Cannabinoids—THC and other psychoactive ingredients found in marijuana—bind to cannabinoid receptors in the brain to produce their effects. A study published online on January 19 by Pablo Castillo, M.D., Ph.D., in the Proceedings of the National Academy of Sciences, has provided a novel mechanism for cannabinoids in dampening neuronal activity in the hippocampus, a brain region important for learning and memory.

The hippocampus contains two highly interconnected populations of excitatory neurons: dentate granule cells and mossy cells. The mossy cells project extensively throughout the hippocampus. As a result, high activity of a single mossy cell can profoundly affect many dentate granule cells. Left unchecked, mossy-cell activity can impair the encoding of memories and potentially cause epilepsy. Dr. Castillo’s team has discovered several mechanisms by which cannabinoid receptors on mossy-cell axons can dampen the excitation of granule cells. The new findings suggest that promoting cannabinoid signaling might be a useful strategy for treating epileptic seizures.

Dr. Castillo is a professor in the Dominick P. Purpura Department of Neuroscience and of psychiatry and behavioral sciences, and is the Harold and Muriel Block Chair in Neuroscience at Einstein.