THC in marijuana reverses learning and memory problems in elderly mice

While THC, the psychoactive ingredient in marijuana, seems to cause memory and learning impairment in young mice, surprising new research suggests that it actually reverses cognitive decline in elderly mice. From Scientific American:

Researchers led by Andreas Zimmer of the University of Bonn in Germany gave low doses of delta 9-tetrahydrocannabinol, or THC, marijuana’s main active ingredient, to young, mature and aged mice. As expected, young mice treated with THC performed slightly worse on behavioral tests of memory and learning. For example, after THC young mice took longer to learn where a safe platform was hidden in a water maze, and they had a harder time recognizing another mouse to which they had previously been exposed. Without the drug, mature and aged mice performed worse on the tests than young ones did. But after receiving THC the elderly animals’ performances improved to the point that they resembled those of young, untreated mice. “The effects were very robust, very profound,” Zimmer says...

When the researchers examined the brains of the treated, elderly mice for an explanation, they noticed neurons in the hippocampus—a brain area critical for learning and memory—had sprouted more synaptic spines, the points of contact for communication between neurons. Even more striking, the gene expression pattern in the hippocampi of THC-treated aged mice was radically different from that of untreated elderly mice. “That is something we absolutely did not expect: the old animals [that received] THC looked most similar to the young, untreated control mice,” Zimmer says.

The findings raise the intriguing possibility THC and other “cannabinoids” might act as anti-aging molecules in the brain.

"Marijuana May Boost, Rather Than Dull, the Elderly Brain" (SciAm)