A new study found that while a low dose of the cannabinoid delta-9-tetrahydrocannabinol caused young mice to perform worse in learning and memory tasks, it restored age-related learning and memory decline in old mice. However, the researchers warn than more work must be done before it can be said that the cannabis compound might reverse cognitive decline in elderly humans.
The study - led by researchers from the University of Bonn and the LIMES Institute, both in Germany, in collaboration with colleagues from the Hebrew University in Jerusalem in Israel - is published in the journal Nature Medicine.
Cannabinoids such as delta-9-tetrahydrocannabinol (THC) and cannabidiol (CBD) are a class of more than 100 psychoactive, or mind-altering, compounds that are found in the cannabis, or marijuana, plant. They exert a powerful effect because they interact with cannabinoid receptors in the brain.
The body also makes its own cannabinoids that interact with cannabinoid receptors to help regulate a range of functions, including awareness of time, concentration, memory, thinking, pleasure, movement, appetite, pain, and the processing of sensory signals such as touch, smell, hearing, vision, and taste.
Although the subject of much heated debate, cannabinoids have been investigated for their medicinal value. For example, CBD is being investigated for its potential to treat childhood epilepsy and other neurological conditions.
Also, some THC-based drugs have been approved by the United States Food and Drug Administration (FDA) for specific conditions, such as treating nausea during chemotherapy and stimulating appetite in patients with AIDS who have wasting syndrome.
THC only benefited older mice
In their study paper, the researchers explain that there is "substantial evidence" to suggest that the brain's cannabinoid receptors belong to a system that "modulates the physiological processes underlying aging," and that this declines during normal aging.
Researchers therefore decided to explore the link between the "endocannabinoid system" that the receptors belong to and symptoms of aging in mice.
They tested the effect of low-dose THC in 2-month-old mice, as well as in mature and old mice (12 and 18 months old, respectively).
Results showed that while the treatment was harmful to the young mice, it appeared to be beneficial to the mature and old mice.
The young mice performed worse in learning and memory tasks, but the mature and old mice showed improvements in these two areas.
The team also found that the memory and learning improvements they observed in the older mice were linked to changes in the expression of genes that regulate the hippocampus - a region of the brain that is important for memory function.
The hippocampus gene expressions patterns became more similar to those seen in young mice.
Low-dose THC may be a potential treatment for the elderly
The researchers say that the next stage of the work should investigate how long these changes last and how they change over time, as well as try to understand the underlying mechanisms involved.
Furthermore, before any conclusions can be made about whether these effects are likely to occur in humans, studies should investigate them in other animal models, such as nonhuman primates.
In their discussion, the authors note that if other methods to reverse age-related changes in gene expression - such as "pharmacological blockade of histone deacetylases" - continue to show harmful side effects, then consideration should be given to THC and other cannabinoids; they have an "excellent safety record and do not produce adverse side effects when administered at a low dose to older individuals." They conclude:
"Thus, chronic, low-dose treatment with THC or cannabis extracts could be a potential strategy to slow down or even to reverse cognitive decline in the elderly."