What are cannabinoid receptors?
Throughout the world, cannabis has been used recreationally and medicinally for thousands of years. However, it was not until the 1960s that the psychoactive element in cannabis, tetrahydrocannabinol (THC) cannabinoid, was discovered and isolated. 20 years later, scientists began to understand how THC interacted with the body to produce the "high". In short, cannabinoids bind to an intricate system of receptors in the human body and produce various effects. This is one of the main mechanisms of the endocannabinoid system.
So far research has discovered two main cannabinoid receptors in humans; CB1 and CB2. The first to be discovered, in 1988, was the Cannabinoid 1 receptor. They were found in abundance in the central nervous system and in the peripheral nervous system. Five years later the Cannabinoid 2 receptor was discovered. These seemed to be more concentrated in areas related to the immune system. However, they are also found in peripheral tissues and organs such as the heart and liver. We now know about other cannabinoid receptors that make up the endocannabinoid system. For example, the metabotropic receptors GPR55, GPR119 and GPR18.
As more research is done on the endocannabinoid system, we are understanding more about these receptors. It appears that THC has the same infinite links to the CB1 and CB2 receptors as some endocannabinoids (to CB1 more than to CB2). Endocannabinoids are cannabinoids produced naturally within the body (Anandamide, AEA, and 2-arachidonoylglyerol, 2-AG). Once the cannabinoid has done its job, it breaks down into various enzymes and the cycle continues. This is how the endocannabinoid system works.
Cannabinoid receptor 1
So far, highly concentrated CB1 receptors have been found in the brain and central nervous system. These areas are associated with multiple processes such as learning, memory, cognitive function, anxiety, pain, sensory perception and more. CB1 receptors have also been found in other places such as the immune system, although to a lesser extent. They are also present in small amounts in various peripheral tissues and organs.
THC has a multitude of links to the CB1 receptors. This makes them the mediators of the psychoactive effects of cannabis. By binding to the CB1 receptors at different locations in the brain, THC can produce various effects. It is responsible for the anxiety that cannabis can cause. On the other hand, THC is responsible for the analgesic or antidepressant effects of cannabis.
Because of their location, CB1 receptors play an important role in the medicinal effects of cannabinoids. In cases of neuropathic pain, increased activity of cannabinoid receptors was found to reduce symptoms. In addition, in a few cases it has slowed the progression of the disease. Their association with certain neuropathic processes and various mental health problems makes them worth understanding.
Cannabinoid receptor 2
CB2 receptors have been found in abundance in areas related to the immune system. The most concentrated areas are the lymph nodes, CNS glial cells and in the spleen. This tells us that the endocannabinoid system plays an important role in modulating our immune system.
A perfect example is inflammation, our immune response to harmful pathogens, tissue damage or infection. The body sends signals to the brain where the damage occurs and the recovery process begins. Blood flows to the affected area and the cells begin to swell, which can cause a lot of pain. In most circumstances this process is necessary and without it, even the smallest cut could become infected and be fatal. However, when this response occurs without any viable trigger it can cause enormous discomfort and pain to the person. Arthritis and inflammatory bowel disease are just two examples of pathologies caused by an unnecessarily overactive inflammatory response.
The studiesBoth in vitro and in vivo have shown that activation of CB2 receptors inhibits the inflammatory response and in some cases slows the progression of certain diseases. More research is being done on CB2 receptors as therapeutic targets.
CBD and cannabinoid receptors
Cannabidiol, or CBD, is another prominent cannabinoid but has no psychoactive effect. Research has found that CBD interacts with cannabinoid receptors in a more complex way than THC. THC has a multitude of very strong links to the CB1 receptors, and some, but not so strong, links to the CB2 receptors. CBD, on the other hand, appears to have a fairly low multitude of links to both. Rather than binding to them, CBD appears to inhibit the binding of other cannabinoids to these receptors and alter their effects.
For example, what happens if THC and CBD are consumed at the same time? CBD appears to inhibit the binding of THC to CB1 receptors in the areas of the brain associated with anxiety. Therefore, it reduces the feelings of anxiety that THC produces. CBD can also enhance the effects of your natural endocannabinoids. This is done by "distracting" the enzymes that are there to break down the endocannabinoids. In other words, endocannabinoids have a longer-lasting effect on cannabinoid receptors.
What is already known about cannabinoid receptors is not only interesting but also incredibly useful. Their discovery has allowed us to understand more about many different types of diseases and how to treat them. Future research will only reveal more about their potential as therapeutic targets.
Turcotte, C., Blanchet, M., Laviolette, M. and Flamand, N. (2016). The CB2 receptor and its role as a regulator of inflammation. [online] NCBI. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5075023/ [Accessed 26 Nov. 2019].
Kalapa Clinic | Plataforma especializada en tratamientos con cannabinoides. (2019). Localization and Utility of Cannabinoid Receptors | Kalapa Clinic. [online] Available at: https://www.kalapa-clinic.com/en/cannabinoid-receptors/ [Accessed 26 Nov. 2019].
Dhopeshwarkar, A. and Mackie, K. (2014). CB2 Cannabinoid Receptors as a Therapeutic Target—What Does the Future Hold?. [online] NCBI. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4164977/ [Accessed 25 Nov. 2019].
Miller, L. and Devi, L. (2019). The Highs and Lows of Cannabinoid Receptor Expression in Disease: Mechanisms and Their Therapeutic Implications. [online] NCBI Lydia K. Miller and Lakshmi A. Devicorresponding author. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3141881/ [Accessed 25 Nov. 2019].
Foria Wellness. (2018). CBD: Benefits for Your Endocannabinoid System. [online] Available at: https://www.foriawellness.com/blogs/learn/your-endocannabinoid-system-cbd [Accessed 25 Nov. 2019].