Chronic treatment with Delta(9)-tetrahydrocannabinol impairs spatial memory and reduces zif268 expression in the mouse forebrain

Neurobiological mechanisms underlying cannabis-induced memory impairment

A growing body of literature suggests that cannabis intake can induce memory loss in humans and animals. Besides the recreational use, daily cannabis users may also belong to the ever-increasing population of patients who are administered cannabis as a medicine. As such, they also can experience impairments in memory as a negative side effect of their therapy. Comprehension of the neurobiological mechanisms responsible for such detrimental effects would be therefore of paramount relevance to public health. The investigation of neurobiological mechanisms in humans, despite the progress in the development of imaging technologies that allow the study of brain structure and function, still suffers substantial limitations. Animal models, instead, enable us to establish a causal relationship and thus to better elucidate the neurobiological mechanisms underlying the process under study. In this review, we will attempt to collect the insight coming from animal models about cannabis effects on memory, trying to depict a picture of the neurobiological mechanisms contributing to the development of cognitive deficits following cannabis use.

Δ9-tetrahydrocannabinol (Δ9-THC) administration after neonatal exposure to phencyclidine potentiates schizophrenia-related behavioral phenotypes in mice

The clinical onset of schizophrenia often coincides with cannabis use in adolescents and young adults. However, the neurobiological consequences of this co-morbidity are not well understood. In this study, we examined the effects of Δ9-THC exposure during early adulthood on schizophrenia-related behaviors using a developmental mouse model of schizophrenia. Phencyclidine (PCP) or saline was administered once in neonatal mice (at P7; 10mg/kg). In turn, Δ9-THC or saline was administered sub-acutely later in life to cohorts of animals who had received either PCP or saline (P55-80, 5mg/kg). Mice who were administered PCP alone displayed behavioral changes in the Morris water waze (MWM) and pre-pulse inhibition (PPI) task paradigm that were consistent with schizophrenia-related phenotypes, but not in the locomotor activity or novel object recognition (NOR) task paradigms. Mice who were administered PCP and then received Δ9-THC later in life displayed behavioral changes in the locomotor activity paradigm (p<0.001) that was consistent with a schizophrenia-related phenotype, as well as potentiated changes in the NOR (p<0.01) and MWM (p<0.05) paradigms as compared to mice that received PCP alone. Decreased cortical receptor expression of NMDA receptor 1 subunit (NR1) was observed in mice that received PCP and PCP+Δ9-THC, while mice that received Δ9-THC and PCP+Δ9-THC displayed decreases in CB1 receptor expression. These findings suggest that administration of Δ9-THC during the early adulthood can potentiate the development of schizophrenia-related behavioral phenotypes induced by neonatal exposure to PCP in mice.

Interactions between cannabidiol and Δ9-THC following acute and repeated dosing: Rebound hyperactivity, sensorimotor gating and epigenetic and neuroadaptive changes in the mesolimbic pathway

The evidence base for the use of medical cannabis preparations containing specific ratios of cannabidiol (CBD) and Δ⁹-tetrahydrocannabinol (THC) is limited. While there is abundant data on acute interactions between CBD and THC, few studies have assessed the impact of their repeated co-administration. We previously reported that CBD inhibited or potentiated the acute effects of THC dependent on the measure being examined at a 1:1 CBD:THC dose ratio. Further, CBD decreased THC effects on brain regions involved in memory, anxiety and body temperature regulation. Here we extend on these finding by examining over 15 days of treatment whether CBD modulated the repeated effects of THC on behaviour and neuroadaption markers in the mesolimbic dopamine pathway. After acute locomotor suppression, repeated THC caused rebound locomotor hyperactivity that was modestly inhibited by CBD. CBD also slightly reduced the acute effects of THC on sensorimotor gating. These subtle effects were found at a 1:1 CBD:THC dose ratio but were not accentuated by a 5:1 dose ratio. CBD did not alter the trajectory of enduring THC-induced anxiety nor tolerance to the pharmacological effects of THC. There was no evidence of CBD potentiating the behavioural effects of THC. However we demonstrated for the first time that repeated co-administration of CBD and THC increased histone 3 acetylation (H3K9/14ac) in the VTA and ΔFosB expression in the nucleus accumbens. These changes suggest that while CBD may have protective effects acutely, its long-term molecular actions on the brain are more complex and may be supradditive.

