Dynamic turnover of mouse brain phospholipids during normal aging and response to ischemia

An in vivo labeling procedure was used to probe the dynamic turnover of mouse brain phospholipids and to evaluate the response of these phospholipids toward decapitation ischemic insult. Within 4 hr after intracerebral injection of [32P]-ATP, the label was effectively incorporated into all phospholipids and uniquely in all subcellular membrane fractions examined. With respect to age, synaptosomes isolated from the 27-month-old mice group showed a higher incorporation of label into polyphosphoinositides and phosphatidic acids and a lower incorporation into the neutral phospholipids than the 10-month-old group. The increase in labeling of these phospholipids with age seems to reflect the increase in basal level of substrates for phosphorylation of phosphoinositol 4-phosphate and diacylglycerols. The increase in substrate level is probably related to a decrease in metabolic turnover of the lipids underlying the phosphoinositide cycle. Decapitation ischemic insult is known to result in a rapid time-dependent breakdown of the polyphosphoinositides in brain. However, a comparison of the ischemia-induced breakdown of polyphosphoinositide between the 10 and 27 month-old groups did not reveal obvious age differences in the rate of their disappearance.