Blunting of the HPA-axis underlies the lack of preventive efficacy of early post-stressor single-dose Delta-9-tetrahydrocannabinol (THC)
Introduction
Delta-9-tetrahydrocannabinol (Δ9-THC) the major psychoactive component in marijuana (Cannabis sativa) (Adams and Martin, 1996) is a ligand for the pre-synaptically located Gi/o protein-coupled cannabinoid receptors CB1 and CB2. These receptors activate G alpha i/o proteins, resulting in the inhibition of adenylyl cyclase activity and of calcium channel activation by depolarization (Felder and Glass, 1998, Piomelli, 2003, Gorzalka et al., 2008). The CB1 cannabinoid receptor is the predominant central one, exhibiting widespread distribution in the brain (Herkenham et al., 1991) and at lower expression levels in peripheral tissue such as blood vessels, immune cells and reproductive tissues (Iverson, 2003, Gorzalka et al., 2008). The CB1 receptors are densely expressed in the hippocampus, amygdala and prefrontal cortex — brain regions involved in the regulation of memory formation and emotional response — suggesting that the endocannabinoid system may be involved in regulating learning and memory. The CB1 receptor is present at high densities at presynaptic axon terminals, where it functions to inhibit neurotransmitter release (Schlicker and Kathmann, 2001, Vaughan and Christie, 2005, Gorzalka et al., 2008) and is expressed by sub-populations of glutamate, gamma-aminobutyric acid (GABA), acetylcholine, serotonin and noradrenergic neurons (Schlicker and Kathmann, 2001), indicating that cannabinoids possess the ability to suppress the release of many neurotransmitters and neuromodulators (Gorzalka et al., 2008).
Endocannabinoid signaling can affect complex pharmacological and behavioral processes, including locomotion, feeding, anxiety, reward and nociception (Zanettini et al., 2011) that probably involve numerous neuronal substrates (Chaperon and Thiebot, 1999). The effects of cannabinoids on anxiety disorders and symptoms have been reported quite extensively for both animal and clinical studies. Their role in the modulation of anxious states is still a matter of controversy and a number contradictory reports exist. For example, in animal studies both cannabinoid agonists and antagonists have been shown to exert anxiolytic-like effects in some studies, but anxiogenic-like effects in others (Haller et al., 2004a, Haller et al., 2004b, Moreira et al., 2006, Degroot, 2008, Moreira et al., 2009, Carvalho et al., 2010, Carvalho and Van Bockstaele, 2012). Moreover, high and low doses of cannabinoid agonists have also often shown opposite effects, with low doses inducing anxiolytic effects, while high doses induce anxiogenic effects (Moreira and Wotjak, 2011), whereas both effects can be inhibited by CB1 antagonists (Haller et al., 2007). In human studies, dual effects have also been reported (Onaivi et al., 1990, Kogan and Mechoulam, 2007, Kinsey et al., 2011). One possible explanation lies in the fact that CB1 receptors are expressed at both glutamatergic and GABAergic synapses, and these neurotransmitter systems often have opposite effects on emotions, especially on anxiety. Due to the expression of CB1 receptors at axon terminals of both subpopulations, it is tempting to predict the relevance of the localization of this receptor as an explanation for the dual role of the endocannabinoid system in the regulation of anxiety. The diversity of cannabinoid roles and the complexity of task-dependent activation of neuronal circuits may lead to the effects of endocannabinoid system modulation being strongly dependent on environmental conditions (Zanettini et al., 2011). Moreover, discrepant findings could also be due to differences in the expression, distribution and functional characteristics of these receptors.
Ample evidence indicates that endocannabinoid signaling participates in the consolidation of memory traces and cannabinoid treatment affects memory encoding and consolidation processes (Marsicano et al., 2002, Castellano et al., 2003, Lutz, 2007). Behavioral studies have reported that activation of CB1 receptors impairs memory acquisition (Pamplona and Takahashi, 2006), facilitates the extinction of contextual fear memory (Pamplona et al., 2006), disturbs the consolidation of fear memory in contextual fear conditioning (Mackowiak et al., 2009) and disrupts long-term consolidation of hippocampal spatial memory (Yim et al., 2008). Blockade of CB1 receptors does not affect consolidation of contextual memory (Arenos et al., 2006); instead, it disrupts memory consolidation in step-down inhibitory avoidance (De Oliveira et al., 2005, De Oliveira et al., 2008).
