Sex-specific effects of CB1 receptor antagonism and stress in adolescence on anxiety, corticosterone concentrations, and contextual fear in adulthood in rats

Leitl K, Megan Gray J, N Petrie G, J.Tellez-Monnery K, N.Hill M. Sex and stressor modality influence acute stress-induced dynamic changes in corticolimbic endocannabinoid levels in adult Sprague Dawley rats

Research over the past few decades has established a role for the endocannabinoid system in contributing to the neural and endocrine responses to stress exposure. The two endocannabinoid ligands, anandamide (AEA) and 2-arachidonoyl glycerol (2-AG), both play roles in regulating the stress response and both exhibit dynamic changes in response to stress exposure. Most of this previous research, however, was conducted in male rodents. Given that, especially in rodents, the stress response is influenced by sex, an understanding of how these dynamic responses of endocannabinoids in response to stress is influenced by sex could provide insight into sex differences of the acute stress response. We exposed adult, Sprague Dawley rats to different commonly utilized acute stress modalities, specifically restraint, swim and foot shock stress. Thirty minutes following stress onset, we excised the amygdala, hippocampus and medial prefrontal cortex, corticolimbic brain regions involved in the stress response, to measure endocannabinoid levels. When AEA levels were altered in response to restraint and swim stress, they were reduced, whereas exposure to foot shock stress led to an increase in the amygdala. 2-AG levels, when they were altered by stress exposure were only increased, specifically in males in the amygdala following swim stress, and in the hippocampus and medial prefrontal cortex overall following foot shock stress. This increase in 2-AG levels following stress only in males was the only sex difference found in stress-induced changes in endocannabinoid levels. There were no consistent sex differences observed. Collectively, these data contribute to our further understanding of the interactions between stress and endocannabinoid function.

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Stressor modality influences acute stress-induced changes in endocannabinoid levels in corticolimbic brain regions.

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There are minimal sex differences with regards to basal levels or stress-induced changes in endocannabinoid levels.

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AEA decreased from acute restraint and swim stresses but increased from acute foot shock stress.

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2-AG levels only showed increases when they were impacted by the different stress modalities.

Endocannabinoid system contributions to sex-specific adolescent neurodevelopment

With an increasing number of countries and states adopting legislation permitting the use of cannabis for medical purposes, there is a growing interest among health and research professionals into the system through which cannabinoids principally act, the endocannabinoid system (ECS). Much of the seminal research into the ECS dates back only 30 years and, although there has been tremendous development within the field during this time, many questions remain. More recently, investigations have emerged examining the contributions of the ECS to normative development and the effect of altering this system during important critical periods. One such period is adolescence, a unique period during which brain and behaviours are maturing and reorganizing in preparation for adulthood, including shifts in endocannabinoid biology. The purpose of this review is to discuss findings to date regarding the maturation of the ECS during adolescence and the consequences of manipulations of the ECS during this period to normative neurodevelopmental processes, as well as highlight sex differences in ECS function, important technical considerations, and future directions. Because most of what we know is derived from preclinical studies on rodents, we provide relevant background of this model and some commentary on the translational relevance of the research in this area.

Sexually Dimorphic Expression of Fear-conditioned Analgesia in Rats and Associated Alterations in the Endocannabinoid System in the Periaqueductal Grey

The endocannabinoid system within the periaqueductal grey (PAG) has been implicated in fear-conditioned analgesia (FCA), the profound suppression of pain upon re-exposure to a context previously paired with an aversive stimulus. Since the endocannabinoid and nociceptive systems exhibit sexual dimorphism, the aim of the present study was to assess possible sex differences in the expression of FCA, fear in the presence of nociceptive tone, and associated sex-dependent alterations in the endocannabinoid system within the PAG. Male and female Sprague-Dawley rats received footshock (10 × 1s; 0.4 mA; every 60 s) or no-footshock in a conditioning arena and 23.5 h later received intraplantar injection of formalin (2.5%) under brief isoflourane anaesthetic into the right hind paw. Nociceptive and fear-related behaviours were assessed 30 min later. Levels of endocannabinoids, N-acylethanolamines and neurotransmitters in the PAG were assessed by LC-MS/MS and expression of endocannabinoid system-related proteins by Western immunoblotting. Male, but not female, rats exhibited robust FCA and greater expression of fear-related behaviours than females. Fear-conditioned formalin-treated males, but not females, had higher levels of N-oleoylethanolamine (OEA) and γ-aminobutyric acid (GABA) in the PAG, compared with non-fear-conditioned controls. There was no effect of fear conditioning on the levels of FAAH or CB₁ receptor expression (CB1R) in the PAG of male or female formalin-treated rats. Non-fear-conditioned females had higher levels of CB1R and PPARγ expression than non-fear-conditioned male counterparts. In summary, our results provide evidence of sexual dimorphism in the expression of FCA and fear-related behaviours, and associated alterations in components of the endocannabinoid system and GABA within the PAG.