Endocannabinoid dysregulation in cognitive and stress-related brain regions in the Nrg1 mouse model of schizophrenia

The endocannabinoid system is dysregulated in schizophrenia. Mice with heterozygous deletion of neuregulin 1 (Nrg1 HET mice) provide a well-characterised animal model of schizophrenia, and display enhanced sensitivity to stress and cannabinoids during adolescence. However, no study has yet determined whether these mice have altered brain endocannabinoid concentrations. Nrg1 application to hippocampal slices decreased 2-arachidonoylglycerol (2-AG) signalling and disrupted long-term depression, a form of synaptic plasticity critical to spatial learning. Therefore we specifically aimed to examine whether Nrg1 HET mice exhibit increased 2-AG concentrations and disruption of spatial learning. As chronic stress influences brain endocannabinoids, we also sought to examine whether Nrg1 deficiency moderates adolescent stress-induced alterations in brain endocannabinoids. Adolescent Nrg1 HET and wild-type (WT) mice were submitted to chronic restraint stress and brain endocannabinoid concentrations were analysed. A separate cohort of WT and Nrg1 HET mice was also assessed for spatial learning performance in the Morris Water Maze. Partial genetic deletion of Nrg1 increased anandamide concentrations in the amygdala and decreased 2-AG concentrations in the hypothalamus. Further, Nrg1 HET mice exhibited increased 2-AG concentrations in the hippocampus and impaired spatial learning performance. Chronic adolescent stress increased anandamide concentrations in the amygdala, however, Nrg1 disruption did not influence this stress-induced change. These results demonstrate for the first time in vivo interplay between Nrg1 and endocannabinoids in the brain. Our results demonstrate that aberrant Nrg1 and endocannabinoid signalling may cooperate in the hippocampus to impair cognition, and that Nrg1 deficiency alters endocannabinoid signalling in brain stress circuitry.

The transcription factor Zif268/Egr1, brain plasticity, and memory

The capacity to remember our past experiences and organize our future draws on a number of cognitive processes that allow our brain to form and store neural representations that can be recalled and updated at will. In the brain, these processes require mechanisms of neural plasticity in the activated circuits, brought about by cellular and molecular changes within the neurons activated during learning. At the cellular level, a wealth of experimental data accumulated in recent years provides evidence that signaling from synapses to nucleus and the rapid regulation of the expression of immediate early genes encoding inducible, regulatory transcription factors is a key step in the mechanisms underlying synaptic plasticity and the modification of neural networks required for the laying down of memories. In the activated neurons, these transcriptional events are thought to mediate the activation of selective gene programs and subsequent synthesis of proteins, leading to stable functional and structural remodeling of the activated networks, so that the memory can later be reactivated upon recall. Over the past few decades, novel insights have been gained in identifying key transcriptional regulators that can control the genomic response of synaptically activated neurons. Here, as an example of this approach, we focus on one such activity-dependent transcription factor, Zif268, known to be implicated in neuronal plasticity and memory formation. We summarize current knowledge about the regulation and function of Zif268 in different types of brain plasticity and memory processes.

