The main active ingredient in cannabis improves age-related learning and memory decline in old mice, even going so far as to improve their cognitive function to levels seen in young, untreated mice, a new study published in Nature Medicine, has found.
Tetrahydrocannabinol (THC) has long been known and used for its psychoactive effects. However, previous studies have found that as humans age, their endogenous cannabinoid system doesn’t function as well. These cannabinoid receptors help to regulate a spectrum of functions, including concentration, appetite, memory, mood, and pain.
These cannabinoid receptors have also been found in a range of animals, including mice. The team from the University of Bonn and the LIMES Institute in Germany, in collaboration with the Hebrew University, therefore decided to see if they could stimulate the endogenous cannabinoid system in older mice to improve function.
For the study, the team implanted minipumps in mice aged two months, 12 months, and 18 months. The pumps gave the mice a chronic low dose of THC – 3 milligrams per kilogram of body weight for 28 days. The animals were then tested on three cognition tests: the Morris water maze, an object location recognition task, and a partner recognition test.
The effects were robust, say the authors, with THC improving the performance of senior mice to the point that it resembled that of young, non-THC mice. The young mice given THC, however, performed worse on tests.
"It seems that the young brain becomes old and the old brain becomes young," co-author Andras Bilkei-Gorzo, from the Institute of Molecular Psychiatry at the University of Bonn in Germany told The Scientist. "At first sight it was totally illogical, but I realized when we gave the same drug to a young [animal], it overdrives the cannabinoid system – it’s [non-typical] hyperactivity and they have to bear the consequences. [But] in the old, the same treatment normalizes pathological low activity."
When they delved even further and examined the brains of old mice, they found that THC-treated mice had more synaptic spines. On top of that, the gene expression pattern in the hippocampi, the memory center, had changed to resemble that of young mice.
Previous work has shown that the endogenous cannabinoid system declines with age. This study, then, fits well with that paradigm. As mice grow old, the activity of their endogenous cannabinoid system does not function as well. However, with some help from THC, it seems some of that function returns to the animals.
This is an interesting finding, particularly in light of the fact that many more seniors are using cannabis. The number of users between the age of 50 and 64 increased by 57.8 percent between 2006 and 2013. For those 65 and older, cannabis use skyrocketed by 250 percent.
It’s important to note that this study was only done on mice and cannot be extrapolated to humans. More work is needed, so the team plans to study the effects of THC on the cognitive function of senior humans next.