Comparison of cannabidiol to citalopram in targeting fear memory in female mice

Cannabidiol effects on fear processing and implications for PTSD: Evidence from rodent and human studies

Cannabidiol (CBD) modulates aversive memory and its extinction, with potential implications for treating anxiety- and stress-related disorders. Here, we summarize and discuss scientific evidence showing that CBD administered after the acquisition (consolidation) and retrieval (reconsolidation) of fear memory attenuates it persistently in rats and mice. CBD also reduces fear expression and enhances fear extinction. These effects involve the activation of cannabinoid type-1 (CB1) receptors in the dorsal hippocampus, bed nucleus of stria terminalis, and medial prefrontal cortex, comprising the anterior cingulate, prelimbic, and infralimbic subregions. Serotonin type-1A (5-HT1A) receptors also mediate some CBD effects on fear memory. CBD effects on fear memory acquisition vary, depending on the aversiveness of the conditioning procedure. While rodent findings are relatively consistent and encouraging, human studies investigating CBD's efficacy in modulating aversive/traumatic memories are still limited. More studies are needed to investigate CBD's effects on maladaptive, traumatic memories, particularly in post-traumatic stress disorder patients.

Dual-step pharmacological intervention for traumatic-like memories: implications from D-cycloserine and cannabidiol or clonidine in male and female rats

RATIONALE

Therapeutic approaches to mitigating traumatic memories have often faced resistance. Exploring safe reconsolidation blockers, drugs capable of reducing the emotional valence of the memory upon brief retrieval and reactivation, emerges as a promising pharmacological strategy. Towards this objective, preclinical investigations should focus on aversive memories resulting in maladaptive outcomes and consider sex-related differences to enhance their translatability.

OBJECTIVES

After selecting a relatively high training magnitude leading to the formation of a more intense and generalized fear memory in adult female and male rats, we investigated whether two clinically approved drugs disrupting its reconsolidation remain effective.

RESULTS

We found resistant reconsolidation impairment by the α2-adrenergic receptor agonist clonidine or cannabidiol, a major non-psychotomimetic Cannabis sativa component. However, pre-retrieval administration of D-cycloserine, a partial agonist at the glycine-binding site of the N-methyl-D-aspartate (NMDA) receptor complex, facilitated their impairing effects on reconsolidation. A similar reconsolidation blockade by clonidine or cannabidiol was achieved following exposure to a non-conditioned but generalized context after D-cycloserine administration. This suggests that sufficient memory destabilization can accompany generalized fear expression. Combining clonidine with cannabidiol without potentiating memory destabilization by D-cycloserine was ineffective.

CONCLUSIONS

These findings highlight the importance of NMDA receptor signaling in memory destabilization and underscore the efficacy of a dual-step pharmacological intervention in attenuating traumatic-like memories, even in a context different from the original learning environment.

The effect of SSRIs on fear learning: a systematic review and meta-analysis

RATIONALE

Selective serotonin reuptake inhibitors (SSRIs) are considered first-line medication for anxiety-like disorders such as panic disorder, generalized anxiety disorder, and post-traumatic stress disorder. Fear learning plays an important role in the development and treatment of these disorders. Yet, the effect of SSRIs on fear learning are not well known.

OBJECTIVE

We aimed to systematically review the effect of six clinically effective SSRIs on acquisition, expression, and extinction of cued and contextual conditioned fear.

METHODS

We searched the Medline and Embase databases, which yielded 128 articles that met the inclusion criteria and reported on 9 human and 275 animal experiments.

RESULTS

Meta-analysis showed that SSRIs significantly reduced contextual fear expression and facilitated extinction learning to cue. Bayesian-regularized meta-regression further suggested that chronic treatment exerts a stronger anxiolytic effect on cued fear expression than acute treatment. Type of SSRI, species, disease-induction model, and type of anxiety test used did not seem to moderate the effect of SSRIs. The number of studies was relatively small, the level of heterogeneity was high, and publication bias has likely occurred which may have resulted in an overestimation of the overall effect sizes.

CONCLUSIONS

This review suggests that the efficacy of SSRIs may be related to their effects on contextual fear expression and extinction to cue, rather than fear acquisition. However, these effects of SSRIs may be due to a more general inhibition of fear-related emotions. Therefore, additional meta-analyses on the effects of SSRIs on unconditioned fear responses may provide further insight into the actions of SSRIs.

