2) determine whether the effects of chronic WIN were reducible to acute effects. In Experiment 1, chronic WIN (7 daily injections, 10 mg/kg, ip) accelerated the recovery of consummatory behavior after a 32-to-4% sucrose downshift relative to vehicle controls. In addition, chronic WIN eliminated the preference for an unshifted lever when the other lever was subject to a 12-to-2 pellet downshift in free-choice trials, but only in animals with previous experience with a sucrose downshift. In Experiment 2, acute WIN (1 mg/kg, ip) reduced consummatory behavior, but did not affect recovery from a 32-to-4% sucrose downshift. The antagonist SR 141716A (3 mg/kg, ip) also failed to interfere with recovery after the sucrose downshift. In Experiment 3, acute WIN administration (1 mg/kg, ip) did not affect free-choice behavior after a pellet downshift, although it reduced lever pressing and increased magazine entries relative to vehicle controls. The effects of chronic WIN on frustrative nonreward were not reducible to acute effects of the drug. Chronic WIN treatment in rats, like chronic marijuana use in humans, seems to increase resistance to the effects of frustrative nonreward.

Neural Substrates of Incidental Associations and Mediated Learning: The Role of Cannabinoid Receptors

The ability to form associations between different stimuli in the environment to guide adaptive behavior is a central element of learning processes, from perceptual learning in humans to Pavlovian conditioning in animals. Like so, classical conditioning paradigms that test direct associations between low salience sensory stimuli and high salience motivational reinforcers are extremely informative. However, a large part of everyday learning cannot be solely explained by direct conditioning mechanisms - this includes to a great extent associations between individual sensory stimuli, carrying low or null immediate motivational value. This type of associative learning is often described as incidental learning and can be captured in animal models through sensory preconditioning procedures. Here we summarize the evolution of research on incidental and mediated learning, overview the brain systems involved and describe evidence for the role of cannabinoid receptors in such higher-order learning tasks. This evidence favors a number of contemporary hypotheses concerning the participation of the endocannabinoid system in psychosis and psychotic experiences and provides a conceptual framework for understanding how the use of cannabinoid drugs can lead to altered perceptive states.

Low-Frequency Stimulation Prevents Kindling-Induced Impairment through the Activation of the Endocannabinoid System

Background

Cannabinoid system affects memory and has anticonvulsant effects in epileptic models. In the current study, the role of cannabinoid 1 (CB1) receptors was investigated in amelioration of the effects of low-frequency stimulation (LFS) on learning and memory impairments in kindled rats.

Methods

Electrical stimulation of the hippocampal CA1 area was employed to kindle the animals. LFS was applied to the CA1 area in four trials following the last kindling stimulation. One group of animals received intraperitoneal injection of AM251 (0.1 μg/rat), a CB1 receptor antagonist, before the LFS application. Similarly, CB1 agonist WIN55-212-2 (WIN) was administrated to another group prior to LFS. The Morris water maze (MWM) and the novel object recognition (NOR) tests were executed 48 h after the last kindling stimulation to assess learning and memory.

Results

Applying LFS in the kindled+LFS group restored learning and memory impairments in the kindled rats. There was a significant difference between the kindled and the kindled+LFS groups in learning and memory. The application of AM251 reduced the LFS effects significantly. Adversely, WIN acted similarly to LFS and alleviated learning and memory deficits in the kindled+WIN group. In addition, WIN did not counteract the LFS enhancing effects in the KLFS+WIN group.

Conclusions

Improving effects of LFS on learning and memory impairments are mediated through the activation of the endocannabinoid (ECB) system.

Regulation of GABAA and 5-HT Receptors Involved in Anxiolytic Mechanisms of Jujube Seed: A System Biology Study Assisted by UPLC-Q-TOF/MS and RT-qPCR Method

The increase of the prevalence of anxiety greatly impacts the quality of life in China and globally. As the most popular traditional Chinese medicinal ingredient for nourishing health and tranquilizing mind, Jujube seed (Ziziphus jujuba Mill., Rhamnaceae) (SZJ) has been proved to exert anxiolytic effects in previous reports. In this study, a system biology method assisted by UPLC-Q-TOF/MS and RT-qPCR was developed to systematically demonstrate the anxiolytic mechanisms of SZJ. A total of 35 phytochemicals were identified from SZJ extract (Ziziphus jujuba Mill. var. spinosa [Bunge] Hu ex H.F. Chow), which interact with 71 anxiolytic targets. Protein-protein interaction, genes cluster, Gene Ontology, and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways analysis were subsequently conducted, and results demonstrated that regulation of serotonergic and GABAergic synapse pathways were dominantly involved in the anxiolytic mechanisms of SZJ extract. The effects of SZJ extract on mRNA expressions of multiple GABA_A (gamma-aminobutyric acid type A) and 5-HT (serotonin) receptors subtypes were further validated in human neuroblastoma SH-SY5Y cells using RT-qPCR. Results showed that SZJ extract (250 μg/mL) significantly up-regulated the mRNA level of GABRA1 and GABRA3 as well as HTR1A, HTR2A, and HTR2B in non-H₂O₂ treated SH-SY5Y cells. However, it exerted an inhibitive effect on the overexpressed mRNA of GABRA1, GABRA2, HTR1A, and HTR2A in H₂O₂ treated SH-SY5Y cells. Taken together, our findings suggest that anxiolytic mechanisms of SZJ mostly involve the regulation of GABAergic and serotonergic synapse pathways, especially a two-way modulation of GABRA1, HTR1A, and HTR2A. Our current results provide potential direction for future investigation of SZJ as an anxiolytic agent.

