03 Oct 2001

Tomorrow's Nature magazine carries an article on head trauma that could inform parts of Alzheimer's research, as well. Esther Shohami at Hebrew University's Medical Faculty in Jerusalem, and colleagues there, report that an endogenous cannabinoid plays a role in the complex protective response prompted by a brain injury.

The compound, 2-Arachidonoyl glycerol (2-AG) occurs in the brain and the intestine but its physiology remains poorly understood. It can protect cerebral rat neurons from ischemia in vitro (Sinor AD et al.), and synthetic cannabinoids have been shown to reduce neuronal death in the hippocampus of rats after experimentally induced ischemia (Nagayama T et al.).

In this study, the researchers subjected mice to head trauma and analyzed the 2-AG response following this injury. 2-AG levels rose, peaking at 10-fold after four hours. When the researchers injected additional 2-AG, the mice developed 50 percent less edema and recovered faster. More directly relevant to Alzheimer's research, the treated mice also suffered less neuronal cell death. The researchers counted neurons in the CA3 area of the hippocampus, and report that control mice (head trauma without exogenous 2-AG) had lost about 40 percent of neurons in that brain area seven days after the trauma, whereas treated mice lost about 10 percent. (The hippocampus is among the brain areas most affected by neuronal death in AD.)

The authors write that these results are the first to record the neuroprotective effects of this cannabinoid. In previous work, the authors had shown that 2-AG suppresses the formation of reactive oxygen species and the inflammatory cytokine tumor necrosis factor-β, both of which contribute to the pathophysiology of brain injury. To the extent that oxidative damage and inflammation spur the loss of cells in AD, this research may well bear attention.—Gabrielle Strobel

Hypothesis Factory: Marijuana and AD