Cannabidiol attenuates fear memory expression in female rats via hippocampal 5-HT1A but not CB1 or CB2 receptors

Growing evidence from male rodent and human studies suggests that cannabidiol (CBD) modulates the expression of aversive memories and anxiety-related responses. The limited data on whether and how CBD influences these aspects in females could have therapeutic implications given the increased susceptibility of women to anxiety- and stress-related disorders relative to men. Female studies are also essential to examine inherent aspects that potentially contribute to differences in responsiveness to CBD. Here we addressed these questions in adult female rats. Contextually fear-conditioned animals acutely treated with CBD (1.0-10 mg/kg) were tested 45 min later. In subsequent experiments, we investigated the estrous cycle effects and the contribution of dorsal hippocampus (DH) serotonin 1A (5-HT1A) and cannabinoid types 1 (CB1) and 2 (CB2) receptors to CBD-induced effects on memory retrieval/expression. The effects of pre-retrieval systemic or intra-DH CBD administration on subsequent fear extinction were also assessed. Lastly, we evaluated the open arms avoidance and stretched-attend postures in females exposed to the elevated plus-maze after systemic CBD treatment. CBD 3.0 and 10 mg/kg administered before conditioned context exposure reduced females' freezing. This action remained unchanged across the estrous cycle and involved DH 5-HT1A receptors activation. Pre-retrieval CBD impaired memory reconsolidation and lowered fear during early extinction. CBD applied directly to the DH was sufficient to reproduce the effects of systemic CBD treatment. CBD 3.0 and 10 mg/kg reduced anxiety-related responses scored in the elevated plus-maze. Our findings demonstrate that CBD attenuates the behavioral manifestation of learned fear and anxiety in female rats.

The effects of preventative cannabidiol in a male neuregulin 1 mouse model of schizophrenia

Cannabidiol (CBD) is a non-intoxicating cannabinoid with antipsychotic-like properties, however it’s potential to prevent schizophrenia development has not been thoroughly investigated. Brain maturation during adolescence creates a window where CBD could potentially limit the development of schizophrenia. The neuregulin 1 transmembrane domain heterozygous (Nrg1 TM HET) mutant mouse shows face, predictive, and construct validity for schizophrenia. Here we sought to determine if CBD given in adolescence could prevent the development of the schizophrenia-relevant phenotype, as well as susceptibility to the psychoactive cannabinoid Δ⁹-tetrahydrocannabinol (THC) in Nrg1 TM HET mice. Adolescent male Nrg1 mutants and wild type-like (WT) animals were administered 30 mg/kg CBD i.p. daily for seven weeks, and were tested for locomotion, social behavior, sensorimotor gating and cognition, and sensitivity to acute THC-induced behaviors. GAD67, GluA1, and NMDAR1 protein levels were measured in the hippocampus, striatum, and prefrontal cortex. Chronic adolescent CBD increased locomotion in animals regardless of genotype, was anxiolytic, and increased social behavior when animals were tested for their acute THC response. CBD did not alleviate the schizophrenia-relevant hyperlocomotive phenotype of Nrg1 mutants, nor deficits in social behaviors. Nrg1 mutant mice treated with CBD and THC showed no habituation to a startle pulse, suggesting CBD increased vulnerability to the startle habituation-reducing effects of THC in mutant mice. CBD increased levels of GluA1, but reduced levels of GAD67 in the hippocampus of Nrg1 mutants. These results suggest adolescent CBD is not effective as a preventative of schizophrenia-relevant behavioral deficits in mutants and may actually contribute to pathological changes in the brain that increase sensitivity to THC in particular behavioral domains.

Cannabidiol impairs fear memory reconsolidation in female rats through dorsal hippocampus CB1 but not CB2 receptor interaction

Women present increased susceptibility to anxiety- and stress-related disorders compared to men. A potentially promising pharmacological-based strategy to regulate abnormal aversive memories disrupts their reconsolidation stage after reactivation and destabilization. Male rodent findings indicate that cannabidiol (CBD), a relatively safe and effective treatment for several mental health conditions, can impair the reconsolidation of aversive memories. However, whether and how CBD influences it in females is still unknown. The present study addressed this question in contextually fear-conditioned female rats. We report that systemically administered CBD impaired their reconsolidation, reducing freezing expression for over a week. This action was restricted to a time when the reconsolidation presumably lasted (< six hours post-retrieval) and depended on memory reactivation/destabilization. Moreover, the impairing effects of CBD on memory reconsolidation relied on the activation of cannabinoid type-1 but not type-2 receptors located in the CA1 subregion of the dorsal hippocampus. CBD applied directly to this brain area was sufficient to reproduce the effects of systemic CBD treatment. Contextual fear memories attenuated by CBD did not show reinstatement, an extinction-related feature. By demonstrating that destabilized fear memories are sensitive to CBD and how it hinders mechanisms in the DH CA1 that may restabilize them in female rats, the present findings concur that reconsolidation blockers are viable and could be effective in disrupting abnormally persistent and distressing aversive memories such as those related to posttraumatic stress disorder.

