A new study shows that the main ingredient in marijuana, THC (Tetrahydrocannabinol), helps to improve age-related learning and memory decline in older mice. There are claims that their cognitive function is improved to levels seen in young, untreated mice. This study was published in Nature Medicine.

THC has long been known and used for its psychoactive effects for decades. However, earlier studies have found that as humans age, the operation of their endogenous cannabinoid system tends to decline. These cannabinoid receptors assist in regulating a number of functions including concentration, appetite, memory, mood, and pain. 

These cannabinoid receptors have been found to be present in a range of animals, including mice. A team of researchers from the University of Bonn and the LIMES Institute in Germany, in collaboration with the Hebrew University, decided to explore the possibility of stimulating the endogenous cannabinoid system in older mice in an attempt to improve function. 

For the study, minipumps were implanted in mice aged two months, 12 months, and 18 months. The pumps delivered a low dose of THC – 3 milligrams per kilogram of body weight for 28 days. Next, the mice were tested on three cognition tests: the Morris water maze (a test of spatial learning for rodents), an object location recognition task, and a partner recognition test.

The results were impressive to say the least. The performance of the senior mice was very similar to that of young, non-THC mice. At the other end of the age spectrum, the young mice given THC didn’t fare as well on the 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 the scientists investigated further and analyzed the brains of old mice, they found that the mice that were treated with THC had more synaptic spines. To add to that, the gene expression pattern in the hippocampi, the memory center, appeared very similar to that of young mice.