Effect of docosahexaenoic acid on long-term learning and memory disorders after hypoxic ischemic brain damage in rats

Objective To explore the effect of docosahexaenoic acid (DHA) on long-term learning and memory disorders and potential mechanism in rats after hypoxic ischemic brain damage. Methods Sixty neonatal 7-day-old SD rats were ramdonly divided into three groups: group S (sham operation+vehicle treatment), group C (hypoxic-ischemic brain damage [HIBD]+vehicle treatment) and group D (HIBD+DHA treatment). After left common carotid artery was isolated and ligated for 2.5 h, rats of group C and group D were put into a condition which oxygen concentration was about 8% for 2 h; rats in the group S were only isolated the left carotid artery, without ligation or hypoxia treatment; rats in the group D were intraperitoneally injected DHA of 15 mg/kg after modeling, and rats in the group S and group C were intraperitoneally injected equivalent volume of vehcle, once a day for 10 consecutive days. The pathomorphology changes of the hypocampal CA1 area, and marginal division of striatum were observed by Nissl staining 48 h after modling; the apoptosis cells were measured by TUNEL; immunohistochemical method was used to detect the expressions of Bax and Caspase-3 positive cells in the two brain areas. Morris water maza test was used to evaluate the long-term lerning and momory functions of 2-month-old rats, and the expressions of N-methyl-D-aspartate receptor 1 (NMDAR1) positive cells were detected by immunohistochemical method. Results The pathomorphology damage was significantly improved, the expressions of Bax and Caspase-3 positive cells and the neuron apoptosis in hypocampal CA1 areas and marginal division of striatum in group D were all signficantly decreased as compared with those in the group C (P<0.05). Rats in group D had significantly decreased escape latency as compared with those in group C in Morris water maze test (P<0.05), and the expression of NMDAR1 positive cells in the two brain areas of group D was significantly increased as compared with that in the group C (P<0.05). Conclusion DHA has the ameliorative effect on longterm learning and memory disorders after hypoxic ischemic brain damage in rats, which may be associated with inhibitory action of cell apoptosis at early phase and up-regulation of expression of NMDA1 at the late phase. Key words: Docosahexaenoic acid; Hypoxic-ischemic brain damage; Learning and momery disorder; Hypocampus; Marginal division of striatum; N-Methyl-D-aspartic acid receptor 1