Sex Differences in the Neuropsychiatric Effects and Pharmacokinetics of Cannabidiol: A Scoping Review

Cannabidiol (CBD) is a non-intoxicating cannabinoid compound with diverse molecular targets and potential therapeutic effects, including effects relevant to the treatment of psychiatric disorders. In this scoping review, we sought to determine the extent to which sex and gender have been considered as potential moderators of the neuropsychiatric effects and pharmacokinetics of CBD. In this case, 300 articles were screened, retrieved from searches in PubMed/Medline, Scopus, Google Scholar, PsycInfo and CINAHL, though only 12 met our eligibility criteria: eight studies in preclinical models and four studies in humans. Among the preclinical studies, three suggested that sex may influence long-term effects of gestational or adolescent exposure to CBD; two found no impact of sex on CBD modulation of addiction-relevant effects of Δ⁹-tetrahydrocannabinol (THC); two found antidepressant-like effects of CBD in males only; and one found greater plasma and liver CBD concentrations in females compared to males. Among the human studies, two found no sex difference in CBD pharmacokinetics in patient samples, one found greater plasma CBD concentrations in healthy females compared to males, and one found no evidence of sex differences in the effects of CBD on responses to trauma recall in patients with post-traumatic stress disorder (PTSD). No studies were identified that considered the role of gender in CBD treatment effects. We discuss potential implications and current limitations of the existing literature.

Effect of long-term cannabidiol on learning and anxiety in a female Alzheimer’s disease mouse model

Cannabidiol is a promising potential therapeutic for neurodegenerative diseases, including Alzheimer’s disease (AD). Our laboratory has shown that oral CBD treatment prevents cognitive impairment in a male genetic mouse model of AD, the amyloid precursor protein 1 x presenilin 1 hemizygous (APPxPS1) mouse. However, as sex differences are evident in clinical populations and in AD mouse models, we tested the preventive potential of CBD therapy in female APPxPS1 mice. In this study, 2.5-month-old female wildtype-like (WT) and APPxPS1 mice were fed 20 mg/kg CBD or a vehicle via gel pellets daily for 8 months and tested at 10.5 months in behavioural paradigms relevant to cognition (fear conditioning, FC; cheeseboard, CB; and novel object recognition test, NORT) and anxiety-like behaviours (elevated plus maze, EPM). In the CB, CBD reduced latencies to find a food reward in APPxPS1 mice, compared to vehicle-treated APPxPS1 controls, and this treatment effect was not evident in WT mice. In addition, CBD also increased speed early in the acquisition of the CB task in APPxPS1 mice. In the EPM, CBD increased locomotion in APPxPS1 mice but not in WT mice, with no effects of CBD on anxiety-like behaviour. CBD had limited effects on the expression of fear memory. These results indicate preventive CBD treatment can have a moderate spatial learning-enhancing effect in a female amyloid-β-based AD mouse model. This suggests CBD may have some preventive therapeutic potential in female familial AD patients.

Long-Term Exposure to SSRI Citalopram Induces Neurotoxic Effects in Zebrafish

Residual antidepressants are of increasing concern worldwide, yet critical information on their long-term neurotoxic impacts on nontarget aquatic animals is lacking. Here, we investigated the long-term effects (from 0 to 150 days postfertilization) of the selective serotonin reuptake inhibitor citalopram (0.1-100 μg/L) on motor function, learning, and memory in zebrafish over two generations and explored the reversibility of the effect in F1 larvae. Unlike F0⁺ larvae, we found that F1⁺ larvae displayed decreased sensorimotor performance when continuously exposed to citalopram at 100 μg/L. No adverse effects were found in F1^- larvae after they were transferred to a clean medium. Whole-mount immunofluorescence assays suggested that the motor impairments were related to axonal projections of the spinal motor neurons (MNs). For F0⁺ adults, long-term citalopram exposure mainly caused male-specific declines in motor, learning, and memory performance. Analysis of serotonergic and cholinergic MNs revealed no significant changes in the male zebrafish spinal cord. In contrast, the number of glutamatergic spinal MNs decreased, likely associated with the impairment of motor function. Additionally, treatment with 100 μg/L citalopram significantly reduced the number of dopaminergic neurons, but no significant neuronal apoptosis was observed in the adult telencephalon. Overall, this study provides neurobehavioral evidence and novel insights into the neurotoxic mechanisms of long-term citalopram exposure and may facilitate the assessment of the environmental and health risks posed by citalopram-containing antidepressant drugs.

