THC present in cannabis appears to alter the structure of specialized immune cells in the brain, which appears to be linked to an increased genetic predisposition to schizophrenia and could be harmful to adolescent development.
A recent study involving experts from the Johns Hopkins University School of Medicine used mice to investigate the role of microglia in mediating the harmful cognitive effects of delta-9-tetrahydrocannabinol (THC). The results have been published in the specialist journal “Nature Communications”.
THC content significantly increased
Adolescents are particularly susceptible to the long-term negative effects of THC, reports study author Professor Dr. Atsushi Kamiya. It is known that THC is psychoactive and that concentrations of THC in cannabis have increased fourfold in the last 20 years.
This poses a particular danger for young people who have a genetic predisposition to psychoactive disorders. In addition, adolescents are generally particularly susceptible to the long-term negative effects of THC, emphasizes Dr. Kamiya.
What are microglial cells?
Microglial cells are a subset of immune cells in the central nervous system. These not only play an important role in the communication of neurons, but also in the immune response. They are also important for the healthy development of the brain, the researchers explain.
In adolescence, microglial cells are crucial for the maturation of the brain in connection with social and cognitive functions. For example, impairments in microglial cells could lead to changes in the wiring and communication systems in teenagers’ brains, which are still developing.
To check this, the experts carried out a study on genetically modified mice with a mutation that mimics a genetic risk of psychiatric disorders in humans. To determine the effects, these animals were compared with a control group of healthy mice.
The mice with the mutation showed changes in the brain, which particularly affected areas responsible for emotions, learning and memory, the researchers report.
What did injections of THC do?
During the puberty of the mice, all animals were treated with daily single injections of THC or with harmless saline control. After 30 days of injections, a three-week period of rest was used before behavioral testing to assess psychosocial development.
The animals’ olfactory perception, object recognition, social interaction and memory were tested. In addition, the number and so-called morphology of microglial cells in the brains of the mice were measured, according to the research team.
Cell death caused by THC?
It was shown that mice exposed to THC had increased microglial apoptosis (programmed cell death). This reduction in the number of microglia was 33 percent higher in mice with the genetic mutation than in healthy animals.
The decline in microglia occurred particularly in the prefrontal cortex of the brain. This part of the brain is responsible for memory, social behavior, decision-making and other executive functions in mice and humans, the experts explain.
Microglia are involved in the neuronal maturation of the brain and a decrease in healthy microglia can lead to an increased number of abnormal cell signals and communications. According to the researchers, the genetically modified mice that were given THC performed 40 percent worse in social memory than animals treated with saline solution.
Teens should be careful with cannabis
The results of animal studies suggest that cannabis use in youth can have long-lasting and negative effects, warns Professor Dr. Kamiya in a press release. Although more research is needed, teenagers are strongly advised to exercise caution when consuming cannabis. (as)