Spontaneous Mouse Behavior in Presence of Dissonance and Acoustic Roughness

According to a novel hypothesis (Arnal et al., 2015, Current Biology 25:2051-2056), auditory roughness, or temporal envelope modulations between 30 and 150 Hz, are present in both natural and artificial human alarm signals, which boosts the detection of these alarms in various tasks. These results also shed new light on the unpleasantness of dissonant sounds to humans, which builds upon the high level of roughness present in such sounds. However, it is not clear whether this hypothesis also applies to other species, such as rodents. In particular, whether consonant/dissonant chords, and particularly whether auditory roughness, can trigger unpleasant sensations in mice remains unknown. Using an autonomous behavioral system, which allows the monitoring of mouse behavior over a period of weeks, we observed that C57Bl6J mice did not show any preference for consonant chords. In addition, we found that mice showed a preference for rough sounds over sounds having amplitude modulations in their temporal envelope outside the "rough" range. These results suggest that some emotional features carried by the acoustic temporal envelope are likely to be species-specific.

Adolescent cannabinoid exposure interacts with other risk factors in schizophrenia: A review of the evidence from animal models

Many factors and their interaction are linked to the aetiology of schizophrenia, leading to the development of animal models of multiple risk factors and adverse exposures. Differentiating between separate and combined effects for each factor could better elucidate schizophrenia pathology, and drive development of preventative strategies for high-load risk factors. An epidemiologically valid risk factor commonly associated with schizophrenia is adolescent cannabis use. The aim of this review is to evaluate how early-life adversity from various origins, in combination with adolescent cannabinoid exposure interact, and whether these interactions confer main, synergistic or protective effects in animal models of schizophrenia-like behavioural, cognitive and morphological alterations. Patterns emerge regarding which models show consistent synergistic or protective effects, particularly those models incorporating early-life exposure to maternal deprivation and maternal immune activation, and sex-specific effects are observed. It is evident that more research needs to be conducted to better understand the risks and alterations of interacting factors, with particular interest in sex differences, to better understand the translatability of these preclinical models to humans.

The role of catecholamines in modulating responses to stress: Sex-specific patterns, implications, and therapeutic potential for post-traumatic stress disorder and opiate withdrawal

Emotional arousal is one of several factors that determine the strength of a memory and how efficiently it may be retrieved. The systems at play are multifaceted; on one hand, the dopaminergic mesocorticolimbic system evaluates the rewarding or reinforcing potential of a stimulus, while on the other, the noradrenergic stress response system evaluates the risk of threat, commanding attention, and engaging emotional and physical behavioral responses. Sex-specific patterns in the anatomy and function of the arousal system suggest that sexually divergent therapeutic approaches may be advantageous for neurological disorders involving arousal, learning, and memory. From the lens of the triple network model of psychopathology, we argue that post-traumatic stress disorder and opiate substance use disorder arise from maladaptive learning responses that are perpetuated by hyperarousal of the salience network. We present evidence that catecholamine-modulated learning and stress-responsive circuitry exerts substantial influence over the salience network and its dysfunction in stress-related psychiatric disorders, and between the sexes. We discuss the therapeutic potential of targeting the endogenous cannabinoid system; a ubiquitous neuromodulator that influences learning, memory, and responsivity to stress by influencing catecholamine, excitatory, and inhibitory synaptic transmission. Relevant preclinical data in male and female rodents are integrated with clinical data in men and women in an effort to understand how ideal treatment modalities between the sexes may be different.

Nightmares and the Cannabinoids

The cannabinoids, Δ9 tetrahydrocannabinol and its analogue, nabilone, have been found to reliably attenuate the intensity and frequency of post-traumatic nightmares. This essay examines how a traumatic event is captured in the mind, after just a single exposure, and repeatedly replicated during the nights that follow. The adaptive neurophysiological, endocrine and inflammatory changes that are triggered by the trauma and that alter personality and behavior are surveyed. These adaptive changes, once established, can be difficult to reverse. But cannabinoids, uniquely, have been shown to interfere with all of these post-traumatic somatic adaptations. While cannabinoids can suppress nightmares and other symptoms of post-traumatic stress disorder, they are not a cure. There may be no cure. The cannabinoids may best be employed, alone, but more likely in conjunction with other agents, in the immediate aftermath of a trauma to mitigate or even abort the metabolic changes which are set in motion by the trauma and which may permanently alter the reactivity of the nervous system. Steps in this direction have already been taken.

Disease-associated polymorphisms within the conserved ECR1 enhancer differentially regulate the tissue-specific activity of the cannabinoid-1 receptor gene promoter; implications for cannabinoid pharmacogenetics

Cannabinoid receptor‐1 (CB1) represents a potential drug target against conditions that include obesity and substance abuse. However, drug trials targeting CB1 (encoded by the CNR1 gene) have been compromised by differences in patient response. Toward addressing the hypothesis that genetic changes within the regulatory regions controlling CNR1 expression contribute to these differences, we characterized the effects of disease‐associated allelic variation within a conserved regulatory sequence (ECR1) in CNR1 intron 2 that had previously been shown to modulate cannabinoid response, alcohol intake, and anxiety‐like behavior. We used primary cell analysis of reporters carrying different allelic variants of the human ECR1 and found that human‐specific C‐allele variants of ECR1 (ECR1(C)) drove higher levels of CNR1prom activity in primary hippocampal cells than did the ancestral T‐allele and demonstrated a differential response to CB1 agonism. We further demonstrate a role for the AP‐1 transcription factor in driving higher ECR1(C) activity and evidence that the ancestral t‐allele variant of ECR1 interacted with higher affinity with the insulator binding factor CTCF. The cell‐specific approaches used in our study represent an important step in gaining a mechanistic understanding of the roles of noncoding polymorphic variation in disease and in the increasingly important field of cannabinoid pharmacogenetics.