Dissociation of the pharmacological effects of THC by mTOR blockade

The potential therapeutic benefits of cannabinoid compounds have raised interest in understanding the molecular mechanisms that underlie cannabinoid-mediated effects. We previously showed that the acute amnesic-like effects of delta9-tetrahydrocannabinol (THC) were prevented by the subchronic inhibition of the mammalian target of rapamycin (mTOR) pathway. In the present study, we assess the relevance of the mTOR pathway in other acute and chronic pharmacological effects of THC. The rapamycin derivative temsirolimus, an inhibitor of the mTOR pathway approved by the Food and Drug Administration, prevents both the anxiogenic- and the amnesic-like effects produced by acute THC. In contrast, THC-induced anxiolysis, hypothermia, hypolocomotion, and antinociception are not sensitive to the mTOR inhibition. In addition, a clear tolerance to THC-induced anxiolysis, hypothermia, hypolocomotion, and antinociception was observed after chronic treatment, but not to its anxiogenic- and amnesic-like effects. Temsirolimus pre-treatment prevented the amnesic-like effects of chronic THC without affecting the downregulation of CB1 receptors (CB1R) induced by this chronic treatment. Instead, temsirolimus blockade after chronic THC cessation did not prevent the residual cognitive deficit produced by chronic THC. Using conditional knockout mice lacking CB1R in GABAergic or glutamatergic neurons, we found that GABAergic CB1Rs are mainly downregulated under chronic THC treatment conditions, and CB1-GABA-KO mice did not develop cognitive deficits after chronic THC exposure. Therefore, mTOR inhibition by temsirolimus allows the segregation of the potentially beneficial effects of cannabinoid agonists, such as the anxiolytic and antinociceptive effects, from the negative effects, such as anxiogenic- and amnesic-like responses. Altogether, these results provide new insights for targeting the endocannabinoid system in order to prevent possible side effects.

Molecular mechanisms of cannabinoid addiction

Cannabis is the world's most widely used illicit substance, with an estimated number of 119-224 million users worldwide. In recent years we assisted to an increased effort aimed to individuate the brain circuits underlying cannabis addiction and dependence. Similarly to other drugs of abuse, repeated exposure to cannabinoids causes brain neuroadaptations that persist long after drug effects, contribute to the negative affective states during withdrawal, and ultimately facilitate relapse. Recently, considerable progress has been made in understanding the cellular and molecular consequences of prolonged cannabis use, among which is the identification of specific set of transcriptional regulations that develop differently after chronic cannabinoids and in the abstinent brain.

Novel molecular changes induced by Nrg1 hypomorphism and Nrg1-cannabinoid interaction in adolescence: a hippocampal proteomic study in mice

Neuregulin 1 (NRG1) is linked to an increased risk of developing schizophrenia and cannabis dependence. Mice that are hypomorphic for Nrg1 (Nrg1 HET mice) display schizophrenia-relevant behavioral phenotypes and aberrant expression of serotonin and glutamate receptors. Nrg1 HET mice also display idiosyncratic responses to the main psychoactive constituent of cannabis, Δ⁹-tetrahydrocannabinol (THC). To gain traction on the molecular pathways disrupted by Nrg1 hypomorphism and Nrg1-cannabinoid interactions we conducted a proteomic study. Adolescent wildtype (WT) and Nrg1 HET mice were exposed to repeated injections of vehicle or THC and their hippocampi were submitted to 2D gel proteomics. Comparison of WT and Nrg1 HET mice identified proteins linked to molecular changes in schizophrenia that have not been previously associated with Nrg1. These proteins are involved in vesicular release of neurotransmitters such as SNARE proteins; enzymes impacting serotonergic neurotransmission, and proteins affecting growth factor expression. Nrg1 HET mice treated with THC expressed a distinct protein expression signature compared to WT mice. Replicating prior findings, THC caused proteomic changes in WT mice suggestive of greater oxidative stress and neurodegeneration. We have previously observed that THC selectively increased hippocampal NMDA receptor binding of adolescent Nrg1 HET mice. Here we observed outcomes consistent with heightened NMDA-mediated glutamatergic neurotransmission. This included differential expression of proteins involved in NMDA receptor trafficking to the synaptic membrane; lipid raft stabilization of synaptic NMDA receptors; and homeostatic responses to dampen excitotoxicity. These findings uncover novel proteins altered in response to Nrg1 hypomorphism and Nrg1-cannabinoid interactions that improves our molecular understanding of Nrg1 signaling and Nrg1-mediated genetic vulnerability to the neurobehavioral effects of cannabinoids.