Neurogenic Interventions for Fear Memory via Modulation of the Hippocampal Function and Neural Circuits

Fear memory helps animals and humans avoid harm from certain stimuli and coordinate adaptive behavior. However, excessive consolidation of fear memory, caused by the dysfunction of cellular mechanisms and neural circuits in the brain, is responsible for post-traumatic stress disorder and anxiety-related disorders. Dysregulation of specific brain regions and neural circuits, particularly the hippocampus, amygdala, and medial prefrontal cortex, have been demonstrated in patients with these disorders. These regions are involved in learning, memory, consolidation, and extinction. These are also the brain regions where new neurons are generated and are crucial for memory formation and integration. Therefore, these three brain regions and neural circuits have contributed greatly to studies on neural plasticity and structural remodeling in patients with psychiatric disorders. In this review, we provide an understanding of fear memory and its underlying cellular mechanisms and describe how neural circuits are involved in fear memory. Additionally, we discuss therapeutic interventions for these disorders based on their proneurogenic efficacy and the neural circuits involved in fear memory.

Hallucinogenic drugs and their potential for treating fear-related disorders: Through the lens of fear extinction

Fear-related disorders, mainly phobias and post-traumatic stress disorder, are highly prevalent, debilitating disorders that pose a significant public health problem. They are characterized by aberrant processing of aversive experiences and dysregulated fear extinction, leading to excessive expression of fear and diminished quality of life. The gold standard for treating fear-related disorders is extinction-based exposure therapy (ET), shown to be ineffective for up to 35% of subjects. Moreover, ET combined with traditional pharmacological treatments for fear-related disorders, such as selective serotonin reuptake inhibitors, offers no further advantage to patients. This prompted the search for ways to improve ET outcomes, with current research focused on pharmacological agents that can augment ET by strengthening fear extinction learning. Hallucinogenic drugs promote reprocessing of fear-imbued memories and induce positive mood and openness, relieving anxiety and enabling the necessary emotional engagement during psychotherapeutic interventions. Mechanistically, hallucinogens induce dynamic structural and functional neuroplastic changes across the fear extinction circuitry and temper amygdala's hyperreactivity to threat-related stimuli, effectively mitigating one of the hallmarks of fear-related disorders. This paper provides the first comprehensive review of hallucinogens' potential to alleviate symptoms of fear-related disorders by focusing on their effects on fear extinction and the underlying molecular mechanisms. We overview both preclinical and clinical studies and emphasize the advantages of hallucinogenic drugs over current first-line treatments. We highlight 3,4-methylenedioxymethamphetamine and ketamine as the most effective therapeutics for fear-related disorders and discuss the potential molecular mechanisms responsible for their potency with implications for improving hallucinogen-assisted psychotherapy.

Long-term exposure to polypharmacy impairs cognitive functions in young adult female mice

The potential harmful effects of polypharmacy (concurrent use of 5 or more drugs) are difficult to investigate in an experimental design in humans. Moreover, there is a lack of knowledge on sex-specific differences on the outcomes of multiple-drug use. The present study aims to investigate the effects of an eight-week exposure to a regimen of five different medications (metoprolol, paracetamol, aspirin, simvastatin and citalopram) in young adult female mice. Polypharmacy-treated animals showed significant impairment in object recognition and fear associated contextual memory, together with a significant reduction of certain hippocampal proteins involved in pathways necessary for the consolidation of these types of memories, compared to animals with standard diet. The impairments in explorative behavior and spatial memory that we reported previously in young adult male mice administered the same polypharmacy regimen were not observed in females in the current study. Therefore, the same combination of medications induced different negative outcomes in young adult male and female mice, causing a significant deficit in non-spatial memory in female animals. Overall, this study strongly supports the importance of considering sex-specific differences in designing safer and targeted multiple-drug therapies.