Disruption of an enhancer associated with addictive behaviour within the cannabinoid receptor-1 gene suggests a possible role in alcohol intake, cannabinoid response and anxiety-related behaviour

The cannabinoid-1 receptor (CB₁) plays a critical role in a number of biological processes including nutrient intake, addiction and anxiety-related behaviour. Numerous studies have shown that expression of the gene encoding CB1 (CNR1) is highly dynamic with changes in the tissue specific expression of CNR1 associated with brain homeostasis and disease progression. However, little is known of the mechanisms regulating this dynamic expression. To gain a better understanding of the genomic mechanisms modulating the expression of CNR1 in health and disease we characterised the role of a highly conserved regulatory sequence (ECR1) in CNR1 intron 2 that contained a polymorphism in linkage disequilibrium with disease associated SNPs. We used CRISPR/CAS9 technology to disrupt ECR1 within the mouse genome. Disruption of ECR1 significantly reduced CNR1 expression in the hippocampus but not in the hypothalamus. These mice also displayed an altered sex-specific anxiety-related behavioural profile (open field test), reduced ethanol intake and a reduced hypothermic response following CB₁ agonism. However, no significant changes in feeding patterns were detected. These data suggest that, whilst not all of the expression of CNR1 is modulated by ECR1, this highly conserved enhancer is required for appropriate physiological responses to a number of stimuli. The combination of comparative genomics and CRISPR/CAS9 disruption used in our study to determine the functional effects of genetic and epigenetic changes on the activity of tissue-specific regulatory elements at the CNR1 locus represent an important first step in gaining a mechanistic understanding of cannabinoid regulatory pharmacogenetics.

Anandamide modulation of circadian- and stress-dependent effects on rat short-term memory

The endocannabinoid system plays a key role in the control of emotional responses to environmental challenges. CB1 receptors are highly expressed within cortico-limbic brain areas, where they modulate stress effects on memory processes. Glucocorticoid and endocannabinoid release is influenced by circadian rhythm. Here, we investigated how different stress intensities immediately after encoding influence rat short-term memory in an object recognition task, whether the effects depend on circadian rhythm and if exogenous augmentation of anandamide levels could restore any observed impairment. Two separate cohorts of male adult Sprague-Dawley rats were tested at two different times of the day, morning (inactivity phase) or afternoon (before the onset of the activity phase) in an object recognition task. The anandamide hydrolysis inhibitor URB597 was intraperitoneally administered immediately after the training trial. Rats were thereafter subjected to a forced swim stress under low or high stress conditions and tested 1 h after training. Control rats underwent the same experimental procedure except for the forced swim stress (no stress). We further investigated whether URB597 administration might modulate corticosterone release in rats subjected to the different stress conditions, both in the morning or afternoon. The low stressor elevated plasma corticosterone levels and impaired 1 h recognition memory performance when animals were tested in the morning. Exposure to the higher stress condition elevated plasma corticosterone levels and impaired memory performance, independently of the testing time. These findings show that stress impairing effects on short-term recognition memory are dependent on the intensity of stress and circadian rhythm. URB597 (0.3 mg kg^-1) rescued the altered memory performance and decreased corticosterone levels in all the impaired groups yet leaving memory unaltered in the non-impaired groups.

Characterization of cerebral cortical endocannabinoid levels in a rat inguinal surgery model using liquid chromatography-tandem mass spectrometry (LC-MS/MS)

BACKGROUND

The brain endocannabinoid system is believed to play significant roles in anti-nociception, fear response, anxiety, and stress. This study investigated the effects of rat inguinal surgery on the levels of endocannabinoids in the cerebral cortex.

AIM

The aim of this study was to investigate the effects of acute post-surgical pain on the levels of endocannabinoids in the cerebral cortex.

METHODS

Quantitation of endocannabinoids in the rat cerebral cortex was performed by liquid chromatography-tandem mass spectrometry.

RESULTS

There was no significant difference in the cerebral cortical levels of anandamide (AEA) and 2-arachidonoylglycerol (2-AG) between the sham and surgery experimental groups. However, there were lateralized differences in the levels of these endocannabinoids between the right and left cerebral cortices irrespective of the two groups. The concentrations of AEA and 2-AG were significantly higher in the right cerebral cortex compared to the contralateral cerebral cortex.

CONCLUSION

Acute post-surgical pain did not induce significant alterations in the cerebral cortical levels of endocannabinoids in this study, but the phenomenon of lateralization of the cerebral cortical AEA and 2-AG levels was observed; this latter finding may be related to the role played by endocannabinoids in fear conditioning.

Regional changes in the type 1 cannabinoid receptor are associated with cognitive dysfunction in Parkinson's disease

PURPOSE

The endocannabinoid system plays a regulatory role in a number of physiological functions, including motor control but also mood, emotion, and cognition. A number of preclinical studies in Parkinson's disease (PD) models demonstrated that modulating the type 1 cannabinoid receptor (CB₁R) may improve motor symptoms and components of cognitive processing. However, the relation between CB₁R, cognitive decline and behavioral symptoms has not been investigated in PD patients so far. The aim of this study was to examine whether CB₁R availability is associated with measures of cognitive and behavioral function in PD patients.

METHODS

Thirty-eight PD patients and ten age- and gender-matched controls underwent a [¹⁸F]MK-9470 PET scan to assess CB₁R availability, as well as volumetric MR imaging. Neuropsychological symptoms were evaluated using an extensive cognitive and behavioral battery covering the five cognitive domains, depression, anxiety, apathy, and psychiatric complications, and were correlated to CB₁R availability using vowel-wise regression analysis (P < 0.05, corrected for familywise error).

RESULTS

PD patients with poorer performance in episodic memory, executive functioning, speed and mental flexibility (range P 0.003-0.03) showed lower CB₁R availability in predominantly the midcingulate cortex and middle to superior frontal gyrus (T_peak-level > 4.0). Also, PD patients with more severe visuospatial dysfunction showed decreased CB₁R availability in the precuneus, midcingulate, supplementary motor cortex, inferior orbitofrontal gyrus and thalamus (T_peak-level = 5.5). These correlations were not related to cortical gray matter atrophy. No relationship was found between CB₁R availability and mood or behavioral symptom scores.

CONCLUSIONS

Decreased CB₁R availability in the prefrontal and midcingulate cortex in PD patients is strongly correlated with disturbances in executive functioning, episodic memory, and visuospatial functioning. Further investigation of regional CB1R expression in groups of PD patients with mild cognitive impairment or dementia is warranted in order to further investigate the role of CB1R expression in different levels of cognitive impairment in PD.

