Challenging the endocannabinoid system in sleep restricted healthy volunteers to modulate physiological arousal

The stress response is a biological cascade of events following real or perceived threat. This response typically requires concerted activation of the hypothalamic-pituitary-adrenal (HPA) axis (neuroendocrine response) triggering hormonal responses primarily via cortisol release, and autonomic nervous system (ANS) activation, causing rapid cardiovascular, respiratory and sweat gland changes. These shifts can provoke neurobehavioural changes to vigilance, stress, memory, reward salience and pain/threat sensitivity. These adaptive physiological, psychological and behavioural processes allow individuals to detect, interpret and react to perceived or actual threat. In the modern world, sleep loss is increasingly common, can be caused by stress, and can exaggerate the stress response in otherwise healthy individuals. Sleep loss, which has been operationalised via self-enforced sleep restriction paradigms, reliably increases physiological arousal, subjective fear of punishment, stress markers, cognitive biases and worry. The endocannabinoid system (ECS) is a key neuromodulatory network that regulates both stress responsivity and sleep. The cannabinoid type-1 receptor (CB1R) is highly expressed in brain regions involved in fear processing and autonomic regulation, including the amygdala (particularly the lateral and basal nuclei, prefrontal cortex and hypothalamus and exposure to chronic stress reliably causes a downregulation of CB1Rs. The ECS is also involved in the modulation of HPA axis activity, contributing to the manifestation and termination of the stress response. The use of stress paradigms has consistently shown that stress induces bidirectional alterations in two primary ECS molecules, anandamide (AEA) and 2-arachidonoyl glycerol (2-AG), where a decline in AEA facilitates expression of the stress response through activation of the HPA axis and an increase in 2-AG signalling supports adaptation and termination. The modulation of the endocannabinoid system via exogenous cannabinoids presents an effective way of studying physiological stress responses related to sleep loss and associated neuro-cognitive changes. The present study aims to examine the pharmacological modulation of the ECS system via the administration of exogenous cannabinoids (tetrahydrocannabinol (THC), cannabidiol (CBD), or combined THC+CBD) in a single-dose, between-subjects design. THC is the primary psychoactive component of the cannabis plant and is a partial agonist at the cannabinoid type-1 receptor (CB1R), modulating neural circuits involved in stress response and fear extinction via activation of the CB1R. Animal literature suggests that potential fear extinction action of THC occurs at lower doses, where higher doses of THC (>5-10mg in humans) can have anxiogenic and psychotomimetic effects, although results from the human literature are mixed and studies involving the administration of isolated, low-dose THC are lacking. A dose of 2.5mg THC has been chosen in this study to never produce an anxiogenic response, avoid potential adverse reactions whilst still engaging CB1R mediated relevant processes. CBD has minimal psychoactive effect and limited activity at CB1Rs, but at high doses is a negative allosteric modulator of the CB1R and boosts AEA levels via the inhibition of fatty acid amide hydrolase (FAAH), the enzyme responsible for its breakdown. CBD also acts on non-ECS targets such as the serotonin 1A receptor (5HT1AR) and the transient receptor potential vanilloid 1(TRPV1), contributing to stress modulation. Studies employing lab-based stress-promoting experimental procedures suggest CBD may significantly attenuate stress in a bell-shaped dose response manner where moderate (e.g. 300mg) doses are most effective and higher doses are not, thus a 300mg dose of CBD has been chosen for this study. In real-world cannabis use, THC and CBD are often co-administered. Preclinical and human experiments have suggested that CBD may attenuate adverse reactions following THC administration, but findings are inconsistent and further research is required to clarify the interaction between THC and CBD, thus a combined arm of CBD+THC (300mg/2.5mg) is included in this study. Given what is known about the effects of sleep loss on acute physiological and psychological states, researchers have previously used acute sleep restriction or sleep deprivation paradigms to study the next day effects of a poor night’s sleep. To better understand the causal role of sleep disturbance on increased psychological (subjective mood states and cognitive performance) and physiological stress response (blood pressure, heart rate), disrupting the causal variable (sleep) in a healthy sample currently experiencing stress is a valid way to test these effects. This pharmacological challenge will allow for the investigation the ECS systems role in physiological fear response under conditions of heightened stress under sleep restriction. The present study will recruit healthy participants who have undergone sleep restriction and are currently experiencing self-reported higher than average anxiety (measured by a score of ≥10 on the GAD-7). This will allow us to reliably and ethically model heightened stress in a non-clinical sample by amplifying the signal of interest, whilst capturing meaningful changes in fear and stress responsivity caused by the pharmacological challenge. Participants will undergo a sleep restriction paradigm as an effective and ecologically valid laboratory model of sleep disturbance. The sleep restriction paradigm used here has been piloted as part of the ‘NO-SLEEP: Sleep Limitation Experimental Pilot’ (KCL Ethics Ref: HR/RGO-24/25-47697). This study will use the same sleep restriction procedure and lab-based outcome measures as NO-SLEEP, introducing a new cannabinoid challenge. Participants will complete online pre-screening procedures and three study visits: an initial online visit to familiarise them with the sleep restriction paradigm, one night of self-enforced sleep restriction at home and one experimental session the following day. At the experimental session, participants will be administered either THC (2.5mg), CBD (300mg), CBD+THC (300mg/2.5mg) or matching placebo oil. Each participant will only receive a single dose of cannabinoid oil. Group allocation will be randomised and double-blinded. Once intoxicated (after 30 mins), participants will complete a series of tasks exploring specific fear and stress related phenomena and associated physiological changes: galvanic skin response (GSR) and heart rate during a Threat of Shock (ToS) paradigm, blood pressure and heart rate during a test of public speaking , and a game based aversive learning task. Measures of cognitive function ((digit span, N-back and verbal fluency) and relevant subjective states (e.g. paranoia, somatic drug effects, sleepiness, anxiety, feel drug effect, like drug effect) will be collected. Repeated blood samples will be obtained prior to drug administration, and at 45-, 90- and 180-minutes post dose to allow for repeated plasma analysis of exogenous cannabinoids and stress hormones. Participants will also be asked which drug group they think they were randomised to. Finally, we will demonstrate that it is feasible to administer single doses of THC and CBD to healthy participants undergoing sleep restriction.