A joint study by German and Israeli scientists has found that the active ingredient in marijuana improves memory performance and cognitive functioning in old mice when given in small controlled doses.The findings by the research team from the University of Bonn and the Hebrew University of Jerusalem were recently published in the journal Nature Medicine, and may pave the way for new treatments for human dementia and other cognitive disorders.The active ingredient in marijuana – tetrahydrocannabinol or THC – was first discovered by a team of researchers from the Hebrew U.’s School of Pharmacy in 1964, with its isolation, structure elucidation and total synthesis reported by organic chemist Prof. Raphael Mechoulam in 1970.As the brain ages, cognitive ability decreases, making it more difficult to learn new things or multitask.Although this process is normal, in some cases, it can evolve into dementia.Researchers have long sought ways to slow or even reverse this process.Over a period of four weeks, the German-Israeli research team administered a small quantity of THC to mice aged two, 12 and 18 months. Mice normally show pronounce cognitive deficits as early as age one.They then tested the mice’s learning capacity and memory performance, including orientation skills and recognition of other mice. Mice that were given only a placebo displayed natural age-dependent learning and memory losses. But the cognitive functions of rodents treated with cannabis were just as good as the two-month-old control animals.“The treatment completely reversed the loss of performance in the old animals,” said Prof. Andreas Zimmer of Bonn University’s Institute of Molecular Psychiatry.The scientists also discovered that a mouse’s brain ages much faster when it lacks functional receptors for THC.These cannabinoid 1 (CB1) receptors are proteins on which the substances dock, triggering a signal chain.CB1 is also the reason for the intoxicating effect of THC in cannabis products, such as hashish or marijuana, which accumulate at the receptor.THC imitates the effect of cannabinoids produced naturally in the body, which fulfill important functions in the brain. “With increasing age, the quantity of the cannabinoids naturally formed in the brain reduces,” explained Zimmer. “When the activity of the cannabinoid system declines, we find rapid aging in the brain.”To discover precisely what effect the THC treatment has in older mice, HU researchers led by Dr. Mona Dvir-Ginzberg from the Faculty of Dental Medicine and the late Prof. Itai Bab, examined the changes in brains of aged mice treated with THC.“The THC treatment induced molecular and epigenetic changes, which no longer corresponded to that of untreated old animals, but rather were similar to what we see in young animals,” said Dvir-Ginzberg. In addition, the number of links between the nerve cells in the brain also increased, which is an important prerequisite for learning ability.A low dose of the administered THC was chosen so that there was no intoxicating effect on the mice.As a next step, the researchers hope to conduct a clinical trial to investigate whether THC also reverses aging processes and improves cognitive ability in the human brain.