Methods and Challenges in Investigating Sex-Specific Consequences of Social Stressors in Adolescence in Rats: Is It the Stress or the Social or the Stage of Development?

Adolescence is a time of social learning and social restructuring that is accompanied by changes in both the hypothalamic-pituitary-gonadal axis and the hypothalamic-pituitary-adrenal (HPA) axis. The activation of these axes by puberty and stressors, respectively, shapes adolescent development. Models of social stress in rats are used to understand the consequences of perturbations of the social environment for ongoing brain development. This paper reviews the challenges in investigating the sex-specific consequences of social stressors, sex differences in the models of social stress used in rats and the sex-specific effects on behaviour and provides an overview of sex differences in HPA responding to stressors, the variability in pubertal development and in strains of rats that require consideration in conducting such research, and directions for future research.

Early Consumption of Cannabinoids: From Adult Neurogenesis to Behavior

The endocannabinoid system (ECS) is a crucial modulatory system in which interest has been increasing, particularly regarding the regulation of behavior and neuroplasticity. The adolescent-young adulthood phase of development comprises a critical period in the maturation of the nervous system and the ECS. Neurogenesis occurs in discrete regions of the adult brain, and this process is linked to the modulation of some behaviors. Since marijuana (cannabis) is the most consumed illegal drug globally and the highest consumption rate is observed during adolescence, it is of particular importance to understand the effects of ECS modulation in these early stages of adulthood. Thus, in this article, we sought to summarize recent evidence demonstrating the role of the ECS and exogenous cannabinoid consumption in the adolescent-young adulthood period; elucidate the effects of exogenous cannabinoid consumption on adult neurogenesis; and describe some essential and adaptive behaviors, such as stress, anxiety, learning, and memory. The data summarized in this work highlight the relevance of maintaining balance in the endocannabinoid modulatory system in the early and adult stages of life. Any ECS disturbance may induce significant modifications in the genesis of new neurons and may consequently modify behavioral outcomes.

Increasing Endocannabinoid Tone Alters Anxiety-Like and Stress Coping Behaviour in Female Rats Prenatally Exposed to Valproic Acid

Given the sex differences evident in the prevalence of autism, there is an increased awareness of the importance of including females in autism research to determine sexual dimorphism and sex-specific treatments. Cannabinoids and endocannabinoid modulators have been proposed as potential novel treatments for autism-related symptoms; however, few studies to date have examined if these pharmacological agents elicit sex-specific effects. The aim of the present study was to use the valproic acid (VPA) model of autism to compare the behavioural responses of male and female rats and examine the effects of increasing endocannabinoid tone on the behavioural responses of VPA-exposed female rats. These data revealed that VPA-exposed male, but not female, rats exhibit reduced social responding in the three-chamber and olfactory habituation/dishabituation (OHD) test during adolescence. In comparison, VPA-exposed female, but not male, adolescent rats exhibited anxiety-like behaviour in the elevated plus maze (EPM) and open field test (OFT). In VPA-exposed female rats, increasing 2-AG levels augmented anxiety-like behaviour in the EPM and OFT, while increasing AEA levels reduced stress coping behaviour in the swim stress test. These data highlight sexual dimorphic behaviours in the VPA model and indicate that enhancing endocannabinoid levels may exacerbate negative affective behaviour in VPA-exposed females. Thus, considerations should be paid to the possible sex-specific effects of cannabinoids for the treatment of symptoms associated with autism.

Transgenerational effects on anxiety-like behavior following adolescent morphine exposure in female rats

Global opioid use and misuse remains high, despite efforts to decrease rates of prescribing and diversion. Chronic exposure to opioids, particularly during critical periods of development, can lead to long-lasting effects, including effects that may extend to future generations. Using a rodent model, we have demonstrated significant transgenerational effects of female adolescent morphine exposure, despite the absence of in utero drug exposure. While these effects have been observed in both sexes, effects on anxiety-like behavior were only observed in F1 females. The current study was designed to examine both inter- and transgenerational effects of adolescent morphine exposure on anxiety-like behavior. Female Sprague Dawley rats were administered increasing doses of morphine (5-25 mg/kg s.c.) or saline for 10 days during adolescence (PND30-39). Adult diestrous female offspring (MORF1 or SALF1) and grand offspring (F2) were tested for anxiety-like behavior using the elevated plus maze (EPM). F1 females cross-fostered to donor mothers were also examined. The results show that MORF1 and MORF2 females spend significantly more time on the open arms of the EPM compared to SALF1 controls, an effect that persisted in cross-fostered females. Additional studies demonstrate that this effect is estrous cycle dependent, as decreased anxiety-like behavior was observed in diestrus, while increased anxiety-like behavior was observed in estrus. These behavioral effects were not associated with any differences in circulating corticosterone either at baseline or following EPM testing. Thus, female adolescent morphine exposure alters the regulation of anxiety-like behavior in an estrous-dependent manner and this effect persists in the F2 generation.

