Memory performance decreases with increasing age. Cannabis can reverse these aging processes in the brain. This was shown in mice by scientists at the University of Bonn with their colleagues at the Hebrew University of Jerusalem. Old animals were able to regress to the state of two–month–old mice with a prolonged low–dose treatment with a cannabis active ingredient. This opens up new options, for instance, when it comes to treating dementia.

The results were now presented in the journal Nature Medicine.

Like any other organ, our brain ages. As a result, our cognitive abilities decrease with increasing age. Thus it becomes more difficult to learn new things or devote attention to several things at the same time. This process is normal, but can also promote dementia. Researchers have long been looking for ways to slow down or even reverse this process.

Scientists at the University of Bonn and the Hebrew University of Jerusalem have now achieved this in mice. With their short life expectancy, these animals display pronounced cognitive deficits even at twelve months of age. The researchers administered a small quantity of THC, the active ingredient in the hemp plant (cannabis), to mice aged two, twelve and 18 months over a period of four weeks. Afterwards, they tested learning capacity and memory performance in the animals – including, for instance, orientation skills and the recognition of other mice. Mice that were only given a placebo displayed natural age–dependent learning and memory losses. In contrast, the cognitive functions of the animals 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,” reported Prof. Andreas Zimmer from the Institute of Molecular Psychiatry at the University of Bonn and member of the Cluster of Excellence ImmunoSensation.

This treatment success is the result of years of meticulous research. First, the scientists discovered that the brain ages much faster when mice do not possess any functional receptors for THC. These cannabinoid 1 (CB1) receptors are proteins to which the substances dock and thus trigger a signal chain. CB1 is also the reason for the intoxicating effect of THC in cannabis products, such as hashish or marihuana, which accumulate at the receptor. THC imitates the effect of cannabinoids produced naturally in the body, which fulfil important functions in the brain.

“With increasing age, the quantity of the cannabinoids naturally formed in the brain reduces,” says Prof. 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 old mice, researchers at the Hebrew University of Jerusalem, led by Dr. Mona Dvir–Ginzberg and the late Prof. Itai Bab, examined the epigenetic 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 Dr. Mona Dvir–Ginzberg from the Institute of Dental Sciences, in the Faculty of Dental Medicine at The Hebrew University of Jerusalem.

Moreover, the number of links between the nerve cells in the brain also increased again, which is an important prerequisite for learning ability. “It looked as though the THC treatment turned back the molecular clock,” says Zimmer. A low dose of the administered THC was chosen so that there was no intoxicating effect in the mice. Cannabis products are already permitted as medications, for instance as pain relief. As a next step, the researchers want to conduct a clinical trial to investigate whether THC also reverses aging processes in the brain in humans and can increase cognitive ability.