Prenatal cannabinoid exposure and altered neurotransmission

Marijuana is one of the most commonly used illicit drugs worldwide. In addition, use of synthetic cannabinoids is increasing, especially among adolescents and young adults. Although human studies have shown that the use of marijuana during pregnancy leads to adverse behavioral effects, such as deficiencies in attention and executive function in affected offspring, the rate of marijuana use among pregnant women is steadily increasing. Various aspects of human behavior including emotion, learning, and memory are dependent on complex interactions between multiple neurotransmitter systems that are especially vulnerable to alterations during the developmental period. Thus, exploration of neurotransmitter changes in response to prenatal cannabinoid exposure is crucial to develop an understanding of how homeostatic imbalance and various long-term neurobehavioral deficits manifest following the abuse of marijuana or other synthetic cannabinoids during pregnancy. Current literature confirms that vast alterations to neurotransmitter systems are present following prenatal cannabinoid exposure, and many of these alterations within the brain are region specific, time-dependent, and sexually dimorphic. In this review, we aim to provide a summary of observed changes to various neurotransmitter systems following cannabinoid exposure during pregnancy and to draw possible correlations to reported behavioral alterations in affected offspring.

An endocannabinoid receptor polymorphism modulates affective processing under stress

Stress has a critical impact on affective and cognitive processing. Based on rodent data suggesting that endocannabinoid signaling via CB1 receptors serves as an emotional buffer, we hypothesized that a common variant of the gene coding for the CB1 receptor modulates affective processing under stress (CNR1; rs1049353 A vs G allele). Therefore, 139 participants, genotyped for this polymorphism, underwent a stress or control manipulation before they viewed emotionally neutral and negative pictures in a magnetic resonance imaging scanner. The ventromedial prefrontal cortex, known for its crucial role in emotion regulation, was significantly more activated in AA/AG vs GG genotype carriers when viewing negative pictures after stress. Under no-stress conditions, AA/AG genotype carriers showed enhanced crosstalk between the ventrolateral prefrontal cortex and the amygdala. We further assessed participants' 24 h-delayed memory for the presented pictures and found that memory performance correlated with amygdala and hippocampus activity and connectivity in stressed carriers of the AA/AG but not the GG genotype. These findings underline the modulatory role of the endocannabinoid system in stress effects on emotion and cognition and provide insights into the neural mechanisms that may contribute to the suggested protective effect of the AA/AG genotype of the CB1 receptor polymorphism against stress-related psychopathologies.

Cannabinoid type-1 receptor blockade restores neurological phenotypes in two models for Down syndrome

Intellectual disability is the most limiting hallmark of Down syndrome, for which there is no gold-standard clinical treatment yet. The endocannabinoid system is a widespread neuromodulatory system involved in multiple functions including learning and memory processes. Alterations of this system contribute to the pathogenesis of several neurological and neurodevelopmental disorders. However, the involvement of the endocannabinoid system in the pathogenesis of Down syndrome has not been explored before. We used the best-characterized preclinical model of Down syndrome, the segmentally trisomic Ts65Dn model. In male Ts65Dn mice, cannabinoid type-1 receptor (CB1R) expression was enhanced and its function increased in hippocampal excitatory terminals. Knockdown of CB1R in the hippocampus of male Ts65Dn mice restored hippocampal-dependent memory. Concomitant with this result, pharmacological inhibition of CB1R restored memory deficits, hippocampal synaptic plasticity and adult neurogenesis in the subgranular zone of the dentate gyrus. Notably, the blockade of CB1R also normalized hippocampal-dependent memory in female Ts65Dn mice. To further investigate the mechanisms involved, we used a second transgenic mouse model overexpressing a single gene candidate for Down syndrome cognitive phenotypes, the dual specificity tyrosine-phosphorylation-regulated kinase 1A (DYRK1A). CB1R pharmacological blockade similarly improved cognitive performance, synaptic plasticity and neurogenesis in transgenic male Dyrk1A mice. Our results identify CB1R as a novel druggable target potentially relevant for the improvement of cognitive deficits associated with Down syndrome.

Psychedelics and reconsolidation of traumatic and appetitive maladaptive memories: focus on cannabinoids and ketamine

RATIONALE

Clinical data with 3,4-methylenedioxymethamphetamine (MDMA) in post-traumatic stress disorder (PTSD) patients recently stimulated interest on the potential therapeutic use of psychedelics in disorders characterized by maladaptive memories, including substance use disorders (SUD). The rationale for the use of MDMA in PTSD and SUD is being extended to a broader beneficial "psychedelic effect," which is supporting further clinical investigations, in spite of the lack of mechanistic hypothesis. Considering that the retrieval of emotional memories reactivates specific brain mechanisms vulnerable to inhibition, interference, or strengthening (i.e., the reconsolidation process), it was proposed that the ability to retrieve and change these maladaptive memories might be a novel intervention for PTSD and SUD. The mechanisms underlying MDMA effects indicate memory reconsolidation modulation as a hypothetical process underlying its efficacy.

OBJECTIVE

Mechanistic and clinical studies with other two classes of psychedelic substances, namely cannabinoids and ketamine, are providing data in support of a potential use in PTSD and SUD based on the modulation of traumatic and appetitive memory reconsolidation, respectively. Here, we review preclinical and clinical data on cannabinoids and ketamine effects on biobehavioral processes related to the reconsolidation of maladaptive memories.

RESULTS

We report the findings supporting (or not) the working hypothesis linking the potential therapeutic effect of these substances to the underlying reconsolidation process. We also proposed possible approaches for testing the use of these two classes of drugs within the current paradigm of reconsolidation memory inhibition.

CONCLUSIONS

Metaplasticity may be the process in common between cannabinoids and ketamine/ketamine-like substance effects on the mediation and potential manipulation of maladaptive memories.