Brain regional differences in CB1 receptor adaptation and regulation of transcription

Cannabinoid CB1 receptors (CB1Rs) are expressed throughout the brain and mediate the central effects of cannabinoids, including Δ(9)-tetrahydrocannabinol (THC), the main psychoactive constituent of marijuana. Repeated THC administration produces tolerance to cannabinoid-mediated effects, although the magnitude of tolerance varies by effect. Consistent with this observation, CB1R desensitization and downregulation, as well as induction of immediate early genes (IEGs), vary by brain region. Zif268 and c-Fos are induced in the forebrain after acute THC administration. Phosphorylation of the cAMP response-element binding protein (CREB) is increased in a region-specific manner after THC administration. Results differ between acute versus repeated THC injection, and suggest that tolerance to IEG activation might develop in some regions. Repeated THC treatment produces CB1R desensitization and downregulation in the brain, although less adaption occurs in the striatum as compared to regions such as the hippocampus. Repeated THC treatment also induces expression of ΔFosB, a very stable isoform of FosB, in the striatum. Transgenic expression of ∆FosB in the striatum enhances the rewarding effects of several drugs, but its role in THC-mediated effects is not known. The inverse regional relationship between CB1R desensitization and ∆FosB induction suggests that these adaptations might inhibit each other, although this possibility has not been investigated. The differential regional expression of individual IEGs by acute or repeated THC administration suggests that regulation of target genes and effects on CB1R signaling will contribute to the behavioral effects of THC.

The endocannabinoid transport inhibitor AM404 differentially modulates recognition memory in rats depending on environmental aversiveness

Cannabinoid compounds may influence both emotional and cognitive processes depending on the level of environmental aversiveness at the time of drug administration. However, the mechanisms responsible for these responses remain to be elucidated. The present experiments investigated the effects induced by the endocannabinoid transport inhibitor AM404 (0.5-5 mg/kg, i.p.) on both emotional and cognitive performances of rats tested in a Spatial Open Field task and subjected to different experimental settings, named High Arousal (HA) and Low Arousal (LA) conditions. The two different experimental conditions influenced emotional reactivity independently of drug administration. Indeed, vehicle-treated rats exposed to the LA condition spent more time in the center of the arena than vehicle-treated rats exposed to the HA context. Conversely, the different arousal conditions did not affect the cognitive performances of vehicle-treated animals such as the capability to discriminate a spatial displacement of the objects or an object substitution. AM404 administration did not alter locomotor activity or emotional behavior of animals exposed to both environmental conditions. Interestingly, AM404 administration influenced the cognitive parameters depending on the level of emotional arousal: it impaired the capability of rats exposed to the HA condition to recognize a novel object while it did not induce any impairing effect in rats exposed to the LA condition. These findings suggest that drugs enhancing endocannabinoid signaling induce different effects on recognition memory performance depending on the level of emotional arousal induced by the environmental conditions.

Alterations of endocannabinoid signaling, synaptic plasticity, learning, and memory in monoacylglycerol lipase knock-out mice

