[Relationship between learning ability and memory and free radical in hippocampus of old rats]

To study the relationship between the amount of free radical in hippocampus and the learning ability and memory in old rats.

Morris water maze was used for 10 days to examine the learning scores, latency scores, and the loci of movement in the maze among 46 old rats (aged 20 months), 36 young rats (aged 6 months), and 34 adult rats (aged 12 months). Salicylate was injected intraperitoneally and hippocampus dialysis was performed. Chromatography was used to measure the basic values of 2,3DHBA and 2,5DHBA in dialysis fluid chemiluminometry was used to measure the superoxide dismutrase (SOD) in the sample. The rats were killed and their brains were taken out. Histological examination was conducted to calculate the number of neurons in CA1, CA4, and PM regions in hippocampus.

The learning scores on the first, fifth, and tenth days were 36.5 +/- 5.9 sec, 38.6 +/- 5.9 sec, and 39.4 +/- 6.9 sec (P > 0.05) in the old rats; 60.2 +/- 5.4 sec, 156.8 +/- 5.8 sec, and 165.1 +/- 6.8 sec in the young rats; and 61.7 +/- 5.8 sec, 152.3 +/- 6.9 sec, and 168.7 +/- 6.5 sec in adult rats. The learning scores at any time point of old rats were significantly lower than those of the young and adults rats (all P < 0.01). The latency scores of the first, fifth, and tenth days were 25.7 +/- 1.2 sec, 27.5 +/- 1.9 sec, and 27.7 +/- 1.9 sec in the old rats without significant difference between any two of these values (P > 0.05), however, the 3 latency scores of the old rats were all significantly larger than those of the young and adult rats (21.8 +/- 1.7 sec, 5.9 +/- 1.0 sec, and 3.6 +/- 0.6 sec, and 21.8 +/- 1.6 sec, 5.0 +/- 0.9 sec, and 4.8 +/- 0.7 sec respectively, all P < 0.01). The basic value of 2,3DHBA after intraperitoneal injection of salicylate was 20.7 +/- 0.3 pmol/ml in the old rats, 5 times that of the young rats and 6 times that of the adult rats (P < 0.01). The basic value of 2,5DHBA after intraperitoneal injection of salicylate was 60.12 pmol/ml in the old rats, 6 times that of the young rats and 5.8 times that of the adult rats (P < 0.01). The SOD activity was 410 U x g(-1) x min(-1) +/- 50 U x g(-1) x min(-1), significantly lower than those in the young and adult rats (880 U x g(-1) x min(-1) +/- 62 U x g(-1) x min(-1) and 860 U x g(-1) x min(-1) +/- 60 U x g(-1) x min(-1) (both P < 0.01). The values of neuron density in CA1, CA4, and PM regions of the old rats were all significantly lower than those of the young and adult rats (all P < 0.01).

The decrease of learning ability in old rat is positively correlated with the increase of free radicals and loss of neurons in hippocampus.