Tetrahydrocannabinol (THC) and cannabidiol (CBD) are the two main compounds found in cannabis. THC is the most active ingredient in marijuana, creating the plant’s mind-altering effects. THC is the main reason a lot of people have an issue with legalizing marijuana, because it produces that euphoric feeling. The second main compound of marijuana — and the main compound of hemp — is CBD, or cannabidiol. Unlike THC, CBD is legal in all fifty states and the District of Columbia, so researchers are more free to study this chemical and how it affects our brain.
THC and CBD are only half of the story, though. Cannabinoids work with our body’s endocannabinoid system, which is made up of natural receptors for these chemicals as well as production of cannabinoids. The endocannabinoid system has two types of cannabinoid receptors: CB1 receptors, found in the brain, and CB2 receptors, mainly in the immune system. Scientists are unclear as to exactly what the cannabinoids do to the endocannabinoid system, but there’s hope. With these rat studies, researchers can see the various effects that CBD has on the body and even trace how they work within the brain.
CBD and the Endocannabinoid System: Hippocampal Neurogenesis Tests on Rats
Why Do We Do Experiments?
Researchers only discovered the Endocannabinoid System in the early 1990s by first studying the effects of cannabis. The official scientific data has made it difficult to confirm exactly how the health benefits of cannabinoids come about. With the Endocannabinoid System being such a new discovery, scientists have been working backwards to track the multitude of positive effects CBD has on the body, from anxiety reduction to pain relief. The experiments serve to strengthen the information we do know and to learn even more about CBD and the benefits it has for our bodies.
But Why Rodents?
Mice and rats make up 95 percent of all lab animals, and they play a crucial role in the development and testing of new medicines. Researchers use mice and rats for many reasons.
- Rodents are easily contained and very convenient. They do not require a lot of space, and can easily adapt to new environments that could cause problems with larger animals.
- These small mammals have a lifespan of only a few years, meaning several generations can be studied in a short period of time. Likewise, breeding rodents missing certain hormones or genetic codes, otherwise known as knockout mice, can be developed in a short period of time compared to other test animals. Mice and rats also reproduce quickly, so scientists can create different breeds or develop a bloodline of rodents that are missing certain traits.
- The last major reason we use rodents as test models is because their genetic biology and behaviors are very similar to humans, and many of our human conditions can be replicated in these animals. In the last few decades, scientists have started breeding rodents with altered genes to study the action of those genes, called “transgenic mice”. Because we have so much flexibility and control over these rodents, our test margin of error is very low.
CBD and Our Hippocampus
The hippocampus is a major part of the human brain that helps organize information from our short-term memory to our long-term memory, and it also has a role in spatial memory. The hippocampus has receptors that render it more vulnerable to the effects of long-term stress, causing that part of the brain to atrophy. Diseases and disorders such as post-traumatic stress disorder, schizophrenia, and severe depression result —at least in part — from hippocampal atrophy.
Since we know from previous rat studies that CBD oil can help schizophrenia, depression, and PTSD, scientists developed this study to look into what effect cannabidiol has on the hippocampus and our endocannabinoid system. This study tests the involvement of hippocampal neurogenesis in the anti-anxiety effect of CBD. This means that scientists are looking at the rate of growth and development of nerve tissue in the hippocampus and how that’s affected by the usage of cannabidiol hemp oil. To do this, scientists set up a study with two types of mice that were exposed to chronic unpredictable stress: “normal” mice and mice that have been genetically altered to lack certain traits. CBD was administered to both groups of rodents every day after their daily stressor, in order to see the changes CBD made in the hippocampus and find out if it can reduce or reverse damage caused by stress.
Stress Tests & Results
To test the effects of CBD, both sets of mice were given two stress tests. They participated in the elevated plus maze and the novelty suppressed feeding test.
- The elevated plus maze tests the anxiety in rodents by measuring the time spent in different corners of the maze. An average rodent seeks out darker areas, but mice under the influence of anxiolytic drugs spend a more balanced time in the dark corners and light corners of the maze. This lets the scientists know whether the mice are stressed or calm.
- The novelty-suppressed feeding test tests the rodent’s response to eating familiar food in a new environment by measuring the delay of time before the creature approaches the food. This measures how nervous they are about the new environment.
In both of these stress tests, the unaltered mice proved to have anxiolytic-like (or anti-anxiety) results while under the influence of CBD. The genetically altered mice had different results. By blocking certain receptors and hormones, researchers blocked the effects of CBD on these rodents. This showed the scientists that those receptors are vital to how CBD works in the body.
The genetically unaltered mice performed as expected when they were administered cannabidiol oil, becoming less nervous. But lots of other studies have shown that CBD helps reduce anxiety. The more interesting part of this test is when the genetically altered mice were given hormones that blocked the effects of the CBD because it highlighted what those effects actually are, or at least how they work in the hippocampus.
This rodent study showed that cannabidiol hemp oil encourages the growth of hippocampal brain cells and uses the endocannabinoid system receptors to do so. When the rodents’ CB1 receptors were blocked, it prevented the cell growth in the brain induced by the CBD. This means that the anxiolytic effects of CBD depends in part on the hippocampus nerve growth, and that CBD works through signalling from the endocannabinoid system receptors.