A group of researchers from Israel has discovered that rats exhibiting the signs of depression have increased levels of the omega-6 fatty acid, arachidonic acid, in their brains. The details of their findings appear in the June issue of the Journal of Lipid Research, an American Society for Biochemistry and Molecular Biology journal.
During recent years, omega-3 fatty acids have enjoyed increased popularity as numerous studies have shown that supplementing diets with fish oil (a natural source of this polyunsaturated fatty acid) does everything from reducing the risk of heart disease to preventing arthritis. There is also evidence that depression may be associated with a dietary deficiency in omega-3 fatty acids. This "phospholipid hypothesis" of depression has been supported by research showing that omega-3 fatty acid concentration in the blood of depressed patients is lower than that in control patients.
"The "phospholipid hypothesis" of depression postulates that decreased omega-3 fatty acid intake, and hence, perhaps decreased brain omega-3 fatty acid content, could be responsible for the disease," explains Dr. Pnina Green of Tel Aviv University. "In humans, because of high dietary variability and the obvious inability to examine brain tissue, the theory is backed up mainly by indirect evidence. The availability of the Flinders Sensitive Line rat, an animal model of depression, overcomes both these obstacles."
In the Journal of Lipid Research study, Dr. Green in collaboration with Dr Gal Yadid of Bar-Ilan University, Ramat Gan, used the Flinders Sensitive Line rats to investigate the link between omega-3 fatty acids and depression. They examined the brains of the depressed rats and compared them with brains from normal rats. Surprisingly, they found that the main difference between the two types of rats was in omega-6 fatty acid levels and not omega-3 fatty acid levels. Specifically, they discovered that brains from rats with depression had higher concentrations of arachidonic acid, a long-chain unsaturated metabolite of omega-6 fatty acid.
Arachidonic acid is found throughout the body and is essential for the proper functioning of almost every body organ, including the brain. It serves a wide variety of purposes, from being a purely structural element in phospholipids to being involved in signal transduction and being a substrate for a host of derivatives involved in second messenger function.
"The finding that in the depressive rats the omega-3 fatty acid levels were not decreased, but arachidonic acid was substantially increased as compared to controls is somewhat unexpected," admits Dr. Green. "But the finding lends itself nicely to the theory that increased omega-3 fatty acid intake may shift the balance between the two fatty acid families in the brain, since it has been demonstrated in animal studies that increased omega-3 fatty acid intake may result in decreased brain arachidonic acid."
Although far less attention has been paid to dietary requirements for omega-6 fatty acids, which can be found in most edible oils and meat, perhaps in the future depression may be controlled by increasing omega-3 fatty acid intake and decreasing omega-6 fatty acid intake.