Since the main feature of the use of cannabis is that it produces relaxation, euphoria and amnesic effects, which can be accompanied by decreased anxiety-like behaviors, the present study sought to determine whether administration of a single dose of Δ9-THC, a CB1 receptor agonist given after immediate exposure to psychogenic stress affected short- and longer-term behavioral responses. We therefore hypothesized that Δ9-THC interfering with memory consolidation processes immediately after a traumatic experience would reduce posttraumatic stress symptoms and incidence.
In this study, the effects of early post-exposure administration of Δ9-THC on behavioral responses to predator scent stress (PSS) were evaluated in an animal model of PTSD. The basic model involved brief (10 min) inescapable exposure of rats to the scent of predator urine — an intangible “psychological” threat — and subsequent behavioral response-testing in the elevated plus-maze (EPM) and acoustic startle response (ASR) seven days post exposure. In this model, populations of exposed rodents are classified according to the degree of their individual behavioral responses using standardized “cut-off behavioral criteria” (CBC), creating three distinct groups: “extreme behavioral response” (EBR) and “minimal behavioral response” (MBR) at the extremes, with a group of “partial responders” (PBR) in between (Cohen et al., 2003b, Cohen and Zohar, 2004b, Cohen et al., 2004, Cohen et al., 2005, Cohen et al., 2012). The relative prevalence rates of individuals displaying the different degrees of disrupted behavior provided an indication of the potential efficacy of the “treatment” under study.
The first aim of the study examines the effect of Δ9-THC administered intraperitoneally 1 h following exposure to PSS. For this purpose the study was designed to distinguish between the short-term anxiolytic and the longer-term preventive potential of brief immediate post-exposure treatment effects in terms of behavior in the EPM and ASR tests at 1, 6 and 24 h and at seven days, respectively. The effects on memory were assessed by the response to the neutral reminder of the trauma (the trauma cue) on day 8. Corticosterone levels were employed as a physiological marker of stress and of the effects of Δ9-THC on the stress response. In light of the interim finding of lack of preventive efficacy of early Δ9-THC treatment, the study was extended to include a CB1 antagonist/inverse agonist treatment arm (AM251) and an assessment of circulating corticosterone levels during treatment, to determine whether the cannabinoid system modulates the behavioral and HPA-axis responses to PSS.
Section snippets
Ethical approval
All procedures were carried out under strict compliance with ethical principles and guidelines of the NIH Guide for the Care and Use of Laboratory Animals. All efforts were made to minimize pain, stress and the number of animals used. Protocols were approved by the University's Committee for Care and Use of Animals in Research, in accordance with NIH guidelines.
Animals
305 adult male Sprague–Dawley rats weighing 150–200 g were employed. The animals were housed four per cage and were habituated to the
Statistical analyses
Behavioral data were analyzed using a two-way ANOVA. Where significant group effects were detected, a Bonferroni test assessed significant post-hoc differences between individual groups. The prevalence of the affected rats as a function of the rat group was tested using cross-tabulation and nonparametric Fisher's exact tests.