Endocannabinoid (eCB) signaling is tightly regulated by eCB biosynthetic and degradative enzymes. The eCB 2-arachidonoylglycerol (2-AG) is hydrolyzed primarily by monoacylglycerol lipase (MAGL). Here, we investigated whether eCB signaling, synaptic function, and learning behavior were altered in MAGL knock-out mice. We report that MAGL⁻/⁻ mice exhibited prolonged depolarization-induced suppression of inhibition (DSI) in hippocampal CA1 pyramidal neurons, providing genetic evidence that the inactivation of 2-AG by MAGL determines the time course of the eCB-mediated retrograde synaptic depression. CB₁ receptor antagonists enhanced basal IPSCs in CA1 pyramidal neurons in MAGL⁻/⁻ mice, while the magnitude of DSI or CB₁ receptor agonist-induced depression of IPSCs was decreased in MAGL⁻/⁻ mice. These results suggest that 2-AG elevations in MAGL⁻/⁻ mice cause tonic activation and partial desensitization of CB₁ receptors. Genetic deletion of MAGL selectively enhanced theta burst stimulation (TBS)-induced long-term potentiation (LTP) in the CA1 region of hippocampal slices but had no significant effect on LTP induced by high-frequency stimulation or long-term depression induced by low-frequency stimulation. The enhancement of TBS-LTP in MAGL⁻/⁻ mice appears to be mediated by 2-AG-induced suppression of GABA(A) receptor-mediated inhibition. MAGL⁻/⁻ mice exhibited enhanced learning as shown by improved performance in novel object recognition and Morris water maze. These results indicate that genetic deletion of MAGL causes profound changes in eCB signaling, long-term synaptic plasticity, and learning behavior.

AAV-Mediated Overexpression of the CB1 Receptor in the mPFC of Adult Rats Alters Cognitive Flexibility, Social Behavior, and Emotional Reactivity

The endocannabinoid (ECB) system is strongly involved in the regulation of cognitive processing and emotional behavior and evidence indicates that ECB signaling might affect these behavioral abilities by modulations of prefrontal cortical functions. The aim of the present study was to examine the role of the CB1 receptor in the medial prefrontal cortex (mPFC) on cognitive flexibility and emotional behavior. Therefore, the CB1 receptor was overexpressed by adeno-associated virus vector-mediated gene transfer specifically in the mPFC of adult Wistar rats. Animals were then tested in different anxiety-related paradigms for emotional reactivity [e.g., elevated plus maze (EPM), light/dark emergence test (EMT), social interaction] and the attentional set shift task (ASST) – an adaptation of the human Wisconsin card sorting test – for cognitive abilities and behavioral flexibility. A subtle increase in exploratory behavior was found in CB1 receptor overexpressing animals (CB1-R) compared to Empty vector injected controls (Empty) in the EMT and EPM, although general locomotor activity did not differ between the groups. During social interaction testing, social contact behavior toward the unknown conspecific was found to be decreased, whereas social withdrawal was increased in CB1-R animals and they showed an inadequate increase in exploratory behavior compared to control animals. In the ASST, impaired reversal learning abilities were detected in CB1-R animals compared to controls, indicating reduced behavioral flexibility. In conclusion, upregulation of the CB1 receptor specifically in the rat mPFC induces alterations in emotional reactivity, leads to inadequate social behavior, and impairs cognitive flexibility. These findings might be relevant for neuropsychiatric disorders, since higher cortical CB1 receptor expression levels as well as similar behavioral impairments as observed in the present study have been described in schizophrenic patients.

The schizophrenia susceptibility gene neuregulin 1 modulates tolerance to the effects of cannabinoids

Cannabis increases the risk of schizophrenia in genetically vulnerable individuals. In this study we aim to show that the schizophrenia susceptibility gene neuregulin 1 (Nrg1) modulates the development of tolerance to cannabinoids in mice. Nrg1 heterozygous (HET) and wild-type (WT) mice were treated daily for 15 d with the synthetic analogue of Δ9-tetrahydrocannabinol, CP55,940 (0.4 mg/kg). We measured the impact of this exposure on locomotor activity, anxiety, prepulse inhibition (PPI), body temperature and FosB/ΔFosB immunohistochemistry. Tolerance to CP55,940-induced hypothermia and locomotor suppression developed more rapidly in Nrg1 HET mice than WT mice. Conversely in the light-dark test, while tolerance to the anxiogenic effect of CP55,940 developed in WT mice over days of testing, Nrg1 hypomorphs maintained marked anxiety even after 15 d of treatment. Repeated cannabinoid exposure selectively increased FosB/ΔFosB expression in the lateral septum, ventral part (LSV) of Nrg1 HET but not WT mice. On day 1 of exposure opposite effects of CP55,940 treatment were observed on PPI, i.e. it was facilitated in Nrg1 hypomorphs and impaired in WT mice, despite the drug significantly impairing the acoustic startle reflex equally in both genotypes. These effects of CP55,940 on PPI were not maintained as both genotypes became tolerant to cannabinoid action with repeated exposure. Our results highlight that Nrg1 modulates the development of cannabinoid tolerance dependent on the parameter being measured. Furthermore, these data reinforce the notion that the VLS is an important brain region involved in Nrg1-cannabinoid interactions.

