Relationship between hippocampal arachidonic acid content and induction of LTP in aged rats

There are several lines of evidence indicating that membrane AA correlates with the ability of aged rats to sustain LTP. The age-related decrease in membrane AA seems to be triggered by increased lipid peroxidation, which is involved with the decline of LTP. The chronic treatment of DHA could decrease membrane AA without an increase in lipid peroxidation. We have thus investigated the effect of chronic treatment of DHA on hippocampal LTP to assess whether the decrease in membrane AA could directly affect the induction of LTP. The effects of daily supplementation of DHA for 3 months on membrane AA, LTP, and Ca²⁺ response were evaluated using hippocampal slices from 26-month-old Wistar rats. Chronic treatment of DHA reduced the hippocampal AA significantly, but did not change the amplitude of LTP. Neither 30 mM K⁺ nor 500 μM NMDA-induced Ca²⁺ response was affected by chronic treatment of DHA, while the 500 μM carbachol-induced Ca²⁺ response was reduced. From these results, the reduction of membrane AA might suppress the carbachol-induced Ca²⁺ response by inhibiting the muscarinic receptor function, IP₃ formation and/or Ca²⁺ release from Ca²⁺ stores by IP₃. However, the reduction of membrane AA is not likely to be a main causal factor of the decline of LTP.