Tests used to assess the cognitive abilities of aged rats: Their relation to each other and to hippocampal morphology and neurotrophin expression

Background: Aged rodents have proven to be a useful tool in studying age-re lated cognitive decline, particularly with regard to hippocampal function. A number of maze tests have been developed to evaluate hippocampal function in aged rodents, including the eight-arm radial maze, Barnes circular plat form maze and Morris water maze. To some extent, these mazes have been used interchangeably to evaluate aged animals. Few researchers, however, have e xamined how performance of individual, aged animals compares in these three mazes. Objective: The purpose of this study was to compare the performance s in the th ree mazes and to examine how such performances are related to e ach other, to hippocampal morphology and to neurotrophin gene expression. M ethods: We screened groups of young and old Fisher 344 x Brown Norway rats for general health and physical abilities, tested the animals in the three mazes and examined correlations among performances in the mazes and in scre ening tests. Hippocampal neu ron density and expression of hippocampal neur otrophin mRNAs were also examined and compared with behavior in the three m azes. Results: Aged animals were found to be impaired in all three mazes an d to have lower hippocampal neuron densities compared with young animals, w ith poor learning behavior significantly correlating with reduced hippocamp al neuron density. Differences were observed between performance in the dif ferent mazes, but in general the Morris water maze and Barnes circular plat form maze were found to give similar results.