Draft:Effects of drugs on the sleep cycle in humans
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Introduction
[edit]Brain waves (alpha, beta, theta, delta) are manifestations of brain activity during the different sleep-wake stages, and can be observed using an electroencephalography (EEG). During sleep, humans pass through 5 stages. First, stage 1 (N1), falling asleep, is mainly characterised by alpha waves. Stage 2 (N2), light sleep, is characterised by theta waves. Stages 3 and 4 (N3 and 4), deep sleep, are essentially defined by the emission of delta waves and are accompanied by low neuronal activity, muscle tone and slowing of vital signs. In addition, deep sleep has a restorative function for the body and plays an essential role in cognitive function. Partial or chronic sleep deprivation leads to a poor circadian cycle and increases the risk of Alzheimer's disease, . Finally, during stage 5 (N5), REM sleep, which is dedicated to intense dreaming, the brain emits waves similar to those in the waking state, i.e. beta waves. This final stage of sleep is characterised by rapid eye movement (REM), loss of muscle tone and improved memory and learning. Other phases are not characterised by REM (NREM) and do not involve temperature regulation. These stages are repeated several times during the night.
Sleep regulation involves three processes to function properly: the circadian cycle, the ultradian cycle and homeostasis. Sleep is achieved by stimulating the hypothalamus with a “sleep hormone”: melatonin. This is because the retina sends a message to the hypothalamus in the posterior lobe of the brain when it is dark. The hypothalamus relays the message to the pineal gland, which secretes melatonin, telling the brain to go into standby mode and begin sleep, .
Sleep regulation is therefore an essential part of the human circadian (24-hour) and homeostatic cycle, allowing the brain to manage information and eliminate waste accumulated during the day.
Alcohol
[edit]Alcohol is a psychoactive substance that is widely consumed around the world. According to the World Health Organization, 2.3 billion people aged 15 and over consumed alcohol in 2016. Average per capita consumption has remained relatively stable since 2010, and Europe has the highest per capita alcohol consumption in the world. It is also the most consumed substance in Quebec and Canada: in 2017-2018, a study showed that 76% of Canadians and 81% of Quebecers aged 12 and over had consumed alcohol at least once in the previous 12 months. The majority of Quebecers consume alcohol because of its effects on the body.
Before being metabolised by the liver, alcohol first diffuses into the blood and travels throughout the bloodstream, rapidly affecting many organs, including the brain. The effects of the presence of ethanol in the blood generally result in a depressant effect, acting at several levels on different regulatory centres and neurotransmitters. The suprachiasmatic nucleus of the hypothalamus is central to the regulation of the endogenous clock, so it is obvious that its affection causes clock desynchronisations.[1]
Overall, the effects of alcohol consumption are reflected in an increase in the NREM phase (N1 and N2) and an increase in the REM phase. As the blood alcohol level gradually decreases, there is an increase in REM sleep, leading to an increase in wakefulness and a decrease in sleep efficiency[2]. These effects, similar to a phase shift or a change in sleep pattern, can manifest themselves in the waking phase and the following day through a lack of sleep and fragmented sleep. This usually leads to poor memory consolidation.
From a hormonal point of view, the presence of alcohol in the blood during sleep would eventually inhibit many pituitary hormones such as growth hormone GH and melatonin. Additionally, it would result in a rise in cortisol secretion[1]. Disorders like depression can result from alterations in these hormones secretion[2]. There is a positive correlation between drinking habits and the effects of alcohol consumption on sleep quality.
In addition, alcohol consumption worsens sleep disorders such as insomnia and sleep apnoea. Alcohol also has the effect of reducing oxygen saturation in the blood, leading to, among other things, poor oxygenation of the brain[1], . Relaxation of the respiratory muscles can lead to longer pauses in breathing in people with obstructive sleep apnoea.
In short, alcohol consumption has many effects on sleep, which generally leads to an increase in morbidity, which reduces life expectancy.
Cannabis
[edit]Cannabis is often used recreationally, but it can also be used therapeutically : it helps to reduce pain, anxiety, nausea, increase appetite, etc. The main psychoactive compound is THC, , , [3]. Cannabinoid compounds can be exogenous or endogenous. Endogenous cannabinoids play a role in the regulation of energy and nutrition[3], , . There are two types of receptors that cannabinoids can bind to: type 1 receptors (CB1), mainly in the central nervous system, and type 2 receptors (CB2), mainly in the peripheral nervous system. The effects of this substance are felt when THC binds to these receptors.
Repeated use of cannabis can lead to tolerance to the drug, requiring an increasing dose to achieve the same effect. Withdrawal also occurs, creating a sense of deprivation that contributes to the development of dependence on the substance. This is due to a change in the neurotransmitter systems in the central nervous system, which are also involved in the sleep cycle, . There is therefore a frequent association between cannabis use and sleep disorders. Dopamine is a neurotransmitter that is essential for the homeostasis of brain function. It plays a role in the regulation of melatonin and serotonin secretion by the pineal gland and thus in the control of the sleep-wake cycle, although there are conflicting results on the exact mechanisms in the presence of THC.
The majority of people who use cannabis report an earlier onset of sleep. However, polysomnographic studies show no change in this aspect, or only at high doses, with a longer time to fall asleep, . There would therefore be a form of altered perception, similar to that observed in alcohol-dependent people in relation to insomnia.
However, research has indicated that cannabinoids are beneficial for sleep. For example, a study on a rat model of nocturnal apnoea measured the effect of endogenous (oleamide) and exogenous (∆9THC) cannabinoids on the regulation of respiratory stability during sleep. The frequency of sleep apnoea is reduced in the presence of these two substances, and this during all stages of sleep. Despite the lack of direct characterisation of the molecular mechanisms involved, the authors suggest that cannabinoids should be considered in the treatment of sleep-related respiratory disorders in humans.
Notes and references
[edit]- ^ a b c Colrain IM; Nicholas CL; Baker FC (2014). "Alcohol and the sleeping brain". Alcohol and the Nervous System. Handbook of Clinical Neurology. Vol. 125. pp. 415–431. doi:10.1016/B978-0-444-62619-6.00024-0. ISBN 978-0-444-62619-6. PMC 5821259. PMID 25307588.
{{cite book}}:|journal=ignored (help). - ^ a b "Alcohol and Health Alcohol and Sleep" (PDF). Alberta Health Services. 2014..
- ^ a b U. Pagotto; G. Marsicano; D. Cota (2006). "The emerging role of the endocannabinoid system in endocrine regulation and energy balance". Endocr Rev. 27 (1): 73–100. doi:10.1210/er.2005-0009. PMID 16306385..