As the mature brain ages in adulthood, its endocannabinoid system weakens. The number of CB1 receptors–the receptors through which cannabis takes its classic effect–decrease with age, and the ones that remain are less effective. It’s thought that the weakened endocannabinoid system in the elderly contributes to their cognitive decline. Last year, a research team from Germany reported that consistently activating CB1 receptors with low doses of THC prevents age-related cognitive decline in mice.
For 28 days, scientists gave a single low-dose of THC to young and old mice, after which they were tested for learning, memory, and cognitive flexibility (i.e., how well they could adapt to changing instructions). Old mice generally perform worse than young mice in these tasks, but THC impaired performance in young mice. However, old mice treated with THC performed similarly to their younger cohorts that did not receive THC, revealing that THC can impair brain function in the young, but rescue age-related decline in old animals.
Less Is More: Why Low-Dose Cannabis Is Important
These beneficial effects of THC in old mice were associated with positive changes at the level of individual brain cells. With aging, the number of connections between brain cells decreases. However, in old mice, THC increased the number of connections brain cells made with one another in a brain region called the hippocampus, which has important roles in learning and memory, and stress and anxiety. In fact, old mice treated with THC had a similar number of connections as untreated young mice.
The scientists revealed that one way in which low-dose THC promotes healthy brain aging is by impacting the pattern in which certain genes are expressed. Genes, which are the DNA instructions for building all the proteins in your body, are differentially expressed depending on age; there are “young” gene expression patterns and “old” gene expression patterns. One of the marquee findings in this study was that low-dose THC shifted the old mice’s gene expression to look like that of the young animals.
These results highlight the differential impact that THC can have on the brain and behavior as a function of age. But while many seek to better understand the harm that THC can have in the developing brain, this study provides the first in a hopefully growing body of evidence showing the benefits it can have in the aged brain