The behavioral effects of Δ9-THC 1 h after PSS exposure
As shown in Fig. 3A–D, the two-way ANOVA revealed a significant effect of PSS exposure in terms of time spent in open arms [F(1,87) = 43.0, p < 0.0001], number of entries to open arms (F(1,87) = 91.35, p < 0.0001), and anxiety index [F(1,87) = 96.9, p < 0.0001]. No effects were observed for treatment or the exposure–treatment interaction. A post-hoc Bonferroni test confirmed that PSS exposure with vehicle or Δ9-THC elicited a significant decrease in overall time spent in open arms, open arm entries and a
Discussion
This study sought to compare the efficacy of early post stress-exposure interventions with Δ9-THC in an animal model of PTSD. The intervention was effective only during the very first hours, whereas, beyond that, i.e., at 24 h to 7 days, it showed no effect in attenuating PTSD-like behavioral stress responses on EPM and ASR paradigms or in altering the prevalence of extreme response patterns compared to exposed-vehicle-treated animals. The observed blunting of the HPA-axis response during the
Conclusions
In this study, a brief course of immediate post-exposure Δ9-THC was demonstrated to possess significant anxiolytic properties only in the short-term with no longer-term effects in a prospective animal model of PTSD. The observed blunting of the HPA-axis response during the first hours after exposure caused by Δ9-THC intervention is very likely a key factor in determining its unfavorable longer-term outcome. In contrast, activation of the HPA-axis response during the first hours after exposure
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2021, NeuropharmacologyCitation Excerpt :Acute THC may differentially modulate rodent anxiety-like behaviours depending on animal strain, age during drug administration, and even behavioural test used (Kasten et al., 2017). Interestingly, administration of high THC doses shortly (1h) following stress exposure promotes anxiolytic effects (alongside blunting of the HPA-response) in the short-term period of several hours, but no longer has an effect 24 h later (Mayer et al., 2014). Thus, the timing of administration following stress-exposure may strongly influence the impact of THC on anxiety-like behavior.
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2021, International Review of NeurobiologyCitation Excerpt :CB1R agonists, like THC, have been shown to dose-dependently activate or inhibit HPA axis activity at high or low doses, respectively. At high doses, exogenous cannabinoids can augment stress-induced corticosterone levels (Jacobs, Dellarca, Manfredi, & Harclerode, 1979; Patel et al., 2004; Sano et al., 2009), while at lower doses they inhibit HPA axis activity (Ganon-Elazar & Akirav, 2012; Mayer, Matar, Kaplan, Zohar, & Cohen, 2014; Patel et al., 2004). Early rodent studies also demonstrated that THC elevates ACTH and corticosterone levels (Johnson, Dewy, Ritter, & Beckner, 1978; Pertwee, 1974; Puder et al., 1982; Weidenfeld, Feldman, & Mechoulam, 1994).
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2020, Pharmacology and TherapeuticsCitation Excerpt :Here we focus on the existing data on ECB/HPA interaction in the context of PTSD (see Table 4). Several studies in rodents demonstrated that cannabinoids normalize alteration in the HPA axis induced by severe or traumatic stress (Ganon-Elazar & Akirav, 2012, 2013; Mayer et al., 2014; Shoshan & Akirav, 2017). Ganon-Elazar and Akirav (2012) found that rats exposed to SPS model for PTSD demonstrated reduced levels of corticosterone in response to a dexamethasone test suggesting enhanced negative feedback on the HPA axis; the CB1/2 agonist WIN55,212–2 (0.5 mg/kg) administered 2 h or 24 h after exposure to SPS normalized this effect.
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2019, Pharmacology Biochemistry and BehaviorCitation Excerpt :For example, the bed nucleus of the stria terminalis appears to be a target wherein the anxiolytic effects of CBD may produce its effects, with 5-HT1a receptors being implicated in this process (Gomes et al., 2011). The efficacy of THC as an early post stress-exposure therapeutic intervention was investigated in an animal model of posttraumatic stress disorder (PTSD) (Mayer et al., 2014). When THC is administered 1 h post predator scent stress (PSS) it is only effective in attenuating short term PTSD-like behavioral stress responses, whereas 24 h to 7 days later there was no persistent attenuation of these stress responses.
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2016, Pharmacological ResearchCitation Excerpt :However, contrasting findings were reported in a recent study that examined the effects of systemic injections of the CB1/CB2 agonist THC, the principal active constituent of cannabis plant, and the CB1 antagonist AM251 [97]. In particular, when THC was given to rats immediately after exposure to predator scent stress, it was able to reduce anxiety measured in the acoustic startle and elevated plus maze tests only in the short-term, with no effects on the long-term neither on anxiety nor on contextual freezing [97]. Conversely, the CB1 antagonist AM251 reduced both anxiety levels and contextual freezing in the long-term showing PTSD-preventing properties [97].