Effects of cannabis exposure in the prenatal and adolescent periods: Preclinical and clinical studies in both sexes

Cannabis is the most commonly used illicit drug among adolescents and young adults, including pregnant women. There is substantial evidence for a significant association between prenatal cannabis exposure and lower birth weight in offspring, and mixed results regarding later behavioural outcomes in the offspring. Adolescent cannabis use, especially heavy use, has been associated with altered executive function, depression, psychosis and use of other drugs later in life. Human studies have limitations due to several confounding factors and have provided scarce information about sex differences. In general, animal studies support behavioural alterations reported in humans and have revealed diverse sex differences and potential underlying mechanisms (altered mesolimbic dopaminergic and hippocampal glutamatergic systems and interference with prefrontal cortex maturation). More studies are needed that analyse sex and gender influences on cannabis-induced effects with great clinical relevance such as psychosis, cannabis use disorder and associated comorbidities, to achieve more personalized and accurate treatments.

Endocannabinoid System Components as Potential Biomarkers in Psychiatry

The high heterogeneity of psychiatric disorders leads to a lack of diagnostic precision. Therefore, the search of biomarkers is a fundamental aspect in psychiatry to reach a more personalized medicine. The endocannabinoid system (ECS) has gained increasing interest due to its involvement in many different functional processes in the brain, including the regulation of emotions, motivation, and cognition. This article reviews the role of the main components of the ECS as biomarkers in certain psychiatric disorders. Studies carried out in rodents evaluating the effects of pharmacological and genetic manipulation of cannabinoid receptors or endocannabinoids (eCBs) degrading enzymes were included. Likewise, the ECS-related alterations occurring at the molecular level in animal models reproducing some behavioral and/or neuropathological aspects of psychiatric disorders were reviewed. Furthermore, clinical studies evaluating gene or protein alterations in post-mortem brain tissue or in vivo blood, plasma, and cerebrospinal fluid (CSF) samples were analyzed. Also, the results from neuroimaging studies using positron emission tomography (PET) or functional magnetic resonance (fMRI) were included. This review shows the close involvement of cannabinoid receptor 1 (CB1r) in stress regulation and the development of mood disorders [anxiety, depression, bipolar disorder (BD)], in post-traumatic stress disorder (PTSD), as well as in the etiopathogenesis of schizophrenia, attention deficit hyperactivity disorder (ADHD), or eating disorders (i.e. anorexia and bulimia nervosa). On the other hand, recent results reveal the potential therapeutic action of the endocannabinoid tone manipulation by inhibition of eCBs degrading enzymes, as well as by the modulation of cannabinoid receptor 2 (CB2r) activity on anxiolytic, antidepressive, or antipsychotic associated effects. Further clinical research studies are needed; however, current evidence suggests that the components of the ECS may become promising biomarkers in psychiatry to improve, at least in part, the diagnosis and pharmacological treatment of psychiatric disorders.

Anxiety-like features and spatial memory problems as a consequence of hippocampal SV2A expression

The Synaptic Vesicle Protein 2A (SV2A) is a transmembrane protein whose presence is reduced both in animal models and in patients with chronic epilepsy. Besides its implication in the epileptic process, the behavioural consequences of the changes in its expression remain unclear. The purpose of our research is to better understand the possible role(s) of this protein through the phenotype of cKO (Grik4 Cre+/-, SV2A lox/lox) mice, male and female, which present a specific decrease of SV2A expression levels in the hippocampal glutamatergic neurons but without any epileptic seizures. In this study, we compare the cKO mice with cHZ (Grik4 Cre+/-, SV2A lox/+) and WT (Grik4 Cre+/+, SV2A lox/lox) mice through a battery of tests, used to evaluate different features: the anxiety-related features (Elevated Plus Maze), the locomotor activity (Activity Chambers), the contextual fear-related memory (Contextual Fear Conditioning), and the spatial memory (Barnes Maze). Our results showed statistically significant differences in the habituation to a new environment, an increase in the anxiety levels and spatial memory deficit in the cHZ and cKO groups, compared to the WT group. No statistically significant differences due to the genotype appeared in the spontaneous locomotor activity or the fear-linked memory. However, sexual differences were observed in this last feature. These results highlight not only an important role of the SV2A protein in the cognitive and anxiety problems typically encountered in epileptic patients, but also a possible role in the symptomatology of other neurodegenerative diseases, such as the Alzheimer’s disease.