Phytocannabinoids modulate emotional memory processing through interactions with the ventral hippocampus and mesolimbic dopamine system: implications for neuropsychiatric pathology

Growing clinical and preclinical evidence suggests a potential role for the phytocannabinoid cannabidiol (CBD) as a pharmacotherapy for various neuropsychiatric disorders. In contrast, delta-9-tetrahydrocannabinol (THC), the primary psychoactive component in cannabis, is associated with acute and neurodevelopmental propsychotic side effects through its interaction with central cannabinoid type 1 receptors (CB1Rs). CB1R stimulation in the ventral hippocampus (VHipp) potentiates affective memory formation through inputs to the mesolimbic dopamine (DA) system, thereby altering emotional salience attribution. These changes in DA activity and salience attribution, evoked by dysfunctional VHipp regulatory actions and THC exposure, could predispose susceptible individuals to psychotic symptoms. Although THC can accelerate the onset of schizophrenia, CBD displays antipsychotic properties, can prevent the acquisition of emotionally irrelevant memories, and reverses amphetamine-induced neuronal sensitization through selective phosphorylation of the mechanistic target of rapamycin (mTOR) molecular signaling pathway. This review summarizes clinical and preclinical evidence demonstrating that distinct phytocannabinoids act within the VHipp and associated corticolimbic structures to modulate emotional memory processing through changes in mesolimbic DA activity states, salience attribution, and signal transduction pathways associated with schizophrenia-related pathology.

Reward-related limbic memory and stimulation of the cannabinoid system: An upgrade in value attribution?

While a lot is known about the mechanisms promoting aversive learning, the impact of rewarding factors on memory has received comparatively less attention. This research investigates reward-related explicit memory in male rats, by taking advantage of the emotional-object recognition test. This is based on the prior association, during conditioned learning, between a rewarding experience (the encounter with a receptive female rat) and an object; afterwards rat discrimination and recognition of the 'emotional object' is recorded in the presence of a novel object, as a measure of positive limbic memory formation. Since endocannabinoids are critical for processing reward and motivation, the consequences of the stimulation of cannabinoid signalling are also assessed by the administration of WIN 55,212-2 at pre- and post-conditioning time. Our results show that rats encode the association between object and rewarding experience, form positive limbic memory of the emotional object, and retrieve this information in the face of novelty. Stimulation of the cannabinoid system at pre-conditioning time is able to strengthen reward-related explicit memory in the presence of novelty, whereas post-conditioning activation increases approach behaviour to novel stimuli. The assessment of limbic memory by the emotional-object recognition test can help unveiling the addictive and confounding properties of psychotropic drugs.

The Role of the Endocannabinoid System and Genetic Variation in Adolescent Brain Development

During adolescence, both rodent and human studies have revealed dynamic changes in the developmental trajectories of corticolimbic structures, which are known to contribute to the regulation of fear and anxiety-related behaviors. The endocannabinoid (eCB) system critically regulates stress responsivity and anxiety throughout the life span. Emerging evidence suggests that during adolescence, changes in eCB signaling contribute to the maturation of local and corticolimbic circuit populations of neurons, such as mediating the balance between excitatory and inhibitory neurotransmission within the prefrontal cortex. This function of the eCB system facilitates efficient communication within and between brain regions and serves a central role in establishing complex and adaptive cognitive and behavioral processing. Although these peri-adolescent changes in eCB signaling promote brain development and plasticity, they also render this period a particularly sensitive one for environmental perturbations to these normative fluctuations in eCB signaling, such as stress, potentially leading to altered developmental trajectories of neural circuits governing emotional behaviors. In this review, we focus on the role of eCB signaling on the regulation of stress and anxiety-related behaviors both during and after adolescence. Moreover, we discuss the functional implications of human genetic variation in the eCB system for the risk for anxiety and consequences of stress across development and into adulthood.

Cannabinoid Modulation of the Stressed Hippocampus

Exposure to stressful situations is one of the risk factors for the precipitation of several psychiatric disorders, including Major Depressive Disorder, Posttraumatic Stress Disorder and Schizophrenia. The hippocampal formation is a forebrain structure highly associated with emotional, learning and memory processes; being particularly vulnerable to stress. Exposure to stressful stimuli leads to neuroplastic changes and imbalance between inhibitory/excitatory networks. These changes have been associated with an impaired hippocampal function. Endocannabinoids (eCB) are one of the main systems controlling both excitatory and inhibitory neurotransmission, as well as neuroplasticity within the hippocampus. Cannabinoids receptors are highly expressed in the hippocampus, and several lines of evidence suggest that facilitation of cannabinoid signaling within this brain region prevents stress-induced behavioral changes. Also, chronic stress modulates hippocampal CB₁ receptors expression and endocannabinoid levels. Moreover, cannabinoids participate in mechanisms related to synaptic plasticity and adult neurogenesis. Here, we discussed the main findings supporting the involvement of hippocampal cannabinoid neurotransmission in stress-induced behavioral and neuroplastic changes.

Psychedelics and reconsolidation of traumatic and appetitive maladaptive memories: focus on cannabinoids and ketamine

RATIONALE

Clinical data with 3,4-methylenedioxymethamphetamine (MDMA) in post-traumatic stress disorder (PTSD) patients recently stimulated interest on the potential therapeutic use of psychedelics in disorders characterized by maladaptive memories, including substance use disorders (SUD). The rationale for the use of MDMA in PTSD and SUD is being extended to a broader beneficial "psychedelic effect," which is supporting further clinical investigations, in spite of the lack of mechanistic hypothesis. Considering that the retrieval of emotional memories reactivates specific brain mechanisms vulnerable to inhibition, interference, or strengthening (i.e., the reconsolidation process), it was proposed that the ability to retrieve and change these maladaptive memories might be a novel intervention for PTSD and SUD. The mechanisms underlying MDMA effects indicate memory reconsolidation modulation as a hypothetical process underlying its efficacy.

OBJECTIVE

Mechanistic and clinical studies with other two classes of psychedelic substances, namely cannabinoids and ketamine, are providing data in support of a potential use in PTSD and SUD based on the modulation of traumatic and appetitive memory reconsolidation, respectively. Here, we review preclinical and clinical data on cannabinoids and ketamine effects on biobehavioral processes related to the reconsolidation of maladaptive memories.

RESULTS

We report the findings supporting (or not) the working hypothesis linking the potential therapeutic effect of these substances to the underlying reconsolidation process. We also proposed possible approaches for testing the use of these two classes of drugs within the current paradigm of reconsolidation memory inhibition.

