Regulation of arachidonic acid metabolism in the perinatal brain during development and under ischemic stress

Arachidonic acid activation of potassium channels in rat visual cortex neurons

We investigated the effects of arachidonic acid on K+ channels in freshly dissociated neurons of 10- to 20-day-old rat visual cortex, using a perforated and conventional whole-cell patch-clamp and inside-out excised patch configurations. Arachidonic acid at 5-30 microM induced an outward current in 88.1% of the neurons in whole-cell mode, and evoked channel opening with a conductance of 170-238 pS in 90.5% of neurons under inside-out patch recording. Arachidonic acid-activated K+ channels were partially blocked by extracellular administration of 1 mM tetraethylammonium and 100 nM charybdotoxin. However, Ba2+ completely blocked the channel in all cases. None of the other K+ channel blockers, including 4-aminopyridine, quinidine, apamin and glibenclamide, inhibited the arachidonic acid-activated channels. Intracellular perfusion with Ca2+-free and 5 mM BAPTA in Ca2+-free extracellular perfusate containing 2 mM EGTA in conventional whole-cell recording did not inhibit the K+ channel, implying that the channel is not Ca2+ dependent. Neither guanosine 5'-O-(2-thiodiphosphate) nor staurosporine applied in inside-out mode affected the arachidonic acid-activated channels, indicating that G-protein and protein kinase C are not involved in this phenomenon. In addition, neither indomethacin nor nordihydroguaiaretic acid blocked the channel currents, demonstrating that it is arachidonic acid itself but not its metabolites that induced the effect. Among the fatty acids tested, only cis-unsaturated fatty acids, having more than two double bonds, such as arachidonic acid, docosahexaenoic acid and linolenic acid, activated the K+ channels. These findings suggest that there exists a novel type of K+ channel activated by arachidonic acid which may play a critical role in modulating neuronal excitability in cortical neurons.

Early dietary intervention with structured triacylglycerols containing docosahexaenoic acid. Effect on brain, liver, and adipose tissue lipids

Newborn rats were fed liquid diets containing 7 wt% fat in which 3.8% of the total fatty acids were 22:6n-3. The fats were either a specific structured oil with 22:6n-3 mostly located in the sn-2 position or a randomized oil with 22:6n-3 equally distributed in the triacylglycerol (TAG) molecules. The oils were manufactured by interesterification of fish oil TAG with free fatty acids from butterfat. The pups were tube-fed three times a day and stayed with their dams during the night. After 14 d they were fed solid diets containing the same oils for the next 7 d. A reference group stayed with the dams and received ordinary rat chow at weaning. In general no significant differences between the two dietary treatments were observed in the tissues examined except for adipose tissue. The levels of 22:6n-3 were significantly increased in brain phosphatidylcholines (PC) and phosphatidylserines (PS) of both experimental groups compared with the reference group after three weeks, whereas no differences were found in brain phosphatidylethanolamines (PE) and phosphatidylinositols (PI). In all groups and all phospholipids examined, the levels of 20:4n-6 generally decreased from 1 to 3 wk and were significantly lower in the experimental groups compared with the reference group at 3 wk except for PI. In liver, PC and PE 22:6n-3 remained constant in the experimental groups but decreased significantly in the reference group, whereas in liver PS 22:6n-3 increased in all groups, but reached significantly higher levels in the experimental groups than in the reference group. In adipose tissue, 22:6n-3 increased in the experimental groups during the study period, but decreased in the reference group, suggesting that a surplus of dietary 22:6n-3 was stored.

Expression of nuclear hormone receptors within the rat hippocampus: identification of novel orphan receptors

Within the hippocampus, stimulus-transcriptional coupling plays an important role in post-seizure neuronal adaptation, post-ischemic cell death and the induction of long-term potentiation. To identify additional mediators of hippocampal transcriptional responses a targeted approach was developed and used to characterize the spectrum of nuclear hormone receptors expressed within this brain region. cDNAs encoding the DNA-binding domains of six different members of the nuclear hormone receptor superfamily were isolated. A majority were identical or closely related to receptors known to be expressed within the hippocampus. Two additional isolates, HZF-2 and HZF-3, encode the DNA-binding domain of novel members of the nuclear hormone receptor superfamily.