Cannabinoid receptor CB1 mediates baseline and activity-induced survival of new neurons in adult hippocampal neurogenesis

Background

Adult neurogenesis is a particular example of brain plasticity that is partially modulated by the endocannabinoid system. Whereas the impact of synthetic cannabinoids on the neuronal progenitor cells has been described, there has been lack of information about the action of plant-derived extracts on neurogenesis. Therefore we here focused on the effects of Δ9-tetrahydrocannabinol (THC) and Cannabidiol (CBD) fed to female C57Bl/6 and Nestin-GFP-reporter mice on proliferation and maturation of neuronal progenitor cells and spatial learning performance. In addition we used cannabinoid receptor 1 (CB1) deficient mice and treatment with CB1 antagonist AM251 in Nestin-GFP-reporter mice to investigate the role of the CB1 receptor in adult neurogenesis in detail.

Results

THC and CBD differed in their effects on spatial learning and adult neurogenesis. CBD did not impair learning but increased adult neurogenesis, whereas THC reduced learning without affecting adult neurogenesis. We found the neurogenic effect of CBD to be dependent on the CB1 receptor, which is expressed over the whole dentate gyrus. Similarly, the neurogenic effect of environmental enrichment and voluntary wheel running depends on the presence of the CB1 receptor. We found that in the absence of CB1 receptors, cell proliferation was increased and neuronal differentiation reduced, which could be related to CB1 receptor mediated signaling in Doublecortin (DCX)-expressing intermediate progenitor cells.

Conclusion

CB1 affected the stages of adult neurogenesis that involve intermediate highly proliferative progenitor cells and the survival and maturation of new neurons. The pro-neurogenic effects of CBD might explain some of the positive therapeutic features of CBD-based compounds.

Anormalidades cognitivas no uso da cannabis

OBJETIVO: Evidências de que o uso de cannabis prejudica funções cognitivas em humanos têm-se acumulado nas décadas recentes. O propósito desta revisão é o de atualizar o conhecimento nesta área com novos achados a partir da literatura mais recente. MÉTODO: As buscas na literatura foram realizadas utilizando-se o banco de dados Web of Science até fevereiro de 2010. Foram buscados os termos "cannabi*" ou "marijuana" e "cogniti*" ou "memory" ou "attention" ou "executive function", e os estudos em humanos foram revisados preferencialmente em relação aos estudos em animais. DISCUSSÃO: O uso de cannabis prejudica a memória, a atenção, o controle inibitório, as funções executivas e a tomada de decisões, tanto durante como após o período de intoxicação aguda, persistindo por horas, dias, semanas ou mais após o último uso. Os estudos de desafio farmacológico em humanos estão elucidando a natureza e os substratos neurais das alterações cognitivas associadas a vários canabinoides. O uso pesado ou de longo prazo de cannabis parece resultar em anormalidades cognitivas mais duradouras e possivelmente em alterações cerebrais estruturais. Efeitos cognitivos adversos maiores estão associados ao uso de cannabis quando este começa no início da adolescência. CONCLUSÃO: O sistema canabinoide endógeno está envolvido nos mecanismos de regulação neural que modulam os processos subjacentes a uma gama de funções cognitivas que estão prejudicadas pela cannabis. Os déficits em usuários humanos muito provavelmente refletem, portanto, neuroadaptações e o funcionamento alterado do sistema canabinoide endógeno.