CONCLUSIONS

Metaplasticity may be the process in common between cannabinoids and ketamine/ketamine-like substance effects on the mediation and potential manipulation of maladaptive memories.

Role of the endocannabinoid system in the emotional manifestations of osteoarthritis pain

In this study, we investigated the role of the endocannabinoid system (ECS) in the emotional and cognitive alterations associated with osteoarthritis pain. The monosodium iodoacetate model was used to evaluate the affective and cognitive manifestations of osteoarthritis pain in type 1 (CB1R) and type 2 (CB2R) cannabinoid receptor knockout and wild-type mice and the ability of CB1R (ACEA) and CB2R (JWH133) selective agonists to improve these manifestations during a 3-week time period. The levels of the endocannabinoids anandamide (AEA) and 2-arachidonoylglycerol (2-AG) were measured in plasma and brain areas involved in the control of these manifestations. Patients with knee osteoarthritis and healthy controls were recruited to evaluate pain, affective, and cognitive symptoms, as well as plasma endocannabinoid levels and cannabinoid receptor gene expression in peripheral blood lymphocytes. The affective manifestations of osteoarthritis were enhanced in CB1R knockout mice and absent in CB2R knockouts. Interestingly, both ACEA and JWH133 ameliorated the nociceptive and affective alterations, whereas ACEA also improved the associated memory impairment. An increase of 2-AG levels in prefrontal cortex and plasma was observed in this mouse model of osteoarthritis. In agreement, an increase of 2-AG plasmatic levels and an upregulation of CB1R and CB2R gene expression in peripheral blood lymphocytes were observed in patients with osteoarthritis compared with healthy subjects. Changes found in these biomarkers of the ECS correlated with pain, affective, and cognitive symptoms in these patients. The ECS plays a crucial role in osteoarthritis and represents an interesting pharmacological target and biomarker of this disease.

Cannabis for posttraumatic stress disorder: A neurobiological approach to treatment

The endocannabinoid system is intricately involved in regulation of the neurobiological processes, which underlie the symptomatology of posttraumatic stress disorder (PTSD). This article discusses the neurobiological underpinnings of PTSD and the use of cannabis for treating PTSD in the New Mexico Medical Cannabis Program.

The endocannabinoid system in guarding against fear, anxiety and stress

The endocannabinoid (eCB) system has emerged as a central integrator linking the perception of external and internal stimuli to distinct neurophysiological and behavioural outcomes (such as fear reaction, anxiety and stress-coping), thus allowing an organism to adapt to its changing environment. eCB signalling seems to determine the value of fear-evoking stimuli and to tune appropriate behavioural responses, which are essential for the organism's long-term viability, homeostasis and stress resilience; and dysregulation of eCB signalling can lead to psychiatric disorders. An understanding of the underlying neural cell populations and cellular processes enables the development of therapeutic strategies to mitigate behavioural maladaptation.

Training-Associated Emotional Arousal Shapes Endocannabinoid Modulation of Spatial Memory Retrieval in Rats

Variations in environmental aversiveness influence emotional memory processes in rats. We have previously shown that cannabinoid effects on memory are dependent on the stress level at the time of training as well as on the aversiveness of the environmental context. Here, we investigated whether the hippocampal endocannabinoid system modulates memory retrieval depending on the training-associated arousal level. Male adult Sprague Dawley rats were trained on a water maze spatial task at two different water temperatures (19°C and 25°C) to elicit either higher or lower stress levels, respectively. Rats trained under the higher stress condition had better memory and higher corticosterone concentrations than rats trained at the lower stress condition. The cannabinoid receptor agonist WIN55212-2 (10-30 ng/side), the 2-arachidonoyl glycerol (2-AG) hydrolysis inhibitor JZL184 (0.1-1 μg/side), and the anandamide (AEA) hydrolysis inhibitor URB597 (10-30 ng/side) were administered bilaterally into the hippocampus 60 min before probe-trial retention testing. WIN55212-2 or JZL184, but not URB597, impaired probe-trial performances only of rats trained at the higher stressful condition. Furthermore, rats trained under higher stress levels displayed an increase in hippocampal 2-AG, but not AEA, levels at the time of retention testing and a decreased affinity of the main 2-AG-degrading enzyme for its substrate. The present findings indicate that the endocannabinoid 2-AG in the hippocampus plays a key role in the selective regulation of spatial memory retrieval of stressful experience, shedding light on the neurobiological mechanisms involved in the impact of stress effects on memory processing.

SIGNIFICANCE STATEMENT

Endogenous cannabinoids play a central role in the modulation of memory for emotional events. Here we demonstrate that the endocannabinoid 2-arachidonoylglycerol in the hippocampus, a brain region crucially involved in the regulation of memory processes, selectively modulates spatial memory recall of stressful experiences. Thus, our findings provide evidence that the endocannabinoid 2-arachidonoylglycerol is a key player in mediating the impact of stress on memory retrieval. These findings can pave the way to new potential therapeutic intervention for the treatment of neuropsychiatric disorders, such as post-traumatic stress disorder, where a previous exposure to traumatic events could alter the response to traumatic memory recall leading to mental illness.

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.

Endocannabinoid signaling within the basolateral amygdala integrates multiple stress hormone effects on memory consolidation

Glucocorticoid hormones are known to act synergistically with other stress-activated neuromodulatory systems, such as norepinephrine and corticotropin-releasing factor (CRF), within the basolateral complex of the amygdala (BLA) to induce optimal strengthening of the consolidation of long-term memory of emotionally arousing experiences. However, as the onset of these glucocorticoid actions appear often too rapid to be explained by genomic regulation, the neurobiological mechanism of how glucocorticoids could modify the memory-enhancing properties of norepinephrine and CRF remained elusive. Here, we show that the endocannabinoid system, a rapidly activated retrograde messenger system, is a primary route mediating the actions of glucocorticoids, via a glucocorticoid receptor on the cell surface, on BLA neural plasticity and memory consolidation. Furthermore, glucocorticoids recruit downstream endocannabinoid activity within the BLA to interact with both the norepinephrine and CRF systems in enhancing memory consolidation. These findings have important implications for understanding the fine-tuned crosstalk between multiple stress hormone systems in the coordination of (mal)adaptive stress and emotional arousal effects on neural plasticity and memory consolidation.

