¹Brain Physiology and Metabolism Section, National Institute on Aging, National Institutes of Health, Bethesda, MD, USA

Correspondence: Dr JS Rao, Brain Physiology and Metabolism Section, National Institute on Aging, National Institutes of Health, 9000 Rockville Pike, Building 9, 1S-126, Bethesda, MD 20892, USA. E-mail: jrao@mail.nih.gov

Received 14 April 2006; Revised 13 July 2006; Accepted 24 July 2006; Published online 19 September 2006.

Abstract

The enzymes that regulate the brain arachidonic acid (AA) cascade have been implicated in bipolar disorder and neuroinflammation. Fifteen weeks of dietary n-3 polyunsaturated fatty acid (PUFA) deprivation in rats decreases the concentration of docosahexaenoic acid (DHA) and increases its half-life within the brain. Based on this, we hypothesized that such dietary deprivation would decrease expression of enzymes responsible for the metabolic loss of DHA while increasing expression of those responsible for the metabolism of AA. Fifteen weeks of n-3 PUFA deprivation significantly decreased the activity, protein and mRNA expression of the DHA regulatory phospholipase A₂ (PLA₂), calcium-independent iPLA₂, in rat frontal cortex. In contrast the activities, protein and mRNA levels of the AA selective calcium-dependent cytosolic phospholipase (cPLA₂) and secretory sPLA₂ were increased. Cyclooxygenase (COX)-1 protein but not mRNA was decreased in the n-3 PUFA-deprived rats whereas COX-2 protein and mRNA were increased. This study suggests that n-3 PUFA deprivation increases the half-live of brain DHA by downregulating iPLA₂. The finding that n-3 PUFA deprivation increases cPLA₂, sPLA₂ and COX-2 is opposite to what has been reported after chronic administration of anti-manic agents to rats and suggests that n-3 PUFA deprivation may increase susceptibility to bipolar disorder.