Information on the prenatal accumulation of rat brain membrane lipids is scarce. In this study we investigated in detail the fatty acid (FA) composition of the rat brain, on each day from embryonic day 12 (E12) up to birth, and on 8 time points during the first 16 days of postnatal life, and correlated the FA changes with well-described events of neurogenesis and synaptogenesis. Between E14 and E17, there was a steep increase in the concentration of all the FAs: 16:0 increased by 136%, 18:0 by 139%, 18:1 by 92%, 20:4n–6 by 98%, 22:4n–6 by 116%, 22:5n–6 by 220%, and 22:6n–3 by 98%. After this period and up to birth, the concentration of the FAs plateaued, except that of 22:6n–3, which accumulated further, reaching an additional increase of 75%. After birth, except 22:5n–6, all FAs steadily increased at various rates. Estimation of the FA/PL molar ratios showed that prenatally the ratios of all the FAs either decreased or remained constant, but that of 22:6n–3 increased more than 2-fold; postnatally the ratios remained constant, with the exception of 22:4n–6 and 22:5n–6, which decreased.
In conclusion, prenatal accumulation of brain fatty acids parallels important events in neurogenesis. 22:6n–3 is exceptional inasmuch in its steep accumulation occurs just prior to synaptogenesis.

key words: brain development, polyunsaturated fatty acids, essential fatty acids, phospholipids