Endogenous cannabinoid release within prefrontal-limbic pathways affects memory consolidation of emotional training

Previous studies have provided extensive evidence that administration of cannabinoid drugs after training modulates the consolidation of memory for an aversive experience. The present experiments investigated whether the memory consolidation is regulated by endogenously released cannabinoids. The experiments first examined whether the endocannabinoids anandamide (AEA) and 2-arachidonoyl glycerol (2-AG) are released by aversive training. Inhibitory avoidance training with higher footshock intensity produced increased levels of AEA in the amygdala, hippocampus, and medial prefrontal cortex (mPFC) shortly after training in comparison with levels assessed in rats trained with lower footshock intensity or unshocked controls exposed only to the training apparatus. In contrast, 2-AG levels were not significantly elevated. The additional finding that posttraining infusions of the fatty acid amide hydrolase (FAAH) inhibitor URB597, which selectively increases AEA levels at active synapses, administered into the basolateral complex of the amygdala (BLA), hippocampus, or mPFC enhanced memory strongly suggests that the endogenously released AEA modulates memory consolidation. Moreover, in support of the view that this emotional training-associated increase in endocannabinoid neurotransmission, and its effects on memory enhancement, depends on the integrity of functional interactions between these different brain regions, we found that disruption of BLA activity blocked the training-induced increases in AEA levels as well as the memory enhancement produced by URB597 administered into the hippocampus or mPFC. Thus, the findings provide evidence that emotionally arousing training increases AEA levels within prefrontal-limbic circuits and strongly suggest that this cannabinoid activation regulates emotional arousal effects on memory consolidation.

Toward a translational approach to targeting the endocannabinoid system in posttraumatic stress disorder: a critical review of preclinical research

Despite the lack of clinical research, marijuana and synthetic cannabinoids have been approved to treat posttraumatic stress disorder (PTSD) in several states in the United States. This review critically examines preclinical research on the endocannabinoid system (ECS) in order to evaluate three key questions that are relevant to PTSD: (1) Does ECS dysfunction impact fear extinction? (2) Can stress-related symptoms be prevented by ECS modulation? (3) Is the ECS a potential target for enhancing PTSD treatment? Disruption of the ECS impaired fear extinction in rodents, and ECS abnormalities have been observed in PTSD. Targeting fear memories via the ECS had mixed results in rodents, whereas augmented cannabinoid receptor activation typically facilitated extinction. However, the translational value of these findings is limited by the paucity and inconsistency of human research. Further investigation is necessary to determine whether incorporating cannabinoids in treatment would benefit individuals with PTSD, with cautious attention to risks.

Chronic exposure to WIN55,212-2 affects more potently spatial learning and memory in adolescents than in adult rats via a negative action on dorsal hippocampal neurogenesis

Several epidemiological studies show an increase in cannabis use among adolescents, especially in Morocco for being one of the major producers in the world. The neurobiological consequences of chronic cannabis use are still poorly understood. In addition, brain plasticity linked to ontogeny portrays adolescence as a period of vulnerability to the deleterious effects of drugs. The aim of this study was to investigate the behavioral neurogenic effects of chronic exposure to the cannabinoid agonist WIN55,212-2 during adolescence, by evaluating the emotional and cognitive performances, and the consequences on neurogenesis along the dorso-ventral axis of the hippocampus in adult rats. WIN55,212 was administered intraperitoneally (i.p.) once daily for 20 days to adolescent (27-30 PND) and adult Wistar rats (54-57 PND) at the dose of 1mg/kg. Following a 20 day washout period, emotional and cognitive functions were assessed by the Morris water maze test and the two-way active avoidance test. Twelve hours after, brains were removed and hippocampal neurogenesis was assessed using the doublecortin (DCX) as a marker for cell proliferation. Our results showed that chronic WIN55,212-2 treatment significantly increased thigmotaxis early in the training process whatever the age of treatment, induced spatial learning and memory deficits in adolescent but not adult rats in the Morris water maze test, while it had no significant effect in the active avoidance test during multitrial training in the shuttle box. In addition, the cognitive deficits assessed in adolescent rats were positively correlated to a decrease in the number of newly generated neurons in dorsal hippocampus. These data suggest that long term exposure to cannabinoids may affect more potently spatial learning and memory in adolescent compared to adult rats via a negative action on hippocampal plasticity.

The endocannabinoid system: an emotional buffer in the modulation of memory function

Extensive evidence indicates that endocannabinoids modulate cognitive processes in animal models and human subjects. However, the results of endocannabinoid system manipulations on cognition have been contradictory. As for anxiety behavior, a duality has indeed emerged with regard to cannabinoid effects on memory for emotional experiences. Here we summarize findings describing cannabinoid effects on memory acquisition, consolidation, retrieval and extinction. Additionally, we review findings showing how the endocannabinoid system modulates memory function differentially, depending on the level of stress and arousal associated with the experimental context. Based on the evidence reviewed here, we propose that the endocannabinoid system is an emotional buffer that moderates the effects of environmental context and stress on cognitive processes.

Cannabis abuse is associated with better emotional memory in schizophrenia: a functional magnetic resonance imaging study

In schizophrenia cannabis abuse/dependence is associated with poor compliance and psychotic relapse. Despite this, the reasons for cannabis abuse remain elusive, but emotions may play a critical role in this comorbidity. Accordingly, we performed a functional magnetic resonance imaging study of emotional memory in schizophrenia patients with cannabis abuse (dual-diagnosis, DD). Participants comprised 14 DD patients, 14 non-abusing schizophrenia patients (SCZ), and 21 healthy controls (HC) who had to recognize positive and negative pictures while being scanned. Recognition of positive and negative emotions was prominently impaired in SCZ patients, relative to HC, while differences between DD and HC were smaller. For positive and negative stimuli, we observed significant activations in frontal, limbic, temporal and occipital regions in HC; in frontal, limbic and temporal regions in DD; and in temporal, parietal, limbic and occipital regions in the SCZ group. Our results suggest that emotional memory and prefrontal lobe functioning are preserved in DD relative to SCZ patients. These results are consistent with previous findings showing that cannabis abuse is associated with fewer negative symptoms and better cognitive functioning in schizophrenia. Longitudinal studies will need to determine whether the relative preservation of emotional memory is primary or secondary to cannabis abuse in schizophrenia.

Cannabinoids and traumatic stress modulation of contextual fear extinction and GR expression in the amygdala-hippocampal-prefrontal circuit

Considerable evidence suggests that cannabinoids modulate the behavioral and physiological response to stressful events. We have recently shown that activating the cannabinoid system using the CB1/CB2 receptor agonist WIN55,212-2 (WIN) in proximity to exposure to single-prolonged stress (SPS), a rat model of emotional trauma, prevented the stress-induced enhancement of acoustic startle response, the impairment in avoidance extinction and the enhanced negative feedback on the hypothalamic-pituitary-adrenal (HPA) axis (Ganon-Elazar and Akirav, 2012). Some of the effects were found to be mediated by CB1 receptors in the basolateral amygdala (BLA). Here we examined whether cannabinoid receptor activation in a putative brain circuit that includes the BLA, hippocampus and prefrontal cortex (PFC), could prevent the effects of traumatic stress on contextual fear extinction and alterations in glucocorticoid receptor (GR) protein levels. We found that: (i) SPS impaired contextual fear extinction tested one week after trauma exposure and that WIN prevented the stress-induced impairment of extinction when microinjected immediately after trauma exposure into the BLA or hippocampus (5 μg), but not when microinjected into the PFC, (ii) the ameliorating effects of WIN on contextual extinction were prevented by blocking GRs in the BLA and hippocampus, and (iii) SPS up regulated GRs in the BLA, PFC and hippocampus and systemic WIN administration (0.5 mg/kg) after trauma exposure normalized GR levels in the BLA and hippocampus, but not in the PFC. Cannabinoid receptor activation in the aftermath of trauma exposure may regulate the emotional response to the trauma and prevent stress-induced impairment of extinction and GR up regulation through the mediation of CB1 receptors in the BLA and hippocampus. Taken together, the findings suggest that the interaction between the cannabinoid and glucocorticoid systems is crucial in the modulation of emotional trauma.

Cannabinoids and glucocorticoids modulate emotional memory after stress

Bidirectional and functional relationships between glucocorticoids and the endocannabinoid system have been demonstrated. Here, I review the interaction between the endocannabinoid and glucocorticoid/stress systems. Specifically, stress is known to produce rapid changes in endocannabinoid signaling in stress-responsive brain regions. In turn, the endocannabinoid system plays an important role in the downregulation and habituation of hypothalamic-pituitary-adrenocortical (HPA) axis activity in response to stress. Glucocorticoids also recruit the endocannabinoid system to exert rapid negative feedback control of the HPA axis during stress. It became increasingly clear, however, that cannabinoid CB1 receptors are also abundantly expressed in the basolateral amygdala (BLA) and other limbic regions where they modulate emotional arousal effects on memory. Enhancing cannabinoids signaling using exogenous CB1 receptor agonists prevent the effects of acute stress on emotional memory. I propose a model suggesting that the ameliorating effects of exogenously administered cannabinoids on emotional learning after acute stress are mediated by the decrease in the activity of the HPA axis via GABAergic mechanisms in the amygdala.

The endocannabinoid system as a possible target to treat both the cognitive and emotional features of post-traumatic stress disorder (PTSD)

Post-traumatic stress disorder (PTSD) is a psychiatric disorder of significant prevalence and morbidity, whose pathogenesis relies on paradoxical changes of emotional memory processing. An ideal treatment would be a drug able to block the pathological over-consolidation and continuous retrieval of the traumatic event, while enhancing its extinction and reducing the anxiety symptoms. While the latter benefit from antidepressant medications, no drug is available to control the cognitive symptomatology. Endocannabinoids regulate affective states and participate in memory consolidation, retrieval, and extinction. Clinical findings showing a relationship between Cannabis use and PTSD, as well as changes in endocannabinoid activity in PTSD patients, further suggest the existence of a link between endocannabinoids and maladaptive brain changes after trauma exposure. Along these lines, we suggest that endocannabinoid degradation inhibitors may be an ideal therapeutic approach to simultaneously treat the emotional and cognitive features of PTSD, avoiding the unwanted psychotropic effects of compounds directly binding cannabinoid receptors.

Pre-encoding administration of amphetamine or THC preferentially modulates emotional memory in humans

RATIONALE

Many addictive drugs are known to have effects on learning and memory, and these effects could motivate future drug use. Specifically, addictive drugs may affect memory of emotional events and experiences in ways that are attractive to some users. However, few studies have investigated the effects of addictive drugs on emotional memory in humans.

OBJECTIVES

This study examined the effects of the memory-enhancing drug dextroamphetamine (AMP) and the memory-impairing drug Δ(9)-tetrahydrocannabinol (THC) on emotional memory in healthy volunteers.

METHODS

Participants completed three experimental sessions across which they received capsules containing placebo and two doses of either AMP (10 and 20 mg; N = 25) or THC (7.5 and 15 mg; N = 25) before viewing pictures of positive (pleasant), neutral, and negative (unpleasant) scenes. Memory for the pictures was assessed 2 days later, under drug-free conditions.

RESULTS

Relative to placebo, memory for emotional pictures was improved by AMP and impaired by THC, but neither drug significantly affected memory for unemotional pictures. Positive memory biases were not observed with either drug, and there was no indication that the drugs' memory effects were directly related to their subjective or physiological effects alone.

CONCLUSIONS

This study provides the first clear evidence that stimulant drugs can preferentially strengthen, and cannabinoids can preferentially impair, memory for emotional events in humans. Although addictive drugs do not appear to positively bias memory, the possibility remains that these drugs' effects on emotional memory could influence drug use among certain individuals.